Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

A study of the manufacturing method and related mechanical properties of SiC reinforced aluminum Wiskel, J. Barry 1986

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1986_A7 W57.pdf [ 9.06MB ]
Metadata
JSON: 831-1.0078554.json
JSON-LD: 831-1.0078554-ld.json
RDF/XML (Pretty): 831-1.0078554-rdf.xml
RDF/JSON: 831-1.0078554-rdf.json
Turtle: 831-1.0078554-turtle.txt
N-Triples: 831-1.0078554-rdf-ntriples.txt
Original Record: 831-1.0078554-source.json
Full Text
831-1.0078554-fulltext.txt
Citation
831-1.0078554.ris

Full Text

A STUDY OF THE MANUFACTURING METHOD AND RELATED MECHANICAL PROPERTIES OF SiC REINFORCED ALUMINUM B.Sc. The U n i v e r s i t y of A l b e r t a , 1984 A T h e s i s Submitted i n P a r t i a l F u l f i l l m e n t of the Requirements f o r the Degree of The F a c u l t y of Graduate S t u d i e s (Department of M e t a l l u r g i c a l E n g i n e e r i n g ) We accept t h i s t h e s i s as conforming to ^he/irequ/ired standard The U n i v e r s i t y of B r i t i s h Columbia September 1986 (c) J . BARRY WISKEL, 1986 By J.Barry Wiskel Masters of A p p l i e d Science i n In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head o f my department or by h i s o r her r e p r e s e n t a t i v e s . I t i s understood t h a t copying o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department o f \ ^ C Z ^ ' ° < U ^ ^ c ^ i r.ra_\ £ n o ^ ^ e p ^ The U n i v e r s i t y of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6 (3/81) 11 ABSTRACT A study i n v o l v i n g manufacturing and t e n s i l e t e s t i n g was conducted to e l u c i d a t e the mechanical p r o p e r t i e s of a SiC f i b r e r e i n f o r c e d aluminum. Areas a n a l y z e d i n c l u d e d p r o d u c t i o n methods, f a i l u r e mechanisms, t e n s i l e behaviour and i n t e r f a c i a l bonding. A w e l l d i s p e r s e d f i b r e d i s t r i b u t i o n i n the as c a s t composite was d i f f i c u l t to o b t a i n . T h i s a r i s e s from the hig h degree of i n t e r m i n g l i n g of f i b r e s i n the a s - r e c e i v e d tows. The poor d i s t r i b u t i o n can lead to incomplete f i b r e u t i l i z a t i o n and i n c r e a s e composite s u s c e p t i b i l i t y to d e l a m i n a t i o n damage. The s t r e n g t h of the composites t e s t e d were below that expected from a r u l e of mixtures (ROM) v a l u e . F i b r e damage i n c u r r e d d u r i n g manufacturing and by the formation of aluminum c a r b i d e on the f i b r e s u r f a c e are p o s s i b l e causes f o r t h i s anomaly. A l s o , f i b r e / ( m a t r i x p l a s t i c deformation) i n t e r a c t i o n can l e a d to premature composite f a i l u r e e s p e c i a l l y at the low volume f r a c t i o n s of f i b r e s being a n a l y z e d . On a m i c r o s c o p i c l e v e l good bonding between the f i b r e and matrix was observed. T h i s adhesion was a t t r i b u t e d to the formation of aluminum c a r b i d e at the f i b r e / m a t r i x i n t e r f a c e . S y n e r g i s t i c s t r e n g t h e n i n g of the matrix was observed f o r s e v e r a l t e n s i l e samples. T h i s phenomena may be a t t r i b u t e d to f i b r e d i s t r i b u t i o n a l t e r i n g the aluminum matrix deformation behaviour. • • t 1X1 TABLE OF CONTENTS PAGE ABSTRACT i i TABLE OF CONTENTS i i i LIST OF FIGURES v LIST OF TABLES v i i i ACKNOWLEDGEMENTS ix CHAPTER 1.0 INTRODUCTION: METAL MATRIX COMPOSITES . .. 1 CHAPTER 2.0 LITERATURE REVIEW 9 2.1 N i c a l o n SiC F i b r e s 9 2.2 SiC R e i n f o r c e d Aluminum Composites 14 2.2.1 Manufacturing Methods 14 2.2.2 Mechanical P r o p e r t i e s 17 2.2.3 I n t e r f a c i a l P r o p e r t i e s 23 CHAPTER 3.0 COMPOSITE PRODUCTION 29 3.1 Die design and Manufacturing 29 3.2 Temperature C o n t r o l 39 3.3 Lay Up P r e p a r a t i o n . . . . 44 3.4 Manufacturing D i f f i c u l t i e s 48 CHAPTER 4.0 EXPERIMENTAL APPARATUS AND TECHNIQUE 49 4.1 T e n s i l e T e s t i n g 49 4.2 Volume F r a c t i o n Determination 58 4.3 M i c r o s t r u c t u r a l A n a l y s i s 59 4.4 D i f f r a c t i o n A n a l y s i s of F i b r e - M a t r i x I n t e r f a c e 59 4.5 Heat Treatments 64 CHAPTER 5.0 EXPERIMENTAL RESULTS 65 5.1 T e n s i l e Test Data 65 i v 5.1.1 As Cast and Heat Tr e a t e d Aluminum Reference Samples 65 5.1.2 Composite T e n s i l e P r o p e r t i e s 68 5.1.3 U l t i m a t e T e n s i l e S trength 69 5.1.4 Rule of Mixtures (ROM) S t r e n g t h 69 5.1.5 F i b r e s C o n t r i b u t i n g 72 5.1.6 F i b r e S trength 80 5.1.7 T e n s i l e Sample Anomalies 81 5.2 M i c r o s t r u c t u r a l A n a l y s i s 85 5.3 I n t e r f a c i a l A n a l y s i s 88 CHAPTER 6.0 DISCUSSION 97 6.1 Manufacturing Technique 97 6.1.1 F i b r e D i s t r i b u t i o n 97 6.1.2 Volume F r a c t i o n 100 6.2 F a i l u r e Mechanisms 101 6.3 T e n s i l e R e s u l t s 105 6.4 I n t r i n s i c Strengthening 107 6.5 F i b r e S t r e n g t h 112 6.6 I n t e r f a c i a l P r o p e r t i e s 112 CONCLUSIONS 114 RECOMMENDATIONS 115 REFERENCES 116 APPENDIX A THERMODYNAMIC CALCULATIONS FOR THE FORMATION OF ALUMINUM CARBIDE IN SOLID ALUMINUM 119 APPENDIX B DRUMWINDING PARAMETERS 121 APPENDIX C TENSILE DATA 123 APPENDIX D ELECTRON DIFFRACTION PATTERNS 128 V LIST OF FIGURES F i g u r e 2.1 P r o b a b i l i s t i c S t r e n g t h of SiC F i b r e s ( r e f . 8) 11 F i g u r e 2.2 S i C / A l Composite T e n s i l e Data ( r e f . 10) 20 F i g u r e 2.3 Free Energy of Aluminum Carbide Formation in L i q u i d Aluminum f o r V a r i o u s A c t i v i t i e s of S i l i c o n ( r e f . 21 ) 25 F i g u r e 2.4 Free Energy of Aluminum Carbide Formation in S o l i d Aluminum f o r V a r i o u s A c t i v i t i e s of S i l i c o n 26 F i g u r e 3.1 Wetting of SiC C r y s t a l s by L i q u i d Aluminum as a F u n c t i o n of Temperature ( r e f . 7) 30 F i g u r e 3.2 Schematic C r o s s - S e c t i o n of P r e s s i n g System 33 F i g u r e 3.3 Lower Die Plunger 34 F i g u r e 3.4 Upper Die Plunger 35 F i g u r e 3.5 Outer Die Ring and F i b r e f r a x Tube 37 F i g u r e 3.6 Time-Temperature P r o f i l e of Manufacturing Run 43 41 F i g u r e 3.7 M e l t i n g and S o l i d i f i c a t i o n Temperatures 42 F i g u r e 3.8 Retention Time of F i b r e s i n Molten Aluminum 43 F i g u r e 4.1 Through Thickn e s s Reduced Cross S e c t i o n T e n s i l e Sample ( r e f . 1.0) 50 F i g u r e 4.2 Curved "Dog Bone" T e n s i l e Sample 50 F i g u r e 4.3 T e n s i l e Sample L a b e l l i n g 52 F i g u r e 4.4 G r i n d i n g Wheel 53 F i g u r e 4.5 S p e c i a l t y V i s e For H o l d i n g T e n s i l e Sample While Making Reduced Cross S e c t i o n 54 F i g u r e 4.6 Wheatstone Bridge C o n f i g u r a t i o n 56 F i g u r e 4.7 T e n s i l e Data A c q u i s i t i o n System 57 F i g u r e 5.1 Comparison of Reference Aluminum (43A) and F i b r e R e i n f o r c e d Aluminum (46A) 66 vi F i g u r e 5.2 Composite S t r e n g t h v s F i b r e Volume F r a c t i o n 73 F i g u r e 5.3 UTS/ROM R a t i o v s F i b r e Volume F r a c t i o n f o r As Cast Specimens 75 F i g u r e 5.4 UTS/ROM R a t i o vs F i b r e Volume F r a c t i o n f o r Annealed and Tempered Specimen 76 F i g u r e 5.5 UTS/ROM R a t i o vs F r a c t i o n of F i b r e s C o n t r i b u t i n g 79 F i g u r e 5.6 Apparent F i b r e S t r e n g t h vs F i b r e Volume F r a c t i o n 82 F i g u r e 5.7 Comparison of S t r e s s - S t r a i n Curve f o r Sample 45A and 44D 83 F i g u r e 5.8 F a i l u r e Modes of Sample 45A and 38C 86 F i g u r e 5.9 As Cast M i c r o s t r u c t u r e of Sample 42 87 F i g u r e 5.10 As Cast M i c r o s t r u c t u r e of Sample 47 87 F i g u r e 5.11 G r a i n S t r u c t u r e of Sample 47 89 F i g u r e 5.12 F r a c t u r e S u r f a c e of Specimen 31E 90 F i g u r e 5.13 F r a c t u r e S u r f a c e of Specimen 44D 90 F i g u r e 5.14 D i f f r a c t i o n P a t t e r n of Sample B 91 F i g u r e 5.15 F i b r e S u r f a c e of Sample B 95 F i g u r e 5.16 Stepped F r a c t u r e S u r f a c e of 44b and 38C . 96 F i g u r e 5.17 F r a c t u r e S u r f a c e of 45A 96 F i g u r e 6.1 T r a n s v e r s e C r o s s S e c t i o n of Sample 46A .. 98 F i g u r e 6.2 T r a n s v e r s e Composite C r o s s S e c t i o n ( r e f . 1 6 ) 99 F i g u r e 6.3 T r a n s v e r s e Composite C r o s s S e c t i o n ( r e f . 1 0 ) 99 F i g u r e 6.4 T r a n s v e r s e C r o s s S e c t i o n of Sample 44B ..102 F i g u r e 6.5 Schematic of Sample 44B C r o s s S e c t i o n ...102 F i g u r e 6.6 H y p o t h e t i c a l Shear L o a d i n g Diagram 104 F i g u r e 6.7 T r a n s v e r s e C r o s s S e c t i o n of Sample 45A ..106 v i i F i g u r e 6.8 Schematic of Sample 45A C r o s s S e c t i o n ...106 v i i i LIST OF TABLES Table 1.1 P r o p e r t i e s of R e i n f o r c i n g F i b r e s 2 Table 1.2 S p e c i f i c M a t e r i a l P r o p e r t i e s 4 Table 1.3 M a t e r i a l F r a c t u r e Toughness 5 Table 2.1 Mechanical P r o p e r t i e s of S i C / A l Composites 18 Table 2.2 S i C / A l Composite P r o p e r t i e s - Avco S p e c i a l t y Products 22 Table 3.1 Pre-Composite S t a c k i n g Sequence 46 Table 4.1 Volume F r a c t i o n Comparison 60 Table 4.2 M i c r o s t r u c t u r a l E t c h a n t s 61 Table 4.3 S e l e c t e d Area D i f f r a c t i o n C o n d i t i o n s ... 63 Table 5.1 As Cast and Heat T r e a t e d Aluminum Reference Samples 67 Table 5.2 As Cast Composite T e n s i l e P r o p e r t i e s ... 70 Table 5.3 Annealed Composite T e n s i l e P r o p e r t i e s .. 71 Table 5.4 Quenched and Tempered Composite T e n s i l e P r o p e r t i e s 72 Table 5.5 Y i e l d S t r a i n s of Aluminum Matrix M a t e r i a l 84 Table 5.6 F i b r e Surface D i f f r a c t i o n P a t t e r n s 92 Table B.1 Drumwinding Parameters 122 Table C.1 Aluminum Reference Sample T e n s i l e P r o p e r t i e s 124 Table C.2 Composite T e n s i l e P r o p e r t i e s 125 Table C.3 Apparent F i b r e S t r e n g t h 127 Table D.1 D i f f r a c t i o n P a t t e r n s 129 i x ACKNOWLEDGEMENTS I wish t o thank Dr. J . Nadeau, Dr. E. Teghtsoonian and Dr. A. P o u r s a r t i p f o r t h e i r r e s p e c t i v e c o n t r i b u t i o n s rendered over the past two y e a r s . A l s o , s i n c e r e thanks i s extended to a l l members of the Composite Group f o r t h e i r p a t i e n c e and a s s i s t a n c e . A p e r s o n a l note of thanks to my f a m i l y (Stan, Sandy Bruce and Bruno) f o r t h e i r great support and to my peers i n room 406 f o r enduring the v a r i o u s t h e s i s p a r a p h e r n a l i a c o l l e c t e d i n and around the o f f i c e . 1 CHAPTER 1.0  INTRODUCTION; METAL MATRIX COMPOSITES Throughout h i s t o r y as man and h i s w o r l d have become i n c r e a s i n g l y s o p h i s t i c a t e d , the need f o r more advanced m a t e r i a l s w i t h h i g h e r s t r e n g t h , s t i f f n e s s and d u r a b i l i t y has r i s e n c o n c u r r e n t l y . A s p e c i f i c example c o n c e r n s the a i r c r a f t / a e r o s p a c e i n d u s t r y where the o b j e c t i v e of d e s i g n e r s i s t o m i n i m i z e weight w h i l e s t i l l m a i n t a i n i n g a c c e p t a b l e s t i f f n e s s and s t r e n g t h . To meet t h i s c h a l l e n g e a composite m a t e r i a l was pr o d u c e d . Composite m a t e r i a l s a r e be s t d e s c r i b e d as a c o m b i n a t i o n of two or more c o n s t i t u e n t s s y n t h e t i c a l l y assembled r e f l e c t i n g the p r o p e r t i e s of the i n d i v i d u a l components a d v a n t a g e o u s l y . Common type s of composi t e m a t e r i a l s c o n s i s t of a polymer m a t r i x r e i n f o r c e d by s t r o n g f i b r e s such as g l a s s , g r a p h i t e or k e v l a r (Table 1.1). Due t o the presence of t h e s e f i b r e s , polymer composite m a t e r i a l s e x h i b i t h i g h s p e c i f i c s t r e n g t h and s t i f f n e s s ( T a ble 1.2). S p e c i f i c p r o p e r t i e s a r e d e f i n e d as the observed s t r e n g t h and s t i f f n e s s d i v i d e d by the m a t e r i a l s d e n s i t y . Thus, co m p o s i t e s a r e s u i t a b l e i n a p p l i c a t i o n s where o v e r a l l component weight i s a p r i m a r y c o n c e r n whether i t be an a i r c r a f t p a r t , t e n n i s r a c q u e t or a u t o m o b i l e e x t e r i o r . 2 T A B L E 1.1 P r o p e r t i e s o f R e i n f o r c i n g F i b r e s ( r e f . l ) F I B R E MODULUS UTS D E N S I T Y E / P U T S / P (GPA) (MPA) ( g / c m 3 ) S - G l a s s 8 5 . 5 2100 G r a p h i t e 3 9 0 . 0 2100 K e v l a r 130 . 0 2800 B o r o n 3 8 5 . 0 2800 S i C ( N i p . ) 2 0 0 . 0 2000 S i C ( A v c o ) 4 2 7 . 0 3447 2 . 5 4 2 8 . 5 830 1 .90 2 0 5 . 0 1100 1 .50 8 7 . 0 1870 2 . 6 3 1 4 6 . 0 1100 2 . 6 7 6 . 9 770 3 . 0 1 4 2 . 3 1149 3 To emphasis the advantages of composites, a d i r e c t comparison with comparable m a t e r i a l s i s needed. Table 1.2 summarizes the s p e c i f i c p r o p e r t i e s of laminated composites, s t e e l , t i t a n i u m , aluminum and polymer m a t e r i a l s . From t h i s t a b l e i t i s obvious that the s p e c i f i c p r o p e r t i e s of the composites meet or exceed those c i t e d f o r the metals l i s t e d . An important f e a t u r e of the composite m a t e r i a l s c i t e d i s that they are o r t h o t r o p i c i n n a t u r e . O r t h o t r o p i c i m p l i e s that the advantageous p r o p e r t i e s of a composite are predominant in s p e c i f i c d i r e c t i o n s . The d i r e c t i o n a l i t y of the mechanical p r o p e r t i e s r e s u l t s from the s p e c i f i c f i b r e o r i e n t a t i o n s of each p l y i n a laminate (eg.0,90,+-45 degrees to the l o a d i n g ) . Metals are on the other hand i s o t r o p i c i n nature and thus are of more use under m u l t i d i r e c t i o n a l l o a d i n g c o n d i t i o n s . The composite m a t e r i a l s s t a t e d i n Table 1.2 can be used in a wide v a r i e t y of a p p l i c a t i o n s . However, there are c o n d i t i o n s i n which t h e i r u s e f u l n e s s i s l i m i t e d . In p a r t i c u l a r , high temperature degradation of the polymer matrix m a t e r i a l s ( r e f . 1,2) p r e c l u d e s t h e i r use at above 200 °c. I t was observed that even with i n d i v i d u a l components p o s s e s s i n g low toughness values (Table 1.3) composite m a t e r i a l s e x h i b i t s r e s p e c t a b l e f r a c t u r e r e s i s t a n c e . In l i g h t of t h i s f a c t , use of a tougher matrix m a t e r i a l (eg. aluminum) may r e s u l t i n an i n c r e a s e i n composite f r a c t u r e toughness above that of the metal i t s e l f . 4 T A B L E 1 .2 S P E C I F I C M A T E R I A L P R O P E R T I E S ( r e f . 1, 2) M a t e r i a l V o l u m e E u t s d e n s i t y E / p U t s / p F r a c t i o n (Gpa) (Mpa) ( g / c m 3 ) G l a s s / e p o x y 60% 17 .2 330 1 . 8 5 9 . 3 178 ( 0 / 9 0 / + - 4 5 ) K e v l a r / e p o x y 60% 4 0 . 0 650 1 .4 29 460 ( 0 / 9 0 ) C a r b o n / e p o x y 58% 8 3 . 0 380 1 .54 5 3 . 5 240 ( 0 / 9 0 ) T i t a n i u m - 1 1 5 . 8 992 4 . 5 4 2 5 . 5 218 ( 6 - A L 4 - V ) S t e e l - 2 1 0 . 0 800 7 . 8 2 6 . 9 103 (4320) A l u m i n u m - 7 0 . 0 310 2 . 7 2 5 . 9 115 ( 6 0 6 1 - T 6 ) D e r a k a n e - 3 . 4 79 1 .2 2 . 8 66 ( p o l y e s t e r ) E p o x y - 3 . 4 102 1 .2 2 . 8 85 5 T A B L E 1 .3 M A T E R I A L F R A C T U R E TOUGHNESS ( r e f . 2) M a t e r i a l K I C M P A ( m * . 5 ) A L U M I N U M ( 2 0 2 4 - T 6 ) 8 0 . 2 T I T A N I U M ( 6 A 1 - 4 V ) 215 B - S i C 3 . 3 8 E P 0 X Y ( F 1 8 5 - H e x c e l ) 3 . 6 9 G R A P H I T E - E P O X Y 2 4 . 2 ( 0 / + - 4 5 / 9 0 ) s 6 Polymer composite m a t e r i a l s have been o b s e r v e d t o f o l l o w a r u l e of m i x t u r e s (ROM) t e n s i l e b e h a v i o r . The ROM b e h a v i o r s t a t e s t h a t the i n d i v i d u a l c omposite components c o n t r i b u t e s t r e n g t h and s t i f f n e s s i n p r o p o r t i o n t o t h e i r volume f r a c t i o n p r e s e n t i n the m a t e r i a l . As the m a t r i x c o m p r i s e s up t o 50% of the composite the m e c h a n i c a l s h o r t c o m i n g s of i t r e l a t i v e t o the f i b r e ( T a b l e 1.2) are q u i t e pronounced. One method of i m p r o v i n g the m e c h a n i c a l p r o p e r t i e s of a composite i s t o improve the m a t r i x m a t e r i a l . S u b s t i t u t i n g the polymer m a t r i x w i t h a m e t a l l i c m a t e r i a l i s a f e a s i b l e a l t e r n a t i v e . The advantages of a m e t a l m a t r i x i n c l u d e 1) improved h i g h t e m p e r a t u r e p r o p e r t i e s 2) enhanced m a t e r i a l toughness 3) improved m e c h a n i c a l p r o p e r t i e s of m a t r i x ( Table 1.2) The advantages of aluminum and t i t a n i u m a t h i g h temperature i n comparison t o polymer m a t r i x m a t e r i a l s a r e t h e i r a b i l i t y t o oppose m a t e r i a l d e g r a d a t i o n above 200 °c. The improved t e m p e r a t u r e r e s i s t a n c e i s a t t r i b u t e d t o the p r o t e c t i v e o x i d e l a y e r b o t h t h e s e m e t a l s p o s s e s s . The d i s a d v a n t a g e s of u t i l i z i n g a m e t a l as a m a t r i x m a t e r i a l i n c l u d e : 1) i n c r e a s e d weight : 2) d i f f i c u l t i e s i n m a n u f a c t u r i n g In c o m parison t o a polymer m a t e r i a l ( d e n s i t y = 1.2) the m e t a l s c i t e d have a s u b s t a n t i a l l y g r e a t e r s p e c i f i c g r a v i t y ( T a b l e 1.2). T h i s would t e n d t o m i n i m i z e the weight s a v i n g advantage which i s 7 c r i t i c a l i n the u t i l i z a t i o n of a composite m a t e r i a l . More im p o r t a n t l y , the l i m i t i n g f a c t o r i n the widespread use of continuous f i b r e metal matrix composites i s the complicated p r o c e s s i n g r e q u i r e d d u r i n g manufacturing. T h i s aspect w i l l d i s c u s s e d i n subsequent c h a p t e r s . Of the three metals a l l u d e d to ( A l , T i and S t e e l ) , aluminum has the most p o t e n t i a l as a p o s s i b l e matrix m a t e r i a l . There are many reasons f o r t h i s some of which are l i s t e d below: 1) low d e n s i t y (2.7 g/cm 3) 2) low m e l t i n g p o i n t (660 °c) 3) economically v i a b l e ($1.50 per kg.) 4) e x c e l l e n t c o r r o s i o n r e s i s t a n c e The r e l a t i v e l y low m e l t i n g p o i n t of aluminum a l l o w s f o r a more p r a c t i c a l manufacturing design e s p e c i a l l y i f a molten metal technique i s u t i l i z e d . In comparison to a polymer m a t e r i a l (epoxy = $9.00 per kg.) aluminum i s more ec o n o m i c a l l y f a v o u r a b l e . The p a r t i c u l a r metal matrix composite d e a l t with i n t h i s t h e s i s i s a continuous SiC f i b r e ( N i c a l o n ) r e i n f o r c i n g an u t i l i t y aluminum matrix. The reasons f o r choosing aluminum as a matrix m a t e r i a l have been b r i e f l y c i t e d . Thus, the advantages of SiC w i l l be c o n s i d e r e d . The mechanical p r o p e r t i e s of SiC are comparable to that f o r other ceramic f i b r e s commercially a v a i l a b l e (Table 1.1). D e t e r r e n t s f o r the usage of other f i b r e s i n r e i n f o r c i n g an aluminum matrix i n c l u d e : 1) g r a p h i t e s e v e r e l y degraded by molten aluminum ( r e f . 5 ) 2) h i g h c o s t of boron f i b r e s ( r e f . 6 ) 3) degradation of k e v l a r and g l a s s above 200 °c ( r e f . l ) 8 Two t y p e s of S i C f i b r e s a r e l i s t e d i n T a b l e 1.1. The type of f i b r e employed i n t h i s t h e s i s i s the c o m m e r c i a l l y a v a i l a b l e N i c a l o n S i C produced by the Nippon C o r p o r a t i o n of Japan. Though m e t a l m a t r i c e s have apparent advantages over polymer m a t r i c e s , r e s e a r c h and development of a m e t a l r e i n f o r c e d w i t h a c o n t i n u o u s c e r a m i c f i b r e i s s t i l l i n i t s i n f a n c y . One reason f o r t h i s r e s u l t s from the p r o p r i e t a r y n a t u r e of c o m p o s i t e m a t e r i a l ( i n c l u d i n g m e t a l m a t r i x ) r e s e a r c h conducted by i n d u s t r y . As metal m a t r i x c o m p o s i t e s are r e l a t i v e l y new t o the Department of M e t a l l u r g i c a l E n g i n e e r i n g a t U.B.C. the e x t e n t of r e s e a r c h on c o n t i n u o u s S i C ( N i c a l o n ) f i b r e r e i n f o r c e d aluminum was of an e x p l o r a t o r y nature..The a r e a s s t u d i e d i n c l u d e d : 1) m a n u f a c t u r i n g 2) t e s t i n g 3) c o m p o s i t e m e c h a n i c a l p r o p e r t i e s 9 CHAPTER 2.0  LITERATURE REVIEW The l i t e r a t u r e s e a r c h i s d i v i d e d i n t o two d i s t i n c t p a r t s d e a l i n g w i t h : 1) N i c a l o n S i C F i b r e s 2) S i C / A l c o m p o s i t e s Each s e c t i o n i n c l u d e s r e c e n t developments on m a n u f a c t u r i n g and r e l a t e d m e c h a n i c a l p r o p e r t i e s p e r t a i n i n g t o e i t h e r the f i b r e s or f i b r e r e i n f o r c e d aluminum r e s p e c t i v e l y . 2.1 N i c a l o n S i C F i b r e s N i c a l o n m u l t i f i l a m e n t S i C tows a r e produced by p y r o l y s i s of an o r g a n i c polymer i n t o an i n o r g a n i c B-SiC f i b r e . The p r o c e s s d e v e l o p e d t o c a r r y out t h i s c o n v e r s i o n i n v o l v e s the d e c h l o r i n a t i o n of d i c h l o r o m e t h y s i l a n e t o produce d i m e t h y l p o l y s i l a n e . T h i s i s heated a t 470 °C f o r 8 hours t o produce p o l y c a r b o s i l a n e . The p o l y c a r b o s i l a n e i s then vacuum d i s t i l l e d i n t o a s e r i e s of polymer m o l e c u l e s . The m o l e c u l e s a r e melt spun i n t o c o n t i n u o u s f i b r e s and are c u r e d i n ozone t o c r o s s l i n k the o r g a n i c m o l e c u l e s . These f i b r e s a r e he a t e d a t 850 °C i n n i t r o g e n t o form amorphous S i C which i s then c r y s t a l l i z e d a t 1200 °C. A s - f a b r i c a t e d f i b r e s range i n s i z e from between 10 t o 20 m i c r o n s i n d i a m e t e r ( r e f . 7 ) w i t h a v a r i a b l e l e n g t h ( f i b r e s used i n t h e s i s were r e c e i v e d i n l e n g t h s of 500 m e t r e s ) . The d e n s i t y of the i n d i v i d u a l f i b r e i s 2.6 g/cm 3 i n comparison t o the d e n s i t y of pure B-SiC (3.19 g/cm 3). The lower 10 d e n s i t y i s a r e s u l t of the f i b r e s having a multicomponent composition c o n s i s t i n g of 30% amorphous s i l i c a (2.19 g/cm 3), 10% amorphous carbon (2.0 g/cm 3) and the remainder c r y s t a l l i n e B-SiC ( r e f . 7 ) . The i n d i v i d u a l f i b r e s produced are subsequently combined i n t o tows c o n s i s t i n g of approximately 500 f i b r e s each. As with other b r i t t l e m a t e r i a l s the SiC f i b r e s do not possess a w e l l d e f i n e d s t r e n g t h ; but r a t h e r , a range of f a i l u r e s t r e s s e s corresponding to a p r o b a b i l i t y of s u r v i v a l . F i g u r e 2.1 ( r e f . 8 ) shows that the s t r e n g t h of the f i b r e can range from 300 Mpa to 3800 Mpa. The l a r g e d i s t r i b u t i o n i n f a i l u r e s t r e s s f o l l o w s from a f i b r e s s t r e n g t h dependence on diameter, l e n g t h and s e n s i t i v i t y to flaws. Prewo ( r e f . 8 ) r e p o r t s an average f a i l u r e s t r e s s of 1600 Mpa f o r a mean f i b r e diameter of 40 microns. For f i b r e s p o s s e s s i n g a mean diameter of 12.5 microns an average f i b r e s t r e n g t h of 2.0 Gpa was observed. Average s t r e n g t h corresponds to a 50% p r o b a b i l i t y of f a i l u r e . The decrease i n s t r e n g t h with i n c r e a s i n g f i b r e diameter i s p o s s i b l y the r e s u l t of a l a r g e r flaw s i z e a s s o c i a t e d with the g r e a t e r diameter. The l e n g t h of f i b r e t e s t e d a l s o has a s u b s t a n t i a l e f f e c t on the observed f a i l u r e s t r e s s . Andersson et a l ( r e f . 9 ) e x p e r i m e n t a l l y determined the s t r e n g t h of N i c a l o n f i b r e s (11.9 micron mean diameter) f o r v a r i o u s l e n g t h s . From these t e s t s the f o l l o w i n g equation was e m p e r i c a l l y d e r i v e d : lnS(50) = 8.12 - 0.128 x l n ( L ) ...2.1 S(50) = s t r e s s at 50% p r o b a b i l i t y of f a i l u r e (Mpa) L = f i b r e l e n g t h i n m i l l i m e t r e s 11 4-5 — n — i i i i i i i — r ~ i — n — 1 2 5 10 20 40 60 80 90 95 98 99 99 8 CUMULATIVE FAILURE PROBABILITY (%) F I G . 2.1 - PROBABILISTIC STRENGTH OF S I C FIBRES (REF. 8) 12 T h i s e q u a t i o n i s e v i d e n c e t h a t f i b r e s t r e n g t h i s i n v e r s e l y p r o p o r t i o n a l t o f i b r e l e n g t h . The v a l u e s of average f i b r e s t r e n g t h were d e t e r m i n e d f o r c a r e f u l l y h a n d l e d s i n g l e f i b r e s . T e s t r e s u l t s by Andersson et a l ( r e f . 7 ) r e v e a l t h a t a d e c r ease i n f a i l u r e s t r e s s of up t o 550 Mpa can occur due t o f i b r e m i s h a n d l i n g . The e x t e n t of m i s h a n d l i n g i s unknown, t h u s , i t can o n l y be g e n e r a l i z e d t h a t f i b r e damage i n c u r r e d d u r i n g h a n d l i n g w i l l r e s u l t i n s t r e n g t h d e g r a d a t i o n . D i s c u s s i n g the u l t i m a t e t e n s i l e s t r e n g t h of a s i n g l e S i C f i b r e i s somewhat t r i v i a l when c o n s i d e r i n g the p r o p e r t i e s of a f i b r e w i t h i n a c o m p o s i t e m a t e r i a l . The anomaly e x i s t s i n a S i C / A l composite t h a t th e f a i l u r e of a tow of f i b r e s encompassed by aluminum i s b e i n g a n a l y z e d and not an i n d i v i d u a l f i b r e . The f a c t o r s which would i n h i b i t a d i r e c t comparison between the s i n g l e f i b r e d a t a p r e s e n t e d and the a c t u a l s t r e n g t h of S i C r e i n f o r c i n g a aluminum m a t r i x are as f o l l o w s : 1) p r o b a b i l i s t i c n a t u r e of f i b r e s t r e n g t h 2) e f f e c t s of f i b r e i n t e r a c t i o n i n tow 3) f i b r e damage i n c u r r e d d u r i n g m a n u f a c t u r i n g In l o a d i n g an u n i d i r e c t i o n a l S i C / A l c o m p o s i t e , i n d i v i d u a l f i b r e breakage c o r r e s p o n d i n g t o the weakest f i b r e w i l l o c cur a t a r e l a t i v e l y low s t r e s s l e v e l . As shown e a r l i e r i n F i g . 2.1 t h i s s t r e s s can be as low as 300 Mpa. The o r i g i n a l l o a d once c a r r i e d by t h e s e broken f i b r e s w i l l then be t r a n s f e r r e d v i a the aluminum t o a d j a c e n t f i b r e s . The c u m u l a t i v e s t r e s s s h i f t e d t o t h e s e f i b r e s would r e s u l t i n a d d i t i o n a l f i b r e f a i l u r e and so on. I t i s e x p e c t e d t h a t due t o t h i s domino e f f e c t a m u l t i f i l a m e n t S i C tow 13 w i l l have a seemingly lower average f a i l u r e s t r e s s than t h a t measured f o r a comparable number of i n d i v i d u a l f i b r e s . The e f f e c t on f a i l u r e s t r e s s as a r e s u l t of 500 f i b r e s i n t e r t w i n e d i n a tow h a v i n g a 0.1 mm^  c r o s s s e c t i o n i s unknown. I t can o n l y be presumed t h a t a b r a s i o n between f i b r e s would induce s u f f i c i e n t damage t o d e c r e a s e the average f i b r e s t r e n g t h i n each tow. The t e n s i l e t e s t s , c i t e d by r e s e a r c h e r s i n the l i t e r a t u r e a r e f o r c a r e f u l l y h andled s i n g l e f i b r e s . As s u b s t a n t i a l s t r e n g t h r e d u c t i o n was observed f o r m i s h a n d l e d f i b r e s ( r e f . 7 ) , the e x t e n t of f i b r e damage i n c u r r e d d u r i n g t h e f a b r i c a t i o n p r o c e s s of an S i C r e i n f o r c e d aluminum i s something t o be c o n s i d e r e d . I t i s l i k e l y t h a t d u r i n g a hot p r e s s i n g o p e r a t i o n some form of f i b r e damage w i l l be induced r e s u l t i n g i n a s t r e n g t h r e d u c t i o n . F i b r e modulus was found t o have a f a i r l y c o n s i s t e n t v a l u e of 200 +- 10 Gpa t e s t e d over an average d i a m e t e r of 12.0 mi c r o n s ( r e f 9 ) . An anomaly was r e p o r t e d i n the l i t e r a t u r e f o r f i b r e s h a v i n g a diameter of 5 m i c r o n s . A modulus f o r t h e s e f i b r e s of 500 Gpa was o b t a i n e d ( r e f . 7 ) . These e x c e p t i o n a l l y h i g h v a l u e s can be a t t r i b u t e d t o a h i g h e r p u r i t y f i b r e b e i n g produced ( i n terms of Si C ) and e r r o r s i n t e s t i n g such a f i n e specimen. I t i s g e n e r a l l y a greed t h a t a modulus of 200 +- 10 Gpa i s c o n s i d e r e d c o r r e c t ( r e f . 7 , 8 , 1 0 , 1 1 ) . U n l i k e g l a s s or k e v l a r the N i c a l o n S i C was found t o p o s s e s s e x c e l l e n t h i g h t e m p e r a t u r e p r o p e r t i e s . Kohara ( r e f . 1 2 ) o b s e r v e d t h a t the f i b r e s m a i n t a i n e d a r e l a t i v e l y c o n s i s t e n t s t i f f n e s s and s t r e n g t h up t o 1200 °C. I t s h o u l d be noted t h a t t h e s e h i g h 14 te m p e r a t u r e t e s t s were c a r r i e d out i n argon g a s . I t c o u l d be p o s t u l a t e d t h a t the f o r m a t i o n of a p r o t e c t i v e o x i d e f i l m ( s i l i c o n o x i d e ) would m a i n t a i n f i b r e i n t e g r i t y i n the p r e s e n c e of oxygen at s i m i l a r t e m p e r a t u r e s . 2.2 S i C R e i n f o r c e d Aluminum Composites Of more c o n c e r n t o the work c a r r i e d out i n t h i s t h e s i s a r e the m e c h a n i c a l p r o p e r t i e s c i t e d f o r a u n i d i r e c t i o n a l S i C / A l c o m p o s i t e . D i s c u s s e d i n t h i s s e c t i o n w i l l be the m a n u f a c t u r i n g t e c h n i q u e s employed, observed m e c h a n i c a l p r o p e r t i e s and c e r t a i n a s p e c t s of the S i C f i b r e aluminum i n t e r f a c e . 2.2.1 M a n u f a c t u r i n g Methods The p r e f e r r e d method of m a n u f a c t u r i n g N i c a l o n S i C r e i n f o r c e d aluminum i s by a molten aluminum hot p r e s s i n g t e c h n i q u e . The r e a s o n i n g f o r the hot p r e s s i n g w i l l be d i s c u s s e d i n the c h a p t e r on d i e d e s i g n . There e x i s t s e v e r a l v a r i a t i o n s of the molten hot p r e s s i n g t e c h n i q u e t h a t have been a p p l i e d t o produce a S i C / A l c o m p o s i t e . These methods w i l l be d e s c r i b e d as p r e c i s e l y as p o s s i b l e and the d i s a d v a n t a g e s / a d v a n t a g e s s t a t e d . I t s h o u l d be no t e d t h a t s p e c i f i c d e t a i l s p e r t a i n i n g t o the v a r i o u s m a n u f a c t u r i n g t e c h n i q u e d e s c r i b e d were not p r e s e n t e d i n the papers r e f e r e n c e d . Tanaka e t a l ( r e f . 1 0 ) produced a S i C / A l composite by the f o l l o w i n g method: 1) The S i C tows were drum wound i n t o s h e e t s u s i n g a v i n l y e s t e r b i n d e r . 2) L a y e r s of S i C s h e e t s and 6061 aluminum d i s c s were then 15 a l t e r n a t e l y stacked i n s i d e a s t a i n l e s s s t e e l v e s s e l 3) The v e s s e l was evacuated and heated to 720 °C. The v e s s e l was then h e l d at t h i s temperature f o r 10 minutes. 5) Upon removal from the furnace the v e s s e l was immediately p r e s s e d at 19.6 Mpa f o r 15 minutes. The advantage of t h i s method i s the s i m p l i c i t y of the manufacturing technique. The disadvantages are that the s t a i n l e s s s t e e l v e s s e l i s non-reusable and the temperature of the S i C / A l l a y up i s a p p a r e n t l y not recorded throughout the procedure. F u r t h e r d e t a i l s on v e s s e l d e s i g n and problems encountered were not a v a i l a b l e . Nakata et a l ( r e f 13) although employing a hot p r e s s i n g technique m e c h a n i c a l l y wrap the SiC tows on an e x t e r n a l s t e e l frame as opposed to drum winding them i n t o s heets. The s t e e l frame i s heated at 500 °C f o r 30 minutes and then h o r i z o n t a l l y p l a c e d i n a metal mould i n t o which molten aluminum (800 °C) i s poured. A p r e s s u r e of 49.0 Mpa i s then immediately a p p l i e d . As with Tanaka et a l , s p e c i f i c d e t a i l on mould design was not g i v e n . The disadvantages with t h i s method stem from the complexity of the procedure. D i f f i c u l t i e s a s s o c i a t e d with winding the tows on the s t e e l frame and mould design would be encountered. Fukunaga et a l (ref.11) p o s i t i o n the SiC tows onto a support frame which i s p l a c e d i n t o a metal d i e . Molten aluminum i s then f o r c e d up i n t o the d i e a r e a . T h i s p r e s s i n g a l l o w s f o r the l o n g i t u d i n a l i n f i l t r a t i o n of the aluminum i n t o the f i b r e tows. Fukunga et a l observed inadequate aluminum p e n e t r a t i o n of the tows i n the c e n t r e p o r t i o n of the d i e . Other disadvantages 16 i n c l u d e the e l a b o r a t e p r e s s i n g equipment r e q u i r e d , c o m p o s i t e s produced as a c y l i n d e r and p r o d u c t i o n i s l i m i t e d t o u n i d i r e c t i o n a l r e i n f o r c e m e n t o n l y . G i g e r e n z e r e t a l ( r e f . 14) m a n u f a c t u r e d u n i d i r e c t i o n a l S i C r e i n f o r c e d aluminum by a hot d r a w i n g p r o c e s s . A r o l l e r d r i v e system was u t i l i z e d t o p u l l the f i b r e s t h r o u g h a b a t h of molten aluminum and then a c a s t i n g d i e . The d i e forms the drawn f i b r e i n t o a c y l i n d r i c a l bar s t o c k c o m p o s i t e . The f i b r e s u t i l i z e d i n t h i s p r o c e s s a r e 100 m i c r o n s i n d i a m e t e r , t h e r e f o r e , problems w i t h i n f i l t r a t i o n of aluminum i n between f i b r e s were not e n c o u n t e r e d . As N i c a l o n S i C comes i n compacted tows, i t i s u n d e r s t a n d a b l e t h a t aluminum p e n e t r a t i o n i n t o the f i b r e s would be a problem w i t h t h i s p r o c e s s . Composites produced by the hot drawing p r o c e s s a r e l i m i t e d t o u n i d i r e c t i o n a l c o n f i g u r a t i o n s . A m o d i f i e d hot p r e s s i n g method was employed by Kohara e t a l ( r e f . 1 5 ) . P r i o r t o the a c t u a l p r e s s i n g p r o c e d u r e a p r e f o r m of S i C and aluminum powder was p r e p a r e d . The impregnated tow was produced by immersing the S i C f i l a m e n t s i n a s l u r r y of aluminum powder and sodium a l g i n a t e s o l u t i o n . The p r e p r e g g e d S i C was c u t i n t o s t r i p s and p l a c e d i n a g r a p h i t e d i e f o r subsequent l i q u i d hot p r e s s i n g . The s l u r r y t e c h n i q u e a l l o w s f o r improved aluminum i n f i l t r a t i o n i n t o the f i b r e tows. The d i s a d v a n t a g e i s t h a t the f i b r e s must s t i l l be hot p r e s s e d i n the molten s t a t e i n o r d e r t o e l i m i n a t e v o i d s and c r e v i c e s i n the c o m p o s i t e . I t was d i f f i c u l t t o a s s e s s the q u a l i t y of c o m p o s i t e produced by Kohara e t a l as m e c h a n i c a l p r o p e r t i e s were not p r o v i d e d . A d d i t i o n a l i n f o r m a t i o n on t h e p r e s s i n g t e c h n i q u e was not a v a i l a b l e . 1 7 The methods of manufacturing as presented above are q u i t e v a r i e d i n nature. Each technique, though a b l e to produce a composite adequately, has s e v e r a l disadvantages a s s o c i a t e d with i t . One predominant drawback i s the complexity of apparatus r e q u i r e d f o r the manufacturing p r o c e s s . An e x c e p t i o n i s the technique employed by Tanaka et a l ( r e f . 1 0 ) . The inherent d i f f i c u l t i e s with t h i s method i s the non-reusable d i e and lack of process c o n t r o l (monitoring of temperature). E x c l u d i n g Tanaka et a l ( ref.10) and Kohara et a l ( r e f . 1 5 ) , the methods presented above a l s o l a c k the f l e x i b i l i t y i n producing anything other than a u n i d i r e c t i o n a l composite. T h i s f a c t o r would tend to l i m i t t h e i r use i n most a p p l i c a t i o n s . 2.2.2 Mechanical P r o p e r t i e s The t e n s i l e p r o p e r t i e s of u n i d i r e c t i o n a l SiC composites, as determined by v a r i o u s r e s e a r c h e r s , are presented i n Table 2.1 . The t e n s i l e s t r e n g t h s of each composite were c a t e g o r i z e d a c c o r d i n g to the matrix m a t e r i a l s s t r e n g t h because the type of aluminum used as the matrix m a t e r i a l v a r i e d . The t e n s i l e s t r e n g t h s of 1050 aluminum and 1100 aluminum are s i m i l a r (76 Mpa and 90 Mpa f o r annealed specimens r e s p e c t i v e l y ) , hence, t h e i r v a l u e s are grouped t o g e t h e r . The 6061 matrix samples (annealed s t r e n g t h of 125 Mpa) were grouped s e p a r a t e l y as were the 5052 composites (annealed s t r e n g t h of 198 Mpa). The t e n s i l e s t r e n g t h s r e p o r t e d i n Table 2.1 i n d i c a t e a wide range of v a r i a b i l i t y i n the mechanical p r o p e r t i e s of SiC r e i n f o r c e d aluminum. The h i g h e s t f a i l u r e s t r e s s was c i t e d f o r a 18 TABLE 2.1 Mechanical P r o p e r t i e s of S i C / A l Composites Volume M a t r i x UTS T e n s i l e Tempered Ref F r a c t i o n M a t e r i a l (Mpa) Specimen UTS (%) Thickness (Mpa) (mm) 34 1050 630 35 pure A l 440 35 1100 861 40 pure A l 420 41 1050 673 (wire) 25 6061 690 25 6061 635 30 6061 630 35 6061 800 40 6061 700 42 6061 313 50 6061 760 31 5052 251 40 5052 781 NA - 16 1.0 - 17 1.2 836-0 10 NA - 11 NA - 16 1.2 680-O 10 1.5 - 18 1.5 - 18 1.5 - 18 1.5 - 18 NA - 16 1.5 - 19 NA - 16 1.2 784-0 10 19 35% volume f r a c t i o n 1100 aluminum m a t r i x sample ( r e f . 1 0 ) . S u r p r i z i n g l y , specimens w i t h volume f r a c t i o n s e x c e e d i n g 35% and p o s s e s s i n g a s t r o n g e r m a t r i x (eg. 6061 or 5052) e x h i b i t e d n o t a b l y l o w e r u l t i m a t e t e n s i l e s t r e n g t h s . T h i s would i n d i c a t e t h a t f o r t h e m a n u f a c t u r i n g t e c h n i q u e s c u r r e n t l y i n use adequate aluminum i n f i l t r a t i o n i n t o the f i b r e tows does not o c c u r f o r h i g h volume f r a c t i o n s of f i b r e s . Kohyama et a l ( r e f . 1 6 ) i s an e x c e l l e n t example of the v a r i a b i l i t y e n c o u n t e r e d i n m a n u f a c t u r i n g a S i C / A l c o m p o s i t e . The s t r e n g t h of the 42%-6061 and 31%-5052 specimens a r e w e l l below t h a t o b s e r v e d f o r a 34%~1050 sample though i d e n t i c a l m a n u f a c t u r i n g p r o c e s s e s were employed. The c o n s i s t e n c y of the t e n s i l e t e s t r e s u l t s f o r r e f e r e n c e s 10, 18 and 19 i s hot s u r p r i s i n g as the a u t h o u r s of each paper a r e i n t e r c o n n e c t e d . A major concern i n h i b i t i n g the a b s o l u t e c o mparison of the t e n s i l e t e s t s c i t e d i s the s t r e n g t h e n i n g c o n t r i b u t i o n p r o v i d e d by the aluminum m a t r i x t o the c o m p o s i t e s s t r e n g t h . S e c o n d l y , i n c o n s i s t e n c i e s r e s u l t i n g from t e n s i l e specimen c o n f i g u r a t i o n a r e i g n o r e d . The l a c k of i n f o r m a t i o n p r o v i d e d i n the l i t e r a t u r e on the s t r e n g t h e n i n g a f f e c t of the aluminum m a t r i x towards composite t e n s i l e p r o p e r t i e s d e t r a c t s from the UTS v a l u e s l i s t e d i n Table 2.1. A v a r i e t y of c a l c u l a t i o n s c a r r i e d out on t e n s i l e d a t a s u p p l i e d by Tanaka et a l ( r e f . 1 0 ) i n d i c a t e s y n e r g i s t i c s t r e n g t h e n i n g of the c o m p o s i t e o c c u r s . The s t r e s s - s t r a i n c u r v e and accompanying d a t a i n F i g u r e 2.2 ( r e f . 1 0 ) was used t o 20 800 600 400 h 200 0 0.5 1.0 Strain ( t ) S t r e s s - s t r a i n behavior of SiC/606l composite 1000 S t r e s s - s t r a i n behavior of SiC/5052 composite SiC/1100 As-Fab. H.T. SiC/5052 As-Fab. H.T. SiC/6061 As-Fab. H.T. v f ( * ) Tensile ( 0°) Strength ( MPa ) (90°) Elastic ( E,) Modulus ( GPa ) ( E 2) 35 861 836 (930*) 15 89 92 73 81 40 781 784 (1060*) 10 121 130 105 111 25 690 680 (710*) 140 100 119 77 86 FIG. 2.2 - SIC/ALUMINUM COMPOSITE TENSILE DATA (REF.10) 21 determine the aluminums c o n t r i b u t i o n t o o v e r a l l composite s t r e n g t h through the f o l l o w i n g e q u a t i o n : E2 = V F F x (200Gpa) + (1-VF F) x (ds/de) E2 = s l o p e of s t r e s s - s t r a i n curve a f t e r y i e l d i n g (78 Gpa) VFp = volume f r a c t i o n f i b r e s (0.25) ds/de = r a t e of aluminum matrix s t r a i n hardening Assuming that a l l f i b r e s c o n t r i b u t e a s t i f f n e s s of 200 Gpa the value f o r the s t r a i n hardening term (ds/de) was c a l c u l a t e d . The apparent s t r a i n hardening of the 6061 aluminum matrix f o r the as-c a s t sample was c a l c u l a t e d to be 37.3 Gpa. The annealed specimen e x h i b i t e d a matrix s t r a i n hardening r a t e , a f t e r y i e l d i n g , of 48 Gpa. The anomaly which e x i s t s i s that the e l a s t i c modulus of aluminum i s o n l y 68 Gpa. A p o s s i b l e e x p l a n a t i o n f o r t h i s phenomenal s t r e n g t h e n i n g w i l l be d i s c u s s e d i n l a t e r c h a p t e r s . The c o n f i g u r a t i o n of the t e n s i l e sample used i n o b t a i n i n g the u l t i m a t e t e n s i l e s t r e n g t h s i s an important f a c t o r . I t was observed ( r e f . 17) that a r e d u c t i o n i n t e n s i l e sample t h i c k n e s s from 1.8 mm to 1.0 mm brought about an i n c r e a s e i n f a i l u r e s t r e s s of 125 Mpa. T h i s would i n d i c a t e that t e n s i l e sample t h i c k n e s s may a f f e c t the s t r e n g t h e n i n g behaviour of the aluminum matrix. For comparative purposes the mechanical p r o p e r t i e s of an u n i d i r e c t i o n a l SiC r e i n f o r c e d aluminum prepared by Avco S p e c i a l t y Products are l i s t e d i n Table 2.2. The f i b r e u t i l i z e d by Avco i s produced by vapour d e p o s i t i o n of B-SiC onto a carbon s u b s t r a t e . The mechanical p r o p e r t i e s of the f i b r e are a l s o presented i n Table 2.2. The p r o p e r t i e s summarized i n Table 2.2 were obtained from s a l e s l i t e r a t u r e provided by Avco. 22 TABLE 2.2 S i C / A l Composite P r o p e r t i e s - Avco S p e c i a l t y Products SiC F i b r e : diameter = 140 microns modulus = 427 Gpa s t r e n g t h = 3474 Mpa d e n s i t y = 3.0 g/cm 3 S i C / A l Composite: volume f r a c t i o n = 42% f a i l u r e s t r e s s = 1.41 Gpa 23 E x a c t d e t a i l s on m a n u f a c t u r i n g and t e s t i n g were not g i v e n because of p r o p r i e t a r y r e a s o n s . 2.2.3 I n t e r f a c i a l P r o p e r t i e s The i n t e r f a c e between a f i b r e and a m e t a l m a t r i x has a v e r y i m p o r t a n t i n f l u e n c e on the m e c h a n i c a l p r o p e r t i e s of a c o m p o s i t e . In g e n e r a l , c o n c e r n i s e x p r e s s e d over the type of i n t e r a c t i o n t h a t o c c u r s a t the f i b r e - m a t r i x i n t e r f a c e s i n c e the q u a l i t y of the bonding c o n t r o l s the l o a d t r a n s f e r c a p a b i l i t i e s . F o r example, the p r e s ence of a weak bond w i l l i n h i b i t f u l l u t i l i z a t i o n of the f i b r e p r o p e r t i e s due t o the poor l o a d t r a n s f e r a b i l i t y between the f i b r e and m a t r i x m a t e r i a l . Other f a c t o r s t h a t a r e a f f e c t e d by the i n t e r f a c i a l bond q u a l i t y a r e f r a c t u r e toughness and h i g h t e m p e r a t u r e s t r e n g t h . D u r i n g the l o a d i n g of a c o m p o s i t e m a t e r i a l , a weak i n t e r f a c i a l bond can be a s i t e f o r p r e f e r e n t i a l composite damage. The premature c r a c k i n g which o c c u r s a t the i n t e r f a c e would i n c r e a s e the co m p o s i t e s toughness by c o n v e r t i n g e l a s t i c energy i n t o s u r f a c e energy. At e l e v a t e d t e m p e r a t u r e s bond s t r e n g t h i s i m p o r t a n t f o r m a i n t a i n i n g composite i n t e g r i t y . D u r i n g h e a t i n g , the l a r g e r t h e r m a l e x p a n s i o n c o e f f i c i e n t of the aluminum (aluminum = 23.6 X10~^, S i C = 5.8 X10~6) would r e s u l t i n p o s s i b l e f i b r e - m a t r i x d e c o h e s i o n . Yajima e t a l ( r e f . 2 0 ) o b s e r v e d a s i g n i f i c a n t r e d u c t i o n i n composite s t r e n g t h a t 500 °C. A photo of the f r a c t u r e s u r f a c e i n d i c a t e d e x t e n s i v e debonding a t the S i C f i b r e aluminum i n t e r f a c e . I f a s t r o n g i n t e r f a c e e x i s t s the e f f e c t s of 24 i n t e r f a c i a l debonding and subsequent d e g r a d a t i o n of the l o a d t r a n s f e r c a p a b i l i t i e s at e l e v a t e d temperatures may be suppressed. The types of bonding that can e x i s t between a f i b r e and a metal matrix m a t e r i a l a r e : 1) p h y s i c a l bonding (mechanical cohesion) 2) r e a c t i o n bonding Mechanical bonding, as i m p l i e d , r e l i e s on the p h y s i c a l i n t e r a c t i o n between a f i b r e and m a t r i x . F a c t o r s such as f i b r e roughness and f i b r e - m a t r i x w e t t a b i l i t y determine the s t r e n g t h of such a bond. Conversely, r e a c t i o n bonding r e s u l t s from the formation of an intermediate phase. The coherency of the r e a c t i o n phase (at an atomic l e v e l ) with both the SiC and aluminum r e s p e c t i v e l y , p r o v i d e s the means f o r f i b r e - m a t r i x bonding. With the i n t r o d u c t i o n of SiC f i b r e s i n t o aluminum v i a a l i q u i d p r e s s i n g technique much has been p o s t u l a t e d on the type of i n t e r f a c e which would e x i s t i n t h i s system. I t i s p o s s i b l e that an i n t e r m e d i a t e phase ( A L 4 C 3 ) would form (ref.21) a c c o r d i n g to the f o l l o w i n g e q u a t i o n : 3 S i C ( s ) + 4A1(1) = A L 4 C 3 ( s ) + 3 S i ( s ) The thermodynamics f o r the above r e a c t i o n have been c a l c u l a t e d f o r S iC f i b r e s i n l i q u i d and s o l i d aluminum. F i g u r e s 2 . 3 (as c a l c u l a t e d by ref.21 and 2.4 ( c a l c u l a t i o n i n appendix A) show the Gibbs Free energy f o r the formation of aluminum c a r b i d e f o r both c o n d i t i o n s r e s p e c t i v e l y . The f r e e energy was determined f o r a range of temperatures and a c t i v i t i e s of s i l i c o n . The a c t i v i t y of s i l i c o n i s assumed to be equal to i t s weight percentage i n 25 F I G . 2.3 - FREE ENERGY OF ALUMINUM CARBIDE FORMATION IN L IQUID ALUMINUM FOR VARIOUS A C T I V I T I E S OF S I L ICON ( R E F . 2 1 ) 26 F I G . 2.4 - FREE ENERGY OF ALUMINUM CARBIDE FORMATION IN SOLID ALUMINUM FOR VARIOUS A C T I V I T I E S OF S IL ICON ( c a l c u l a t i o n s i n A p p e n d i x A) 27 s o l u t i o n which f o r the u t i l i t y aluminum i s between 0.4 and 0.6 p e r c e n t S i . The f r e e energy v a l u e s t e n d t o be a t b e s t o n l y s l i g h t l y n e g a t i v e f o r both s c e n a r i o s ( F i g s . 2.3 and 2.4); t h e r e f o r e , f o r m a t i o n of the aluminum c a r b i d e i s q u e s t i o n a b l e . The p o s s i b i l i t y of the r e a c t i o n o c c u r r i n g i n e i t h e r the l i q u i d or s o l i d s t a t e i s then dependent on the r a t e of r e a c t i o n . I n t u i t i v e l y , the k i n e t i c s f o r the r e a c t i o n a re c o n s i d e r a b l y g r e a t e r i n the l i q u i d aluminum as opposed t o t h e s o l i d s t a t e . Assuming t h i s statement i s c o r r e c t , the p e r i o d of time i n which the f i b r e s a re i n c o n t a c t w i t h the molten aluminum can be c o n s i d e r e d c r i t i c a l w i t h r e g a r d s t o the p o s s i b l e f o r m a t i o n of aluminum c a r b i d e . The thermodynamics p r e s e n t an u n c l e a r p i c t u r e of whether or not aluminum c a r b i d e w i l l form. T h i s u n c e r t a i n t y c a r r i e s over t o the l i t e r a t u r e . I s e k i e t a l ( r e f . 2 1 ) , by means of TEM a n a l y s i s , d e t e r m i n e d t h a t aluminum c a r b i d e had formed a t the i n t e r f a c e between aluminum and a b l o c k of p r e s s u r e l e s s s i n t e r e d S i C . The S i C was i n c o n t a c t w i t h the aluminum f o r one hour a t 1000 °C. C o n v e r s e l y , under i d e n t i c a l c o n d i t i o n s the pr e s e n c e of aluminum c a r b i d e was not d e t e c t e d on the s u r f a c e of a r e a c t i o n s i n t e r e d S i C b l o c k . The d i s c r e p a n c y was r e l a t e d t o the l a r g e amount of f r e e S i p r e s e n t i n the r e a c t i o n s i n t e r e d S i C i n h i b i t i n g the r e a c t i o n ( a c t i v i t y of S i approaches o ne). Kohyama e t a l ( r e f . 1 6 ) d e t e r m i n e d from the e l e c t r o n d i f f r a c t i o n p a t t e r n of a s u f f i c i e n t l y t h i n n e d S i C / A l sample the pr e s e n c e of aluminum c a r b i d e a t the f i b r e - m a t r i x i n t e r f a c e . Y ajima e t a l ( r e f . 1 9 ) 28 e x t r a c t e d f i b r e s from an aluminum matrix and s u b j e c t e d them to d e t a i l e d X-ray a n a l y s i s . The presence of aluminum c a r b i d e was not d e t e c t e d . I t should be note that comparisons between Rohyama et a l (ref.16) and Yajima et a l (ref.19) p e r t a i n i n g to the formation of aluminum c a r b i d e i s d i f f i c u l t as the exact time spent by the f i b r e s i n the molten aluminum f o r each process was not g i v e n . Though a r e a c t i o n between aluminum and SiC can improve i n t e r f a c i a l bonding, f i b r e degradation may occu r . Kohara (ref.12) observed a c o n s i d e r a b l e drop in f i b r e s t r e n g t h (up to 50%) a f t e r s u b j e c t i n g N i c a l o n SiC f i b r e s to molten aluminum f o r 30 minutes. The decrease i n s t r e n g t h was a t t r i b u t e d to the formation of aluminum c a r b i d e i n i t i a t i n g flaws on the f i b r e s u r f a c e ( r e f . 5 ) . Owing to the b r i t t l e nature of the f i b r e s the flaws have a s u b s t a n t i a l e f f e c t on the u l t i m a t e f i b r e s t r e n g t h . In c o n t r a d i c t i o n Yajima et a l ( r e f . 1 9 ) found that i n d i v i d u a l f i b r e s t r e n g t h , a f t e r removal from the aluminum m a t r i x , was comparable to the pre composite f i b r e s t r e n g t h . However, Yajima et a l (ref.19) d i d not d e t e c t the presence of f i b r e degrading aluminum c a r b i d e . The l i t e r a t u r e reviewed i s somewhat i n c o n c l u s i v e i n p r e s e n t i n g a c o n s i s t e n t d e s c r i p t i o n of a S i C / A l composites p r o p e r t i e s . The ambiguity may in part r e s u l t from the v a r i o u s manufacturing methods used i n producing the S i C / A l composite. I t i s hoped t h a t t h i s t h e s i s w i l l p r ovide more c o n c l u s i v e r e s u l t s p e r t a i n i n g to the many f a c e t e d aspects of t h i s m a t e r i a l . 29 CHAPTER 3.0  COMPOSITE PRODUCTION 3.1 D i e De s i g n and M a n u f a c t u r i n g In t r y i n g t o d e v e l o p a m a n u f a c t u r i n g p r o c e s s f o r the p r o d u c t i o n of a S i C / A l composite s e v e r a l problems needed t o be overcome. These d i f f i c u l t i e s a r e not o n l y i n h e r e n t t o the S i C i t s e l f , but a r e a l s o dependent on the form i n which the f i b r e s a r e r e c e i v e d . For the N i c a l o n S i C f i b r e s on which t h i s r e s e a r c h p r o j e c t i s based, a c o m b i n a t i o n of two f a c t o r s make m a n u f a c t u r i n g a composite w i t h t h i s m a t e r i a l a c h a l l e n g e : 1) poor w e t t a b i l i t y of S i C by aluminum 2) i n f i l t r a t i o n of aluminum i n t o S i C tows W e t t a b i l i t y i s a measure of the a n g l e which a molten m a t e r i a l assumes when i n c o n t a c t w i t h a s o l i d s u b s t r a t e . By d e f i n i t i o n a c o n t a c t a n g l e of l e s s than 90° i s i n d i c a t i v e of good s o l i d s u r f a c e coverage by the molten m a t e r i a l ( r e f . 3 0 ) . C o n v e r s e l y , n a t u r a l w e t t i n g of the s o l i d by the molten m a t e r i a l i s not p o s s i b l e f o r c o n t a c t a n g l e s g r e a t e r than 90°. F i g u r e 3.1 ( r e f . 7 ) d e p i c t s the c o n t a c t a n g l e s between v a r i o u s molten aluminum a l l o y s and S i C f o r a range of t e m p e r a t u r e s . C o n t a c t a n g l e s of a p p r o x i m a t e l y 135° f o r t e m p e r a t u r e s under 900 °C v e r i f y t h a t n a t u r a l w e t t i n g of the S i C by molten aluminum i s u n l i k e l y . To ensure s u i t a b l e f i b r e aluminum m a t r i x c o n t a c t , the poor w e t t a b i l i t y i s overcome by hot p r e s s i n g the aluminum d u r i n g s o l i d i f i c a t i o n . 30 — i 1 i i 800 900 1000 1100 Temperature (°C) F I G . 3.1 - WETTING OF S IC CRYSTAL BY ALUMINUM AS A FUNCTION OF TEMPERATURE ( R E F . 7 ) 31 C oupled w i t h the i n h e r e n t problem of poor f i b r e w e t t a b i l i t y by m olten aluminum i s the compacted form i n which the N i c a l o n f i b r e s a r e r e c e i v e d . As mentioned e a r l i e r , the f i b r e s a r e o n l y a v a i l a b l e i n tows c o n s i s t i n g of 500 f i b r e s each. The h i g h p a c k i n g d e n s i t y of the S i C f i b r e s i n c o m b i n a t i o n w i t h t h e i r poor w e t t a b i l i t y i n h i b i t s adequate aluminum i n f i l t r a t i o n i n t o the tows. By a p p l y i n g p r e s s u r e t o the molten aluminum d u r i n g f a b r i c a t i o n t h i s d i f f i c u l t y can be overcome t o some e x t e n t . As c i t e d i n the l i t e r a t u r e , r e s e a r c h e r s have manufactured c o n t i n u o u s S i C f i b r e r e i n f o r c e d aluminum by a v a r i e t y of hot p r e s s i n g t e c h n i q u e s . Though these methods have g i v e n s a t i s f a c t o r y r e s u l t s a number of f a c t o r s p r e c l u d e t h e i r use. These i n c l u d e : 1) complex d i e d e s i g n s 2) m a n u f a c t u r i n g system employed i s n o n - r e u s a b l e 3) some methods a b l e t o produce o n l y u n i d i r e c t i o n a l c o m p o s i t e s To c i r c u m v e n t the problems mentioned above, w h i l e s t i l l o vercoming poor f i b r e w e t t a b i l i t y and i n f i l t r a t i o n , a new m a n u f a c t u r i n g system was d e s i g n e d . The o b j e c t i v e of the m a n u f a c t u r i n g p r o c e d u r e d e v e l o p e d f o r t h i s t h e s i s i s t o i n c r e a s e the s o l i d phase c o n t a c t between the m a t r i x and f i b r e . Thus , a s u b s t a n t i a l amount of p r e s s u r e i s a p p l i e d o n l y a t the p o i n t of aluminum s o l i d i f i c a t i o n . The advantage w i t h t h i s method i s t h a t a much s i m p l e r d i e d e s i g n can be u t i l i z e d . F i b r e - m a t r i x bonding i s a c h i e v e d by a p p l y i n g a s u f f i c i e n t l y h i g h s t r e s s t o p l a s t i c a l l y deform the aluminum 32 i n t o c o n t a c t w i t h the SiC f i b r e . Weinberg (re f . 2 3 ) i n v e s t i g a t e d the high temperature s t r e n g t h of aluminum, and a reasonable e x t r a p o l a t i o n of h i s r e s u l t s i n d i c a t e that pure aluminum possesses a s t r e n g t h of approximately 10 Mpa at 560 °C. A s t r e s s i n excess of t h i s value (a pressure of 46 Mpa was used by other r e s e a r c h e r s ) i s deemed s u f f i c i e n t to induce p l a s t i c deformation i n the u t i l i t y aluminum used i n the manufacturing p r o c e s s . Besides e n s u r i n g i n t i m a t e f i b r e matrix c o n t a c t , the p l a s t i c deformation of the aluminum w i l l e l i m i n a t e v o i d s c r e a t e d by aluminum c o n t r a c t i o n (%6.0) d u r i n g the l i q u i d to s o l i d phase t r a n s f o r m a t i o n . Though e x c e l l e n t f i b r e c o n t a c t i s obtained by t h i s method, p e n e t r a t i o n of aluminum i n t o the f i b r e tows i s q u e s t i o n a b l e . Aluminum i n f i l t r a t i o n , as w i l l be d i s c u s s e d l a t e r , i s obtained by a p p l y i n g a minimal amount of p r e s s u r e to the molten aluminum d u r i n g i n i t i a l c o o l i n g . To b e t t e r f a c i l i t a t e the understanding of the d i e design a s s o c i a t e d with the quasi hot p r e s s i n g technique i t would be u s e f u l to d e s c r i b e the manufacturing process employed. From t h i s procedure s p e c i f i c d e t a i l s on d i e c o n f i g u r a t i o n and m a t e r i a l setup w i l l be d i s c u s s e d . F i g u r e 3.2 i s a schematic c r o s s s e c t i o n of the d i e system used f o r the q u a s i hot p r e s s i n g procedure. B a s i c a l l y , the d i e c o n s i s t s of a s e m i - s t a t i o n a r y lower plunger ( F i g . 3.3) (the lower plunger i s immobile duri n g hot p r e s s i n g but i s removable to a l l o w easy access to the produced composite) and a mobile upper plunger ( F i g . 3.4) to which pr e s s u r e i s a p p l i e d . Encompassing the upper and lower plungers i s a s t a i n l e s s s t e e l r F I BREFRAX TUBE UPPER PLUNGER CAVITY FOR SIC/AL COMPOSITE OUTER RING A CHROMEL - ALUMEL THERMOCOUPLE LOWER PLUNGER CO FIG. 3.2 - SCHEMATIC CROSS-SECTION OF PRESSING SYSTEM 2.8 FIG. 3.3 - LOWER DIE PLUNGER (dimensions i n nun) FIG. 3 . 4 - UPPER DIE PLUNGER (dimensions i n mm) LO cn 36 r i n g ( F i g . 3.5) l i n e d on the i n n e r c i r c u m f e r e n c e w i t h a f i b r e f r a x t u b e . The upper and lower p l u n g e r s a r e t a p e r e d t o a l l o w easy movement w i t h i n the f i b r e f r a x t u b i n g w h i l e s t i l l m a i n t a i n i n g a s u i t a b l e s t a t i c s e a l a g a i n s t aluminum l e a k a g e from the c o m p o s i t e c a v i t y . The p r o c e d u r e used t o produce a S i C r e i n f o r c e d aluminum composi t e i s as f o l l o w s : 1 ) C i r c u l a r d i s c s of u t i l i t y aluminum and u n i d i r e c t i o n a l s h e e t s of S i C a r e a l t e r n a t e l y s t a c k e d i n d i e c a v i t y . 2) The e n t i r e d i e system i s p l a c e d i n t o a 815 °C f u r n a c e u n t i l the S i C / A l l a y u p reaches 733 °C 3) At t h i s t e m p e r a t u r e the d i e i s removed from the oven and p l a c e d i n a h y d r a u l i c p r e s s . A water c o o l e d copper j a c k e t i s then p l a c e d around d i e p e r i m e t e r . 4) A s l i g h t p r e s s u r e i s a p p l i e d w h i l e the aluminum i s s t i l l i n the molten s t a t e . 5) At the p o i n t of aluminum s o l i d i f i c a t i o n a p r e s s u r e of 46 Mpa i s a p p l i e d t o the d i e . 6) The p r e s s u r e i s h e l d t i l l c o mposite reaches a temperature of 250 °C The c h o i c e of d i e m a t e r i a l was made c o n s i s t e n t w i t h the f a c t t h a t the d i e i s r e p e a t e d l y s u b j e c t e d t o 815 °C. F u r t h e r m o r e , the t o p and lower p l u n g e r must be a b l e t o w i t h s t a n d a s t r e s s of 46 Mpa a t 600 °C. To meet the r e q u i r e d s p e c i f i c a t i o n s a 316 s t a i n l e s s s t e e l was chosen as the d i e m a t e r i a l . R e f e r r i n g t o the ASM s p e c i f i c a t i o n s ( r e f . 2 2 ) i t was found t h a t 316 s t a i n l e s s s t e e l FIG. 3.5 - OUTER DIE RING AND FIBREFRAX TUBE (dimensions in mm) to 38 has a short term y i e l d s t r e n g t h of 150 Mpa at 600 °C and a maximum a l l o w a b l e i n t e r m i t t e n t s u r f a c e temperature of 870 °C. A unique f e a t u r e p e r t a i n i n g to manufacturing and d i e design f o r the q u a s i hot p r e s s i n g system i s the i n c o r p o r a t i o n of a f i b r e f r a x tube. F i b r e f r a x i s a f i b r o u s mat c o n s i s t i n g of 45% alumina, 50% s i l i c a and the remaining 5% of v a r i o u s o x i d e s . The f i b r e f r a x which l i n e s the outer d i e r i n g s e r v e s a v a r i e t y of purposes i n c l u d i n g : 1) Prevents welding together of the s t a i n l e s s s t e e l p l ungers and outer r i n g d u r i n g the h e a t i n g o p e r a t i o n . 2) In combination with the tapered p l u n g e r s the f i b r e f r a x p r o v i d e s an e x c e l l e n t s t a t i c s e a l a g a i n s t molten aluminum leakage dur i n g h e a t i n g o p e r a t i o n . 3) The low thermal c o n d u c t i v i t y of the f i b r e f r a x l i m i t s heat flow away from composite i n the r a d i a l d i r e c t i o n . The f i b r e f r a x t u b i n g , by e l i m i n a t i n g p o s s i b l e f u s i n g together of d i e components duri n g manufacturing,enables m u l t i p l e use of the d i e . B a s i c a l l y , the tubing a c t s as the s a c r i f i c i a l component of the hot p r e s s i n g d i e system and must be r e p l a c e d a f t e r each run. Another advantage of using a f i b r e f r a x d i e l i n i n g i s that an e x c e l l e n t s t a t i c s e a l can be achieved i n combination with the tapered p l u n g e r s . T h i s f e a t u r e i s important i n m a i n t a i n i n g S i C / A l i n t e g r i t y p r i o r to hot p r e s s i n g . Though the f i b r e f r a x p r o v i d e s a s t a t i c s e a l a g a i n s t aluminum leakage, l i q u i d p r e s s i n g molten causes aluminum to flow from the d i e c a v i t y . As excess aluminum 39 i s present i n the i n i t i a l l a y up, c o n t r o l l i n g the flow of t h i s aluminum allows f o r the composite t h i c k n e s s to be a d j u s t e d . C o n t r o l l e d p r e s s i n g of the molten aluminum a l s o enables a c l o s e r f i b r e p l y spacing to be ac h i e v e d . The low thermal c o n d u c t i v i t y of the f i b r e f r a x t u b i n g (0.0052 w/m k) compared to 316 s t a i n l e s s s t e e l (21.5 w/m k) i n h i b i t s r a d i a l heat flow from the i n t e r i o r of the d i e . T h i s i s important i n p r e v e n t i n g the edges of the composite from s o l i d i f y i n g prematurely e s p e c i a l l y when the water c o o l e d copper j a c k e t i s attac h e d . An important requirement i n p l a c i n g the f i b r e f r a x tube on the inner circumference of the s t a i n l e s s s t e e l i s that a very t i g h t f i t between the s t a i n l e s s s t e e l r i n g and tube i s needed. I t was observed d u r i n g p r e s s i n g that i f the tubing was loose f i t t i n g the t e n s i l e hoop s t r e s s e s induced by the top plunger would cause the f i b r e f r a x to crack and subsequently leak. In c o n j u n c t i o n with t h i s requirement, i t was necessary to a t t a c h a c o o l i n g j a c k e t onto the circumference of the outer r i n g upon removal from the fu r n a c e . The o b j e c t i v e f o r t h i s procedure was to s u f f i c i e n t l y c o o l the s t a i n l e s s s t e e l r i n g so as to t h e r m a l l y c o n t r a c t i t around the f i b r e f r a x t u b i n g and p r o v i d e a c l o s e r f i t . 3.2 Temperature C o n t r o l The temperature of the manufacturing process i s e v a l u a t e d by a chromel-alumel thermocouple p l a c e d j u s t below the s u r f a c e of the lower plunger ( F i g . 3.2). Because of the l a r g e thermal mass of the d i e r e l a t i v e t o that of the aluminum, measurement of the 40 d i e temperature i s a good measure of the system temperature. A t y p i c a l temperature - time p l o t of a manufacturing run i s shown in F i g u r e 3.6. The m e l t i n g and s o l i d i f i c a t i o n temperatures of the aluminum correspond to the i n f l e c t i o n p o i n t s A and B. These i n f l e c t i o n s are due to the r e l e a s e and a b s o r p t i o n of the l a t e n t heat d u r i n g the s o l i d / l i q u i d t r a n s f o r m a t i o n f o r aluminum. F i g u r e 3.7 d i s p l a y s the e x p e r i m e n t a l l y determined m e l t i n g and s o l i d i f i c a t i o n temperatures f o r the d i f f e r e n t manufacturing runs. The experimental melting v a l u e s correspond q u i t e w e l l to the t h e o r e t i c a l m e l t i n g temperature of 660 °C ,but, the observed s o l i d i f i c a t i o n temperatures are w e l l below that c i t e d i n the standards (643 ° C ) . The l a r g e d e v i a t i o n s i n c u r r e d d u r i n g c o o l i n g can be a t t r i b u t e d to temperature g r a d i e n t s being set up i n the s t a i n l e s s s t e e l between the thermocouple and aluminum. The purpose of the temperature - time p l o t i s not to o b t a i n exact composite temperatures as to s t a n d a r d i z e the manufacturing p r o c e s s . An important parameter connected with the composite temperature i s the time p e r i o d i n which the f i b r e s are exposed to molten aluminum. T h i s f a c t o r i s important with regard to p o s s i b l e aluminum c a r b i d e formation. D u r a t i o n of f i b r e exposure to molten aluminum i s measured as the time between the m e l t i n g and s o l i d i f i c a t i o n i n f l e c t i o n p o i n t s . The molten r e t e n t i o n times f o r each manufacturing procedure are shown in F i g u r e 3.8 and given in Appendix A. 0.0 tim* (Bins.) «0.0 F I G . 3.6 - T IME TEMPERATURE PROFILE OF MANUFACTURING RUN 43 (A ,B a r e m e l t i n g and s o l i d i f i c a t i o n i n f l e c t i o n po i n t s ) 740 720 -700 -680 -cn 3 10 • i-i 10 rH 0) U 660 640 w 620 EH 2 W X w E-600 H 580 560 -540 -520 -500 31 • 36 • 38 • 39 - O -• JlSL 46 47 -B— 37 • 42 -O— 43 + 38 + 39 + 44 + 45 + 36 + 46 + 47 + 42 + 37 + 43 + 31 ~r 2 i 4 , 6 SAMPLE T" 8 10 12 F I G . 3.7 - MELTING AND SOL ID IF ICAT ION TEMPERATURES I F I G . 3.8 - R E T E N T I O N T I M E OF F I B R E S IN M O L T E N ALUMINUM 44 A maximum thermocouple r e a d i n g of 733 °C was used as a r e f e r e n c e p o i n t i n the m a n u f a c t u r i n g p r o c e s s . When t h i s t e m p e r a t u r e was reached the d i e was removed from the f u r n a c e and i n s e r t e d i n the p r e s s i n g d e v i c e . I t was e x p e r i m e n t a l l y observed t h a t a r e f e r e n c e thermocouple temperature of l e s s than 710 °C was inadequate t o a c h i e v e complete d i s s o l u t i o n of the aluminum o x i d e p r e s e n t . The o x i d e was i n t r o d u c e d t h r o u g h the aluminum d i s c s i n the o r i g i n a l c o m p o s i t e l a y up. C o n v e r s e l y , h e a t i n g above a thermocouple t e m p e r a t u r e of 733 °C i s not recommended. The i n c r e a s e d time of f i b r e / m o l t e n aluminum c o n t a c t a s s o c i a t e d w i t h a h i g h e r r e f e r e n c e temperature may r e s u l t i n e x t e n s i v e f i b r e d e g r a d a t i o n . One problem a s s o c i a t e d w i t h measuring t e m p e r a t u r e by t h i s method i s t h a t a t any p a r t i c u l a r time the e x a c t c o m p o s i t e t e m p e r a t u r e i s not a v a i l a b l e . T h i s d i s c r e p a n c y i s a r e s u l t of the t e m p e r a t u r e / t i m e d e l a y induced by the s t a i n l e s s s t e e l between the thermocouple and c o m p o s i t e . As mentioned i n t h e p r o c e d u r e i t i s d e s i r a b l e t o a p p l y p r e s s u r e t o the aluminum a t i t s s o l i d i f i c a t i o n t e m p e r a t u r e . C o r r e c t i n g f o r d e l a y s i n t e m p e r a t u r e r e a d out d u r i n g the p r e s s i n g p r o c e d u r e r e q u i r e s o p e r a t o r e x p e r i e n c e and judgment. 3.3 Lay Up P r e p a r a t i o n The S i C and aluminum a r e i n t r o d u c e d i n t o the d i e c a v i t y by a l t e r n a t i n g l a y e r s of each of t h e s e c o n s t i t u e n t s . For example, run 36 has an i n i t i a l p r e c o m p o s i t e l a y u p o f : 3 A l / ( S i C / A l ) 4 By v a r y i n g the number of S i C l a y e r s i n t r o d u c e d , t h e volume f r a c t i o n of the as c a s t c o m p o s i t e can be c o n t r o l l e d t o some 45 e x t e n t . A l l m a n u f a c t u r i n g p r o c e d u r e s have b a s i c a l l y the same l a y up as f o r run 36. Ta b l e 3.1 l i s t s t he number of S i C p l i e s used and the p a t t e r n i n which they a r e s t a c k e d . Each aluminum l a y e r c o n s i s t s of a c i r c u l a r d i s c of u t i l i t y aluminum c u t from a 0.83 m i l l i m e t r e t h i c k r o l l e d s h e e t . U t i l i t y aluminum has the f o l l o w i n g c o m p o s i t i o n : 1.0 -1.5% Mn, 0.7% Fe, 0.6% S i , 0.1% Zn and 0.1% Cu. P r i o r t o b e i n g s t a c k e d i n the d i e , the d i s c s a re c l e a n e d w i t h e t h a n o l . P r e p a r a t i o n of the S i C p r e p r e g g i s not o n l y more complex but i s an i m p o r t a n t f a c t o r i n the m a n u f a c t u r i n g p r o c e s s . To s i m p l i f y the h a n d l i n g of the S i C tows p r i o r t o s t a c k i n g i n the d i e i t was n e c e s s a r y t o drum wind the f i b r e s i n t o u n i d i r e c t i o n a l s t r i p s . The tows a r e bound t o g e t h e r by a v i n y l e s t e r r e s i n (Derakane 411). C i r c u l a r d i s c s of the S i C a r e then c u t and s t a c k e d w i t h the aluminum i n the d i e c a v i t y . To ensure adequate S i C p r e p r e g g p r e p a r a t i o n a v a r i e t y of f a c t o r s needed t o be c o n t r o l l e d d u r i n g the drum w i n d i n g o p e r a t i o n . These i n c l u d e d : 46 TABLE 3. 1 Pre-composite S t a c k i n q Sequence Run Number of S t a c k i n g SiC l a y e r s Sequence 31 4 3 A l / ( S i C / A l ) 4 36 4 3 A l / ( S i C / A l ) 4 38 4 3 A l / ( S i C / A l ) 4 39 6 3 A l / ( S i C / A l ) 6 41 6 3 A l / ( S i C / A l ) 6 44 6 3 A l / ( S i C / A l ) 6 45 6 3 A l / ( S i C / A l ) 6 46 12 3 A l / ( 2 S i C / A l ) 6 47 1 2 3 A l / ( 2 S i C / A l ) 6 47 1) c o n t r o l of tow s p a c i n g i n p r e p r e g g 2) amount of r e s i n used t o b i n d tows 3) s p r e a d i n g out of the i n d i v i d u a l tows F i b r e s p a c i n g i n the drum wound s t r i p i s i m p o r t a n t because tow o v e r l a p p i n g would i n h i b i t aluminum i n f i l t r a t i o n . C o n v e r s e l y , e x c e s s i v e tow s p a c i n g reduces the volume f r a c t i o n of f i b r e s o b t a i n e d i n the f i n i s h e d p r o d u c t . To p r e v e n t s u b s t a n t i a l amounts of unwanted b y - p r o d u c t s from i t s combustion, t h e q u a n t i t y of r e s i n used t o b i n d the tows s h o u l d be m i n i m i z e d . C o n v e r s e l y , i f not enough r e s i n i s used t o b i n d the tows, h a n d l i n g of the S i C p r e p r e g g becomes d i f f i c u l t . S p r e a d i n g out t h e i n d i v i d u a l f i b r e s i n a tow would improve f i b r e d i s t r i b u t i o n and aluminum i n f i l t r a t i o n i n the manufactured c o m p o s i t e . The i n i t i a l drum p r e p r e g g i n g was done a t Canadian A i r c r a f t P r o d u c t s i n Richmond. The e a r l y runs r e s u l t e d i n a p r e p r e g w i t h poor tow s p a c i n g and e x c e s s i v e r e s i n . L a t e r , a b e t t e r q u a l i t y p r e p r e g was made and s u c c e s s f u l l y i n c o r p o r a t e d i n t o samples #31 and #36. Subsequent p r e p r e g g i n g was c a r r i e d out on a newly i n s t a l l e d department f a c i l i t y . The Composites Group drum winder p o s s e s s e s s e v e r a l i n n o v a t i v e f e a t u r e s which a l l o w s f o r improved r e s i n c o n t r o l and tow s p a c i n g . Due t o the s t r o n g c o h e s i o n between f i b r e s , s p r e a d i n g of the i n d i v i d u a l tows was not s u c c e s s f u l l y c a r r i e d out f o r any p r e p r e g g i n g o p e r a t i o n . The drum c o n d i t i o n s found t o g i v e the b e s t r e s u l t s a r e summarized i n T a b l e B.1 i n appendix B. 48 3.4 M a n u f a c t u r i n g D i f f i c u l t i e s A m a j o r p r o b l e m w i t h u s i n g a s t a i n l e s s s t e e l d i e was t h a t m o l t e n a l u m i n u m t e n d s t o a d h e r e t o i t s s u r f a c e s . T h i s d i f f i c u l t y was a l l e v i a t e d by c o a t i n g t h e u p p e r a n d l o w e r p l u n g e r s u r f a c e s w i t h c a r b o n f r o m an a c e t y l e n e t o r c h . I t was o b s e r v e d t h a t t h e c a r b o n a d h e r e d q u i t e w e l l t o t h e p l u n g e r s u r f a c e s a n d d i d n o t a p p e a r t o mix i n w i t h t h e m o l t e n a l u m i n u m . A p r o b l e m more d i f f i c u l t t o c o r r e c t r e s u l t e d f r o m a d i s c o n t i n u i t y i n t h e f i b r e f r a x t u b i n g . A s t h e f i b r e f r a x i s r o l l e d f r o m s h e e t f o r m i n t o a t u b e , a g a p c o r r e s p o n d i n g t o i n i t i a t i o n o f t h e r o l l i n g p r o c e s s e x i s t s on t h e i n n e r c i r c u m f e r e n c e . D u r i n g p r e s s i n g o f t h e l i q u i d a l u m i n u m e x c e s s i v e l e a k a g e f r o m t h i s g a p o c c u r s . T h e p r o b l e m was r e c t i f i e d t o some e x t e n t by a l l o w i n g t h e i n i t i a l l e a k a g e t o s o l i d i f y a n d e f f e c t i v e l y s e a l t h e h o l e b e f o r e c o n t i n u i n g p r e s s i n g . T h o u g h t h i s m e t h o d a l l e v i a t e s t h e p r o b l e m t o some e x t e n t a more p r a c t i c a l s o l u t i o n i s r e q u i r e d . 49 CHAPTER 4.0  EXPERIMENTAL APPARATUS AND TECHNIQUE The purpose of the t e s t i n g procedures performed on the S i C / A l composite was to provide a more complete understanding of i t s mechanical p r o p e r t i e s . Parameters to be examined i n c l u d e t e n s i l e p r o p e r t i e s , m i c r o s t r u c t u r e and f i b r e - m a t r i x i n t e r f a c i a l a n a l y s i s . 4.1 T e n s i l e T e s t i n g The most d i f f i c u l t aspect of t e n s i l e t e s t i n g was i n the p r e p a r a t i o n of s u i t a b l e samples. The f i r s t s t e p was to o b t a i n an adequate number of r e p r e s e n t a t i v e t e n s i l e samples from a 3 inch diameter as c a s t composite. Once sample s i z e was determined, problems with machining the specimens were encountered. Tanaka et a l ( r e f . 10) s u c c e s s f u l l y t e s t e d t e n s i l e specimens having the f o l l o w i n g dimensions 80 mm i n l e n g t h 8.0 mm wide 1.0 mm t h i c k at curved reduced s e c t i o n The v a l i d i t y of v a r i o u s shaped t e n s i l e samples was t e s t e d f o r a u n i d i r e c t i o n a l S i C / A l composite ( r e f . 17). The t e n s i l e samples deemed to g i v e the most c o n s i s t e n t r e s u l t s were a through t h i c k n e s s reduced c r o s s s e c t i o n as used by Tanaka et a l (ref.10) ( F i g . 4.1) and a curved "dog bone" shape sample ( F i g . 4.2). The curved dog bone s t y l e t e n s i l e specimen was deemed e a s i e r to implement, hence, i t was adopted f o r use i n t h i s r e s e a r c h . 50 co 1 5 0 " 60 T I 30 *| sL.21-F I G . 4 .1 - THROUGH THICKNESS REDUCED CROSS -SECT ION T E N S I L E SAMPLE ( d i m e n s i o n s i n mm R E F . 1 0 ) SEE NOTE A 7.6 3.3 64.0 F I G . 4 . 2 - CURVED NOTE A 46 and "DOG BONE" T E N S I L E SAMPLE ( d i m e n s i o n s i n mm) - r e d u c e d l e n g t h i s 19 mm e x c e p t f o r s a m p l e s 47 f o r w h i c h r e d u c e d l e n g t h i s 25 mm 51 To f a c i l i t a t e the understanding of t e n s i l e sample p r e p a r a t i o n a c o n c i s e procedure w i l l be d e s c r i b e d . From the as-c a s t composite, a 64 mm by 38 mm r e c t a n g l e p a r a l l e l to the f i b r e d i r e c t i o n was c u t . The r e c t a n g l e was d i v i d e d i n t o 5 equal p a r t s and l a b e l l e d a c c o r d i n g to p o s i t i o n ( F i g . 4 . 3 ) . Each t e n s i l e sample was then cut from the r e c t a n g l e by a slowcut diamond saw and hand / ground to the s p e c i f i c a t i o n s i n F i g . 4.2. The c i r c u l a r dog bone reduced s e c t i o n (Fig.4.2) was necessary to f a c i l i t a t e composite f a i l u r e i n the d e s i r e d l o c a t i o n (underneath bonded s t r a i n gauge). To produce the reduced c r o s s s e c t i o n , a s p e c i a l g r i n d i n g wheel was designed. The g r i n d i n g wheel ( F i g . 4.4) c o n s i s t s of a s o l i d aluminum core to whose ci r c u m f e r e n c e i s fas t e n e d a l a y e r of double s i d e d tape and a s t r i p of #80 SiC p o l i s h i n g paper. The wheel i s adapted f o r use with a c o n v e n t i o n a l d r i l l p r e s s . During g r i n d i n g , the sample i s h e l d by the s p e c i a l l y f a b r i c a t e d chuck shown i n F i g u r e 4.5. The c u r v a t u r e of the g r i n d i n g wheel was designed with a r a d i u s of 55 mm. T h i s i s i n accordance with the minimum r a d i u s of c u r v a t u r e of 50 mm found necessary to a l l e v i a t e any s t r e s s c o n c e n t r a t i o n e f f e c t s a s s o c i a t e d with a curved reduced s e c t i o n ( r e f . 1 7 ) . The s t r a i n measurements recorded during t e n s i l e t e s t i n g were obtained from bonded r e s i s t a n c e s t r a i n gauges. The gauges c o n s i s t of a m e t a l l i c conductor which undergoes a change i n e l e c t r i c a l r e s i s t a n c e when s t r a i n e d . Gauge r e s i s t a n c e ( s t r a i n ) i s measured by a Wheatstone Bridge c o n f i g u r a t i o n where the s t r a i n gauge i s , F I G . 4 .3 - T E N S I L E SAMPLE L A B E L L I N G 53 ATTACHES TO DR ILL PRESS I 110.0 d i a . NOTE B 9.0 d i a . 20.0 F I G . 4 . 4 - GRINDING WHEEL ( d i m e n s i o n s i n mm) NOTE B - o u t e r c i r c u m f e r e n c e c o n s i s t s o f d o u b l e s i d e d t a p e and 80 S IC p o l i s h i n g p a p e r 54 16.9 4.5 [:: J L 2.4-7.8 59.5 74.0 13.0 2.0 F I G . 4.5 - SPEC IALTY V I S E MAKING REDUCED FOR HOLDING SAMPLE WHILE CROSS -SECT ION ( d i m e n s i o n s i n mm) 55 of the f u l l b r i d g e . A change i n the gauge r e s i s t a n c e produces a v o l t a g e across the Wheatstone Bridge ( F i g u r e 4.6) which i s c a l i b r a t e d d i r e c t l y i n t o true s t r a i n and recorded as such. The type of s t r a i n gauge used i s a LY-61-3/120 manufactured by Omega En g i n e e r i n g Inc. The r e s i s t a n c e g r i d possesses a l e n g t h of 3 mm and a width of 1.4 mm. Once the "dogbone" reduced s e c t i o n has been machined, the s t r a i n gauge i s cen t e r e d on the t e n s i l e sample at the p o i n t of minimum c r o s s s e c t i o n a l area. A s p e c i a l epoxy adhesive i s used to bind the gauge to the composite. Owing to the short g r i d l e n g t h of the s t r a i n gauge (3 mm), a c o r r e c t i o n to account f o r the c o n t i n u a l change i n c r o s s s e c t i o n a l area (due to the curved "dog bone" shape) over which the gauge spans was deemed unnecessary. I t was c a l c u l a t e d that the maximum change i n area at the gauge e x t r e m i t i e s was at most 2%. To s i m p l i f y the s t r a i n gauge o p e r a t i o n , an Orion data logger was employed. The data logger (possesses i n t e r n a l Wheatstone Bridge) measured the v o l t a g e drop induced by the s t r a i n gauge and converted i t i n t o a t r u e s t r a i n r e a d i n g . A l o a d i n g v o l t a g e produced by the I n s t r o n t e n s i l e t e s t machine allowed f o r simultaneous r e c o r d i n g of s t r e s s and s t r a i n . T h i s data was s t o r e d on compact tape and subsequently t r a n s f e r r e d to an IBM - PC f o r f u r t h e r manipulation ( F i g . 4 . 7 ) . A l l t e n s i l e t e s t s were c a r r i e d out on an I n s t r o n T e s t i n g Machine at a c r o s s head speed of 0.51 mm/min. T e n s i l e sample dimensions are given i n Appendix C. 5 6 I G . 4 .6 - WHEATSTONE BRIDGE C O N F I G U R A T I O N 5 7 INPUT FROM STRAIN GAUGE INSTRON LOAD INPUT DATA LOGGER IBM P .C , H . P . PLOTTER DATA ANALYS I S F I G . 4 . 7 - T E N S I L E DATA ACQUIS IT ION SYSTEM 58 4.2 Volume F r a c t i o n Determination The volume f r a c t i o n of SiC f i b r e s present i n a composite were obtained by a matrix d i s s o l u t i o n method ( r e f s . 5 and 18). The exact d i s s o l u t i o n process i n v o l v e s c u t t i n g a 12.5 mm long sample from an area adjacent to the reduced s e c t i o n on the t e n s i l e sample. The sample and a corresponding #4 mesh f i l t e r paper are i n d i v i d u a l l y weighed. The sample i s then p l a c e d i n 80 ml. of 10% NaOH s o l u t i o n at 55 °C u n t i l a l l the aluminum i s d i s s o l v e d . The s o l u t i o n c o n t a i n i n g the f i b r e s i s decanted and subsequently f i l t e r e d . Samples 31,36,38,39,41,and 45 were furnace d r i e d at 60 °C f o r 2 hours while specimens 44,45,46 and 47 were a i r d r i e d f o r 48 hours. The volume f r a c t i o n of f i b r e s was then c a l c u l a t e d using the f o l l o w i n g equation: V F f = (Wt f/2.60) / (Wt f/2.6 + Wt A 1/2.72)) Wtf = weight of f i b r e s i n sample (grams) w t A l = weight of aluminum i n sample To c o r r e c t f o r f i l t e r paper weight changes d u r i n g d r y i n g a r e f e r e n c e t e s t was c a r r i e d out. Three f i l t e r papers of known weights were su b j e c t e d to c o n d i t i o n s s i m i l a r to those mentioned above ( i n c l u d i n g f i l t e r i n g and furnace d r y i n g ) . I t was found that on average a decrease i n f i l t e r paper weight of 0.100 grams was observed. T h i s c o r r e c t i o n was a p p l i e d d u r i n g c a l c u l a t i o n of volume f r a c t i o n . To e l i m i n a t e t h i s c o r r e c t i o n f a c t o r an a i r d r y i n g procedure i n s t e a d of furnace d r y i n g was attempted. Sample 44,45,46 and 47 were, as mentioned e a r l i e r , a i r d r i e d f o r 48 hours. Three 59 r e f e r e n c e f i l t e r papers were a l s o s u b j e c t e d t o s i m i l a r c o n d i t i o n s . A c o r r e c t i o n of -0.100 grams was found to be needed to account f o r f i l t e r paper weight gain a f t e r a i r d r y i n g as a l l the water i n t r o d u c e d d u r i n g f i l t e r i n g was not evaporated. For comparative purposes samples 45(A,B,D) were a i r and furnace d r i e d . The volume f r a c t i o n of f i b r e s determined a f t e r c o r r e c t i o n s f o r both methods are summarized i n Table 4.1. The s i m i l a r i t y between the values v e r i f i e s t h a t e i t h e r procedure i s a c c e p t a b l e . 4.3 M i c r o s t r u c t u r e A n a l y s i s P o l i s h i n g a S i C / A l composite p r e s e n t s a problem due to the presence of the a b r a s i v e SiC f i b r e . To overcome t h i s d i f f i c u l t y , p o l i s h i n g was c a r r i e d out p a r a l l e l to the f i b r e d i r e c t i o n as opposed to p o l i s h i n g a t r a n s v e r s e c r o s s s e c t i o n . I t was hoped t h i s would minimize f i b r e breakage and the subsequent s c o r i n g of the aluminum by these p a r t i c l e s . The p o l i s h i n g steps i n c l u d e d a f i n a l rough p o l i s h i n g with 600 g r i t paper f o l l o w e d by 5.0 and 1.0 micron diamond paste . The etchants used f o r p r e c i p i t a t e and g r a i n boundary enhancement are l i s t e d i n Table 4.2. 4.4 D i f f r a c t i o n A n a l y s i s of F i b r e - M a t r i x I n t e r f a c e E l e c t r o n beam microscopy was used to study the S i C / A l i n t e r f a c e because of the methods a b i l i t y to examine minute areas. By a n a l y z i n g the f i b r e s u r f a c e u s i n g e l e c t r o n d i f f r a c t i o n p a t t e r n s , the presence of A l 4 C 3 would be v e r i f i e d . TABLE 4.1  Volume F r a c t i o n Comparisons Sample A i r Furnace Dry Dry (%) (%) 4 5A 9.2 8.6 45B 6.9 8.4 4 5D 9.8 9.4 TABLE 4.2 M i c r o s t r u c t u r a l Etchants P r e c i p i t a t e Enhancement Etc h a n t : '' 1 ml HF (48%) 200 ml water Grain Boundary E t c h a n t : 50 ml Poultons S o l u t i o n 25 ml HN0 3 12 grams Chromic A c i d 40 ml water 6 2 Kohyama et a l (ref.16) employed an e l e c t r o n d i f f r a c t i o n technique on t h i n S i C / A l f o i l s . By t h i s method the e x i s t e n c e of A l 4 C 3 was d e t e c t e d . F o l l o w i n g t h i s example, attempts were made to produce the r e q u i r e d t h i n S i C / A l TEM f o i l s by f i r s t p h y s i c a l l y p o l i s h i n g (Dimpler) and then argon ion m i l l i n g . T h i s procedure d i d not prove very s u c c e s s f u l due to composite c r a c k i n g . I d e a l l y a chemical t h i n n i n g procedure would be p r e f e r r e d ; however, the lack of in f o r m a t i o n on t h i s method p r e c l u d e d i t s use. To circumvent the problems r e l a t e d to specimen t h i n n i n g an a l t e r n a t i v e method of f i b r e s u r f a c e examination was c a r r i e d out. Kohara et a l ( r e f . 5 ) d e t e c t e d A l 4 C 3 c r y s t a l s on the su r f a c e of a carbon f i b r e using a s e l e c t e d area d i f f r a c t i o n technique (SAD). The carbon f i b r e s were removed from a carbon/aluminum composite by d i s s o l v i n g the aluminum i n a 10% NaOH s o l u t i o n . T h i s procedure used by Kohara et a l ( r e f . 5 ) s u b s t a n t i a t e s that NaOH i n low c o n c e n t r a t i o n s would not d i s s o l v e AI4C3; and thus, was adopted in t h i s work. F i b r e s obtained from the volume f r a c t i o n procedure of specimen 31A were i n d i v i d u a l l y a n alyzed i n both the STEM and TEM. The f o l l o w i n g c o n d i t i o n s used i n the SAD a n a l y s i s are shown i n Table 4.3. The camera constant term r e l a t e s p h y s i c a l measurements taken on the d i f f r a c t i o n p a t t e r n to c r y s t a l l o g r a p h i c plane spacing i n Angstrom u n i t s . I t i s obt a i n e d from a m u l t i c r y s t a l l i n e g o l d d i f f r a c t i o n p a t t e r n u s i n g c o n d i t i o n s i d e n t i c a l t o those i n Table 4.3. As the plane spacings f o r g o l d are w e l l documented, p h y s i c a l l y measuring the r a d i i of the go l d d i f f r a c t i o n r i n g s TABLE 4.3 S e l e c t e d Area D i f f r a c t i o n C o n d i t i o n s Stem A n a l y s i s : a c c e l e r a t i n g v o l t a g e = 200 KeV camera le n g t h = 1.2 metre camera c o n s t a n t : Run A = 1.403 i n . Run B = 1.456 i n . Run C = 1.456 i n . TEM A n a l y s i s : a c c e l e r a t i n g v o l t a g e = 100 KeV camera le n g t h = 0.8 metre camera c o n s t a n t : Run D = 2.040 i n . 64 g i v e s a camera constant which can be c a l c u l a t e d from the f o l l o w i n g equation: CC = R x D CC = camera constant R = d i f f r a c t i o n r i n g r a d i u s i n inches D = c r y s t a l l o g r a p h i c plane spacing i n angstroms 4.5 Heat Treatments The heat t r e a t i n g procedures to which the S i C / A l composites were su b j e c t e d correspond to ASM standard anneal and T6 tempers f o r 6061 aluminum. However, i t was d i s c o v e r e d that the m a t e r i a l s u p p l i e d was not the 6061 ordered but an u t i l i t y grade aluminum. The a n n e a l i n g procedure ( s u i t a b l e f o r u t i l i t y aluminum) i n v o l v e d soaking the specimens at 415 °C f o r 2 hours and 10 minutes. The samples were then c o o l e d 30 °C per hour u n t i l a temperature of 260 °C was reached. To s t a n d a r d i z e the aluminum p r o p e r t i e s , two r e f e r e n c e samples (43A and 43B) underwent s i m i l a r heat treatments. The T6 tempers used, though not c o r r e c t , are as f o l l o w s . T6A temper used on samples 41D, 42A and 42B i n v o l v e d s o l u t i o n i z i n g the samples at 525 °C f o r 50 minutes. The samples were quenched immediately and tempered at 175 °C f o r 7 hours and 30 minutes. T6B i n v o l v e d s o l u t i o n i z i n g samples 44, 47, 37D and 42C at 525 °C f o r 1 hour and 35 minutes. A f t e r water quenching, the specimens were soaked at 175 °C f o r 7 hours and 30 minutes. Standards f o r the T6A temper are 42A, 42B and f o r a T6B temper specimens 42C, 37D. 65 CHAPTER 5  Experimental R e s u l t s 5.1 T e n s i l e Test Data The i n f o r m a t i o n obtained from the t e n s i l e t e s t i n g procedure r e v e a l s more than j u s t the u l t i m a t e s t r e n g t h of the S i C / A l composite samples. The data presented, which i n c l u d e s r u l e of mixtures s t r e n g t h , f i b r e s t r e n g t h and apparent number of f i b r e s c o n t r i b u t i n g , w i l l be used to enhance the understanding of metal matrix t e n s i l e behaviour. Due to the d i f f i c u l t y i n producing a l a r g e q u a n t i t y of t e n s i l e samples i t was not p o s s i b l e to have r e p e t i t i v e t e s t i n g f o r any one specimen. The t e n s i l e data p r e s e n t e d are f o r each i n d i v i d u a l sample and not an average value taken from a number of spec imens. 5.1.1 As Cast and Heat Treated Aluminum Reference Samples T e s t i n g on a s - c a s t and heat t r e a t e d r e f e r e n c e samples was performed as a b a s i s f o r d e s c r i b i n g the behaviour of the aluminum matrix. The c h a r a c t e r i s t i c f e a t u r e s of each t e s t , i n c l u d i n g y i e l d s t r e n g t h and s t r a i n , u l t i m a t e s t r e n g t h and r a t e of s t r a i n hardening, w i l l be c o r r e l a t e d to the matrix t e n s i l e behaviour observed i n the composite m a t e r i a l . Table 5.1 summarizes the r e s u l t s of the aluminum r e f e r e n c e samples t e s t e d . The rate of s t r a i n hardening (ds/de) corresponds to the s l o p e of the aluminum s t r e s s - s t r a i n curve f o l l o w i n g 0.2% s t r a i n . Region A i n F i g u r e 5.1 i n d i c a t e s the p o r t i o n of s t r e s s - s t r a i n curve where ds/de i s 66 o d co o d CN' CO CO CJ QL f— CO o d. L E G E N D SAMPLE 43A x SAMPLE 46'A < Q_ B q d 0.0 1000.0 2000.0 3000.0 MICRO STRAIN 4000.0 5000.0 F I G . 5.1 - COMPARISON OF REFERENCE ALUMINUM (43A) AND F IBRE REINFORCED ALUMINUM ( 4 6 A ) . REGIONS A AND B REPRESENT AREAS WHERE ( d s / d e ) IS CALCULATED 6 7 T A B L E 5 .1 AS C A S T AND H E A T T R E A T E D ALUMINUM R E F E R E N C E SAMPLES S a m p l e H e a t UTS T r e a t m e n t (Mpa) Y i e l d S t r e s s (.2%) (Mpa) R a t e o f S t r a i n H a r d e n i n g (Gpa) 37A 37B AS C A S T AS C A S T 1 1 8 . 5 1 1 8 . 2 4 9 . 4 4 3 . 0 3 .1 3 . 4 42A 42B T6A T6A 1 2 0 . 7 1 2 0 . 0 51 .0 5 2 . 3 2 . 8 2 . 7 37D 42C T6B T6B 1 2 7 . 7 1 2 2 . 6 51 .0 5 2 . 4 3 . 0 3 . 2 43A 43B ANNEAL ANNEAL 1 1 6 . 7 1 1 2 . 7 5 0 . 6 5 0 . 1 2 . 5 2 . 4 ASTM ANNEAL 1 1 0 . 0 4 1 . 0 68 o b t a i n e d . A d d i t i o n a l i n f o r m a t i o n on t e n s i l e specimen dimensions i s a v a i l a b l e i n Table C.1 i n appendix C. The u l t i m a t e s t r e n g t h s observed f o r the annealed r e f e r e n c e samples compare f a v o u r a b l y to the ASTM standard. As a r e s u l t of the improper heat treatment a p p l i e d to samples 42 A,B,C and 37D, comparisons with known standards c o u l d not be c a r r i e d out f o r these specimens. I t was observed t h a t a l l the aluminum r e f e r e n c e samples e x h i b i t e d an i n c l i n e d f r a c t u r e s u r f a c e . The sloped s u r f a c e (from 15° to 40°) i s r e p r e s e n t a t i v e of a shear f a i l u r e mode. T h i s o b s e r v a t i o n i s c o n s i s t e n t with the d u c t i l e nature of the u t i l i t y aluminum used (eg. low r e s i s t a n c e to shear deformat i o n ) . 5.1.2 Composite T e n s i l e P r o p e r t i e s F i g u r e 5.1 compares the s t r e s s - s t r a i n curves of a non-r e i n f o r c e d aluminum r e f e r e n c e sample (43A) and an annealed composite (46A) p o s s e s s i n g 13.9% volume f r a c t i o n of f i b r e s . Stage I of the 46A s t r e s s - s t r a i n curve corresponds to both the aluminum matrix and f i b r e s being e l a s t i c a l l y s t r a i n e d . At approximately 400 m i c r o s t r a i n the aluminum matrix begins y i e l d i n g . T h i s value c o r r e l a t e s w e l l with the y i e l d s t r a i n observed f o r the r e f e r e n c e sample (43A) shown i n F i g u r e 5.1. A f t e r matrix y i e l d i n g the composite e n t e r s a q u a s i - e l a s t i c s t a t e i n which the aluminum matrix s t r a i n hardens up to composite f a i l u r e . The f i b r e s remain e l a s t i c throughout the t e n s i l e t e s t . Composite f a i l u r e i s d e f i n e d at the onset of f i b r e f a i l u r e . The l o a d at t h i s p o i n t becomes e n t i r e l y supported by the matrix which i s r a p i d l y s t r a i n e d to f a i l u r e . 69 The m a j o r i t y of t e n s i l e samples, e i t h e r r e f e r e n c e or S i C / A l composite, d i s p l a y s t r e s s - s t r a i n curves s i m i l a r to those d i s p l a y e d i n F i g u r e 5.1. Owing to the l a r g e number of specimens t e s t e d (26) a l l the t e n s i l e t e s t s cannot be shown. Instead, the important t e n s i l e p r o p e r t i e s of each sample are l i s t e d i n Tables 5.2, 5.3 and 5.4. A d d i t i o n a l t e n s i l e t e s t i n f o r m a t i o n such as s t r a i n to f a i l u r e and sample dimensions are p r o v i d e d i n Table C.2 i n Appendix C. 5.1.3 U l t i m a t e T e n s i l e Strength The e x p e r i m e n t a l l y observed t e n s i l e s t r e n g t h s versus volume f r a c t i o n of f i b r e s are presented i n F i g u r e 5.2. Though a trend showing i n c r e a s e d composite s t r e n g t h with i n c r e a s i n g volume f r a c t i o n i s d i s c e r n i b l e , some of the s t r o n g e s t samples possess a r e l a t i v e low volume f r a c t i o n of f i b r e s . In a d d i t i o n , these specimens a l s o possess the weakest matrix (annealed c o n d i t i o n ) . An e x p l a n a t i o n r e g a r d i n g t h i s anomaly w i l l be d i s c u s s e d i n subsequent s e c t i o n s . 5.1.4 Rules of Mixture (ROM) S t r e n g t h To determine the p r e d i c t a b i l i t y of S i C / A l composites t e n s i l e behaviour a ROM s t r e n g t h was c a l c u l a t e d . The ROM value p r e d i c t s the t h e o r e t i c a l s t r e n g t h of the composite based on the assumptions t h a t : 1) A l l f i b r e s present c o n t r i b u t e to the composites mechanical p r o p e r t i e s and e x h i b i t an e l a s t i c modulus of 200 Gpa. T A B L E 5 . 2 AS C A S T C O M P O S I T E T E N S I L E P R O P E R T I E S S a m p l e UTS ROM (Mpa) (Mpa) 31A 1 1 2 . 0 1 0 4 . 2 31B 1 1 5 . 8 1 0 0 . 0 31C 1 1 2 . 0 7 7 . 0 31D 1 1 5 . 7 7 7 . 9 31E 1 0 6 . 4 1 1 8 . 7 36B 1 1 1 . 2 1 1 7 . 7 36C 1 0 7 . 5 117.1 36D 1 0 3 . 7 1 7 4 . 8 38A 1 1 6 . 7 1 7 0 . 0 38B 1 1 3 . 0 1 4 7 . 6 38C 1 0 6 . 0 1 2 8 . 3 38D 1 3 3 . 0 1 2 5 . 6 V o l u m e U T S / R O M F F C F r a c t i o n R a t i o (%) (%) 7 .0 1 .07 0 . 9 0 7 . 6 1 .16 0 . 7 8 10 .2 1 .45 6 . 6 1 .48 8 . 0 0 . 8 9 0 . 9 8 8 . 7 0 . 9 5 0 . 7 9 9 . 9 0 . 9 2 0 . 7 9 10 .4 0 . 5 8 0 . 5 5 1 1 . 5 0 . 6 9 0 . 6 2 9 .8 0 . 7 7 0 . 8 4 9 . 6 0 . 8 3 0 . 5 9 9.1 1 .06 1 .03 T A B L E 5 . 3 A N N E A L E D COMPOSITE T E N S I L E P R O P E R T I E S S a m p l e UTS ROM (Mpa) (Mpa) 39A 1 3 0 . 4 158 .0 39E 1 5 0 . 0 143 .2 45A 1 5 0 . 0 9 1 . 3 45B 1 5 3 . 0 1 1 0 . 9 45D 1 5 6 . 3 9 5 . 5 46A 1 4 9 . 0 156 .8 46B 1 3 8 . 5 158 .7 46C 1 4 4 . 0 154 .6 46D 1 5 6 . 0 1 2 7 . 5 V o l u m e U T S / R O M F F C F r a c t i o n (%) (%) 1 1 . 3 0 . 8 3 0 . 8 8 1 1 . 2 0 . 9 5 1 .13 8 . 6 1 .64 8 . 5 1 .38 9 . 4 1 .64 1 3 . 9 0 . 9 5 0 . 9 5 1 3 . 2 0 . 8 7 0 .81 1 5 . 0 0 . 9 3 1 3 . 9 1 .22 T A B L E 5 . 4 QUENCHED AND TEMPERED C O M P O S I T E T E N S I L E P R O P E R T I E S S a m p l e UTS (Mpa) ROM (Mpa) V o l u m e F r a c t i o n (%) U T S / R O M R a t i o F F C (%) 41D (T6A) 1 3 0 . 0 1 7 3 . 0 12.1 0 . 7 5 0 . 8 2 44B 1 2 1 . 0 1 0 9 . 2 7 . 7 1 . 1 0 1 .12 44C 1 3 8 . 0 1 2 3 . 9 7 .4 1.11 1 .14 44D 1 3 3 . 0 1 3 4 . 7 8 . 4 0 . 9 8 1 .14 47B 1 4 7 . 0 134 . 1 1 1 . 9 1 . 1 0 1 .23 LEGEND • = AS CAST x = T6 TEMPER •= ANNEALED X X A1-T6 X • * X A l - a s c a s t X • u u u n A l - a n n e a l e d u • u • • • • i 1 i i r 0.0 4 .0 8.0 12.0 16. VOLUME FRACTION (PERCENT) FIG. 5.2 - COMPOSITE STRENGTH VERSUS FIBRE VOLUME FRACTION 74 2) The matrix m a t e r i a l behaves i n a f a s h i o n s i m i l a r to that observed i n the ref e r e n c e sample. ROM s t r e n g t h s v a l u e s as l i s t e d i n Tables 5.2, 5.3, and 5.4 are c a l c u l a t e d by the f o l l o w i n g equation: ROM = (VFf x 200 Gpa x e C F ) + A l C F x ( l - V F f ) VFf = volume f r a c t i o n of f i b r e s e C F = f a i l u r e s t r a i n of composite (Table C.2 appendix C) A l C F = s t r e s s c a r r i e d by aluminum matrix at e^ -p (Table C.2) The p r e d i c t e d ROM s t r e n g t h i s compared t o the e x p e r i m e n t a l l y observed composite s t r e n g t h (UTS). T h e o r e t i c a l l y , the UTS/ROM r a t i o should be u n i t y i f the s t a t e d assumptions are c o r r e c t . The p l o t s of the UTS/ROM r a t i o versus volume f r a c t i o n ( F i g . 5.3 and 5.4) f o r a s - c a s t and heat t r e a t e d samples i n d i c a t e l a r g e d e v i a t i o n s of UTS/ROM from the t h e o r e t i c a l value (represented by s o l i d l i n e ) . The v a r i a t i o n s can be a t t r i b u t e d to e i t h e r s y n e r g i s t i c matrix s t r e n g t h e n i n g (UTS/ROM g r e a t e r than 1) or poor composite q u a l i t y (UTS/ROM l e s s than one). UTS/ROM value s s u b s t a n t i a l l y g r e a t e r than one (eg. >1.2) are c o n s i d e r e d the r e s u l t of matrix s t r e n g t h e n i n g . Sample 45A,B,D, 46D and 31C,D a l l e x h i b i t r e l a t i v e h i g h UTS/ROM v a l u e s . In a d d i t i o n , these specimens a l s o d i s p l a y t e n s i l e anomalies thought to be a s s o c i a t e d with s y n e r g i s t i c matrix s t r e n g t h e n i n g . T h i s s u b j e c t w i l l be d e a l t with i n f o l l o w i n g c h a p t e r s . C o n v e r s e l y , a UTS/ROM r a t i o of l e s s than 0.85 i s a strong i n d i c a t i o n of poor composite q u a l i t y i n terms of f i b r e u t i l i z a t i o n . As the t h e o r e t i c a l ROM s t r e n g t h assumes that a l l f i b r e s p r e s e n t c o n t r i b u t e to the composites t e n s i l e p r o p e r t i e s , a 75 i 6.0 7.0 8.0 9.0 10.0 11.0 12.0 VOLUME FRACTION (PERCENT) F I G . 5.3 - U T S / R O M R A T I O V E R S U S F I B R E V O L U M E F R A C T I O N F O R A S - C A S T S A M P L E S LEGEND • = T6 TEMPER x = ANNEALED X X X X X I I I I I I I I I 1 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16. VOLUME FRACTION (PERCENT) G . 5.4 - UTS/ROM RATIO VERSUS F IBRE VOLUME FRACTION FOR ANNEALED AND TEMPERED SPECIMENS 77 decrease i n the a c t u a l number of f i b r e s p a r t i c i p a t i n g w i l l r e s u l t i n a UTS/ROM r a t i o below u n i t y . The a c t u a l number of f i b r e s u t i l i z e d can be d i r e c t l y r e l a t e d to the l o a d t r a n s f e r c a p a b i l i t i e s of the composite. I f aluminum i n f i l t r a t i o n i n t o the f i b r e tows i s inadequate the i n t i m a t e f i b r e / m a t r i x contact necessary f o r proper t r a n s f e r i s not a v a i l a b l e . T h i s would r e s u l t i n a decrease i n the number of f i b r e s i n v o l v e d i n matrix r e i n f o r c i n g , t h e r e f o r e , a r e d u c t i o n i n composite s t r e n g t h . The paradox a r i s e s t h a t , although f i b r e u t i l i z a t i o n i s poor (expect low UTS/ROM r a t i o ) , i n t r i n s i c matrix s t r e n g t h e n i n g may r e s u l t i n an apparent UTS/ROM r a t i o near u n i t y and v i c e v e r s a . To ensure that t h i s s c e n a r i o i s not p r e v a l e n t , the apparent q u a n t i t y of f i b r e s c o n t r i b u t i n g i s c a l c u l a t e d . 5.1.5 F i b r e s C o n t r i b u t i n g The percentage of f i b r e s c o n t r i b u t i n g i s a measure of the apparent q u a n t i t y of f i b r e s i n v o l v e d i n s t r e n g t h e n i n g a composite. C a l c u l a t i o n of t h i s term i s based on the same assumptions used f o r the ROM p r e d i c t i o n . However, f i b r e s c o n t r i b u t i n g are c a l c u l a t e d from the slope of the q u a s i - e l a s t i c p o r t i o n of the composite s t r e s s - s t r a i n curves (re g i o n B F i g . 5.1). The equation used to obta i n the apparent q u a n t i t y of f i b r e s c o n t r i b u t i n g i s as f o l l o w s : E 2 = (200 Gpa x FC/100) + (ds/de x (1-FC/100)) E 2 = slope of composite s t r e s s - s t r a i n curve FC = percentage of f i b r e s c o n t r i b u t i n g ds/de = slope of aluminum r e f e r e n c e s t r e s s - s t r a i n curve Values f o r v a r i a b l e s are given i n Table C.2 appendix C. 78 The percentage of f i b r e s c o n t r i b u t i n g i s then compared to the a c t u a l measured volume f r a c t i o n of f i b r e s p r e s e n t i n the specimen. The r a t i o of f i b r e s c o n t r i b u t i n g / v o l u m e f r a c t i o n i s l i s t e d i n Tables 5.2, 5.3 and 5.4 under f r a c t i o n of f i b r e s c o n t r i b u t i n g (FFC). A value of FFC c o u l d not be c a l c u l a t e d f o r samples 31C,D, 45A,B,D and 46D. The p a r a b o l i c shape of these samples s t r e s s - s t r a i n curves i n h i b i t o b t a i n i n g an a c c u r a t e value for E 2 . It can be p o s t u l a t e d that a low FFC r a t i o ( l e s s than 0.85) suggests poor f i b r e u t i l i z a t i o n . T h i s s c e n a r i o f o l l o w s from inadequate f i b r e / m a t r i x c o n t a c t i n h i b i t i n g proper l o a d t r a n s f e r between the aluminum and f i b r e s . A FFC value of u n i t y (+- 0.1) i n d i c a t e s that a l l f i b r e s present i n the composite are c o n t r i b u t i n g to the t e n s i l e p r o p e r t i e s . T h i s a n a l y s i s assumes that a d d i t i o n a l matrix s t r e n g t h e n i n g i s not o c c u r r i n g . Though a r r i v e d at independently the v a l u e s of UTS/ROM and FFC are e q u i v a l e n t i n t h e i r d e s c r i p t i o n of S i C / A l composites. A p l o t of UTS/ROM vs FFC ( F i g . 5.5) d i s p l a y s the c o r r e l a t i o n between these two v a l u e s . The s o l i d l i n e i n F i g u r e 5.6 repr e s e n t s a one to one correspondence. I t i s observed that low UTS/ROM r a t i o s correspond to e q u a l l y low FFC. A l s o , t e n s i l e samples e x h i b i t i n g a UTS/ROM r a t i o near one have comparable FFC va l u e s . In combination with each other, i t i s f e l t t h a t the values of UTS/ROM and FFC provide a v a l i d d e s c r i p t i o n of a metal matrix composites t e n s i l e behaviour. Low value of UTS/ROM and FFC, i n d i c a t i v e of substandard composite q u a l i t y , are observed to be c o n s i s t e n t with a set of 79 FRACTION OF FIBRES CONTRIBUTING FIG. 5.5 - UTS/ROM RATIO VERSUS FRACTION OF FIBRES CONTRIBUTING 80 p a r t i c u l a r samples. For example, specimens 38 ( e x c l u d i n g 38D) e x h i b i t a low UTS/ROM r a t i o and co r r e s p o n d i n g low FFC (Table 5.2). I t can be p o s t u l a t e d that the manufacturing procedure f o r t h i s sample d i d not pr o v i d e adequate aluminum i n f i l t r a t i o n i n t o the f i b r e tows. Conversely, sample 44 possess r a t i o s near u n i t y , s u g g e s t i n g that the q u a l i t y of these specimens i s adequate. I t should be noted that metallography of samples 44C and 38A proved i n c o n c l u s i v e i n supp o r t i n g the v a r i a t i o n s observed i n composite q u a l i t y . The a n a l y s i s presented above i s b a s i c a l l y q u a l i t a t i v e i n nature. The composite d e s c r i p t i o n s are by no means exact but they do p r o v i d e a general understanding p e r t a i n i n g to metal matrix t e n s i l e behaviour. For any given sample i t i s p o s s i b l e that i n t r i n s i c matrix s t r e n g t h e n i n g i s o c c u r r i n g and can be c o n s i d e r e d n e g l i g i b l e except f o r samples 31C,D, 45A,B,D and 46D. 5.1.6 F i b r e Strength In the pre v i o u s s e c t i o n i t was observed that some composites behaved a c c o r d i n g to a ROM e x p e c t a t i o n up u n t i l the f a i l u r e . The anomaly e x i s t s that the composites are f a i l i n g at s t r a i n s f a r below that p r e d i c t e d f o r a SiC f i b r e p o s s e s s i n g a s t r e n g t h of 2000 Mpa and a s t i f f n e s s of 200 Gpa. In a ROM l o a d i n g a f a i l u r e s t r a i n of 1.0% i s expected. The f a i l u r e s t r a i n s observed are approximately 0.5%. To determine composite f i b r e s t r e n g t h f o r the samples analyzed i n t h i s work the f o l l o w i n g c a l c u l a t i o n was c a r r i e d out: F i b r e Strength = ( U T S c o m p - A l c f )/ V F f U T S _ o m D = s t r e n g t h of composite (Tables 5.2, 5.3, 5.4) 81 A l c £ = s t r e s s c a r r i e d by aluminum matrix a t f a i l u r e s t r a i n VFj = volume f r a c t i o n of f i b r e s F i b r e s t r e n g t h s are l i s t e d i n Table C.3 appendix C. Because of the v a r y i n g q u a l i t y of composites produced, to o b t a i n a r e p r e s e n t a t i v e f i b r e s t r e n g t h , only those samples which d i s p l a y e d a UTS/ROM r a t i o of 1.0 +-0.1 w i l l be an a l y z e d . F i g u r e 5.6 i s a p l o t of f i b r e s t r e n g t h versus volume f r a c t i o n f o r the samples that meet t h i s c r i t e r i a . The maximum f i b r e s t r e n g t h observed (1102 Mpa) i s c o n s i d e r a b l y lower than that c i t e d i n the l i t e r a t u r e (2000 Mpa). The s o l i d l i n e i n F i g u r e 5.6 ( l i n e a r r e g r e s s i o n of p o i n t s ) r e p r e s e n t s the de c r e a s i n g f i b r e s t r e n g t h with volume f r a c t i o n observed f o r the composites p l o t t e d . The r e d u c t i o n i n f i b r e s t r e n g t h with i n c r e a s i n g volume f r a c t i o n c o n t r i b u t e s to the i n c o n s i s t e n t t e n s i l e s t r e n g t h s observed i n F i g u r e 5.1. F a c t o r s c o n t r i b u t i n g to f i b r e s t r e n g t h l o s s w i l l be d i s c u s s e d i n subsequent c h a p t e r s . 5.1.7 T e n s i l e Sample Anomalies I t was not p o s s i b l e to c h a r a c t e r i z e t e n s i l e samples 31D, 45A, 45B, 45D, and 46D along with the other specimens due to the s y n e r g i s t i c s t r e n g t h e n i n g e f f e c t of the aluminum matrix (high UTS/ROM r a t i o ) . A comparison was made between the s t r e s s s t r a i n curves of samples 45A and 44A. 44A has a s i m i l a r volume f r a c t i o n to 45A and possesses a p r e d i c t a b l e s t r e s s - s t r a i n curve ( i n terms of UTS/ROM and FFC). An obvious i n c r e a s e i n the st r e n g t h e n i n g of specimen 45A over 44D i s apparent as shown i n F i g u r e 5.7. The s t r e s s - s t r a i n curve f o r 45A does not e x h i b i t as d i s t i n c t i v e 82 d LEGEND q • = AS CAST o o - X X = T6 TEMPER = ANNEALED (MPA) 1000.0 1 STRENGTH 900.0 X • FIBRE 800.0 X q d o - • o d u> 1 1 1 1 1— 6.0 8.0 10.0 12.0 14.0 VOLUME FRACTION (PERCENT) F I G . 5.6 - APPARENT F IBRE STRENGTH VERSUS F I B R E VOLUME FRACTION 83 q d oo F I G . 5 .7 - COMPARISON OF S T R E S S - S T R A I N CURVE FOR SAMPLES 45A AND 44D T A B L E 5 . 5 Y I E L D S T R A I N S OF ALUMINUM MATRIX M A T E R I A L S a m p l e Y i e l d S t r a i n (u) 4 5 A * 723 45B* 883 45D* 923 46D* 866 46A 402 43A ( r e f ) 519 43B ( r e f ) 281 44B 422 44C 381 44D 361 37D ( r e f ) 307 42C ( r e f ) 321 31A 554 31B 617 3 1 C * 946 31D* 760 31E 258 37A ( r e f ) 500 37B ( r e f ) 743 i n d i c a t e s m a t r i x s t r e n g t h e n e d s a m p l e s 85 a matrix y i e l d p o i n t i n comparison to that observed i n specimen 44A. The apparent break f o r samples 31C,D, 45A,B,D and 46D from Stage I behaviour occurs at a much higher s t r a i n s i n d i c a t i n g i n c r e a s e d matrix s t r e n g t h e n i n g (Table 5.5). A unique f e a t u r e with these samples ( e x c l u d i n g samples 31C and D) i s that the f r a c t u r e s u r f a c e s are i n c l i n e d at above 30% to the h o r i z o n t a l ( F i g . 5.8 l e f t ) . A l l other samples e x h i b i t a predominantly h o r i z o n t a l stepped f r a c t u r e s u r f a c e with some evidence of shear f a i l u r e i n i s o l a t e d s e c t i o n s of the t e n s i l e specimen ( F i g . 5.8 r i g h t ) . The i n c l i n e d s u r f a c e i n d i c a t e s that composite f a i l u r e o c c u r r e d due to shearing f o r c e s . V a r i o u s aspects p e r t a i n i n g to the a d d i t i o n a l s t r e n g t h e n i n g e f f e c t w i l l be d i s c u s s e d i n the f o l l o w i n g chapter. 5.2 M i c r o s t r u c t u r a l A n a l y s i s Metallography was performed on sample 42 and 47 to determine a s - c a s t m i c r o s t r u c t u r e and the e f f e c t s of f i b r e presence on t h i s m i c r o s t r u c t u r e . I t was observed that the a s - c a s t aluminum r e f e r e n c e sample c o n s i s t e d of a l i g n e d p r e c i p i t a t e s ( F i g . 5.9). An EDX a n a l y s i s confirms p r e c i p i t a t e s c o n t a i n Mn, Fe and AL. T h i s i s c o n s i s t e n t with the expected p r e c i p i t a t e composition i n regards to the elements present i n the u t i l i t y aluminum. The presence of f i b r e s ( F i g . 5.10) does not appear to a f f e c t the observed m i c r o s t r u c t u r e when compared to F i g u r e 5.9. A l s o , FIG. 5.8 - FAILURE MODES OF SAMPLE 45A ( l e f t ) AND 38C ( r i g h t ) (9x) F I G . 5 . 1 0 - AS CAST MICROSTRUCTURE OF SAMPLE 47 (792 x ) (DARKER AREAS A R E F I B R E S ) 8 8 e x c e s s i v e n u c l e a t i o n of p r e c i p i t a t e s on the f i b r e s u r f a c e s was not observed. The g r a i n s t r u c t u r e of sample 47 ( a s - c a s t ) shown i n F i g u r e 5.11 c o n s i s t s of r e l a t i v e l y uniform equiaxed g r a i n s . T h i s i s c o n s i s t e n t with the f a s t c o o l i n g r a t e i n h i b i t i n g e x t e n s i v e d e n d r i t i c c e l l f ormation. 5.3 I n t e r f a c i a l A n a l y s i s The bonding between the SiC f i b r e s and aluminum matrix was q u a l i t a t i v e l y determined by SEM a n a l y s i s . F i g u r e s 5.12 and 5.13 are the f r a c t u r e s u r f a c e s of samples 31E and 44D r e s p e c t i v e l y . The lack of f i b r e p u l l o u t at the f r a c t u r e s u r f a c e f o r these samples e s t a b l i s h e s the e x i s t e n c e of a good bond between the f i b r e and aluminum. To determine i f the bonding i s only mechanical adhesion or r e a c t i o n bonding, a s e l e c t e d area d i f f r a c t i o n of the f i b r e s u r f a c e was performed. The r e s u l t s from four separate d i f f r a c t i o n p a t t e r n s are l i s t e d i n Table 5.7 and F i g u r e 5.14 shows the d i f f r a c t i o n p a t t e r n f o r Sample B. The v a l u e s f o r the a c t u a l plane spacings of aluminum c a r b i d e , s i l i c o n c a r b i d e , g r a p h i t e , aluminum and carbon are presented i n Table D.1 (Appendix D). In comparing the d i f f r a c t i o n p a t t e r n s of Table 5.6 with the v a l u e s i n Appendix D samples B, C and D give s t r o n g i n d i c a t i o n s that aluminum c a r b i d e i s present at the f i b r e s u r f a c e . Though aluminum c a r b i d e and beta s i l i c o n c a r b i d e have very s i m i l a r d i f f r a c t i o n p a t t e r n s , the d i f f e r e n c e e x i s t s i n that aluminum F I G . 5 .11 - GRAIN STRUCTURE OF SAMPLE 47 (530 F I G . 5.13 - FRACTURE SURFACE OF SPECIMEN 44D (792 x) 91 1 • V • FIG. 5.14 - DIFFRACTION PATTERN OF SAMPLE B (1.6 x) T A B L E 5 . 6 F I B R E S U R F A C E D I F F R A C T I O N P A T T E R N S S a m p l e A : R i n g # 1 2 3 4 5 6 R e l a t i v e I n t e n s i t y 3 1 f a i n t f a i n t 2 f a i n t R a d i u s ( i n . ) 0 . 57 0 . 6 7 0 . 7 7 0 . 9 4 1 .10 1 . 2 9 P l a n e S p a c i n g (A) 2 . 4 6 2 . 0 9 1.81 1 .48 1 . 27 1 . 08 S a m p l e B : 1 2 3 4 5 6 2 1 f a i n t 3 f a i n t f a i n t 0 . 5 4 0 . 6 4 0 . 7 7 0 . 8 9 1 . 0 9 1 . 2 8 2 . 7 0 2 . 2 8 1 . 8 9 1 .64 1 .34 1 .13 93 TABLE 5.6 CONT. Sample C: 1 2 3 4 5 6 3 1. f a i n t 2 f a i n t f a i n t 0.55 0.65 0.75 0.91 1.11 1 .28 2.65 2.24 1 .87 1 .60 1.31 1.13 Sample D: 1 2 3 4 2 3 1 f a i n t 0.75 0.91 1 .28 1 .50 2.72 2.25 1 .59 1 .36 Note: 1 2 3 = b r i g h t e s t p a t t e r n = 2nd b r i g h t e s t p a t t e r n = 3 r d b r i g h t e s t p a t t e r n 94 c a r b i d e has a d i f f r a c t i n g plane with a spacing of 2.23 A. The e l e c t r o n d i f f r a c t i o n from t h i s plane i s very predominant i n samples B, C and D. A photo of the f i b r e s u r f a c e ( F i g . 5.15) corresp o n d i n g to sample B r e v e a l s the presence of a p o s s i b l e r e a c t i o n product. The abnormality e x i s t s t h a t f o r sample A the presence of aluminum c a r b i d e was not d e t e c t e d . 5.5 F r a c t u r e Surface The m a j o r i t y of composites t e s t e d e x h i b i t r e l a t i v e l y h o r i z o n t a l f r a c t u r e s u r f a c e s . A s s o c i a t e d with each of these samples i s e x t e n s i v e d e l a m i n a t i o n at the p o i n t of f a i l u r e . F i g u r e 5.16 shows the stepped f r a c t u r e s u r f a c e r e s u l t i n g from t h i s f a i l u r e mode f o r samples 38C and 44C. The i r r e g u l a r i t i e s are samples 45A,B,D and 46D which d i s p l a y s l a n t e d f r a c t u r e s without the presence of any e x t e n s i v e amount of d e l a m i n a t i o n ( F i g . 5.17). F I G . 5.15 - FIBRE SURFACE OF SAMPLE B (292000 x) (DARKER AREA IS FIBRE) F I G . 5.17 - FRACTURE SURFACE OF 45A (13 x) 97 CHAPTER 6.0  DISCUSSION 6.1 Manufacturing Technique The hot p r e s s i n g technique employed i n t h i s work f o r the p r o d u c t i o n of S i C / A l composites i s deemed s u i t a b l e . The m e r i t s of t h i s p r o c e s s i n g method r e l a t i v e to the techniques c i t e d i n the l i t e r a t u r e w i l l be d i s c u s s e d . A l s o i n c l u d e d w i l l be suggestions f o r improvements to the manufacturing procedure. 6.1.1 F i b r e D i s t r i b u t i o n Comparison of the t r a n s v e r s e c r o s s s e c t i o n a l view of specimen 46A ( F i g . 6.1) with that of an u n i d i r e c t i o n a l composite ( F i g . 6.2.) manufactured by Kohyama et a l ( r e f . 16) i n d i c a t e only s u b t l e d i f f e r e n c e s . A s s o c i a t e d with each composite are t r a c e s of p r i o r SiC f i b r e l a m i n a t i o n and non-uniform f i b r e d i s t r i b u t i o n , e s p e c i a l l y grouping of i n d i v i d u a l f i b r e s . Photo micrographs of a t r a n s v e r s e composite c r o s s s e c t i o n (Fig.6.3) p r o v i d e d by Tanaka et a l (ref.10) show extremely poor f i b r e d i s t r i b u t i o n and subsequently inadequate aluminum i n f i l t r a t i o n at 40% volume f r a c t i o n f i b r e . However, a b e t t e r f i b r e d i s t r i b u t i o n i s observed f o r 35% volume f r a c t i o n . As these photos ( F i g . 6.3) are l i m i t e d i n the scope of area analyzed i t i s d i f f i c u l t to assess i f they are r e p r e s e n t a t i v e of the e n t i r e composite. I t i s apparent that r e g a r d l e s s of the manufacturing technique used d i f f i c u l t i e s i n o b t a i n i n g adequate i n d i v i d u a l f i b r e d i s t r i b u t i o n are encountered. T h i s problem stems from the 98 2 - TRANSVERSE COMPOSITE CROSS SECTION (REF. 16) (50 x) .3 - TRANSVERSE COMPOSITE CROSS SECTION (REF.10) 100 form i n which the N i c a l o n SiC f i b r e s are produced. Understandably a tow c o n s i s t i n g of 500 i n t e r t w i n n e d f i b r e s does not lend i t s e l f to any s i g n i f i c a n t amount of d i s p e r s i o n when i n c o r p o r a t e d i n t o a metal matrix by a hot p r e s s i n g technique. Poor f i b r e d i s t r i b u t i o n may l e a d to inadequate aluminum p e n e t r a t i o n i n t o the SiC tows and thus, below average f i b r e u t i l i z a t i o n . To a l l e v i a t e t h i s problem i t would be necessary to a l t e r the form i n which the f i b r e s are o b t a i n e d or d e v i s e a new p r o d u c t i o n method. I n c o r p o r a t i n g a monofilament SiC f i b r e p o s s e s s i n g a l a r g e diameter such as that produced by Avco, may minimize problems a s s o c i a t e d with f i b r e tow d i s p e r s i o n . 6.1.2 Volume F r a c t i o n A major drawback a s s o c i a t e d with the q u a s i hot p r e s s i n g method used i s the low volume f r a c t i o n s o b t a i n e d (maximum 15%) r e l a t i v e to other r e s e a r c h e r s (over 40%). The obvious s o l u t i o n would be to i n c r e a s e the number of SiC prepreggs in t r o d u c e d i n the i n i t i a l composite layup. For example, an i n i t i a l s t a c k i n g p a t t e r n with the sequence: 3A1 / ( 3 S i C / A l ) 6 c o u l d be used. However, i t i s a n t i c i p a t e d that the i n c o r p o r a t i o n of the a d d i t i o n a l prepregg l a y e r would induce f u r t h e r problems p e r t a i n i n g to aluminum/fibre tow i n f i l t r a t i o n . An a l t e r n a t i v e s o l u t i o n i n v o l v e s m i n i m i z i n g the excess aluminum present by c o n t r o l l e d p r e s s i n g of the composite while i t i s s t i l l i n the l i q u i d s t a t e . T h i s method of ma n i p u l a t i n g volume f r a c t i o n appears to be used by Tanaka et a l ( r e f . 10) i n t h e i r manufacturing procedure. The t h i n samples t e s t e d by Tanaka et a l 101 (1.2 mm) i n d i c a t e that the composite was p r e s s e d to a t h i c k n e s s necessary to o b t a i n a s u i t a b l e volume f r a c t i o n . I f specimen 46A were 1.2 mm t h i c k i n s t e a d of 3.5 mm i t s volume f r a c t i o n would be approximately 40.5%. T h i s c a l c u l a t i o n j u s t i f i e s that the number of SiC prepreggs c u r r e n t l y used i s s u f f i c i e n t t o o b t a i n s u i t a b l e volume f r a c t i o n s ( r e l a t i v e to other r e s e a r c h e r s ) i f b e t t e r c o n t r o l i n the q u a n t i t y of aluminum present i n the as c a s t composite i s c a r r i e d out. 6.2 F a i l u r e Mechanisms The c i r c u m s t a n c e s under which a S i C / A l composite f a i l s appears to be p a r t i a l l y dependent on f i b r e d i s t r i b u t i o n . For most specimens t e s t e d , grouping of the f i b r e tows i n t o d i s t i n c t laminate l a y e r s was observed ( F i g . 6.4). The non uniform f i b r e d i s t r i b u t i o n shown i n F i g u r e 6.4 can be modeled s c h e m a t i c a l l y as in F i g u r e 6.5. Each l a y e r i n the schematic r e p r e s e n t s e i t h e r an a l l aluminum area or a r e g i o n of high f i b r e c o n c e n t r a t i o n . T h i s schematic o v e r - s i m p l i f i e s the micro f i b r e d i s t r i b u t i o n (the i n t e r f a c e between the aluminum and SiC f i b r e r i c h l a y e r i s more d i s p e r s e d than i n d i c a t e d by the s o l i d d i v i d i n g l i n e ) , but, on a macroscopic s c a l e i s r e p r e s e n t a t i v e of the a c t u a l composite. In a r u l e of mixtures l o a d i n g the s e p a r a t i o n of the two phases i n t o d i s t i n c t l a y e r s would not a f f e c t the o v e r a l l composite modulus and s t r e n g t h . The problem a r i s e s from the i n i t i a t i o n of matrix p l a s t i c deformation a f f e c t i n g the macroscopic f i b r e / m a t r i x i n t e r f a c e . Consider the s i m p l i f i e d F I G . 6.4 - TRANSVERSE CROSS SECTION OF SAMPLE 44B (15 x) / / / / / / / / m . / / / ~7~ ~7~ 7 7 / / / / / S / — 7 7 7 / / 7 7 — x / / / / / / •» / / / / / / / ' / / / / / / / / / / / / / / / SIC CONCENTRATED REGION F I G . 6.5 - SCHEMATIC OF SAMPLE 44B CROSS SECTION 103 l o a d i n g diagram ( F i g . 6.6) i n which a d i s t i n c t SiC l a y e r i s s u b j e c t to a shear s t r e s s o r i g i n a t i n g from the adjacent aluminum l a y e r s . The s o l i d l i n e r e p r e s e n t the h y p o t h e t i c a l s h e a r i n g plane. The area of importance i s the i n t e r s e c t i o n of the s h e a r i n g plane and the f i b r e l a y e r . The c l o s e packing of the h i g h l y shear r e s i s t a n t f i b r e s i n h i b i t s the shear s t r a i n to be t r a n s m i t t e d through t h i s a r e a. T h i s r e s u l t s i n a s t r e s s b u i l d u p which can cause e i t h e r f i b r e breakage or del a m i n a t i o n along the i n t e r f a c e . The type of d e l a m i n a t i o n d e s c r i b e d above was observed f o r a l l t e n s i l e samples t e s t e d ( F i g . 5.16) except f o r specimens 45A,B,D and 46D i n which the amount of d e l a m i n a t i o n that had oc c u r r e d was minimal. Thus, the f a i l u r e mechanism p r e d i c t e d f o r d i s t i n c t l y l a y e r e d composites i s supported by observed r e s u l t s . The b a s i s f o r t h i s f a i l u r e mechanism i s dependent on the f a c t that the maximum shear s t r a i n i s p e r p e n d i c u l a r to the f i b r e l a y e r s ( F i g . 6 . 6 ) . As shown i n F i g u r e 6.5 the i n t e r v e n i n g aluminum l a y e r s can be c o n s i d e r e d as t h i n p l a t e s and thus can be expected to behave as such. A c c o r d i n g to plane s t r e s s c r i t e r i a , a t h i n p l a t e s u b j e c t e d to a t e n s i l e s t r e s s does not have a f o r c e a c t i n g p e r p e n d i c u l a r to i t s s u r f a c e . R e l a t i n g t h i s to Mohrs c i r c l e , a zero s t r e s s p e r p e n d i c u l a r to the aluminum s u r f a c e r e s u l t s i n a maximum shear s t r e s s i n the plane c o n t a i n i n g both the maximum and minimum s t r e s s d i r e c t i o n s . For our s c e n a r i o t h i s corresponds to a maximum shear plane p e r p e n d i c u l a r to the f i b r e l a y e r as shown i n F i g u r e 6.6. 104 P A R A L L E L S H E A R D I R E C T I O N F I B R E D I R E C T I O N S I D E V I E W S I C C O N C E N T R A T E D R E G I O N F I G . 6.6 - H Y P O T H E T I C A L S H E A R L O A D I N G D I A G R A M 105 Samples 45A,B,D and 46D e x h i b i t only a minimal amount of del a m i n a t i o n and possess an i n c l i n e d f a i l u r e s u r f a c e p a r a l l e l to the SiC l a y e r s . As the apparent maximum shear d i r e c t i o n i s p a r a l l e l to the f i b r e l a y e r s the observed amount of de l a m i n a t i o n p e r p e n d i c u l a r to the SiC r i c h l a y e r i s n e g l i g i b l e . The change i n the d i r e c t i o n of maximum shear s t r e s s f o r samples 45A,B,D and 46A can be r e l a t e d to f i b r e d i s t r i b u t i o n w i t h i n these specimens. With the other samples, the SiC l a y e r s were w e l l spaced apart ( F i g . 6.4) and the aluminum was present as a number of d i s t i n c t l a y e r s . However, specimens 45A,B,D and 46D e x h i b i t a co n c e n t r a t e d f i b r e packing such that the m u l t i p l e SiC l a y e r s can be c o n s i d e r e d as one d i s t i n c t macroscopic l a y e r ( F i g . 6.7). T h i s r e s u l t s i n the s t a c k i n g sequence shown s c h e m a t i c a l l y i n F i g u r e 6.8. In l i g h t of t h i s c o n c e n t r a t e d f i b r e s t a c k i n g , the approximation that the aluminum l a y e r s behave as t h i n p l a t e s becomes q u e s t i o n a b l e , ( i n s t e a d of 5 or 6 d i s t i n c t l a y e r s the aluminum i s d i v i d e d i n t o 2 l a r g e r r e g i o n s ) . Thus, due to the p o s s i b l e breakdown of the plane s t r e s s c r i t e r i a , the maximum shear i s not expected to occur i n any p a r t i c u l a r d i r e c t i o n . From t h i s , the shear f a i l u r e of specimens 45A,B,D and 46D p a r a l l e l to the f i b r e l a y e r s i s not s u r p r i s i n g . 6.3 T e n s i l e R e s u l t s The t e n s i l e t e s t r e s u l t s c i t e d i n Table 5.2, 5.3 and 5.4 are i n d i c a t i v e of the range of S i C / A l composite p r o p e r t i e s that can be encountered. D e v i a t i o n s i n the mechanical p r o p e r t i e s can F I G . 6.7 - TRANSVERSE CROSS SECTION OF SAMPLE 45A (20 x ) F IBRE D IRECTION S IC CONCENTRATED REGION F I G . 6.8 - SCHEMTAIC OF SAMPLE 45A CROSS SECTION 1 07 be a t t r i b u t e d to the v a r i a b i l i t y i n the manufacturing process used. Due to c o n t i n u a l improvements i n the p r o d u c t i o n technique the composites produced near the end of the r e s e a r c h (44,45,46,47) are i n terms of s t r e n g t h , volume f r a c t i o n and UTS/ROM r a t i o of higher q u a l i t y than e a r l i e r samples. 6.4 I n t r i n s i c S trengthening In a n a l y z i n g the t e n s i l e p r o p e r t i e s of a SiC f i b r e r e i n f o r c e d aluminum m a t e r i a l not only should the u l t i m a t e s t r e n g t h be c o n s i d e r e d but how the composite behaved i n reachin g t h i s v a l u e . To a v a r y i n g extent a l l authors c i t e d i n the l i t e r a t u r e review are n e g l i g e n t i n a d d r e s s i n g composite behaviour up u n t i l f a i l u r e . Of s p e c i a l note i s the paper by Tanaka et a l (ref.10) i n which the authors f a i l to d i s c u s s the matrix m a t e r i a l s c o n t r i b u t i o n to o v e r a l l composite s t r e n g t h . As presented i n the l i t e r a t u r e review, t e n s i l e data s u p p l i e d by Tanaka et a l ( r e f . 10) i n d i c a t e s aluminum s t r a i n hardening r a t e s of up to 52 Gpa. C o n s i d e r i n g the e l a s t i c modulus of aluminum i s only 70 Gpa the observed s t r a i n hardening r a t e s are q u i t e phenomenal. Furth e r c a l c u l a t i o n s on the data s u p p l i e d by Tanaka et a l were c a r r i e d out. Assuming a ROM l o a d i n g , the r e l a t i v e c o n t r i b u t i o n of the annealed 6061 and 5052 matrix m a t e r i a l s to o v e r a l l composite s t r e n g t h was c a l c u l a t e d from data presented i n F i g u r e 2.2. The 6061 matrix c o n t r i b u t e d a c a l c u l a t e d s t r e n g t h of 373 Mpa at a s t r a i n of 0.82%. S i m i l a r l y , the 5052 matrix was s t r e s s e d to 233 Mpa at a s t r a i n of 0.6%. The u l t i m a t e s t r e n g t h s f o r annealed 6061 and 5052 are 124 Mpa and 199 Mpa r e s p e c t i v e l y . 108 For the lows s t r a i n s at which the s t r e n g t h e n i n g c o n t r i b u t i o n s were c a l c u l a t e d a comparison with the y i e l d s t r e n g t h s of these m a t r i c e s would be more p e r t i n e n t . The y i e l d s t r e n g t h of 6061-O i s 55.2 Mpa and 9 0 . 0 Mpa f o r 5052-O. The e x t r a o r d i n a r y amount of s t r e n g t h e n i n g observed i n the aluminum m a t r i c e s above i s not o v e r l y s u r p r i s i n g . A w e l l known advantageous f e a t u r e of aluminum i s i t s a b i l i t y to be h i g h l y strengthened by second phase p a r t i c l e s . For example, an Al-Zn-Mg-Cu a l l o y s can e x h i b i t s t r e n g t h s up to 670 Mpa. From t h i s , i t can be h y p o t h e s i z e d that the N i c a l o n SiC f i b r e s present i n the matrix i n t e r a c t with the aluminum in a f a s h i o n s i m i l a r to that of second phase p a r t i c l e s . By examining the s y n e r g i s t i c a l l y strengthened samples observed i n t h i s work, i t i s hoped t h a t f a c t o r s a f f e c t i n g the s t r e n g t h e n i n g mechanisms can be determined. Samples 45A,B,D, 46A and 31C,D by v i r t u e of t h e i r h i g h UTS/ROM r a t i o s and c h a r a c t e r i s t i c s t r e s s - s t r a i n curves are deemed to e x h i b i t matrix s t r e n g t h e n i n g . To determine what f a c t o r s i n f l u e n c e the a d d i t i o n a l s t r e n g t h e n i n g mechanisms observed a comparison of f e a t u r e s unique to these samples with non s y n e r g i s t i c a l l y strengthened specimens i s c a r r i e d out. The t e n s i l e f e a t u r e s unique to i n t r i n s i c a l l y strengthened specimens a r e : higher y i e l d s t r a i n s (Table 5.7), p a r a b o l i c r a t e s of hardening up u n t i l f a i l u r e and f o r sample 45A,B,D and 46A, the i n c l i n e d f r a c t u r e s urface and d i s t i n c t l a c k of d e l a m i n a t i o n . I t can be p o s t u l a t e d that the a d d i t i o n a l matrix s t r e n g t h e n i n g can be a t t r i b u t e d to the SiC f i b r e s a c t i n g as d i s l o c a t i o n b a r r i e r s . T h i s type of s t r e n g t h e n i n g i s analogous to 109 t h a t o b t a i n e d from second phase p r e c i p i t a t e s . The i n c r e a s e o b s e r v e d i n y i e l d s t r a i n may be a t t r i b u t e d t o an Orowan s t r e n g t h e n i n g mechanism ( r e f . 2 4 ) . Orowan p r o p o s e d t h a t t h e y i e l d s t r e n g t h of a p a r t i c u l a t e r e i n f o r c e d m a t e r i a l i s d e t e r m i n e d by the shear s t r e s s r e q u i r e d t o move a d i s l o c a t i o n l i n e between two p a r t i c l e s ( r e f . 2 4 ) . In i t s most s i m p l i s t i c form the a d d i t i o n a l shear s t r e s s r e q u i r e d can be c a l c u l a t e d a c c o r d i n g t o the f o l l o w i n g e q u a t i o n : T = G x b / 1 G = m a t r i x shear modulus b = b u r g e r s v e c t o r 1 = p a r t i c l e s e p a r a t i o n T h i s e q u a t i o n i s based on s p h e r i c a l p a r t i c l e r e i n f o r c e m e n t and i s i n t e n d e d o n l y t o i n t r o d u c e the f a c t o r s t h a t would a f f e c t y i e l d s t r e n g t h . For a c o n s t a n t shear modulus and b u r g e r s v e c t o r the y i e l d s t r e s s i s c o n s i d e r e d i n v e r s e l y p r o p o r t i o n a l t o p a r t i c u l a t e s p a c i n g . The p a r t i c l e s p a c i n g (analogous t o f i b r e s p a c i n g ) i s dependent on the volume f r a c t i o n and s i z e of t h e second phase. The importance of t h e s e f a c t s w i l l be c o n s i d e r e d i n a l a t e r s e c t i o n . On the i n i t i a t i o n of p l a s t i c f l o w a second phase hardened m a t e r i a l e n t e r s a r e g i o n e x h i b i t i n g a p a r a b o l i c r a t e of s t r e n g t h e n i n g ( r e f . 2 8 ) . A f t e r the p a r a b o l i c h a r d e n i n g r e g i o n , the s t r e s s - s t r a i n c u r v e f o l l o w s a l i n e a r work h a r d e n i n g r a t e . The s t r e s s - s t r a i n c u r v e s f o r samples 31C,D, 45A,B,D and 46D a l l e x h i b i t d i s t i n c t p a r a b o l i c t r a n s i t i o n a f t e r y i e l d i n g . The anomaly e x i s t s t h a t c o m p o s i t e f a i l u r e o c c u r s b e f o r e t h e o n set of l i n e a r 1 10 work hardening. T h i s may be due to shear s t r e s s e s present i n d u c i n g premature f i b r e f a i l u r e . The i n c r e a s e i n hardening r a t e above that of the u n r e i n f o r c e d matrix i s p o s s i b l y the r e s u l t of f i b r e d i s l o c a t i o n loops i n t e r a c t i n g with g l i s s i l e d i s l o c a t i o n s ( r e f . 2 8 , 3 2 ) . The d i s l o c a t i o n loops are formed by p r e v i o u s g l i s s i l e d i s l o c a t i o n s by p a s s i n g the second phase p a r t i c l e s . The increment of s t r a i n hardening by t h i s method was proposed to be p r o p o r t i o n a l to volume f r a c t i o n and i n v e r s e l y p r o p o r t i o n a l to f i b r e s p a c i n g ( r e f . 28,32). Though the above s t r e n g t h e n i n g mechanism i s f o r s p h e r i c a l p a r t i c l e s Tanaka et a l ( r e f . 28) proposed t h a t a l i g n e d needle shaped p a r t i c l e (analogous to a u n i d i r e c t i o n a l f i b r e ) would i n c r e a s e the s t r a i n hardening r a t e by a f a c t o r of 2 above that f o r a s p h e r i c a l p a r t i c l e . In an a r t i c l e by A r s e n a u l t (ref.25) the s y n e r g i s t i c s t r e n g t h e n i n g of a d i s c o n t i n u o u s S i C / A l composite was a t t r i b u t e d to high d i s l o c a t i o n d e n s i t y and a small, subgrain s i z e . The d i s l o c a t i o n s were proposed to have been produced by aluminum deformation r e s u l t i n g from d i f f e r e n c e s i n the thermal c o n t r a c t i o n c o e f f i c i e n t of the aluminum and SiC (21.6 x 10~ 6 and 5.0 x 10~ 6 r e s p e c t i v e l y ) . S e v e r a l concepts d i s p e l s t r e n g t h e n i n g of t h i s type in the samples t e s t e d . The low volume f r a c t i o n of f i b r e s present r e l a t i v e t o the aluminum would not lend i t s e l f to any s u b s t a n t i a l amount of t h e r m a l l y induced work hardening. More i m p o r t a n t l y , the quenched samples (T6A and T6B) would be expected to e x h i b i t a g r e a t e r amount of thermal work hardening. As the i n t r i n s i c a l l y strengthened samples were e i t h e r annealed or as c a s t the e f f e c t 111 of t h e r m a l l y induced s t r e n g t h e n i n g can be c o n s i d e r e d n e g l i g i b l e f o r the volume f r a c t i o n s d i s c u s s e d here. In a q u a l i t a t i v e sense the parameters deemed most important to matrix strengthening are volume f r a c t i o n and p a r t i c l e s p a c i n g . I n h e r e n t l y a s s o c i a t e d with these f a c t o r s i s p a r t i c l e s i z e . C o n s i d e r i n g that the m a j o r i t y of composites e x h i b i t i n g s y n e r g i s t i c s trengthening possessed a c l o s e packing of f i b r e s i n s p e c i f i c areas (samples 45A,B,D and 46D) ( F i g . 6.7) the a d d i t i o n a l strengthening observed may be a t t r i b u t e d to these parameters. T h i s o b s e r v a t i o n i s s e m i - q u a l i t a t i v e in nature and deserves f u r t h e r a n a l y s i s . I d e a l l y an evenly separated d i s t r i b u t i o n of small diameter f i b r e s would be r e q u i r e d to p r o v i d e maximum matrix hardening. The problem a r i s e s in o b t a i n i n g a s u i t a b l e f i b r e d i s t r i b u t i o n from a N i c a l o n SiC tow. As mentioned e a r l i e r , by i n c o r p o r a t i n g a monofilament SiC f i b r e such as produced by Avco, the d i s t r i b u t i o n problem would be minimized. The drawback of such a s o l u t i o n i s t h a t f o r s i m i l a r volume f r a c t i o n s the i n c r e a s e i n f i b r e s p a c i n g due t o the l a r g e r f i b r e s i z e would d e t r a c t from the s t r e n g t h e n i n g mechanisms proposed. The extent of matrix s t r e n g t h e n i n g o c c u r r i n g i n a composite i s an important f a c t o r when high temperature p r o p e r t i e s are being c o n s i d e r e d . If a s u b s t a n t i a l p o r t i o n of a composites s t r e n g t h i s due t o matrix s t r e n g t h e n i n g than d i f f i c u l t i e s with t h e r m a l l y a c t i v a t e d matrix creep would be encountered. Creep i n the aluminum matrix would r e s u l t i n a d d i t i o n a l l o a d being p l a c e d on 1 12 the f i b r e s and the p o s s i b i l i t y of premature composite f a i l u r e . F u r t h e r study i n t h i s area would be r e q u i r e d . 6.5 F i b r e Strength The maximum f i b r e s t r e n g t h c a l c u l a t e d was 1102 Mpa. T h i s value i s f a r below that c i t e d i n the l i t e r a t u r e of 2000 MPa. The dramatic decrease i n f i b r e s t r e n g t h can be a t t r i b u t e d to three p o s s i b l e f a c t o r s . In l i g h t of the p r e v i o u s a n a l y s i s the a d d i t i o n a l s t r e s s p l a c e d on the f i b r e s due to matrix shearing and d e l a m i n a t i o n would reduce the apparent f i b r e s t r e n g t h . A l s o , f i b r e degradation by aluminum c a r b i d e formation and damage i n c u r r e d d u r i n g the hot p r e s s i n g o p e r a t i o n would c o n t r i b u t e to a s t r e n g t h r e d u c t i o n . The r e l a t i v e c o n t r i b u t i o n of each of these parameters towards f i b r e s t r e n g t h d e g r a d a t i o n i s unknown, but, i t can be s p e c u l a t e d that matrix s h e a r i n g and aluminum c a r b i d e formation would have the s t r o n g e s t e f f e c t s . 6.6 I n t e r f a c i a l P r o p e r t i e s The r e s u l t s of the S e l e c t e d Area D i f f r a c t i o n p a t t e r n i n d i c a t e the presence of aluminum c a r b i d e at the f i b r e s u r f a c e . T h i s would account f o r the l a c k of f i b r e p u l l o u t observed on the composite f r a c t u r e s u r f a c e s (Figure 5.12 and 5.13). On a m i c r o s c a l e the bonding between the f i b r e and matrix i s deemed adequate. However, c o n s i d e r i n g the macroscopic d e l a m i n a t i o n observed the cohesion between the d i s t i n c t p l i e s i s i n s u f f i c i e n t in m a i n t a i n i n g composite i n t e g r i t y at the onset of matrix deformation. 1 13 Though the aluminum c a r b i d e may improve the bonding between the f i b r e and m a t r i x some of the r e d u c t i o n o b s e r v e d i n apparent f i b r e s t r e n g t h may be a t t r i b u t e d t o i t s f o r m a t i o n . As a l l samples were exposed t o molten aluminum f o r e q u i v a l e n t p e r i o d s ( F i g . 3.8) any change i n apparent f i b r e s t r e n g t h from sample t o sample cannot be a t t r i b u t e d t o d i f f e r i n g amounts of aluminum c a r b i d e f o r m i n g d u r i n g m a n u f a c t u r i n g . 1 14 CONCLUSIONS 1) The m a n u f a c t u r i n g p r o c e s s used i n p r o d u c i n g a S i C / A l c o m p o s i t e p l a y s an im p o r t a n t r o l e i n a c o m p o s i t e s m e c h a n i c a l p r o p e r t i e s . Such p a r a m e t e r s as molten r e t e n t i o n time (aluminum c a r b i d e f o r m a t i o n ) , p r e s s i n g p r e s s u r e ( m a t r i x v o i d c o n t r o l and p o s s i b l e f i b r e damage) and i n t e r l a m i n a r s p a c i n g must be more c a r e f u l l y c o n t r o l l e d t o ensure the q u a l i t y of the c o m p o s i t e s b e i n g produced. 2) The c o n d i t i o n l i m i t i n g the use of N i c a l o n S i C tows f o r r e i n f o r c i n g a m e t a l l i c m a t e r i a l i s the poor i n d i v i d u a l f i b r e d i s t r i b u t i o n o b t a i n e d i n c o m p o s i t e s made from t h i s m a t e r i a l . T h i s s c e n a r i o r e s u l t s i n in a d e q u a t e f i b r e m e c h a n i c a l p r o p e r t y u t i l i z a t i o n and i n c o m b i n a t i o n w i t h m a t r i x d e f o r m a t i o n may l e a d t o premature c o m p o s i t e f a i l u r e due t o d e l a m i n a t i o n . 3) The f o r m a t i o n of aluminum c a r b i d e a t t h e S i C / A l i n t e r f a c e i s thought t o c o n t r i b u t e t o the good f i b r e - m a t r i x bonding o b s e r v e d . The e x t e n t of f i b r e damage i n c u r r e d due t o aluminum c a r b i d e f o r m a t i o n i s unkown. 4) An advantage of u s i n g a m e t a l l i c m a t e r i a l i n c o m b i n a t i o n w i t h a r e i n f o r c i n g f i b r e i s the s y n e r g i s t i c m a t r i x s t r e n g t h e n i n g t h a t may be o b t a i n e d t h r o u g h m a t r i x - f i b r e i n t e r a c t i o n . 115 RECOMMENDATIONS 1) An important aspect of metal matrix composites that r e q u i r e s f u r t h e r a n a l y s i s concerns the f i b r e - m a t r i x deformation i n c o m p a t a b i l i t y . T h i s i r r e g u l a r i t y r e s u l t s from the f i b r e s remaining e l a s t i c through the e n t i r e l o a d i n g procedure while the aluminum matrix p l a s t i c a l l y deforms p r i o r t o f a i l u r e . By using a high y i e l d s t r e n g t h aluminum matrix the amount of p l a s t i c deformation f o r a given l o a d can be minimized. However, the e f f e c t on composite f r a c t u r e toughnes and high temperature s t r e n g t h must be c o n s i d e r e d . 2) As continuous f i b r e r e i n f o r c e d metal m a t r i c e s are used only i n very s p e c i a l i z e d a p p l i c a t i o n s i t i s suggested that f u t h e r work on metal matrix composites be implimented on d i s c o n t i n u o u s and p a r t i c u l a t e strengthened aluminum. 116 REFERENCES 1) Hull,Derek. An I n t r o d u c t i o n to Composite M a t e r i a l s . Cambridge U n i v e r s i t y Press, 1981. 2) Agarwal,B.D. and Broutman,L.J. A n a l y s i s and Performance of  F i b r e Composites. New York: Wiley, 1980. 3) Aluminum V o l . I. e d i t e d Kent R. Van Horn, ASM, 1967. 4) Broek,David. Elementary E n g i n e e r i n g F r a c t u r e Mechanics. 3rd e d i t i o n , Martinus N i j h o f f , 1981. 5) Kohara,S and Muto,N. Proceedings of ICCM 4, San Diego, C a l i f . , 1985, pp. 631-637. 6) M e l v i n M e t t i c k . p e r s o n a l correspondence, 1985. 7) Andersson,C.H. and Warren,R. Composites, (1), v o l . 15, 1984, pp. 16-24. 8) Prewo,K.M. Composites Technology Review, v o l . 5, (2), 1983, pp. 69-71. 9) Andersson,C.H. and Warren,R. Proceedings ICCM 3, P a r i s , v o l . 2, 1980, pp. 1129-1139. 10) Tanaka,J., Ichikawa,H., Okamura,K. and Matsuzawa,T. Procs. ICCM 4, Tokyo, 1982, pp. 1407-1413. 11) Fukunga,H. and Ohde,T. i b i d , pp.1443-1450. 12) Kohara,S. Procs. Japan-U.S. Conference on Composite M a t e r i a l s , Tokyo, 1981, pp. 224-231. 13) Nakata,E., Kagawa,Y., Terao,H. and Komori,M. Procs. of the 26th Japan Congress on M a t e r i a l Research, Kyoto, 1983, pp. 19-23. 1 1 7 14) Gigerenzer,H., Pepper,R.T. and Lachman,W.L. Procs. ICCM 2, 1978, pp. 175-188. 15) Kohara,S. and Muto,N. Pr o c s . ICCM 4, Tokyo, 1982, pp.1451-1 455. 16) Kohyama,A. and Igata,N. Procs. ICCM 5, San Diego, 1985, pp. 609-621 . 17) John Nadeau, p e r s o n a l correspondence, 1985. 18) Yajima,S., K i y o h i t o , 0 . , Tanaka,J. and Hayase,T. J o u r n a l of M a t e r i a l Science, 16, 1981, pp. 3033-3038. 19) Yajima,S., K i y o h i t o , 0 . , Tanaka,J. and Hayase,T. J o u r n a l of M a t e r i a l Science L e t t e r s , 15, 1980, pp.2130-2131. 20) Yajima,S., Okamura,K., Matzuzawa,T., Tanaka,J. and Hayase,T. Procs. Composites M a t e r i a l s Japan-U.S. Conf., Tokyo, 1981, pp. 232-238. 21) I s e k i , T . Kameda,T. and Maruyan,T. J o u r n a l of M a t e r i a l S c i e n c e , 19, 1984, pp. 1692-1698. 22) Source Book on S t a i n l e s s S t e e l s . ASM, Metals Park, Ohio, 1976. 23) Weinberg,F. Procs. of Conference on A p p l i e d M e t a l l u r g y and Metals Technology, Warwick, Conventry, England, 1980, pp. 131-136. 24) Dieter,George E. Mechanical M e t a l l u r g y 2nd E d i t i o n . McGraw-H i l l Inc., 1976. 25) A r s e n a u l t , R . J . M a t e r i a l Science and E n g i n e e r i n g , 64, 1984, pp. 171-181. 26) A r s e n a u l t , R . J . and Fisher,R.M. S c r i p t a M e t a l l u r g i c a , 17, 1983, pp.67-71. 118 27) Ashby,M.F. P h i l i s o p h i c a l Magazine, 14, 1966, pp. 1157-1177. 28) Tanaka,K. and Mori,T. Acta M e t a l l u r g i c a , 18, 1970, pp. 931-941 . 29) ASM Handbook. Metallography, S t r u c t u r e s and Phase Diagrams, volume 8, 8th e d i t i o n . 30) Warren,R. and Andersson,C.H. Composites, 15, (2), 1984, pp.101-111. 31) Tom Alden, p e r s o n a l correspondence, 1986. 32) P h y s i c s of S t r e n g t h and P l a s t i c i t y , e d i t e d A l i S. Argow, Hirsch,P.B. and Humphreys,F.J. pp. 189-216. 119 THERMODYNAMIC C A L C U L A T I O N S IN A P P E N D I X A FOR T H E FORMATION OF ALUMINUM C A R B I D E S O L I D ALUMINUM 120 E q u a t i o n s : 4 A 1 ( 1 ) + 3C = A 1 4 C 3 -63330 + 22.72 x T ( c a l / m o l ) 4 A 1 ( S ) = 4 A 1 ( X ) 10320 - 11.04 x T ( c a l / m o l ) 3SiC = 3 S i + 3C 52380 - 5.49 x T ( c a l / m o l ) 3SiC + 4 A 1 ( S ) = A l 4 C 3 + 3 S i -630 + 6.19 x T ( c a l / m o l ) Non - S t a n d a r d C o n d i t i o n s : G = G° + RT x In K eq K e g = In ( a S i ) 3 *** G = -630 + (6.19 x T) + (5.961 x T x In ( a S i ) ) c a l / m o l *** e q u a t i o n used f o r c a l c u l a t i o n s i n F i g u r e 2.4 1 2 1 A P P E N D I X B DRUMWINDING PARAMETERS TABLE B.1 DRUMWINDING PARAMETERS R e s i n B i n d e r : Derakane 411 Drum Speed: 325 rpm Comb S e t t i n g : 14.0 Cr o s s Head Speed: 0.0 (on d i a l ) R o l l e r P r e s s u r e : 10.0 p s i . 1 23 APPENDIX C TENSILE TEST DATA 124 T A B L E C . 1 R E F E R E N C E ALUMINUM T E N S I L E D I M E N S I O N S SAMPLE T H I C K N E S S WIDTH AREA (mm) (mm) (mm2) 37A 5 .71 3 . 3 7 1 9 . 3 37B 5 . 9 7 3 . 8 8 2 3 . 1 43A 6 . 6 0 3 . 0 9 2 0 . 4 43B 6 . 1 8 3 . 0 7 1 9 . 0 42A 6 . 4 5 3 . 2 0 2 0 . 6 42B 6 . 5 5 3 . 1 5 2 0 . 6 42C 6 . 3 5 3 . 5 4 2 2 . 5 37D 6 . 3 5 3 . 5 4 2 2 . 5 T A B L E C . 2 COMPOSITE T E N S I L E DATA SAMPLE e C p A l C p F C AREA d s / d e (%) (Mpa) (%) (mm 2 ) (Gpa) 31A .37 5 5 . 8 6 . 3 2 3 . 8 15 .8 31B .33 54 .1 5 . 9 2 3 . 7 1 4 . 7 31C .17 47 .1 - 2 6 . 3 31D .23 5 0 . 3 - 2 5 . 4 31E .42 5 6 . 9 7 . 8 2 5 . 0 1 8 . 4 36B .38 5 5 . 8 6 . 9 2 1 . 9 1 6 . 7 36C .34 5 4 , 7 7 . 8 2 4 . 8 1 8 . 5 36D .58 6 0 . 4 5 . 7 2 4 . 6 1 4 . 5 38A .51 5 9 . 0 7.1 19.1 1 7 . 0 38B . 4 9 5 7 . 7 8 . 2 1 8 . 2 19 .2 38C .41 5 5 . 8 5 . 7 2 2 . 9 14 .2 38D .41 5 5 . 8 9 . 4 2 2 . 1 2 1 . 9 39A . 4 6 6 2 . 0 9 . 9 2 0 . 7 2 3 . 8 39E .4 6 0 . 0 1 2 . 6 2 0 . 6 2 8 . 9 126 TABLE C.2 c o n t . . . 45A .25 53.0 45B .35 54.8 45D .25 53.0 46A .38 58.9 46B .41 59.6 46C .36 58.7 46D .29 55.4 41D .49 61.8 44B .37 57.3 44C .46 60.9 44D .47 61.2 47B .35 57.0 17.0 16.6 17.9 13.2 20.7 28.5 10.7 21.5 23.8 19.6 20.8 9.9 19.8 22.5 8.1 19.8 20.1 8.4 19.4 19.6 9.6 19.0 21.9 14.2 20.5 32.0 T A B L E C . 3 APPARENT F I B R E STRENGTH SAMPLE 31A 36B 38D 39E 44B 44C 44D 46A 47B VOLUME F R A C T I O N (%) 7 . 0 8 . 7 9 . 1 11 .2 7 . 7 7 .4 8 . 4 1 3 . 9 1 1 . 9 STRENGTH (Mpa) 866 692 904 864 885 1 1 02 913 707 81 1 APPENDIX D ELECTRON DIFFRACTION PATTERNS 1 29 T A B L E D . 1 D I F F R A C T I O N PATTERNS OF A l 4 C ^ , S I L I C O N , G R A P H I T E , B - S i C a n d CARBON SAMPLE R E L A T I V E P L A N E I N T E N S I T Y S P A C I N G (A) A 1 4 C 3 100 1 . 6 6 62 2 . 8 0 62 2 . 2 3 B e t a S i C 100 2 .51 63 1 . 5 3 50 1.31 G r a p h i t e 100 3 . 3 5 80 1 . 68 60 1 .54 C a r b o n 100 2 . 0 6 27 1 . 2 6 1 6 1 . 08 S i l i c o n 100 3 . 1 4 60 1 . 93 35 1 .64 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0078554/manifest

Comment

Related Items