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The deformation behaviour of fibre-reinforced copper. Howard, Graeme Claude 1964-12-31

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THE DEFORMATION BEHAVIOUR OF FIBRE-REINFORCED COPPER by >GRAEME CLAUDE HOWARD A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER. OF APPLIED SCIENCE IN THE DEPARTMENT OF METALLURGY We accept t h i s t h e s i s as conforming t o the standard r e q u i r e d from candidates f o r the degree of MASTER OF APPLIED SCIENCE Members of the Department of M e t a l l u r g y THE UNIVERSITY OF BRITISH COLUMBIA March, 1964 In presenting this thesis in p a r t i a l fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives.. It i s understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department .of Metallurgy The University of British Columbia, Vancouver. 8, Canada. Date March 1964 •ABSTRACT : The deformation "behaviour of copper, rein f o r c e d with i r o n and s t e e l f i b r e s has been investigated. Parameters studied include: f i b r e diameter, - matrix mean free path, and r e l a t i v e strength of f i b r e and matrix. No strengthening e f f e c t has.been observed which can.be a t t r i b u t e d to f i b r e . s i z e alone. However, i t i s suggested that the strength of - metal f i b r e - r e i n f o r c e d metal, composites are gr e a t l y influenced, by a . " s i z e . e f f e c t " in. the matrix. A modification of the theory of combined action, has been proposed f o r p r e d i c t i n g the strength of a f i b r e - r e i n f o r c e d composite, v i z ; ^~c = A f + Am ^ m + A f l A K d f " l / 2 . where A i s volume f r a c t i o n , f r e f e r s to f i b r e , m r e f e r s to matrix, d^. is. f i b r e diameter, and. K i s a constant whose. value depends on the-hardness of the f i b r e . Weakening of the matrix-fibre i n t e r f a c e i n composites of copper and s t e e l f i b r e s has been a t t r i b u t e d . t o segregation, of carbon to the i n t e r f a c e . •Alloys containing 6 to 8 weight per cent copper i n - i r o n have been shown.to exhibit a.martensitic transformation when cooled from the V region of the; Fe-Cu phase diagram,.. i i i . TABLE OF CONTENTS . • •Page I. INTRODUCTION 1 A. General. 1 B. Previous Work .2 C• ' S C O p 6 • % • - • • • • * • • * • • • • • • *. • ^ ; I I . EXPERIMENTAL PROCEDURE ... .• 11 A. Materials .11 •B.-Composite Preparation ... 12 1. Wire Composites .12 2. Powder Composites . . . . . ... . . . . . . . . 13 C. Swaging and Drawing .16 D. Heat Treating 16 E. Measurement of Fibre" Concentration 18 F. Tens i l e Testing 18 G. Metallography . ......... .. . . . . 18 I I I . RESULTS 19 A. . Composites Made From High Carbon S t e e l Wire Bundles . 19 1. Structures . ... . . . . . . . . . "19 .2. Size E f f e c t s . \ . . . 22 3. Studies of Heterogeneous Y i e l d i n g . . ......... 29 a) E f f e c t of Cold Working 32 b) Properties of Single S t e e l Wires . . . . . . 32 c) E f f e c t of Interrupted Loading 32 d) E f f e c t of S t r a i n Ageing 32 e) Observations During Loading . 35 B. Composites Made From Sintered Armco Iron Powder . ... 35 1. - Structures . 35 2. Size E f f e c t s 37 3. Heterogeneous Y i e l d i n g 3^ k. Heat Treatments on Saturated Iron Powder Composites . . . ....... . .Uk a) Results with -100 +150 mesh Powder Composites ... .... . . . . . . . . . . .... . kk b) Results with -325 mesh Powder. Composites . 48 IV. DISCUSSION • • '57 A. Structure and Aspect Ratios of Composites • 57'. B. Y i e l d Behaviour of Unsaturated Powder Composites . . 59 1 ''':. 1. Heterogeneous Y i e l d i n g 59 2. Size Dependence of Y i e l d Stress 60 C. Y i e l d Behaviour of Wire Composites 61 1.. O r i g i n of Two Y i e l d Points . . . 61 2. Heterogeneous Y i e l d i n g . . . . . . . . . . . . . 61 3. Size Dependence of Y i e l d Stress . . . . . . . . . 64 D. E f f e c t of Heat Treatment on Saturated Powder Composites 65 E. Deformation Behaviour of Metal Fibre Reinforced Metals 73 • Table of Contents Continued... Page V. CONCLUSIONS 79 VI. SUGGESTED FUTURE WORK ,' 80 VII'. BIBLIOGRAPHY . ' , 8 1 VIII. APPENDICES . . 83 V. LIST OF FIGURES Figure '.". Page 1. • Schematic Relation Between Fibre Tensile Stress (^T^) I n t e r f a c i a l -Shear' Stress . ("f ) and Fibre • Length .. . 5 2. • Relationship. Between Composite.Tensile Strength and Volume Per Cent'Fibres for'Various Fibre.Lengths . 6 3. - Tensi l e Strengths of Wires Drawn from"Several A l l o y s , " • Reproduced-.from R o b e r t s ~ . . . . . . . . . . . . . . . . . . . .9 ...4. - System, f o r I n f i l t r a t i o n of Steel ; Wire. Bundles .. ... . •. .14 5 . Cross-section (a) and Longitudinal'Section (b) of Specimen W-l-A-6 . . . . .20 .6. .Effect of Annealing 1 hour at 680°C, Specimen W-l-A-11 . -21 7. D i s t r i b u t i o n of Fibres i n the Copper Matrix, Specimen ••W-l-12 ..... ... . . ... . . . . . . . ... . ..... .21 •8. T y p i c a l 1 S t r e s s - P l a s t i c ' S t r a i n Curves f o r Various Specimen Sizes (a).-Composite W-l-A,; •• 23 (b) Composite W-3-A . . . . . . . . . . .24 9. Composite Y i e l d Stress Versus Specimen Diameter f o r Composites•W-l-A, W-2-A, and W-3-A. 25 10. Composite Ultimate Tensile Stress.Versus Specimen Diameter f o r Composites W-l-A,. W-2-A, and W-3-A . .26 11. Method-of Determining Y P m o + „ n - v and YP ., from , , . „ matrix composite Load-Elongation Curves 27 12. Matrix Yield-Stress Versus Specimen-Diameter f o r Composites W-l-A,.'W-2-A, and W-3-A 28 13. Distance "D" (Figure 11) i n Per Cent Elongation Versus Specimen Diameter f o r Composites W-l-A,' W-2-^ A, and W-3-A . . . . ... ... ... ... ... ..... ..... . 30 -14. Discontinuous.Yield Elongation as Measured From ;^comx>osite Versus- Specimen Diameter f o r Composites W-l-A,: W-2^A, and-W-3-A 31 15. S t r e s s - P l a s t i c S t r a i n Curve For Single S t e e l Wire . . . .34 16. Deformation Bands on Polished'Surface of Specimen W4L . v.36 17. Sections Through"Iron Powder-Composites . ........... .38 18. Stress'Versus P l a s t i c S t r a i n f o r Selected-Specimen.. •: Sizes f o r -100 ; +150 mesh"Powder Composites . . . . 3 9 , 4 0 v i . L i s t of Figures Continued.. Figure Page 1 9 . Ultimate Ten s i l e Stress Versus Specimen Diameter f o r - 1 0 0 +I50 mesh Powder Composites . . . . . . . . . kl 2 0 . Composite Yield-Stress Versus Specimen Diameter f o r - 1 0 0 +I50 mesh Powder Composites . . . . "' k2 2 1 . Photomicrograph of - 1 0 0 + 1 5 0 mesh Powder Composite "Aircooled" from 1 0 2 0 ° C . . ~. k^ 2 2 . S t r e s s - P l a s t i c S t r a i n Curves f o r Various Heat Treatments on - 1 0 0 +I50 mesh Powder Composites . . . . . . . H-9 23. Photomicrograph of - 3 2 5 mesh Powder Composite,-Quenched i n l i q u i d nitrogen and aged f o r 1 hour at - 8 0 ° C . 5 0 2k. Photomicrograph of - 3 2 5 mesh Powder Composite,••Pack carburized at 9 2 0 ° C f o r 1 0 0 minutes . . . . . . . . 5k 2 5 . S t r e s s - P l a s t i c S t r a i n Curves f o r Various Heat Treatments on - 3 2 5 mesh Powder Composites . 5 5 . 2 6 . Y i e l d Stress Versus Cooling Rate f o r "Saturated" Iron Powder Composites . . . . 5 6 2 7 . Specimen Diameter Versus Predicted Strengths of the Matrix and Fibres 6 6 2 8 . Proposed Cooling-Transformation Diagram f o r I r o n - 7 $ > Copper A l l o y . .. . . . . . . . . . ... 7 1 = 2 9 . Assumed Fibre D i s t r i b u t i o n : 7 5 v i i . LIST OF TABLES Table Page I. Swaging and Drawing Schedule ' . 16 I I . •Work-Hardening Exponents 32 I I I . S t r a i n Ageing Results 35 IV. Work-Hardening Exponents kj> • ACKNOWLEDGEMENT The author i s g r a t e f u l f o r the advice and encouragement given by his,research d i r e c t o r y Dr. J . A . L u n d . • Thanks are al s o extended to', other f a c u l t y members and fellow graduate students f o r many h e l p f u l discussions. F i n a n c i a l assistance in.the form.of Defence Research Board Grants No. 7 5 0 1 - 0 2 and No. 75OI-03 i s g r a t e f u l l y acknowledged. I. INTRODUCTION A. . General The advance of science and technology depends to a large degree upon the development of improved s t r u c t u r a l components. . To t h i s end a large amount of time and e f f o r t has been a l l o t t e d to the creation and i n v e s t i g a t i o n of composite materials which e x p l o i t the best properties of d i f f e r e n t i n d i v i d u a l materials. . The greatest strengths i n composite materials are found i n those which contain a.large volume f r a c t i o n of a dispersed hard phase coupled with a high density of d i s l o c a t i o n s i n the matrix. This type of microstructure can be produced i n several ways, in c l u d i n g : p r e c i p i t a t i o n at low temperatures from a supersaturated s o l i d s o l u t i o n , eutectoid decomposition,.mechanical mixing and subsequent s i n t e r i n g of powders, and internal' oxidation of s u i t a b l e a l l o y s . •A study 'of the strengthening mechanisms involved i n these types of microstructures has l e d to the r e a l i z a t i o n that the greatest strengths would, be achieved i f the dispersed hard phase p a r t i c l e s were very strong and loaded to f r a c t u r e C o n s e q u e n t l y , considerations have been given to methods, of load t r a n s f e r from:the d u c t i l e matrix, t o the harder dispersed phase. . The r e s u l t of such investigations, has been the conclusion that greater strengths would be r e a l i z e d i f the dispersed p a r t i c l e s were needle shaped, thus accommodating maximum.load t r a n s f e r . Accordingly, recent i n v e s t i g a t o r s have considered combining fibrous materials with r e l a t i v e l y weak binder, materials, thus u t i l i z i n g the f a c t that f i b r e s or wires can be exceedingly strong and can e x h i b i t - 2 - mechanical properties superior to those of the bulk material from which they are derived. Several techniques have been developed f o r incorporating strong f i b r e s i n r e l a t i v e l y weaker matrices and a theory p r e d i c t i n g composite strengths has been developed. B. Previous Work; Much of the research associated with the fundamentals of f i b r e reinforcement has been i n the f i e l d of glass r e i n f o r c e d p l a s t i c s . Coleman"'" has s t a t i s t i c a l l y related- the strength of bundles of f i b r e s to the strength of i n d i v i d u a l f i b r e s . Coleman's i d e a l i z e d mathematical-., analysis indicated that the average t e n s i l e strength of the bundle would be;less than the average strength obtained f o r the i n d i v i d u a l f i b r e s making up the bundle. 2 • Paratt has studied the e f f e c t s of defects i n glass fib r e s ' and v a r i a t i o n s i n length t o diameter r a t i o s (aspect r a t i o s ) f o r both f u l l length and discontinuous f i b r e s . A method of p r e d i c t i n g composite strength termed "The Theory of Combined Action" has been developed by Dietz from his work on f i b r e g l a s s 4,5,6,7 r e i n f o r c e d p l a s t i c s . Various workers have shown that t h i s theory i s a l s o a p p l i c a b l e to m e t a l l i c and ceramic f i b r e s i n m e t a l l i c matrices. What follows i n the present review i s a b r i e f discussion of the theory f o r p r e d i c t i n g composite strengths plus an outline of some experimental r e s u l t s p e r t a i n i n g to m e t a l l i c systems. For a volume f r a c t i o n of f i b r e s greater than a c e r t a i n c r i t i c a l value (to be discussed l a t e r ) the breaking stress of a f i b r e composite, M" c , i s given by: - 3 - % = ^ f A f + ^m C 1 ) where = the!.fracture stress of f i b r e s removed from ' the composite •srj^  = the stress supported, by the matrix when the f i b r e s fracture A J ^ A J J J = the volume f r a c t i o n s of the f i b r e s and matrix • r e s p e c t i v e l y . g •McDanels et a l . have generalized equation (1) to allow f o r > the p r e d i c t i o n of the stress i n a composite at any. value of s t r a i n , i . e . •ft ft „ ft ^ c = V F A f + . . . . , ( 2 ) where the ^J^'s represent stresses at a p a r t i c u l a r value of s t r a i n , taken from the s t r e s s - s t r a i n curves of the i n d i v i d u a l components of the composite, i n the condition i n which they e x i s t i n the composite. McDanels et a l . i n t h e i r work on tungsten-fibre-reinforced copper composites defined four stages of t e n s i l e behaviour and applied equation (2) to each one of'them. The four stages were: I. E l a s t i c deformation of f i b r e ; e l a s t i c deformation of matrix, I I . E l a s t i c deformation of f i b r e ; p l a s t i c deformation of matrix, I I I . Plastic.deformation of f i b r e ; p l a s t i c deformation of matrix,. IV. F a i l u r e of the composite. Returning to equation (1), i t i s necessary to consider the e f f e c t s of low volume f r a c t i o n s of f i b r e s . I f the volume per cent of f i b r e s i s small, then f a i l u r e of the f i b r e s need not lead to immediate f a i l u r e of the composite since the matrix may work-harden-sufficiently. Expressing : t h i s mathematically, equation (1) holds only i f the breaking stress of the composite i s greater than that of the matrix, i . e . - 3 - % = A f + A i (!) where SJ~£ = the \,f racture stress, of f i b r e s removed from the composite = the stress supported, by the matrix when the f i b r e s fracture A f , ^ = the volume f r a c t i o n s of the f i b r e s and matrix • r e s p e c t i v e l y . g McDanels et a l . have generalized equation (1) t o allow f o r the p r e d i c t i o n of the stress i n a composite at any value of s t r a i n , i . e . ^ c = V F A f + TTm ^ ,(2) where the ^rj^' s represent stresses at a p a r t i c u l a r value of s t r a i n , taken from the s t r e s s - s t r a i n curves of the i n d i v i d u a l components of the composite, i n the condition i n which they e x i s t i n the composite. McDanels et a l . i n t h e i r work on tungsten-fibre-reinforced copper composites defined four stages of t e n s i l e behaviour and applied equation (2) to each one of them. The four stages were: I. E l a s t i c deformation of f i b r e ; e l a s t i c deformation of matrix, I I . - E l a s t i c deformation of f i b r e ; p l a s t i c deformation of matrix, I I I . Plastic.deformation of f i b r e ; p l a s t i c deformation of matrix, IV. F a i l u r e of the composite. Returning to equation (1), i t is.necessary to consider the e f f e c t s of low; volume f r a c t i o n s of f i b r e s . I f the volume per cent o f f i b r e s i s small, then f a i l u r e of the f i b r e s need not- lead to immediate f a i l u r e of the composite since the matrix may work-harden s u f f i c i e n t l y . Expressing t h i s mathematically, equation (1) holds only i f the breaking stress of the composite i s greater than that of the matrix, i . e . - k - .where XTu i s the ultimate t e n s i l e strength of the matrix. 6 Combining-equations (1) and (3) gives r i s e to an~expression f o r the c r i t i c a l volume per cent ef f i b r e s . • A ( ^"u " ) 9 Dow has done a d e t a i l e d study of the r e l a t i o n s h i p s between -the applied load,. i n t e r f a c i a l shear stresses, and fibre, t e n s i l e stresses i n a filament-reinforced composite metal. A schematic representation of these quantities i s shown in- Figure 1. Assuming-uniform packing and alignment of. the f i b r e s and. equal s t r a i n i n g in/the f i b r e s and matrix at t h e i r i n t e r f a c e , a.plausible d i s t r i b u t i o n of shear and t e n s i l e .stresses i s 15 as shewn i n Figure l b . . From.this.model, i t becomes evident that a c r i t i c a l f i b r e length,. designated : L c , i s required i f maximum f i b r e t e n s i l e stresses are to be achieved. Dow reports that L c.depends on the e l a s t i c and shear properties of the f i b r e s and matrix'. . The mechanism by which a . f i b r e contributes i t s strength to a •k composite i s one of shear . Thus, f o r a given.pair of materials, the length of f i b r e that i s bonded:to the. matrix must be s u f f i c i e n t - t o support • a.shear stress that i s equivalent to t h e - t e n s i l e stress on-the f i b r e . Equating the shear load- ©n the.interface to the t e n s i l e load necessary -'to cause f a i l u r e ; of .the f i b r e gives the .so-called, c r i t i c a l aspect r a t i o , ' %y- W f ^ f .= ^ f L c r Schematic Relation Between Fibre Tensile Stress i ^ } ^ Interfacial Shear Stress {Z ), and Rbre Length (L) - 6 - o r ''Lc l ^ f (5) k r where d f i s the diameter of.the f i b r e , and T i s the shear stress at the i n t e r f a c e . Equation (1) predicts a l i n e a r r e l a t i o n s h i p between strength and volume f r a c t i o n of f i b r e s . The f i b r e s however, w i l l carry the f u l l p r edicted load o n l y - i f L ^ .Lc« • F o r shorter f i b r e s the proportion of the load c a r r i e d by the f i b r e s w i l l he l e s s and the r e s u l t s w i l l be a weaker composite. This concept i s shown schematically i n Figure 2. v o l u m e p e r c e n t fibres,of constant diameter ( df) Figure 2. Relationship.Between Composite Tensile Strength and Volume Per'Cent Fibres f o r Various Fibre Lengths. Figure 2, however, i s o v e r - s i m p l i f i e d .since the c r i t i c a l 8 aspect r a t i o may. be complicated by v a r i a t i o n s i n i n t e r f i b r e spacing . ..The bond at the f i b r e - m a t r i x i n t e r f a c e r e s t r a i n s movement of" the matrix r e l a t i v e t o the f i b r e but the e f f e c t of t h i s r e s t r a i n t i s reduced as the dis tance from. :the i n t e r f a c e i s i n c r e a s e d . Thus,, there e x i s t s the p o s s i b i l i t y , t h a t . t h e aspect r a t i o f o r a g iven f i b r e diameter w i l l be lowered at h i g h volume percentages of f i b r e and w i l l become higher at l o w . f i b r e contents . Along these l i n e s , , Koppenaal and" Parikh"1"^ state that the s trengthening mechanism prevalent i n the m i c r o s t r a i n i n g region of t h e i r s i l v e r - i n f i l t r a t e d , f e l t s i s analogous i n some respec ts , to g r a i n boundary strengthening i n p o l y c r y s t a l l i n e metals . The f i b r e s act as obstacles f o r s l i p , and d i s l o c a t i o n s p i l e up at the m a t r i x - f i b r e i n t e r f a c e s . -With i n c r e a s i n g . f i b r e d e n s i t y the a v a i l a b l e s l i p . l e n g t h decreases and a l a r g e r number of d i s l o c a t i o n s p i l e up f o r a g iven s t r a i n . The rate of work- hardening a c c o r d i n g l y increases s ince l a r g e r s t resses are required to force new d i s l o c a t i o n s i n t o each p i l e - u p . . P a r i k h , u s i n g the H a l l - P e t c h . type of r e l a t i o n s h i p : -j/2 ^ y = + ,K d " . (6) and a s s o c i a t i n g d w i t h the average distance between f i b r e s and STQ wi th the f ibre - independent p o r t i o n of ^J* , has shown that v a r y i n g the a v a i l a b l e y s l i p l e n g t h by changing, the f i b r e d e n s i t y ; i s qui te analogous to changing the g r a i n s i z e i n p o l y c r y s t a l l i n e metals . • The v a l i d i t y of equation (6) ; was e s t a b l i s h e d experimental ly f o r the 0.2%. y i e l d s t rqngth i n s i l v e r - i n f i l t r a t e d , fe l t s , of m i l d s t e e l , . molybdenum, tungsten and m a r t e n s i t i c s t a i n l e s s s tee l , f i b r e s . - 8 - The r e s u l t s of various workers are somewhat contradictory on the e f f e c t of wire diameter i n r e i n f o r c i n g m e t a l l i c systems. Jech et-.al found a siz e e f f e c t i n tungsten-fibre-reinforced copper. Their r e s u l t s showed that the composites containing f i n e r wires had higher strengths 7 f o r a given volume f r a c t i o n of the components. Cratchley found, that 0.002 i n . diameter f i b r e s gave stronger composites than 0 .005 i n . diameter f i b r e s but a t t r i b u t e d t h i s strength increase to differences i n wire drawing conditions. The load t r a n s f e r , f o r a given aspect r a t i o , was a c t u a l l y s l i g h t l y l e s s e f f i c i e n t f o r the thinner f i b r e s but t h i s was a t t r i b u t e d to e f f e c t s due to o r i e n t a t i o n . . Of the several methods used to produce f i b r e - r e i n f o r c e d composites, k 11 the i n f i l t r a t i o n technique has been used most widely. .Sutton ' has used vacuum i n f i l t r a t i o n to incorporate alumina whiskers i n s i l v e r and 5 6 aluminum. Jech et a l and K e l l y have used i n f i l t r a t i o n techniques i n t h e i r i n v e s t i g a t i o n s of the tungsten wire-copper matrix system. Koppenaal 10 and Parikh a l s o concentrated on i n f i l t r a t i o n as a means of producing metal-wire f e l t s with a s i l v e r matrix. Some other techniques which have been s u c c e s s f u l l y employed to produce f i b r e - r e i n f o r c e d systems include: (a) the compacting and 7,12 s i n t e r i n g . o f m e t a l l i c powders around m e t a l l i c and non-metallic f i b r e s ; (b) the production of f i b r e s of an i n t e r m e t a l l i c i n s i t u i n the matrix 6 13 metal by su i t a b l e s o l i d i f i c a t i o n or heat treatment ^; and (c) the working i n t o wire of c e r t a i n copper-iron a l l o y s i n which an excess of i r o n over the s o l i d s o l u b i l i t y l i m i t i n copper i s present as i r o n dendrites i n the lk o r i g i n a l cast a l l o y - 9 - C . Scope For the purpose of the present i n v e s t i g a t i o n i t was f e l t that use might be made of the f a c t that the t e n s i l e s trength of wires drawn from many m e t a l l i c elements, increase w i t h decreasing wire diameter (Figure 3). » 2 4 t I 10 DIAMETER. MILS Figure 3» T e n s i l e Strengths of Wires Drawn From S e v e r a l A l l o y s . Reproduced from Roberts-*-". - 10 - Thus, i f s t e e l or i r o n wires could be incorporated i n t o a d u c t i l e matrix and the r e s u l t i n g composite swaged and drawn to small s i z e s , a study could be. made of the strengthening e f f e c t of very small diameter (whisker s i z e and below) p o l y c r y s t a l l i n e wires. Proper choice of a system would allow v a r i a t i o n s to be obtained i n the r e l a t i v e properties of the matrix and the f i b r e s by suitable, heat treatments. In t h i s way a study of the deformation behaviour of f i b r e s and matrices of varying r e l a t i v e strengths could be made. . Two possible methods, of producing the desired type of micro- structure were v i s u a l i z e d : (a) I n f i l t r a t i o n of a bundle of i r o n or s t e e l wires with molten copper followed by swaging and drawing' of the r e s u l t i n g composite, and (b) I n f i l t r a t i o n of porous, sintered, i r o n powder compacts with molten copper followed by swaging and drawing to produce fibrous i r o n i n copper. - 1 1 . - I I . EXPERIMENTAL PROCEDURE A. M a t e r i a l s ' The h i g h carbon s t e e l wire used i n t h i s p r o j e c t was s u p p l i e d . b y P r e c i s i o n Steel-Warehouse,- I n c . , (Downers. Grove, 1 1 1 . ) . -The wire was. of " s p r i n g . g r a d e " and was 0 . 0 1 2 inches i n - d i a m e t e r . The chemical a n a l y s i s , as rece ived , 'was as f o l l o w s : Carbon 0 . 8 6 <fo •Manganese O.kk^o. - S i l i c o n 0 , 2 0 - f 0 Sulphur 0 . 0 1 5 % Armco i r o n powder, having near ly p e r f e c t l y s p h e r i c a l p a r t i c l e s was suppl ied by the F e d e r a l - M o g u l , Power Plant D i v i s i o n . , of Ann A r b o r , - M i c h . .The nominal composition of the powder was: .: I ron 9 9 . 9k <f0 min. Carbon 0 . 0 1 2 $ Manganese 0 . 0 1 7 ' % Phosphorus 0 . . 0 0 5 % Sulphur 0 . 0 2 5 1° max. S i l i c o n Trace o n l y . Two screened f r a c t i o n s of the a s - r e c e i v e d powder were used i n t h i s work; (a) a ..minus 1 0 0 mesh (Tyler ) plus : 1 5 0 mesh ; f r a c t i o n , and (b) a minus 3 2 5 mesh f r a c t i o n of average p a r t i c l e s ize 2 5 microns. • The matrix metal f o r a l l composites was " E l e c t r o l y t e Tough P i t c h " copper, a n a l y z i n g 9 9 ' 9 2 % copper w i t h a nominal, oxygen content of Q.Ok°jo. - 12 - An equilibrium diagram f o r the Fe-Cu system i s given i n Appendix I. This system was chosen f o r several reasons. I t was f e l t that iron-copper composites would respond well to the required swaging and drawing operations, with the copper ac t i n g as a natural " l u b r i c a n t " f o r deformation of the i r o n and s t e e l . Furthermore, the system, a f t e r saturation of the i r o n with copper, would be heat treatable and thus the r e l a t i v e strengths of the matrix and f i b r e could be r e a d i l y varied. The s o l u b i l i t y of each component i n the other i s l i m i t e d and 18,19 w e l l defined and no i n t e r m e t a l l i c compounds are present i n the 20 system which might detract from a sharp matrix-fibre i n t e r f a c e . In a d d i t i o n , i t was appreciated that the system s a t i s f i e s the basic conditions necessary f o r i n f i l t r a t i o n i n that (a) melting points of pure i r o n and copper are su b s t a n t i a l l y d i f f e r e n t (1,527*!C and 1,083°'C r e s p e c t i v e l y ) , (b) no phases of higher melting point e x i s t which might obstruct the continuity of ^ . i n f i l t r a t i o n , and (c) i r o n i s known to be wetted r e a d i l y 21" by l i q u i d copper B. Composite Preparation 1. Wire Composites Bundles of 0.012 inch diameter high carbon s t e e l wire were : i . i n f i l t r a t e d with copper using the following procedures: (a) W i r e s of approximately 9 inches i n length were cleaned i n an aqueous s o l u t i o n containing U0 g . p . l . Na 2C0 3, 13 g.p.l..NaOH, 13 g.p.l. Na 2P0 4.12H 2 0, 13 g . p . l . NaCN, and 6 g.p.l. Na 2 S i 0 3 at about 80°C. (b) One-hundred and twenty wires were placed inside a.copper tube measuring 8 inches long by 0.250 inches outside diameter. The w a l l - 13 - thickness of the tubing used was 0.040 inches. (c) The r e s u l t i n g assembly was drawn.through a 0.200 inch diameter hardened s t e e l die t o increase the closeness of packing and. to a i d i n the alignment of the wires p r i o r to i n f i l t r a t i o n . (d) I n f i l t r a t i o n was c a r r i e d out i n a closed-end, fused quartz tube of inside diameter s l i g h t l y greater than the drawn s t e e l wire-copper tube assembly. -The fused quartz tube was so placed i n a Glo-Bar furnace that a l l but the top one inch of the copper tube melted. The geometry of the system i s as shown i n Figure k. A l l i n f i l t r a t i o n s were performed at 1150°C .for 9 minutes under fore-pump vacuum followed by 1 minute under a s l i g h t p o s i t i v e pressure of argon. (The argon treatment was found necessary t o eliminate b l i s t e r i n g the outside l a y e r of copper.) Cooling to room temperature was done under a p o s i t i v e pressure of argon. The r e s u l t i n g composite was e s s e n t i a l l y free of voids. The part of the copper tube which d i d not melt kept the wires together and i n the center of the fused quartz tube during.the time the remaining cdpper was i n the molten state. The r e l a t i v e l y t h i c k coating of copper-which res u l t e d on the outside surface of the composite was desirable from.the point of view of subsequent reduction by wire-drawing. 2. Powder Composites Compacts of -100 +150 mesh Armco i r o n powder were i n f i l t r a t e d with copper using the following procedure: -.Ik - ^.quortz tube copper tube steel wo res molten copper furnace elements O !; O o y o o | | o s ' I s I ^ B s I i > o I! I o Figure 4 System For Infiltration of Steel Wwre Bundles - 15 - (a) Powders were pressed h y d r o s t a t i c a l l y i n bags made from Gooch t u b i n g , at a pressure of approximately 25,000 p . s . i . (b) S i n t e r i n g of green compacts was e f f e c t e d i n 10 minutes at 1150°C under dry hydrogen. (e) I n f i l t r a t i o n f o r 10 .minutes at II10°C'. was c a r r i e d out-under fore-pump,, vacuum i n a V i t r e o s i l tube, p r o v i d i n g an excess of copper over t h a t needed t o f i l l the voids i n the i r o n s k e l e t o n . The technique, used was developed by K r a n t z ' ^ . . This procedure y i e l d e d composites 3 t o k inches long by 0.460 inches i n diameter w i t h the f o l l o w i n g c h a r a c t e r i s t i c s : - d e n s i t y of s i n t e r e d i r o n s k e l e t o n 7^.0 ± 2% of t h e o r e t i c a l - d e n s i t y of i n f i l t r a t e d compact 96.7 * 1% °f t h e o r e t i c a l . The composites were annealed f o r one hour at 680°C under dry hydrogen t o ensure t h a t the:,matrix was not supersaturated i n i r o n ; i . e . th a t the m a t r i x was as d u c t i l e as p o s s i b l e f o r subsequent forming operations. The procedure used f o r the -325 mesh Armco i r o n powder was e s s e n t i a l l y i d e n t i c a l t o t h a t d e s c r i b e d above except t h a t no pressure was used t o prepare green "compacts". -A tube of the loose powder was simply v i b r a t e d by tapping u n t i l no f u r t h e r change i n volume was observed and the r e s u l t i n g mass s i n t e r e d a t 1150°C. S i n t e r i n g i n t h i s case was done i n a fore-pump vacuum. The composites produced from -325 mesh powder had the f o l l o w i n g c h a r a c t e r i s t i c s : - d e n s i t y of s i n t e r e d i r o n s k e l e t o n 57•3% of t h e o r e t i c a l - d e n s i t y o f i n f i l t r a t e d compact 96.5% of t h e o r e t i c a l . - 16 C. -Swaging and Drawing The reduction i n s i z e of the wire and powder composites was c a r r i e d out using the schedule shown i n Table I. - TABLE;I. Swaging and Drawing' Schedule O r i g i n a l F i n a l Operation • Annealing Diameter Diameter "... Treatment* 1* (in.) (in.) o.46c* •ft 0.270 Swaging 1 hr. at 680°C 0.270 (powder) 0.163 Swaging 1 hr. at 680°C O.25O (wires) 0.163 0.126 Drawing 1 hr.; at 680°C 0.126 O .O98 Drawing 1 nr." at 680°C O .O98 O.O77 Drawing 1 hr. at 680°C O .O77 0.060 Drawing 1 hr. at 680°C 0.060 0.046 Drawing 1 hr. at 680°C 0.046 O.035 Drawing 1 :hr..at 680°C O.O35 0.028 Drawing 1 hr. at 680°C 0.028 0.021 Drawing 1 hr. at 680°C ft Powder composites only. ftft A l l annealing treatments were c a r r i e d out i n a flow of dry hydrogen. D. Heat Treating Heat treatments were c a r r i e d out on samples produced from i r o n •powder composites i n which the i r o n component v, • had been completely saturated with copper at 1020°C. -Six pieces of composite, each 3 inches long, were placed i n a ceramic boat. Small alumina spacers were placed-.at each end to ensure that the wires were not i n contact. Treatment was c a r r i e d out i n a .small tube furnace under dry hydrogen gas. Heating f o r 15 hours'at 1020°C to ensure a l l o y e q u i l i b r i u m was followed by cooling at various rates. The term "aircooled" w i l l be applied to describe the rate of cooling which prevailed-when the boat was withdrawn from-the hot zone at approximately - 17 - 3 inches per second to a point 12 inches di s t a n t where the temperature was below 200°C. The a c t u a l rate of cooling i s estimated.to be 120 to l80°C./second. • Cooling by t h i s method was e n t i r e l y e f f e c t e d i n dry hydrogen. Several specimens were quenched i n l i q u i d , nitrogen from the s o l u t i o n treatment temperature (1020°C)." Specimens which had previously been s o l u t i o n treated and "aircooled" were, i n t h i s case, reheated to 1020°C f o r 20 minutes i n a v e r t i c a l tube furnace under a flow of dry hydrogen gas. The suspension was then cut, allowing.the specimens to drop i n t o a dewar of l i q u i d nitrogen. •After s o l u t i o n treatment at 1020°C as before,, one group of specimens was carburized using a commercial pack carburizing compound. Carburization f o r various times was c a r r i e d out i n a. tube furnace open at both ends to the atmosphere. The pack carburizing compound was placed around, the specimens i n a ceramic boat and the. furnace brought to a. temperature of 920°C. Homogenization was c a r r i e d out f o r 2 hours at 1020°C followed by " a i r c o o l i n g " . In a d d i t i o n to the heat treatments mentioned above several other annealing and cooling procedures were c a r r i e d out on c e r t a i n specimens. A l l such treatments were done i n a small tube furnace under dry hydrogen. The a c t u a l procedure used f o r each specimen along with the pertinent r e s u l t s w i l l be given i n "Experimental Results". - 18 - -E. Measurement of Fibre Concentration The volume percentage of f i b r e s present i n the s t e e l wire- copper matrix composites was- cal c u l a t e d from cross-section micro graphs using a random l i n e technique. The length of l i n e occupied by one phase was r e l a t e d to the t o t a l length of the l i n e and averaged out over 12 random .lines. The volume percentage of f i b r e s present i n the composites made from i r o n powders was-, reasonably assumed to be equal to the density of i r o n i n the as-sintered composites, since no detectable growth or shrinkage of the i r o n compacts accompanied iinfiltration:-.... F. •• Tensile Testing A l l t e s t s were c a r r i e d out at room temperature on an Instron Ten s i l e Testing machine using e i t h e r wedge type grips or f r i c t i o n grips 22 plus s p e c i a l u n i v e r s a l mountings . The cross-head speed i n a l l t e s t s was 0.01 inch/ minute r e s u l t i n g i n s t r a i n rates of O.OO67 m i n - 1 f o r a l l the steel-wire composites and 0.01 min" 1 f o r the composites made from i r o n powder. Per cent elongations reported are based on cross-head motion and thus are r e l a t i v e values, rather than absolutely accurate. G-. - Metallography An a l t e r n a t i n g p o l i s h - e t c h technique was found necessary to eliminate smearing of copper over the surfaces of metallographic specimens. Specimens to be viewed were mounted, i n "bakel i t e " and polished on f i v e emery papers. The mounts were then lapped with 1 micron diamond powder 1 i n kerosene. Each lapping step was followed by etching with k^> p i c r i c a c i d i n ethanol f o r 15 seconds. Four or f i v e cycles were required to give the desired p o l i s h . -.19 - I I I . • RESULTS A. Composites Made from.High Carbon S t e e l Wire-Bundles . 1. •Structures Obtaining f i b r e composites of the desired structure b y ' i n f i l t r a t i n g s t e e l wire bundles with l i q u i d copper proved to be only p a r t i a l l y successful. •A reduction of the composite diameter t o a f i n a l specimen siz e of 0.022 inches (corresponding to i n d i v i d u a l s t e e l wire diameters of 0.0023) was the maximum obtainable. Attempts to draw below.this dimension l e d t o cracking i n the copper coating or random ''necking" of. the composite. I t was o r i g i n a l l y f e l t that t h i s problem was associated with imperfect alignment of the s t e e l wires in. the wire composites. However, i n l a t e r work with powder composites d i f f i c u l t i e s were experienced i n the same size range, and i t became apparent .that the drawing dies a v a i l a b l e were n e c e s s i t a t i n g an unusually large r e  duction i n one pass at the c r i t i c a l dimension. Mechanical properties and structures of the wire composites were examined over the range of sizes which could be f a b r i c a t e d . . Tensile t e s t i n g was done on composite specimens of 0.100 inches diameter ( i n d i v i d u a l wire diameter approximately 0.00k inches) and smaller. Micrographs of a cross- section and a l o n g i t u d i n a l section of a t y p i c a l specimen are.shown i n Figure 5. The r e l a t i v e l y sharp matrix-fibre i n t e r f a c e and the e f f e c t of annealing at 680°C are. shown i n Figure 6. As expected, the annealing treatment spheroidized the carbide i n the s t e e l wires. , . The volume percentage ef f i b r e s present i n these composites was measured.using.the method outlined' i n 'the Experimental Procedure. Over the range of specimen diameters investigated the volume per cent f i b r e s Figure 5. Cross-section (a) and Longitudinal Section (b) of Specimen W-l-A-6, approximate wire diameter 0 .0033 inches, annealed 1 hour at 680°C, 2$ n i t a l etch, (a) X 200 (b) X 6 0 . Figure 7- D i s t r i b u t i o n of F i b r e s i n the Copper M a t r i x , Specimen W-l-12, n i t a l e t c h , X 5 0 . - 22 - remained v i r t u a l l y constant at kk.Ofy. This value was calculated using the complete c r o s s - s e c t i o n a l area of the composite, i . e . including the r e l a t i v e l y t h i c k surface l a y e r of copper. The f i b r e s were c l o s e l y packed at the centre of the composites (Figure 7)- A more r e a l i s t i c packing f r a c t i o n of f i b r e s , based on measurements near the centre, i s O.75. 2. Size E f f e c t s T e n s i l e t e s t s were made on annealed composite specimens i n the size range O .O98 inches to 0.022 inches. T y p i c a l s t r e s s - p l a s t i c s t r a i n curves f o r two composites,-W-l-A and W-3-A are shown i n Figures 8a,and 8b. These curves are p l o t t e d not t o f r a c t u r e , but t o the ultimate t e n s i l e stress of the specimens. Curves of composite y i e l d stress and ultimate t e n s i l e stress versus specimen diameter f o r three d i f f e r e n t composites are shown i n Figures 9 and 10. The diameter of the i n d i v i d u a l s t e e l wires i s a l s o p l o t t e d on the abscissa. It was observed that the Ipad-elongation curves' exhibited two apparent y i e l d points; an i n i t i a l y i e l d point (designated . YP. . . ) which could p o s s i b l y be a t t r i b u t e d t o the i n i t i a t i o n of flow i n the matrix, and a second y i e l d point, (designated YP C Omposite) w n i c n apparently corresponded, t o the s t a r t of p l a s t i c flow throughout the composite. The method of obtaining these two y i e l d points from load-elongation curves i s shown i n Figure 11. (Figures 9 a n d 10 do not show the two y i e l d points; they are p l o t t e d to s t a r t at the composite y i e l d stress.) Figure 12 shows a p l o t of the "matrix y i e l d s t r e s s " versus specimen diameter. 6d- I- * 4o\ o W-l-A D W-2-A O W-3-A A individual wire diameters 0.0024 in. _L _L 0.0027 0.0034 _L 10.0037 ro o.C9o O.O/O O.OZO 0030 O.Q40 0-050 0.060 0.070 0.080 Specimen D/ometer (inches) Figure 9 Compost Yield Stress Vs. Specimen Diameter-Composites W- i-A ,W2-A 7 W-3A. 43 • • • • 4 o • W - l -A O A W-2-A O A _ W-3-A A P A O nd. wire d ia?s— * - 10.0024in lo.0027 |o.0034 lo.0037 o.ozo ^~ also ' oc*o 1 oioso ' 0-060 ' 0^070 ' 0.080 ' ao9o Specimen O i a t v e i e r (inches? Ultimate Tensile Stress Vs.Specimen Diameter, Composites WH-A,W2A,W-3-A. ro - 27 - Elongation V- :\ ». Figure 11 Method of Determining ' Y P ^ ^ d'nd-Y P 0 $ M e From ; Load-Elongation Curves. Specimen Diameter (inche s) 00 Figure 12 Motrix Yield Stress Vs.Specimen Diameter, Composites W-l-A,W-2-A7W-3-A. - 29 - An attempt was made to r e l a t e the. thickness.of copper on the outside of the composites to the c h a r a c t e r i s t i c s of the load-elongation curves. To t h i s end the distance D ( i n Figure 1 1 ) measured i n percentage elongation i s shown plotted.versus specimen diameter i n Figure 1 3 . Figures 8a and 8b i n d i c a t e the heterogeneous y i e l d i n g which was found.to occur i n c e r t a i n specimens. Both the existence and extent ©f'this behaviour were specimen siz e dependent i n the manner shown i n Figure lk. Discontinuous y i e l d i n g was never observed with specimen diameters greater than 0.070 inches. • The extent of the phenomenon increased to a maximum.of about kfy ( i n per cent elongation "over a l l / 2 inch gauge length) at a specimen diameter of 0.C47. inches and then diminished at smaller diameters as shown. In an attempt to determine, the work-hardening c h a r a c t e r i s t i c s of the composites, values-of n, the work-hardening exponent, i n the empirical expression f o r the flow curve T-T- 1 i n - ; ~ = K € . . . . - ( 7 ) were cal c u l a t e d from the slopes of log - l o g p l o t s of true stress ( ^  ) 1 versus true s t r a i n (£ ). The r e s u l t s (Table II) show.no d e f i n i t e trends. 3 . Studies of Heterogeneous Y i e l d i n g - The appearance of heterogeneous y i e l d i n g i n c e r t a i n specimens of composites made from the i n f i l t r a t i o n of s t e e l wire bundles prompted furth e r studies to determine the cause of the phenomenon. 1 § 3-0 5 t.s 8 O.S W - l - A • W-2-A O" W-3-A A • _L -A- o.o/o Figure 13 O.&&O O.C30 G.040 O.&SO 0.060 Specimen Dfometer (inches) Distance V D" (Figure 11) V s . Specimen Diameter ao70 o.oao o.o30 o.o40 o.oso 0.060 o.oro Specimen Diameter (inches) F igure 14 Discontinuous Yie ld Elongation Vs. Specimen Diameter. - 3 2 - • TABLE I I . Work-Hardening' Exponents . w-r-A W-3-A Specimen-Diameter n j Specimen"Diameter n O.O98 0.297 0.070 0.150 O .O89 O..I77 0.060 0.169 0.081 0.125 O.O53 o . io4 • 0.075 0.213 0.. 032 0.217 O.O67 O.I79 O.OV7 O.O95 O..054 0.174 - 33 - (a) . E f f e c t of Cold-Working - Cold working specimens by wire drawing p r i o r to t e s t i n g removed any trace of discontinuous y i e l d i n g . Reductions i n area of as l i t t l e as 2.5$ gave t h i s r e s u l t . (b) Properties of Single S t e e l Wires - A single piece of the high carbon s t e e l wire was annealed f o r 5 hours at 680°C and, tested i n tension. The same type of discontinuous y i e l d i n g as found i n the composites was found to occur but with somewhat smaller load drops, (Figure 15). I t i s a l s o i n t e r e s t i n g t o note that the s t r a i n hardening exponent of the annealed wire was found to be 0.167- (c) E f f e c t of Intemgfted; Loading - Several t e s t s were stopped a f t e r discontinuous y i e l d i n g was completed and,the specimens unloaded. Loading was immediately re-applied and the t e n s i l e t e s t was allowed to proceed to rupture of the specimen. The y i e l d stress and work-hardening c h a r a c t e r i s t i c s of these specimens were not a f f e c t e d by i n t e r p j p t i n g the loading. (d) E f f e c t of S t r a i n Ageing - Several specimens at a s i z e e x h i b i t i n g the maximum amount of discontinuous y i e l d i n g , i . e . 0.0*4-7 inches, were given s t r a i n ageing treatments. The specimens were strained u n t i l uniform deformation and work-hardening had commenced, and were then unloaded as i n section (c) above. The samples were then aged f o r e i t h e r l / 2 or 1 hour at 200°C followed by r e t e s t i n g . The e f f e c t of ageing on the matrix and composite y i e l d stresses i s summarized i n Table I I I . A1 discontinuous y i e l d region Was not resolvable i n specimens aged f o r 1/2 hour but was d e f i n i t e l y present i n specimens aged f o r 1 hour. Approximately 70$ of the o r i g i n a l extent of discontinuous y i e l d i n g had - 34 - Figure 15 Stress-Plastic'Strain Curve For Single Steel Wire, Diameter 0 .049 in , Annealed 5hrs at 680°C. -35 - returned, but with smaller load drops. TABLE I I I . • S t r a i n Ageing Treatment Y-S-M. Y.S. C l/2 hour at 200°C :Before Ageing 13,300 p . s . i . 34,500 p . s . i . • A f t e r Ageing 20,000 43,000 1 hour at 200°G Before Ageing 15,900 39,500 •After Ageing 21,400 41,500 (e) Observations During-Loading - The:surface of several specimens was polished with 4/o emery paper and then - observed during a ^ t e n s i l e t e s t . Deformation bands appeared at random points along the gauge lengths of the specimens, simultaneously with sudden load drops on the load-elongation curve. Continued loading caused the deformation bands t o widen v i s i b l y u n t i l tbey inte r a c t e d with each other. A shadowgraph of such a specimen i s shown i n Figure 16. The deformation bands are. barely d i s c e r n i b l e at the perimeter of the specimen. The arrows indi c a t e observed d i r e c t i o n of deformation f r o n t motion. B. Composites Made:From- Sintered Armco Iron Powder 1 . Structures The product of i n f i l t r a t i n g pure i r o n powder skeletons with l i q u i d copper followed by f a b r i c a t i o n to.produce.fibrous i r o n i n a.copper- matrix proved.to be more i n t e r e s t i n g and more, u s e f u l than that obtained from,steel wire bundles. One advantage of the powder composites was that Figure 16. Deformation Bands on Polished Surface of Specimen W-k-L, X 30. - 37 - complications due t o carbon and i t s p a r t i a l depletion during annealing treatments were not present. A d d i t i o n a l l y , i t was convenient t o obtain much f i n e r f i b r e s by the powder approach. •Photomicrographs of some powder comppsites a f t e r drawing are shown i n Figure 17. The materials shown were made from the two d i f f e r e n t powder f r a c t i o n s -100 +150 mesh and -325 mesh. Metallographic measurements on composite specimens of diameter 0.035 inches gave, f o r the average diameter of the f i b r e s (a) 10 microns f o r the coarser powder composites and (b) approximately 2 microns f o r the f i n e r powder composites. The p r o b a b i l i t y that a f i b r e would l i e i n the plane of p o l i s h i n g over i t s en t i r e length was n e g l i g i b l e . Consequently,. metallographic measurements could not be expected to give an accurate i n d i c a t i o n of the lengths of f i b r e s . However an estimate of f i b r e lengths can be made from t h e i r diameters, as w i l l be discussed l a t e r . 2. • Size E f f e c t s Tensile t e s t s were done on -100 +I50 mesh powder composites at various stages of reduction to determine the e f f e c t of specipen and f i b r e diameter i n much the same way as f o r the s t e e l wire composites. T y p i c a l s t r e s s - p l a s t i c s t r a i n curves f o r some specimen sizes are shown i n Figures l 8 a and l 8 b . Plots of ultimate t e n s i l e stress and composite y i e l d stress versus specimen diameter are shown i n Figures 19 and 20. Only a s l i g h t increase i n strength with decreasing composite diameter was suggested by the data. - 3 8 - Figure 17. Sections through Iron Powder Composites, iSpecimen diameter 0 . 0 3 5 inches, annealed 1 hour at 6 8 0 ° C , 2$ n i t a l etch, (a) - 1 0 0 + 1 5 0 mesh, X 2 6 , (b) - 1 0 0 + 1 5 0 mesh, X 2 0 0 , (c) - 3 2 5 mesh, X kj, (d) - 3 2 5 mesh X 2 0 0 . - 39 - 50\- AOr- 30 cL •n 0 X b 20 to 0.077 I I I I I l _ IS 16 Figure IB'Stress-PI o she Strom Curves For Various Specimen Dameters - 1 0 0 + 1 5 0 Mesh Powder Composites -kO -70 •I a 30 Powcter No 2 O Powder No 3 A OOJO O.OSO &oao C&fO O.OS0 0-060 Specimen Diameter (inches) O.OTO O.OSO C090 I -p- Figure 19 U.T.S. Vs. Specimen Diameter,-100+150 Mesh Powder Composites - 4 3 - The load-elongation curves f o r a l l the powder composites were such as to indic a t e a single y i e l d point rather than two as observed f o r the s t e e l wire composites. Consequently t h i s one y i e l d point has been designated as YP^ ^ ^ composite i • Work-hardening exponents were ca l c u l a t e d at various specimen diameters. I f heterogeneous y i e l d i n g was present the work-hardening exponent was c a l c u l a t e d from that part of the. flow curve immediately following completion of discontinuous y i e l d i n g . For t h i s purpose, the point of zero p l a s t i c s t r a i n was a r b i t r a r i l y taken as being at the end of the discontinuous y i e l d i n g region. The r e s u l t s are tabulated i n Table IV. •TABLE.IV. Work-Hardening Exponents Powder No. 3 Specimen Diameter n O .O77 inches 0 . 1 1 5 O . O 6 9 0 . 1 1 7 O.O59 0 . 1 4 9 0 . 0 4 6 0 . 1 4 5 0 . 0 5 4 0 . 1 0 0 0 . 0 2 5 0 . 1 2 1 As i n the case of the s t e e l wire composites, no d e f i n i t e trend i n these values was apparent. 3 . Heterogeneous Y i e l d i n g Discontinuous y i e l d i n g was sometimes observed with powder composites. The extent of the phenomenon was markedly le s s than that obtained i n s t e e l wire composites and seemed to be v i r t u a l l y random i n i t s dependence on - 44 - specimen diameter. Sold working of the powder specimens (as l i t t l e as 2%) p r i o r to t e s t i n g eliminated any trace of discontinuous y i e l d i n g . 4. Heat Treatments on Saturated Iron-Powder Composites Various heat treatments were c a r r i e d out on the powder composites. Specimens were i n i t i a l l y s o l u t i o n treated to saturate the i r o n f i b r e s with copper at 1020°C and were then cooled at varying r a t e s . Several d i f f e r e n t secondary treatments were a l s o applied i n c e r t a i n cases. A car b u r i z i n g treatment was given to one series of specimens i n an attempt t o a s c e r t a i n the possible e f f e c t of carbon additions t o the i r o n f i b r e s . (a). Results with -100 +I50 mesh powder composites - A l l the following r e s u l t s are from specimens which had been s o l u t i o n treated under dry hydrogen f o r 15 hours at 1020°C, then cooled and.further heat treated as i n d i c a t e d . The elongations reported are as measured from the y i e l d point to the ultimate t e n s i l e s t r e s s . The gauge length used i n a l l cases was 1 inch. ( i ) "Aircooled" (120 t o 180°C per second) Specimen Diameter U.T.S, l b s / i n 2 , Y.S. l b s / i n 2 EtLong. $ 0.035 138,000 108,300 12.2 0.035 140,500 110,200 14.1 0.035 141,500 119,500 11.7 A photomicrograph of the corresponding structure i s shown i n Figure 21. Figure 2 1 . Photomicrograph of - 1 0 0 +150 mesh Powder Composite "aircooled" from 1020°C, 2$ n i t a l etch, X 2^0 . - 46 - ( i i ) "Aircooled" and Reheated 1 hour at 400°C Specimen U.T.S. Y.S. Elong. Diameter l b s / i n 2 l b s / i n 2 i 0.035 135,700 123,500 13.0 0.035 138,000 127,700 13.0 No discontinuous y i e l d i n g was observed i n specimens from ( i ) or ( i i ) above. ( i i i ) "Aircooled" and Reheated 1 hour at 750°C Discontinuous y i e l d i n g occurred i n these specimens. Specimen U.T.S. Y.S. Elong. • Discontinuous; Diameter l b s / i n 2 : l b s / i n 2 . i Y i e l d Elong. % 0.035 " 59,600 47,800 22.7 2.2 0.035 61,500 49,000 2 3 . 1 . 1,8 (iv) "Aircooled" and Cold Drawn Several specimens were saturated, "aircooled" and drawn cold t o obtain--^.n a d d i t i o n a l 40% reduction i n area. • They were then annealed 1. hour at 250°C t o induce r e c r y s t a l l i z k t i o n of the matrix. Specimen Diameter' ' U.T.S. l b s / i n 2 Y.S. l b s / i n 2 Elong. % 0.035 O.O35 0.035 0,035 163,000 173,000 178,000 173,000 .56,200 55,100 79,000 : 64,300 5.8 . 5.2 5.2 5-1 (v) "Aircooled" Reheated at 400°C, and Cold Drawn Several specimens were saturated, "aircooled", reheated 1 hour at 400°C, drawn an additional 40% reduction in area and annealed 1 hour at 250°C. - 4 7 - Specimen U.T.S. Y.S. Elong. Diameter l b s / i n 2 l b s / i n 2 $' O.O35 175,500 88,400. 4.4 0.035 179,500 72,800 5.4 (vi) Quenched i n L i q u i d Nitrogen and Aged at Room Temperature Saturated and "aircooled" specimens were reheated to 1020°C f o r 20 minutes followed by rapid quenching i i i a bath of l i q u i d nitrogen (-196°C). The specimens were then allowed to reheat to room temperature, and were held there f o r various times p r i o r to t e s t i n g . A l l specimens were found to be magnetic at -196°C . Specimen - Diameter Aging Time U.T.S. l b s / i n 2 Y.S. l b s / i n 2 Elong. 0.035 0 hrs 107,700 84,200 1 .0 0.035 0 104,500 86;200 1.4 0.035 -3 ,120,800 94,100 6.5 0.055 24 121,000 106,700 6 . 0 0.035 100 •133,000 118,500 5.7 0.035 300 130,500 ' 76,000 2.4 ( v i i ) Slow cooled from 1020°C Two specimens were sealed o f f , i n a fused quartz tube under vacuum. The sealed tube was placed i n the centre of a resistance-heated box furnace and surrounded by r e f r a c t o r y b r i c k s . Solution treatment was c a r r i e d out at 1020°C f o r 15 hours and., them the power supply t o the furnace was shut o f f . ;The maximum rate of cooling experienced between 1020°C and 25°C, was 2°C/minute. - 1+8 - Specimen U.T.S. Y.S. Elong. Discontinuous Diameter l b s / i n 2 l b s / i n 2 Y i e l d Elong. <j0 0 . 0 3 5 5 0 , 8 0 0 3 9 , 2 0 0 2 8 . 0 2 . 4 0 . 0 3 5 H - 9 , 9 0 0 3 9 , 3 0 0 2 6 . 8 2 . 9 Representative s t r e s s - p l a s t i c s t r a i n curves f o r the various heat treatments are shown i n F i g u r e . 2 2 . The work-hardening exponents are shown with each curve. (b) Results with - 3 2 5 mesh Powder Composites - During the so l u t i o n treatment of a l l composites produced f r o m . - 3 2 5 mesh i r o n powder, a marked loss o f . c o n t i n u i t y i n the f i b r e s was found to occur. The r e s u l t i n g structure (shown i n Figure 2 3 ^ was considerably d i f f e r e n t .'from that of composites made from wire or coarser powders. I t i s l i k e l y that d i s i n t e g r a t i o n of the f i b r e s i n f i n e powder composites i s associated with the r e l a t i v e l y high volume per cent of copper ( i n i t i a l l y not saturated with i r o n at 1 0 2 0 ° C ) which might be capable of d i s s o l v i n g an appreciable, f r a c t i o n of the i r o n present during s o l u t i o n treatment. Because of the di s c o n t i n u i t y of many of the f i b r e s i n these composites, i t may not be j u s t i f i e d . t o compare the r e s u l t s which follow with those obtained f o r the coarser powder materials. • ( i ) "Airepoled" Specimen Diameter U.T.S. Ibs/in2 Y.S. l b s / i n 2 .Elong. 0 . 0 3 5 0 . 0 3 5 1 2 2 , 7 0 0 1 2 0 , 7 0 0 . 1 1 4 , 0 0 0 1 1 1 , 0 0 0 1 2 . 0 1 2 . 6 160- 140 & - to n - 0 .222 Aircooled From'' 1020°C n= 0.167 Oufcnched in Liq Nz From 1020 °C rvO.179 Slow Cooled From I020°C at ^  l°c/mfn j L J 1 i 6 T S 9 /b,/.. ^ i3 i4 15 1 6 Nf J L £ (%) ,4f 13 ,e N 2 5 *°*7 Fqure 22 Stress Plastic Strain Curves For Representative H e a t Treatments O n - 1 0 0 + 1 5 0 M e s h Fbwder C o m p o s i t e s - 5 0 Figure 2 5 . Photomicrograph of - 3 2 5 mesh Bowder Composite Quenched in liquid nitrogen and aged for 1 hour at - 8 0 ° C . Picric etch, X llkO. - 51 - ( i i ) . Cooled at Rates of i to 25 qC/second Whereas the "aircooled'.! specimens were withdrawn a distance of 12 inches from the hot zone of the furnace i n 4 seconds, f o r a cooling rate of 120 to l80°G/§eeond, (Experimental Procedure,. Section D.) t e s t s were a l s o made on specimens which were withdrawn from the furnace at slower rates t o determine the e f f e c t of rate of cooling from the so l u t i o n temperature. i - 30 seconds withdrawal time (estimated cooling rate l g to 25°'C/sec.) Specimen U.T.S. Y.S. Elong. Diameter l b s / i n 2 l b s / i n 2 i 0.035 122,800 113,700 15.5 0.035 116,300 110,100 1A.5 - 14 minutes withdrawal time (estimated cooling rate l / 2 to l q C / s e c . ) Specimen U.T.S. Y.S. Elong. Discontinuous Diameter l b s / i n 2 l b s / i n 2 i Y i e l d Elong. % 0.035 78,000 66,700 10.5 0.7 0.035 78,000 67,900 9-9 0.7 ( i i i ) Furnace Cooled. A f t e r s o l u t i o n treatment i n a tube furnace, some specimens were l e f t i n the hot zone a f t e r the power to the furnace was cut o f f . The average rate of cooling was 500°C per hour f o r the f i r s t hour, and became incr e a s i n g - \ l y slower as 30°C was approached. Specimen U.T.S. Y.S. • Elong Discontinuous Diameter l b s / i n 2 l b s / i n 2 •* Y i e l d Elong. % 0.035 64,500 52,600 28.3 3.5 0.035 64,500 52,000 26.6 2.8 -52. - ( i v ) . Quenched i n Liquid'Nitrogen Several s o l u t i o n treated specimens were quenched i n l i q u i d nitrogen from 1020°C, then; brought to room temperature and tested within 5 minutes. Specimen • Diameter U.T.S. l b s / i n 2 Y.S. l b s / i n 2 Elong. ••* 0.035 0.035 110,400 110,400 105,000 104,000 6.1 8.0 (v) Quenched i n L i q u i d Nitrogen and Aged at -80°C. Specimens were quenched to -196°C, then allowed t o reheat and age at -80°C f o r various times as i n d i c a t e d below,, (see also' Figure 25). Specimen Ageing U.T.S. Y.S. Elong. Diameter • Time l b s / i n 2 l b s / i n 2 0.035 10 min. 118,700 111,800 11.2. 0.035 30 111,000 105,000 10.5 0.035 . 1 hr. 117,000 110,200 10.7 0.055 3 114,700 106,800 11.7 0.035 6 111,200 106,500 7.9 ( v i ) Carburized at 920°C. Specimens were "pack" carburized as outlined i n Experimental Procedure f o r various times. Specimen Carburizing U;T,S. Y.S. Elong. Diameter Time l b s / i n 2 l b s / i n 2 0.035 = . 125,900 119,500 16.9 0.035 5 min. 118,000 109,700 10.2 0.035 o n 118,800 105,000 7.0 O .O55 126,500 109,200 6.8 0.055 , o n 109,800 73,800 1.6 0.035 110,100 72,200 1.3 The e f f e c t of long c a r b u r i z i n g times on the microstructure i s shown i n Figure 24. I t seems l i k e l y that the large pores are associated with the l i b e r a t i o n of dissolved gas on-cooling from the carb u r i z i n g temperature. Representative s t r e s s - p l a s t i c s t r a i n curves f o r the above mentioned heat treatments are shown i n F i g u r e J 25 along with the corresponding work-hardening exponents. • Figure 26 shows the v a r i a t i o n of the y i e l d stress of s o l u t i o n treated i r o n powders composites with cooling rate. - 5 4 - Figure 2k. Photomicrograph of -325 mesh Powder Composite, Pack carburized at 920°C f o r 100 minutes, unetched. X 6 5 . n = 0 -047 hgure25_ Stress-Plastic Strain Curves-Representative Heat Treatments O n - 3 2 5 Mesh Powder Composites Log Cooling Rote °C/Sec. Figure 2 6 Y. S . V s . Coo l ing Ra te For Saturated ! lron Powder Composi tes - 57 - IV. DISCUSSION A. .Structures and Aspect R a t i o s of Composites Both methods used t o produce a metal f i b r e r e i n f o r c e d composite proved t o be s u i t a b l e t o some extent. For the purpose of f u l f i l l i n g i t h e ~ o b j e c t i v e of t h i s work, however, the powder technique was s u p e r i o r . Much f i n e r f i b r e s could be produced and aspect r a t i o s and i n t e r f i b r e spacings co u l d be e a s i l y v a r i e d over a wide range. In a d d i t i o n , the m a t e r i a l p r e  pared from pure i r o n powders" in v o l v e d . o n l y two components, and was s t r u c  t u r a l l y s impler than t h a t prepared from h i g h carbon s t e e l w i r e . That the f i b r e s i n specimens made from the coarser i r o n powder compacts d i d i n f a c t have favourable aspect r a t i o s can r e a d i l y be proved. The diameters of the f i b r e s are known as. they were measured m e t a l l o g r a p h i c a l l y . .However> as mentioned p r e v i o u s l y , the lengths of the f i b r e s could not be obtained by meta l l o g r a p h i c examination. None the l e s s , the volume of each i r o n p a r t i c l e i s constant, and assuming t h a t d u r ing the f a b r i c a t i o n process the shape of the i r o n p a r t i c l e changes from a sphere t o an e l l i p s o i d of minor a x i s a=b and major a x i s c, then, Volum^e of f i b r e V f = h fjTabc = k Tf a 2 c = k rf r 3 3 3 3 where r i s the o r i g i n a l i r o n sphere diameter. .Therefore the aspect 4 * r a t i o of the f i b r e s i s « £ = r ^ . I f the diameter of a specimen was a a 3 ' reduced by a f a c t o r of 10 then "a" of the f i b r e = r _ , t h e r e f o r e e,, ='1000. 10 • a " ( I t should be noted t h a t a . i s the. maximum diameter of the f i b r e . . The average diameter would be somewhat smaller.) Using t h i s treatment, the aspect r a t i o of the f i b r e s at a specimen diameter of 0;080 inches i sv,ih ... theory,not l e s s than 185:1. . S u b s t i t u t i n g . t h i s value i n t o the equation f o r the c r i t i c a l aspect r a t i o (equation 5) gives f o r the shear s t r e n g t h r e q u i r e d - 58- at the fibre-matrix i n t e r f a c e nr - • 1 l r r = f L '• IB5 ? f 7H0" where Xl^. is. the t e n s i l e stress i n the f i b r e s . Thus, over the specimen siz e range investigated a.maximum shear strength of i s required i n theory f o r f u l l f i b r e reinforcement. The higheststress i n an i r o n f i b r e encountered i n t h i s i n v e s t i g a t i o n i s i n the order of 240,000 p s i . Consequently,..the maximum shear stress required, even f o r a 0.080 .inch-diameter specimen i s i n the order of 325 p s i . Since the shear y i e l d stress f o r pure annealed p o l y c r y s t a l l i n e copper i s approximately 5,000 p s i , the aspect r a t i o s i n a l l coarse i r o n powder composites i n . t h i s i n v e s t i g a t i o n are believed to be favourable. The above an a l y s i s assumes that the f i b r e s remain continuous d u r i n g . f a b r i c a t i o n , which may not be true^ However, the estimate of shear strength i s conservatively high due to the nature of the other assumptions used. C l e a r l y the aspect r a t i o s of f i b r e s i n saturated composites pro duced, from ^325 mesh i r o n powder were much l e s s than discussed above (Figure 23). An estimate of the aspect r a t i o i n t h i s case i s very d i f f i c u l t t o make, since the coarser of the f i b r e s present d i d r e t a i n a high r a t i o . Another feature of the f i n e r powder composites is. that a smaller volume f r a c t i o n of i r o n was present ( 57$) • The aspect r a t i o i n composites prepared from high carbon s t e e l wires was approximately 200. i n a s - i n f i l t r a t e d specimens of normal t e s t length (2 inches). With reduction of the i n f i l t r a t e d material by swaging and drawing the length of f i b r e s i n a t e s t specimen cannot increase, and - 59 - "2 the aspect r a t i o i s then proportional to d^ (d^ = f i b r e diameter). .Thus a 90 per cent reduction i n area of the composite produces at most a 90 per cent increase i n the aspect r a t i o . Again, however, there i s the p o s s i b i l i t y that the o r i g i n a l wires do not remain continuous during reduction of the composite. Indeed, metallographic observations of as-drawn material indicate that some wire breakage d i d occur during f a b r i c a t i o n . Thus i t seems u n l i k e l y that the aspect r a t i o i n wire composites was.ever much greater than-200. At t h i s r a t i o , the maximum shear strength required at the f i b r e matrix i n t e r f a c e should not have .exceeded 3 0 0-psi. .B. Y i e l d i n g Behaviour of Unsaturated Powder Composites 1. . Heterogeneous Y i e l d i n g Heterogeneous y i e l d i n g , i n v o l v i n g r e l a t i v e l y small load drops, was detected i n some composites produced from i r o n powder. The occurrence of the phenomenon was not r e l a t e d t o specimen s i z e . In the case of saturated, heat-treated material, i t only occurred i n annealed specimens of low.yield s t r e s s . There was no evidence to suggest that the discontinuous- y i e l d i n g was i n any way due to breakage of i n d i v i d u a l f i b r e s or to a l o s s of bonding at the f i b r e matrix i n t e r f a c e s . - In f a c t , f i b r e breakage would cause serrations i n the s t r e s s - s t r a i n curve at the ultimate stress (as Q observed by McDanels et a l . with copper-reinforced tungsten filaments ) and not at the y i e l d s t r e s s . Thus, the heterogeneous y i e l d i n g observed.in powder composites i s believed, to be of the type normally observed i n annealed i r o n and low-carbon s t e e l , and to be a t t r i b u t a b l e to the large volume f r a c t i o n of i r o n (or the b.c.c. s o l u t i o n of copper i n iren} which i s present i n these composites. - 60 - 2. Size Dependence of Y i e l d Stress Figure 20 reveals- that only a s l i g h t increase i n y i e l d stress occurred i n unsaturated powder composites (from coarse powders) with decreasing specimen diameter over the size range investigated; i . e . corresponding to a range of i n d i v i d u a l f i b r e diameters of approximately 26 to 7 microns. There a r e s e v e r a l . p o s s i b l e reasons f o r the increase observed. a) There i s a true si z e e f f e c t within.the i r o n f i b r e s over t h i s s i z e range, (a true si z e e f f e c t being one which i s d i r e c t l y a function of the diameter such as the strength of a whisker.). There was no a p r i o r i reason, however, to expect such a size e f f e c t i n a mixture of d u c t i l e phases, and i t i s u n l i k e l y that such an e f f e c t i s involved. b) The matrix mean free path decreases as the composite i s reduced i n diameter. Thus, strengthening of the matrix might be expected " due t o a reduction i n the path length a v a i l a b l e f o r d i s l o c a t i o n p i le-up during i n i t i a l p l a s t i c s t r a i n ( i . e . a g r a i n s i z e e f f e c t e x i s t s ) , c) As the composite i s reduced i n s i z e , the dissol v e d copper content of the i r o n f i b r e s increases with the acciamulationnQf annealing time at 680°C. However, the maximum s o l u b i l i t y of copper i n ir o n at 680°C i s reported to be 0.5 per cent. Moreover, although age-hardening i s e xhibited by a l l o y s i n t h i s composition range, the s o l u t i o n hardening e f f e c t i n t h i s system i s small. " ' I t therefore seems probable that much of the 17.5-. Ver cent increase i n y i e l d strength shown i n Figure 20 i s due to (b) with a contribution from ( c ) . - 61 - C . Yield. Behaviour of Wire Composites 1. • Or i g i n of Two Y i e l d Points The load-elongation curves f o r the wire composites exhibited two apparent y i e l d points, ^Pmatrix a n < ^ ^composite* The corresponding "matrix y i e l d s t r e s s " increased f a i r l y r a p i d l y with decreasing specimen diameter (Figure 12). Coupling t h i s with the observations shown i n Figure 1J, i n which the thickness of the copper coating on the outside of the specimen i s r e l a t e d to specimen diameter,, suggests that the i n i t i a l y i e l d i n g observed was due to a gr i p e f f e c t . I t i s suggested that the copper coating y i e l d e d i n the grips g i v i n g r i s e to. YP^-trix• -As evidence of t h i s , at smaller specimen;.; diameters corresponding to thinner copper coatings, the matrix y i e l d stress rose, probably due to increasing r e s t r a i n t from the s t e e l f i b r e s . In f a c t , at small specimen diameters the matrix y i e l d stress.became very close i n value to that which has. been termed the composite y i e l d s t r e s s . Consequently, i t i s believed that only the l a t t e r y i e l d stress i s t r u l y i n d i c a t i v e of the properties of the composites. 2. Heterogeneous Y i e l d i n g The extent of heterogeneous y i e l d i n g i n wire composites was d i s t i n c t l y related: to composite diameter (Figure 14). The phenomenon was a l s o much more marked i n wire than i n powder composites. Since discontinuous y i e l d i n g was only observed i n materials of r e l a t i v e l y low composite y i e l d s t r e s s , i t i s u n l i k e l y that i t can be a t t r i b u t e d even p a r t i a l l y t o a gr i p e f f e c t ) i . e . i r r e g u l a r g r i p slippage. Also, breakage of f i b r e s would be expected, t o cause serrations to appear i n the stress 8 s t r a i n curve at higher stresses ratherr. than just at the onset of y i e l d i n g . - 62 - I t was demonstrated that a s i n g l e , spheroidize-annealed, s t e e l wire exhibited discontinuous y i e l d i n g of the type observed i n mild s t e e l . 23 I t has been stated elsewhere that a spheroidized eutectoid i n a high carbon s t e e l can e x h i b i t the phenomenon, whereas a p e a r l i t i c structure of the same o v e r a l l composition does not. Bredz and Schwartzbart have observed a decarburizing phenomenon when copper was melted i n contact with steels of various carbon contents. The carbon (due. t o the influence of the copper) became concentrated at the grain boundaries of,'the s t e e l . i The Q.012 inches diameter s t e e l wires contained i n the composites used i n t h i s i n v e s t i g a t i o n were i n contact with l i q u i d copper at 2100°F f o r 10 minutes followed by quenching. Iron at t h i s temperature can contain 17 up t o 8.5 per cent copper i n s o l u t i o n . I t has been stated elsewhere that a -100 +150 mesh pure i r o n powder composite becomes saturated with copper i n approximately 200 minutes of i n f i l t r a t i o n time at 1100°C, . Thus, due to the large s i z e of the i n d i v i d u a l wires and r e l a t i v e l y short time i n contact with liquid.copper, i t i s f e l t that only the surface of the wires Vas i n i t i a l l y saturated with copper. The structure of the s t e e l f i b r e s then, p r i o r to the i n i t i a l swaging operation, was tempered martensite (quenching from 1150°C followed by tempering at 680°C). Experiments i n v o l v i n g the e f f e c t of cold work and s t r a i n annealing indicated, that heterogeneous y i e l d i n g i n the wire composites might be of the normal mild s t e e l type observed i n spheroidized: high-carbon s t e e l s . However, the siz e dependence of the phenomenon i s not adequately explained on t h i s b a s i s . Moreover, the f a c t that a marked decrease i n wire composite y i e l d strength occurred at sizes where heterogeneous y i e l d i n g was a maximum suggests that another mechanism may be involved i n the process. I t i s proposed; that much of the discontinuous y i e l d i n g i n wire composites i s a t t r i b u t a b l e to shearing at the matrix-fibre i n t e r f a c e s . With progressive reduction and annealing of the composite, carbon-segregates 24, to the s t e e l wire surfaces (as per Bredz and Schwartzbart ) and eventually appears as graphite at the i n t e r f a c e . The f a c t that t h i s phenomenon would be dependent on total'.annealing time and hence specimen diameter accounts f o r the observed-variation i n extent of the discontinuous y i e l d i n g with specimen s i z e shown i n Figure lk. Thus, with decreasing composite diameter, down, t o about Q'i046 inches, the f r a c t i o n of t o t a l i n t e r f a c e area on which shearing can occur i s increasing. Below t h i s s i z e , separation over a l l the matrix f i b r e i n t e r f a c e s occurs a f t e r progressively l e s s t o t a l s t r a i n . This argument pr e d i c t s that below,0.046 inches diameter, the t e n s i l e load on the composites i s being c a r r i e d e n t i r e l y by the matrix i n the e a r l y stages of flow.' The strain-hardening behaviour (Table I I , page 32) does, not support t h i s model too w e l l , however. The observed e f f e c t s of ageing and cold work can be r a t i o n a l i z e d i n terms of the proposed interface-shear mechanism. At the specimen diameter which exhibited the maximum amount of discontinuous y i e l d i n g , i . e . 0.6k6 inches, cold working of the specimen to a reduction of 4-1/2 per cent not only eliminated the discontinuous y i e l d i n g but a l s o r a i s e d the y i e l d stress to 44,000 p s i which i s an increase of approximately 33 per cent over the annealed condition (Figure 9 ) . This implies that c o l d working has p a r t i a l l y restored the bond between the f i b r e s and the matrix, by mechanically breaking down graphite or other i n t e r f e r i n g l a y e r s . Ageing of specimens i n t h i s size range f o r 1 hour at 200°C p a r t i a l l y restored the discontinuous y i e l d i n g - 6k - while a l s o s l i g h t l y r a i s i n g the composite y i e l d stress (by approximately 6 per cent). According t o the interface-shear argument above,this would imply that the ageing treatment has allowed the creation of new ; shear points or areas which shear at higher stress values than i n the i n i t i a l specimen. . O p t i c a l microscopy/unfortunately, f a i l e d t o reveal c l e a r l y the formation of the weakening in t e r f a c e layers postulated above. Also, there was no p o s i t i v e evidence i n the microstructure of p a r t i a l l y deformed or fractured wire composites that the shear mechanism had or had not been operative. The main basis f o r the p o s t u l a t i o n that i n t e r f a c i a l shear must have occurred in.these materials was the observed dependence of composite y i e l d stress on specimen s i z e , as discussed i n the following section. 3• Size Dependence of Y i e l d Stress The composite y i e l d stress versus specimen diameter curve f o r the s t e e l wire composites (Figure 9) shows a d i s t i n c t anomaly within a c r i t i c a l s i z e range. The composites used i n t h i s i n v e s t i g a t i o n were given one hour anneals at 680°C subsequent t o each kO per cent reduction i n cross s e c t i o n a l area. This annealing tended to fur t h e r spheroidize and coarsen the carbide i n the s t e e l wires (Figure 6). Associated with spheroidization would be expected a s l i g h t lowering of the y i e l d strength of the f i b r e s with decreasing f i b r e diameter (increasing t o t a l annealing time). The matrix, on the other hand, would be expected to show an increase i n strength with decreasing specimen diameter due to a matrix mean free path e f f e c t analogous t o the major strengthening mechanism proposed f o r the i r o n powder composites. - 65, - Based on observations reported f o r other systems, y i e l d stress increases N -1/2 x with (\ where f ) = mean free path. The f i b r e strength curve, i t i s suggested, i s interrupted by shearing at the m a t r i x r f i b r e i n t e r f a c e . The matrix c a r r i e s the e n t i r e load on the composite once shearing of the i n t e r f a c e i s complete. However, r e l a t i v e l y high stresses (approaching the true fr a c t u r e stress of the . . . i matrix a l l o y ) can be c a r r i e d since necking of the matrix i s r e s t r a i n e d by the f i b r e s , i . e . there i s a hydrostatic pressure e f f e c t . i n , t h e 'matrix. Superimposing the above e f f e c t s gives the schematic summation, curve shown i n Figure 27 , . which i s of the general form of the experimental, y i e l d stress.curve obtained f o r wire composites (Figure 9 ) • D. E f f e c t of Heat Treatment on Saturated Powder Composites The strengths observed i n powder composites a f t e r saturating the i r o n f i b r e s with copper at 1020°C were extremely dependent on cooling rate from 1020°C. Consideration of the possible phase transformations involved became necessary i n order to explain t h i s behaviour and to explain the r e l a t i v e l y high strengths obtainable i n saturated composites. The s o l u b i l i t y of copper i n o<.-iron at 1020°C has been reported . 1 7 at 7-8 per cent by weight^Krantz has shown that saturation of -100 +150 mesh p a r t i c l e s of i r o n with copper w i l l occur at 1100°C i n approximately 200 minutes. Thus, powder composites which were solution.treated i n the present studies as described previously, involved .copper^saturated i r o n f i b r e s . Previous reported studies, of non-equilibrium phase transformations i n the iron-copper system have been l a r g e l y confined: to a l l o y s containing up t o k weight per cent copper. I t i s recognized that these a l l o y s can be 32 /\ / matrix shears from fibres / / /  specimen diameter *~ .. ON 1 ON Figure 2 / S p e c i m e n Diameter Vs. Pred ic ted Matrix and F i b r e Strengths - 67 - s o l u t i o n treated and quenched from above or below the eutectoid temperature, 20 then precipitation-hardened at a few hundred degrees Centigrade . However, no studies have been reported i n the l i t e r a t u r e of the non-equilibrium decomposition of the eutectoid at 4 weight per cent copper. S p e c i f i c a l l y , there i s no reference to a martensite transformation in, t h i s system i n the 26 extensive studies of such transformations by Zackay et a l or B i l b y and 28 C h r i s t i a n 25 White performed some unpublished work on i r o n - 6 weight per cent copper, a l l o y s prepared by melting and casting. He hot and cold r o l l e d ingots to obtain s t r i p material which was cut i n t o shaped t e n s i l e specimens. These were homogenized ( s o l u t i o n treated) at 1100°C, cooled at various rates to 20°C, and tested i n tension with the following r e s u l t s : 1. Water Quenched From 1100°C U.T.S. l b s / i n 2 Y.S. l b s / i n 2 Elong. i Hardness Rockwell 109,ooo 107,000 n.a. 1100,000 6.0 6.0 C 5 B 90 2. "Aircooled" From 1100°C U.T.S. l b s / i n 2 Y.S. l b s / i n 2 Elong, * Hardness Rockwell 153,000 151,000 156,000 143,000 l4l,000 146,000 4.0 4.0 5.0 c 31 c 31 c 32 -68 - 3. Furnace Cooled From: 1100°C U.T.S. l b s / i n 2 Y.S. l b s / i n 2 Elong •* Hardness Rockwell 72,000 76,700 72,500 61,600 64,800 61,600 15 •16 18 B 66 B 67 B 65 White a l s o examined the e f f e c t of reheating a i r c o o l e d specimens f o r 1 hour at varioustemperatures, followed by a i r c o o l i n g to 20°C. .4. "Aircooled" From 1100°C,. Reheated to 400°C f o r 1 hour. U.T.S. Ibs/in2 Y.S. l b s / i n 2 Elong •* 130,000 127,000 135,000 119,000 117,000 123,000 10 10 7 5. "Aircooled" From 1100°C, Reheated to 600°C f o r 1 hour. U.T.S. l b s / i n 2 Y-.S. Ibs/in2 Elong *' 89,000 91,000 95,000 80,000 84,000 86,000 13 13 13 6. ."Aircooled" From 1100°C, Reheated to 750°C f o r 1. hour. U.T.S. l b s / i n 2 Y.S. lbs/mn 2 Elong. ••* • 84,000 85,000 80,000 74,000 79,000 72,000 16 16 15 These r e s u l t s bear a c l e a r r e l a t i o n s h i p t o those obtained i n the present studies by heat-treating powder composites. In view of the known and rather small e f f e c t s of age-hardening the o& s o l i d s o l u t i o n i n Fe-Cu, the enormous di f f e r e n c e between the a i r - c o o l e d and furnace-cooled 6-8$ Cu a l l o y s cannot be explained i n such terms. • I n - f a c t , consistent with the phase diagram f o r Fe-Cu, i t i s d i f f i c u l t to explain the high strength of ai r c o o l e d (or even quenched) materials by other than a martensite trans formation. I t remains to explain why, the properties of these a l l o y s respond •to c o o l i ng rate i n the manner observed. There are several known martensite transformations including 26 07 Cu-Al and Fe-Ni 1 i n which the Mg and Mf temperatures are strongly dependent on s l i g h t v a r i a t i o n s i n the concentrations of the minor components. Of p a r t i c u l a r i n t e r e s t i s the Cu^Al system where a change i n A l concentration of from 11 to 15$ (hypereutectoid range) lowers the , 2 6 •Ms-by approximately 450 C . I t i s f e l t that a s i m i l a r e f f e c t occurs i n the Fe-Cu system, with increasing copper contents lowering.the Mg. For purposes of discussion, consider the quenching of a homo geneous Fe-7$ Cu a l l o y from 1020°C. Quenching at a rate greater than some c e r t a i n c r i t i c a l value would allow, v i r t u a l l y f u l l r etention of the copper i n s o l u t i o n . The high copper concentration, however, w i l l depress the value of the M s and Mf from those which would e x i s t at a lower copper concentration. Thus, the amount of martensite that would be formed at a p a r t i c u l a r temperature between M s and Mf f o r the 7$ copper a l l o y would be les s than that r e s u l t i n g from quenching to the same temperature an a l l o y of lower copper concentration. Compare t h i s r e s u l t with that predicted from cooling the same a l l o y at a lower rate ( i . e . below the c r i t i c a l r a t e ) . - 7 0 . - This would a l l o w . p a r t i a l p r e c i p i t a t i o n of the epsi l o n phase during cooling. In t h i s manner, the copper content that would be retained i n s o l i d s o l u t i o n on furth e r cooling would be somewhat reduced and the r e s i d u a l X would have a higher" Mg and M|., The net consequence i s that a s u b s t a n t i a l l y greater amount of martensite would r e s u l t on furth e r c o o l i n g t o the reference temperature, provided the rate of cooling was r a p i d enough i n t h i s range of temperature. Figure - 2 8 shows a suggested cooling-transformation diagram f o r the iron ~ 7 $ copper a l l o y , the form-of which i s consistent with the above argument.,, and. the use of which permits observations i n the present i n v e s t i g a t i o n to be explained. I t i s i n t e r e s t i n g to note that i n the Cu-Al.system martensite 28 transformations are reported only f o r hypereutectoid compositions . I f s i m i l a r behaviour i s exhibited by the Fe-Cu system, t h i s could explain the absence of previous observations of a martensite reaction, since nearly a l l e a r l i e r work with t h i s system has been with a l l o y s of l e s s than k weight per cent copper. Some of the saturated powder composites studied i n the present work were quenched i n l i q u i d nitrogen from the s o l u t i o n treatment temp erature and.then t e s t e d - i n tension at room temperature. For the above mechanism t o explain the. r e s u l t s obtained,,the martensite transformation would be required to be completely r e v e r s i b l e , a.condition.that e x i s t s i n most other systems which e x h i b i t martensitic type transformations 2^. In the powder composites the rate of cooling due to " a i r c o o l i n g " i s apparently such as;, to produce the maximum amount of martensitic phase consistent with the proposed- transformation. Reheating of "ai r c o o l e d " -11> - Time Figure 28 Cooling Rate -Transformation Diagram For an Iron- 7 % Copper Alloy - 72 - specimens at kOO°C f o r one hour i s presumed to have p a r t i a l l y tempered the martensite, whereas a one hour treatment at rJc^Q°C has apparently transformed the metastable martensitic phase i n t o a r e l a t i v e l y coarse , mixture of low-copper <oC and the ep s i l o n phase..- The l a t t e r transformation would be expected to allow a.return of heterogeneous y i e l d i n g i n the f e r r i t e , a condition which was, i n f a c t , observed. An i n t e r e s t i n g r e s u l t of the heat treatments of "saturated" composites (and one which cannot be explained i n terms of a simple martensitic transformation) i s the apparent-age-hardening of specimens quenched i n l i q u i d nitrogen and he l d at room temperature. In studies of p r e c i p i t a t i o n of £ from oC i t has been revealed that maximum hardness 20 occurs as a r e s u l t or ageing at temperatures between kOO and "JQ0°C. In a d d i t i o n , measureable p r e c i p i t a t i o n of oC from £ occurs only at 19 temperatures above 600°C and then only to a very l i m i t e d extent . Thus i t i s apparent that the normal p r e c i p i t a t i o n phenomenon generally observed i n the Fe-Cu system does not apply i n t h i s case. I t i s pos s i b l e that some tempering of the high copper martensite formed by auenching the saturated (7-8$ copper) )£ occurs at 20°C i n view of the high degree of supersaturation involved. Also, p r e c i p i t a t i o n from retained V may occur. This could i n turn cause hardening of the e x i s t i n g martensite by the formation of coherency s t r a i n s , and/or r e s u l t i n the conversion of some retained ¥ to lower-copper martensite. Of p a r t i c u l a r i n t e r e s t i s Figure 26, which shows the v a r i a t i o n of the y i e l d stress of the composites with changes i n cooling rate from the saturation temperature. I t i s apparent that the maximum strengths i n the composites occur as a r e s u l t of cooling rates of between 20 and Pj C C / s e c . The curve a l s o shows v i r t u a l l y a l i n e a r dependence of y i e l d stress with v a r i a t i o n s i n cooling rates l e s s than the values just mentioned. This i s consistent with what would would he expected from a consideration of the cooling-temperature curve shown i n Figure 2 8 . Slower cooling rates would allow d i f f u s i o n - c o n t r o l l e d phase transformations t o occur during cooling with a subsequent softening e f f e c t . E. Deformation Behaviour- of Metal Fibre Reinforced Metals 17 Krantz 1 has examined the properties i n the bulk form.of a copper-iron a l l o y e s s e n t i a l l y i d e n t i c a l t o the matrix a l l o y i n these f i b r e composites. He found, the ultimate t e n s i l e strength to be 4 7 , 0 0 0 p s i with an elongation to fr a c t u r e of 3 0 per cent i n 1 inch. - The true fr a c t u r e stress however, can be taken as approximately 118,000 p s i on the basis of area at the f r a c t u r e . The saturated and heat-treated powder composites provided an excellent opportunity to examine the e f f e c t of the r e l a t i v e strengths of f i b r e and matrix on composite pro p e r t i e s . Thus i n furnace-cooled material, the y i e l d and ultimate strengths were low ( 3 9 , 0 0 0 and 5^,000 p s i re s p e c t i v e l y ) and the elongation to fr a c t u r e was high ( 2 7 per cent). - These properties are i n . f a c t s i m i l a r to those of unsaturated composites of s i m i l a r s i z e . Clearly, i n t h i s case, deformation of the matrix i s not being r e s t r i c t e d appreciably by the f i b r e s , since the l a t t e r are f e r r i t e (Q£) of low diss o l v e d copper content with deformation behaviour s i m i l a r t o that of the matrix. By contrast, a i r c o o l e d composites contained f i b r e s f o r which the y i e l d and ultimate strengths could be expected to be at l e a s t 142,000 and 1 5 2 , 0 0 0 p s i r e s p e c t i v e l y according to White's r e s u l t s . . The f a c t that such composites exhibited strengths of 110,000 p s i ( y i e l d ) and 140,000 p s i • - Ik - (ultimate) can be accounted f o r by a "size e f f e c t " i n the matrix rather than i n the f i b r e s . The high-strength f i b r e s constitute strong b a r r i e r s t o flow i n the matrix. That i s , d i s l o c a t i o n p i l e-up i n the very e a r l y stages of p l a s t i c s t r a i n i n the matrix ( p r i o r to the attainment of the reported y i e l d stress) leads to very rapid.matrix hardening. The fa c t that the length of pile>ups i s severely r e s t r i c t e d at the small composite and. f i b r e diameters involved,. means that the'matrix s i z e e f f e c t " being r e a l i s e d i a l a r g e . The matrix accordingly can support stresses much higher than i t s bulk ultimate strength, perhaps approaching i t s true fracture s t r e s s . - S i m i l a r arguments provide an explanation.for the strength properties of composites with other thermal h i s t o r i e s i n the present work. I t remains, however, to compare the theories advanced by previous i n v e s t i g a t o r s with the arguments proposed above. 5 The " f i b r e s i z e e f f e c t " reported by Jech et a l . i n tungsten f i b r e - r e i n f o r c e d copper can probably, be p a r t l y a t t r i b u t e d to the matrix si z e e f f e c t discussed previously. On the basis of several assumptions, an expression for'the pre d i c t e d v a r i a t i o n of composite strength with matrix mean free path can be developed mathematically. Assuming that the f i b r e s i n the composite are continuous and have the uniformly packed array shown i n Figure 2 9 , then the area of a f i b r e can be r e l a t e d to the t o t a l composite area as follows: -7,5- - Figure 2 9 . Assumed Fibre D i s t r i b u t i o n . 76 - T o t a l area of t r i a n g l e i n Figure 29 A t = 1 S f S t = S f 2 2 2 k Area of f i b r e i n s i d e t r i a n g l e • A F = i d / Tt = Tf CLT 2 f TT "8" Volume F r a c t i o n Fibres = N, ^ t 2 ^ S f 2 f Thus, the i n t e r f i b r e spacing (S^.) i s : S f 2 j N f Also, since there i s a l i n e a r r e l a t i o n s h i p between i n t e r f i b r e spacing and matrix mean free path f o r the case of continuous f i b r e s , then: .M.F-.P. c* . d f YN"f Gensamer,. working with s t e e l s , has shown.that the strength of a matrix containing a hard dispersed phase i s proportional to the log of r e c i p r o c a l mean free path. Other i n v e s t i g a t o r s , with various two-phase J -1/2 -1/2 systems have found a . (M.F.P.) dependence of strength. Mathematically, both these functions are quite s i m i l a r . Therefore, assuming a .(M.F.P.) r e l a t i o n s h i p , -1/2 strength of matrix ( ^ V ) o< (M.F.P.) o< N f ° " 2 5 . . . . . ( 7 ) d f I t now becomes necessary t o modify the theory of combined a c t i o n , which assumes that the matrix strength SJ~m i s independent of the volume -77 - f r a c t i o n or diameter of the f i b r e s present, i . e . XT = A f STf .+ A T f f i •Consider the e f f e c t of increasing.the volume f r a c t i o n of the f i b r e s ( i . e . A^) while keeping d^ constant. This w i l l decrease the value of Am,. the volume f r a c t i o n of the matrix. The theory of combined act i o n indicates that the composite strength increase i s l i n e a r , i . e . there i s no accompanying change in. the values.of t h e . f i b r e and matrix stresses. The theory proposed.however, i s that the matrix, strength i s p r o p o r t i o n a l to (volume f r a c t i o n of f i b r e s ) 0 ' 2 5 and, thus any- increase in.the volume f r a c t i o n of f i b r e s causes an increase in. the strength of the matrix. - The e f f e c t , a l t h o u g h ' r e l a t i v e l y small, has maximum influence at low volume f r a c t i o n s . o f f i b r e s ( i . e . . l e s s than 20%); This could p o s s i b l y account f o r the discrepancy between the experimental points and 8 the c a l c u l a t e d s t r a i g h t l i n e observed by McDanels et a l . In t h e i r work, p l o t s of composite ultimate t e n s i l e stress versus volume per cent f i b r e s f o r three separate f i b r e diameters gave experimental values at low volume per cent f i b r e s that were greater than the values calculated, from the theory of combined a c t i o n . Equation.(7) i n d i c a t e s an inverse square root dependence of matrix strength with f i b r e diameter. The e f f e c t i s greater, the smaller the diameter of the f i b r e . Unfortunately, there i s no d i r e c t experimental evidence to support t h i s premise. I t i s thus proposed.that the e x i s t i n g theory'for p r e d i c t i n g the strength of f i b r e - r e i n f o r c e d composites should be modified.to become: ^ = A f ^ " f + \ ^ m + V K d f (8) where K i s a constant depending on the r e l a t i v e strengths' of the f i b r e and.the matrix. A value of K can be calculated from one set of r e s u l t s obtained i n t h i s i n v e s t i g a t i o n , namely, the " a i r c o o l i n g " of the coarse i r o n powder composites. S u b s t i t u t i n g pertinent values i n t o equation (8) and solving gives; K equal to 2 8 l l b s / i n ' at a . f i b r e diameter of 10 microns. I f K depends only- on the r e l a t i v e strengths of the f i b r e and. the matrix, then equation (8) should give the composite strength f o r the "aircooled" -325 mesh powder composites with a s u b s t i t u t i o n of the corresponding values of A^ ,, A m and d^. Such a c a l c u l a t i o n gives a value f o r the composite strength of 137>600-psi, which i s 13 per cent greater than that determined experi mentally (122,000 p s i ) . The theory of combined a c t i o n , on the other hand, pr e d i c t s 109,500 p s i . as the composite strength. The c a l c u l a t e d value of the strength i s based on the assumption that the mean free path i s l i n e a r l y dependent on the diameter of the f i b r e ( i . e . continuous f i b r e s are assumed). This i s not true f o r the case of -525 mesh powder composites (Figure 23). Apparently the mean free path i s s everal times greater than has been assumed i n the mathematical develop ment. -This w i l l have the e f f e c t of lowering the value of the t h i r d term i n equation ( 8 ) , thus.bringing the calculated value c l o s e r to that deter mined experimentally. On the other hand, i t i s hard to v i s u a l i z e any a d d i t i o n a l e f f e c t increasing the strength as calculated from the. theory of combined actio n , (apart from increasing the strength of the f i b r e s due to a "si z e e f f e c t " , a condition whichhas not been found to occur i n . t h i s i n v e s t i g a t i o n ) . - 79 - V . CONCLUSIONS 1. No strengthening e f f e c t has been observed i n f i b r e - r e i n f o r c e d composites i n t h i s work which can.be a t t r i b u t e d to f i b r e " s i z e e f f e c t s " . However, the s t rength of metal f i b r e r e i n f o r c e d metal composites i s b e l i e v e d to be g r e a t l y i n f l u e n c e d by a . " s i z e e f f e c t " i n the matr ix . 2. Any. f a c t o r which a f f e c t s the matrix mean f ree path (e . g . volume f r a c t i o n of f i b r e and f i b r e diameter) can be expected to a f f e c t composite s t r e n g t h . .However,. the extent to which such e f f e c t s are important i s c o n t r o l l e d by the r e l a t i v e hardness or s t rength of -the f i b r e ; i.e. by< i t s e f f e c t i v e n e s s as a b a r r i e r t o flow, i n the matr ix . . 3 . The f o l l o w i n g m o f i d i c a t i o n of the theory of combined a c t i o n i s proposed f o r p r e d i c t i n g the s t rength of a f i b r e - r e i n f o r c e d . c o m p o s i t e : — —- + 1 A -1/2 ^~c = A f *t + A i ^ m + A f K d f where A i s volume f r a c t i o n , f r e f e r s to f i b r e , m r e f e r s to matr ix , df i s f i b r e diameter and-K i s a constant whose value depends on the hardness .of the f i b r e . k. •In composites of copper r e i n f o r c e d by s t e e l w i r e s , weakening of the m a t r i x - f i b r e i n t e r f a c e can occur as a consequence of carbon segregation t o the i n t e r f a c e . This leads to shearing at the i n t e r f a c e i n the e a r l y stages of t e n s i l e deformation. 5. A l l o y s c o n t a i n i n g 6 t o 8 weight per cent copper i n i r o n e x h i b i t a martensite t ransformat ion when cooled from the V r e g i o n of the Fe-Cu phase diagram. The martensite formed at 6 per cent copper has an u l t imate s t rength of approximately 150,000 p s i and e x h i b i t s apprec iable d u c t i l i t y . This martensite t ransformation apparent ly has not been observed heretofore i n s tudies by other i n v e s t i g a t o r s of Fe-Cu a l l o y s . - 80 - VI. - SUGGESTED FUTURE WORK This work has been p r i m a r i l y of an exploratory, nature and the re s u l t s have suggested d i r e c t i o n s of future work which might be p r o f i t a b l y explored. I t i s recommended: that f u r t h e r studies be c a r r i e d out-on. the phase.transformations i n hypereutectoid Fe-Cu a l l o y s of bulk form. Experimental v e r i f i c a t i o n of the proposed r u l e f o r p r e d i c t i n g composite strength i s recommended. This could be done by the extension of experimental work to other systems and by means of experiments i n which the f i b r e s i z e , d^, i s varied-without varying the inherent f i b r e strength. In a d d i t i o n , i t i s f e l t that t h i s work could be extended to even smaller f i b r e sizes and/or smaller matrix mean free path distances by a judicious choice of wire drawing equipment, powder s i z e s , and heat t r e a t i n g conditions. Saturation of the f i b r e s with copper p r i o r to f i n a l drawing could help t o obtain the desired r e s u l t . - 81 - VII. BIBLIOGRAPHY 1, Coleman, B.D., J . Mech and Phys. of S o l i d s , 7, 60 (I958). 2. P a r r a t t , N. J . , Rubber and P l a s t i c Age, 4 l (3) , 263 ( I 9 6 0 ) . . 3 . Dietz, A. G. H., "Design Theory of Reinforced P l a s t i c s " , Fiberglass. Reinforced P l a s t i c s , Chapter 9, Reinhold, New York, N.Y., (1954). k. Sutton, W. H., J . Amer. Rocket Society, A p r i l I.962, 593. 5. Jech, R. W., McDanels, D. L., and Weeton, J . W., "Composite Materials and Composite Structures", Proc. S i x t h Sagamore Ordnance Materials Conference, August 1959, 116. 6. K e l l y , A., Private communication. 7. Cratchley, D., Powder Met., (11), 59 ( I 9 6 3 ) . 8. McDanels, D. L., Jech, R. W., Weeton, J . W., Technical Note D-l88l, N.A.S.A., Washington D.C., October 1963. 9. Dow, N.F., Technical Information Series, R 63SD6I, General E l e c t r i c , Space Sciences Laboratory, ( I 9 6 I ) . 10. . Koppenaal, A . , P a r i k h , N., Trans. A.I.M.E., 224, I I 7 3 ( I 9 6 3 ) . 11. Sutton, W. H., Rep. No. R 6 2 S D 6 5 Class 1, General E l e c t r i c , ( I 9 6 2 ) . 12. Whitehurst, H. B., Michener, J . W., Lockwood, P., Proc. Sixth Sagamore Ordnance Materials Conference, August 1959, 248. 13. Cratchley, D., Heywood, D. M., to be published. 14. Wagner, H . J . , B a t t e l l e Technical Review, 12 (12) 8 (1963). 15. Sutton, W. H., Chorne, J . , Metals Engineering Quarterly, 3 (1), 1963. 16. Roberts, D. A., Memorandum 80, Defence Metals Information Center, January 196I . 17. Krantz, T., Private communication based on M.A.Sc. pro j e c t , U n i v e r s i t y of B r i t i s h Columbia. 18. Wriedt, H. A., Darken, L. S., Trans. A.I.M.E. 218, ( i960) . 19. Newkirk, J . B., Trans. A.I.M.E. 209, 1214 (1957). 20. Hornbogen, E., Glenn, R.C., Trans. A.I.M.E., 218, 1064 ( i 9 6 0 ) . 82 - B i b l i o g r a p h y C o n t i n u e d . . . . 21. B e n d i , A . , Chem.. Rev. ^2, 417(1955) ." 22. Snowbal l , R . F . , • M . A . S c . T h e s i s , U n i v e r s i t y of B r i t i s h Columbia , 1961 . 23. Gensamer, M . , P e a r s a l l , , E . B . , • P e l l i n i , , W.S. Low J r . , J . R . , Trans „ , A . S . M . 30, 983 (1942). 24. B r e d z , . N . , Schwartzbart , H . , Welding Research Supp. 4 l , 129-S ( 1 9 6 2 ) . 25. White, H . , Unpublished work, U n i v e r s i t y of B r i t i s h Columbia, 1965 . 26. Zackay, V . F . , Jus tusson, M.W., Schmatz, D . J . , "Strengthening Mechanisms i n S o l i d s " , - Strengthening by M a r t e n s i t i c Transformations , Chapter J,- A . S . M . (I960)-. : • 27. Kaufman,• L . Cohen, M . , " T h e Mechanism of Phase Transformations i n M e t a l s " , N u c l e a t i o n i n M a r t e n s i t i c Transformations , I n s t i t u t e of M e t a l s , London, (I956) I87.. . - 28. B i l b y , B . A . , , C h r i s t i a n , J . W . , I b i d . 121. 29. T r o i a n o , A . R . , 'Greninger, A . B . , A . S . M . Handbook (1948) 263. VIII. APPENDICES APPENDIX I.. Iron-Copper System 950 900 O 850 a. z> < cr UJ a. s Ul 800 750 700 650 -OANILOFF DIAGRAM -WRIEDT AND DARKEN"1 I 2 , 3 4 WEIGHT PERCENT COPPER F e - r i c h End Reproduced from Wriedt and Darken, Trans. A.I.M.E., 218, ( i 9 6 0 ) Cu-rich End Reproduced from Butts, "Copper, the Metal, I t s A l l o y s and Compounds New York, U7I (1954). - 84 - •APPENDIX I I . A. Data f o r S t e e l Wire-Reinforced Composites Composite Number Specimen Diameter (in) Y.S. Matrix p s i Y.S. Composite p s i U.T.S, p s i Disc. Y i e l d Unit S t r a i n (in) W-l-A W-2-A W-3-A O.O98 O.O89 O.O75 O.O67 0.052 0.051 0.047 0.047 0.043 O.O38 0.034 0.057 0.047 0.047 0.047 0.070 0.063 0.060 •O.O58 0.053 0.051 0.042 0.040 0.036 0.036 0.032 0.022 5,800 8,600 10,500 18,200 '21,500 26,100 16,800 23,600 18,200 19,500 24,000 15,000 18,700 16,800 15,900 14,500 12,300 13,900 18,300 15,200 14,000 21,400 •25,500 24,500 31,400 4o,ooo .45,200 21,600 26,500' •31,300 35,100 34,300 32,000 38,300 •39,200 •34,000 36,300 .45,400 42,700 53,800 31,900 34,500 34,400 39,200 .41,300 38,600. 35,300 32,000 .33,000 :33,500 36,300 35,400 •44,100 ,50,800 47,200 48,700 68,500 63,100 54,400 53,700 53,400 54,700 61,700 64,500 74,500 49,600 42,8oo •37,800 42,600 63,400 68,600 66,400 56,100 52,500- 48,100 46,400 4o,000 44,200 54,800 74,700 71,200 0 0 0 0 . 0 2 3 0.040 0 . 0 3 6 0 . 0 6 3 0 . 0 6 3 0.047 O0O34 0 . 0 2 8 0 . 0 4 6 0 . 0 5 0 n . a . 0 . 0 4 3 0 . 0 3 9 0 . 0 3 5 0 . 0 3 0 0 . 0 3 8 0 . 0 3 5 0 . 0 4 6 0 . 0 1 7 0 . 0 3 0 0 . 0 2 7 0 . 0 1 8 0 . 0 0 0 0 . 0 2 0 •Appendix II„ Continued. B. •Data f o r Iron Powder Composites Composite Specimen Composite .U-.T-.S. • Disc. • Number Diameter Yield- Stress p s i Yield-Elong. (in) p s i '(%•) Powder 2 O.O96 . , 2 9 , 7 0 0 , . , 1 .1,41,100 0 ' O.076 2 8 , 5 0 0 45,600. 0 0.073 5 7 , 2 0 0 45,700 0.1 •• 0.061 2 9 , 4 0 0 40,000 ft 0.057 33,600 42,200 • f t o.o46 2 9 , 1 0 0 44,800 ft 0 . 0 5 0 3 3 , 0 0 0 49,400 ,4.2 0.027 3 3 , 5 0 0 48,800 4.1 Powder 3 0 . 0 7 7 3 3 , 1 0 0 46,800 -2..1 0.074 3 2 , 9 0 0 45,800 •. 0 0.071 2 8 , 7 0 0 42,400 ft 0.069 2 9 , 8 0 0 42,600 -1.4 0.063 27,900 .45,400 1.8 0.059 26,200 ^ 3 , 5 0 0 0.8 0.051 34,000 39,960 2 . 9 0.046 30,600 43,500 ,1.0 o.o4o . 3 8 , 0 0 0 ,47,500 3 . 2 0.038 3 3 , 2 0 0 ' .41,800 3 , 0 0.034 3 3 , 0 0 0 45,600 2 . 5 0.028 34,700 :42,300 -ft 0.025 34,700 4 l , 6 0 0 ft ft Discontinuous Y i e l d i n g was present but range over which i t acted could not be c l e a r l y defined. 

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