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The relationship of interfacial energy to graphite shape in the Fe-C system. Hawbolt, Edward Bruce 1964

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THE RELATIONSHIP OF INTERFACIAL ENERGY TO GRAPHITE SHAPE IN THE Fe-C SYSTEM BY EDWARD BRUCE HAWBOLT B.A.Sc, The U n i v e r s i t y of B r i t i s h Columbia, i 9 6 0 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE.DEGREE OF MASTER OF APPLIED. SCIENCE i n 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 Metal l u r g y . THE UNIVERSITY OF BRITISH COLUMBIA August 1964 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of • B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that per.-? m i s s i o n f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood that, copying or p u b l i -c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission* Department of M e t a l l u r g y .The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 8, Canada Date September 4, 1964 ABSTRACT The r e l a t i o n s h i p between surface energy and p r e c i p i t a t e d graphite form i n Fe-C a l l o y s was examined i n t h i s t h e s i s . -Surface tension and contact angle data were obtained using the s e s s i l e drop technique. Carbon saturated, puron i r o n c r u c i b l e s were melted on p y r o l y t i c graphite, the e f f e c t of time, temperature (1500-l600°C) and additions of Niy Mn,.S or Ce being examined. The graphite form;was established.by metallographic examination. An average of H 5 2 dynes/cm was determined f o r the Fe-C al l o y s {h.6$ C) at approximately 1300°C, the average contact angle being .128°. No s i g n i f i c a n t change occurred with additions of.Ni ( 0.85$) and'-Mn ( 1.65$) • Additions of S lowered the surface energy and increased the e q u i l i b r i u m contact angle. Ce additions had a s i m i l a r e f f e c t although a d i r e c t comparison with the Fe-C a l l o y s could not be made as d i f f e r e n t temperatures were used. However, the i n t e r f a c i a l energy diffe r e n c e apparently increased with increasing Ce content, implying an adsorption of Ce to the graphite-melt i n t e r f a c e . The change from the flake to the nodular form was accomplished i n several t r a n s i t i o n stages, the i n t e r f a c i a l energy differences being small, i n d i c a t i n g a marked dependence on the s o l i d i f i c a t i o n and growth conditions. ACKNOWLEDGEMENT The author g r a t e f u l l y acknowledges the advice and guidance given.by Professor W. M. Armstrong throughout the i n v e s t i g a t i o n . .The author i s e s p e c i a l l y indebted-to Mrs. A. M. Armstrong f o r assistance i n i n t e r p r e t i n g and preparing the f i n a l manuscript. Thanks are a l s o extended to R. G. Butt e r s / R. J . Richter and P..R..Musil f o r t h e i r t e c h n i c a l assistance and to fellow graduate students and other f a c u l t y members f o r t h e i r h e l p f u l discussions. F i n a n c i a l support was received from the Defence Research Board o f Canada under Grant No.. 7501-02 and from the Aluminium'Laboratories i n the form of a graduate research fellowship. This support i s g r a t e f u l l y acknowledged. TABLE OF CONTENTS Page •.I. • INTRODUCTION 1 A. .General Discussion of Cast Irons 1 B. Background Theory . . . . . . . . . . . . . . . . . . . . . . . . 2 1..The•Surface Tension Parameter . . . . . . . . . . . . 2 2 . . The Relationship of Surface Energy to P r e c i p i t a t -ing Form 3 3 . The E f f e c t of Solute Additions on I n t e r f a c i a l Energy k C. .Review of Previous:Work 6 1 . . Surface Tension Measurements 6 - 2 . S o l i d i f i c a t i o n of a Hypereutectic Iron . . . . . 9 a. . E f f e c t 'of. A l l o y Additions . 1 2 b. .Effect of Cooling Rate on Structure . . . . . 1 3 3 . S o l i d i f i c a t i o n of a Hypereutectic Nodular Iron . 1*4-^..Relationship Between I n t e r f a c i a l Energy and Graphite Form . . . . . . 1 6 D. S e s s i l e Drop Technique . . . . 1 7 E. Choice of System and Aim of Investigation . . . . . . . 1 9 I I . EXPERIMENTAL . . . 2 2 • A.. Materials Used . . . . 2 2 B. • Apparatus . . 2k C. Experimental Procedure 2k I I I . RESULTS . 2 7 continued... .Table of Contents C o n t i n u e d . . . Page A . S e s s i l e Drop Resul ts 27 1. Basic Iron-Carbon A l l o y . . . . . . . . . . . . . . 27 2 . . E f f e c t of Ni and Mn-Additions . . . . . . . . . . . .JO : 3 . . E f f e c t of Sulphur A d d i t i o n s 30 A..Effec t of Ce A d d i t i o n s . . . . . . . . . . . . . 32 B. Resul ts of Meta l lographic Examination . . . . . . . 36 1. Fe-C A l l o y .36 2 . E f f e c t of N i and'Mn A d d i t i o n s . . 38 3 . . E f f e c t of Sulphur A d d i t i o n s 38 k. E f f e c t of Ce A d d i t i o n s .. hi C .• Thermodynamic C a l c u l a t i o n s . . . . . . . . . . . . . . . . 52 I V . DISCUSSION AND CONCLUSIONS . . 55 V . RECOMMENDATIONS FOR FUTURE WORK . . . . . . . . . . . . . 6 l V I . APPENDICES . 6 2 V I I . REFERENCES . 79 LIST OF FIGURES Figure . Page 1. a. Keverian's Data Showing Versus A c t i v i t y S . . . . . . 8 b.. Kozakevitch's Data Showing the E f f e c t of S and C on l^^y* 8 2. Fe-C E q u i l i b r i u m Diagram 10 3 . .Graphite Development i n a Hypereutectic A l l o y 11 4 . S t a b i l i t y of Graphite.Versus Fe 3C as Affected by Cooling Rate . .13 5 . Graphite Form a's Related'to .Specific-Areas'in. the Fe-C Diagram 15 6. Growth C h a r a c t e r i s t i c s of a Graphite Nodule . . . . . . . . . .16 7. Outline of S e s s i l e Drop . . . . . . . . . 18 8 . .Forces Present at the Drop, Interface .. . .18 9. Apparatus 25 10. Fe-C Data Showing the E f f e c t of Time and Temperature on the Contact Angle 29 11. Comparison of the Wetting C h a r a c t e r i s t i c s of an Fe-C A l l o y and Pur on Iron J>0 12. Drop Silhouettes Showing the Effect- of S Additions . . . 31 13. Silhouettes of Drop. Containing Ce 33 14. E f f e c t of. Increasing Temperature on the Ce A l l o y Contact Angles . J>k 15. General-Structure of Fe-C Drops 37 16. C r y s t a l s Remaining on Base Plate i n Fe-C Test .38 17. Structure of the Fe-C-Ni A l l o y -. 39 18. Structure of the Fe-C-Mn A l l o y , 40 • 19. Structure of the High S A l l o y s kl 2 0 . Structure of the Low S A l l o y s .. k2 21 . Shrinkage of a 0.05$ Ce A l l o y 43 2 2 . Structure of a Low-Ce A l l o y 46 L i s t of Figures Continued. Figure Page 23. Structure of a 0.0k wt.fo Ce A l l o y . V7 2k. Structure of a O.O5 wt,$ Ce A l l o y .kg •25. • Structures of the Master A l l o y s 51 26. Structure of P y r o l y t i c Graphite 66: • LIST. OF TABLES Page Table I. Analyses of Materials Used 23 Table I I . "Y 's and-Contact Angles f o r the Fe-C A l l o y s .... 28 * • LV Table I I I . The Change i n Y with * 0 . 0 1 " V a r i a t i o n i n the 0 LV z. Parameter . . . . ...... . ... . . . . ... ... .28 Table IV. ^ > s and Contact Angles f o r the Fe-C-S A l l o y s . . 32 • J_iV Table V. tf-Lv'3 a n d Contact Angles f o r the Fe-C-Ce A l l o y s . . Table VI. I n t e r f a c i a l Energy Cal c u l a t i o n s . . . . . . . . . . . .35 Table VII. Probe Scan Results f o r Fe-C-Ce A l l o y . . . . . . . . . . 4 5 Table V I I I . Spectrographs Ce Analyses on Top and' Bottom of Drop Sample kQ Table IX. Average Analyses of A l l o y A f t e r Test . . . \.1 . . . . 50 LIST OF'APPENDICES Page I. .-ExperinenteADifficulti.es and' Errors Inherent i n the S e s s i l e Drop: Approach . . . . . . . . . . . . . . 62 I I . Production and Properties of P y r o l y t i c Graphite . . . 65 I I I . S e s s i l e Drop Data . . . 67 IV. S t a t i s t i c a l Analysis of Three Fe-C Tests . . . . . . . 73 V. Cooling Rate Considerations . . . . . . . . . 76 I. INTRODUCTION A. General Discussion of Cast Irons Cast irons comprise a large group of Fe-C a l l o y s with carbon i n the range 1.7 to 6.7 wt..$. In the s o l i d i f i e d alloy, the carbon may occur as a.carbide or as free graphite. Moreover, the graphite may assume a v a r i e t y of forms. Since the p h y s i c a l properties of a composite material are strongly, dependent on i t s microstructure both the shape and d i s t r i b u t i o n of the r e l a t i v e l y weak, dispersed graphite phase are of major s i g n i f i c a n c e i n determining the f i n a l strength c h a r a c t e r i s t i c s of a cast i r o n . The microstructure i s dependent on the carbon content, the a l l o y and impurity content, the cooling.rate during and a f t e r f r e e z i n g and the conditions of heat treatment. While the general e f f e c t s of these variables on the r e s u l t i n g microstructure are w e l l known, the d e t a i l s of the formation and growth mechanisms operating are s t i l l not completely, understood. • The most pronounced change in. the shape of the graphite phase i s from the fl a k e form of grey i r o n to the spheroidal form of nodular i r o n . In the production of nodular or d u c t i l e i r o n a spheroidizing agent, e i t h e r Mg as a NiMg or FeSiMg a l l o y , o r Ce as mischmetal (an a l l o y of rare earths containing 50$ Ce) i s added to a grey i r o n composition following.tapping of the melt from the furnace. The;, graphite i n the s o l i d i f i e d a l l o y i s thereby changed from a flake to a spheroid with an accompanying increase i n strength and d u c t i l i t y . This change i n graphite shape has been r e l a t e d to an increase 1 2 3 i n the graphite-melt, i n t e r f a c i a l energy ' ' . • I t i s the r e l a t i o n s h i p between the surface energy and the. resulting, graphite form which w i l l be examined i n t h i s t h e s i s . - 2 -B..Background Theory k 1. .The- Surface Tension Parameter The most general approach to v a r i a t i o n s of the free energy, of a homogeneous hulk phase can be considered i n terms of the following basic thermodynamic r e l a t i o n s h i p : dF = - SdT + VdP + <^,M± dnj_ where dF i s the change i n the. Gibbs free energy S i s the entropy T i s the absolute temperature V i s the volume P i s the pressure JJL^ i s the chemical p o t e n t i a l of component i n-j_ i s the number of moles of component i In a two phase system a surface of separation w i l l be present and thus an a d d i t i o n a l energy term w i l l be required. This a d d i t i o n a l energy i s associated with the change i n the surroundings of the surface atoms. A 5 simple but d e s c r i p t i v e p i c t u r e of a metal surface has been proposed by U h l i g . It i s considered to be apportion of the l a t t i c e where atoms have fewer than the usual number of nearest neighbours. . The strength of each interatomic bond must therefore be greater. Since the strength per bond.is d i r e c t l y associated with the degree of a t t r a c t i o n of the atoms, the c h a r a c t e r i s t i c -atomic radius or the distance of c l o s e s t approach must be l e s s . . I t i s the r e s t r a i n t of the parent l a t t i c e to t h i s tendency f o r cl o s e r approach that gives r i s e to what i s c a l l e d surface tension (\/ ). To increase the area of a surface by an i n f i n i t e s i m a l amount, . dA, at constant T, P and composition, these bonds must be stretched and the work required i s ydA. Thus the surface free energy change can be written: s s s • ^ s * dF = -S dT + V dP + s/ dA + J>_ d ^ ^   ^-JU and at constant T, P and n^ 2> s or the surface free energy/unit area and the surface tension are i d e n t i c a l i n the l i q u i d , leading to the dimensions of ^being. dynes/cm, i.e., force/unit length or ergs/cm 2, .i.e., energy/unit area. 2 . The Relationship of Surface Energy to P r e c i p i t a t i n g Form It i s known that nucleating•shapes can be c o n t r o l l e d or at l e a s t 6,7 modified by variations' i n the i n t e r f a c i a l energy 8 9 Turnbull and Turnbull and Fisher have derived the following t h e o r e t i c a l expressions f o r the rate of homogeneous and heterogeneous nucleation i n the s o l i d i f i c a t i o n of a r s o n s component system: 3 I v •= K y exp [ ( ^ ) 2 . k T ] .3 . ' -a V f ( Q ) , and ..IS = K s exp k T 3 where I v and I g are the rates of homogeneous and heterogeneous nucleation r e s p e c t i v e l y , ^ e i n " t e r f a c i a l energy between.the s o l i d i f y i n g c r y s t a l and the parent l i q u i d ^ i s the free energy change per u n i t volume for. the t r a n s i t i o n of the l i q u i d to the s o l i d , a i s the constant dependent on the nucleus shape, f(9) i s a function of the eq u i l i b r i u m contact angle between the nucleus and the nucleating phase ( f o r heterogeneous nucleation), ft In most developments .V ^ 0 since :the i n t e r f a c e ' i s assumedplanar.. - k -K y and K s are constants dependent on the nucleus shape, surface area of the c r i t i c a l nucleus, free energy of a c t i v a t i o n f o r transport of an atom from the l i q u i d t o the c r y s t a l , temperature of the system, etc. These r e l a t i o n s h i p s i l l u s t r a t e the s i g n i f i c a n c e of the i n t e r -f a c i a l energy with respect to the rate of nucleation. The number of growing n u c l e i i s dependent on the rate of nucleation which i n turn i s 6 associated with the degree of undercooling . .It i s s p e c i f i c a l l y these two properties, the number of growing n u c l e i and the degree of undercooling, which may a f f e c t the rate of growth and hence the shape of the s o l i d i f y i n g form. The i n t e r f a c i a l energy i s thus an important parameter when considering changes i n the shape of a p r e c i p i t a t i n g material. . Although the nucleating form i s c o n t r o l l e d by such thermodynamic parameters as the i n t e r f a c i a l energy, the f i n a l shape observed i s a l s o dependent on the growth conditions following nucleation. Although the s o l i d - l i q u i d i n t e r f a c i a l energy i s the parameter of i n t e r e s t , i t s direct:.. experimental determination i s not possible at t h i s time. The best approach to the problem.can only indicate the d i r e c t i o n and magnitude of changes in.the i n t e r f a c i a l energy due to additions of various elements. 3. The E f f e c t of Solute Additions on I n t e r f a c i a l Energy Solute atoms can change i n t e r f a c i a l energies by p r e f e r e n t i a l l y adsorbing on the i n t e r f a c e i n question. I f the interatomic forces are such that the solute element i s rejected.by the matrix atoms, the solute.may become p r e f e r e n t i a l l y concentrated at the surface of the m a t e r i a l - hence the term, surface active element. The r e s u l t i n g excess surface concentration - 5 -would change the surface tension of the a l l o y . Thus those elements that e x h i b i t a p o s i t i v e deviation from Raoult's law should be surface active to varying degrees. The t h e o r e t i c a l approach to excess surface concentrations and the r e s u l t i n g e f f e c t on the i n t e r f a c i a l energy-makes use of Gibbs Adsorption 10 Theory . .For a binary a l l o y t h i s has the general form where d.-Y' i s the change i n the' i n t e r f a c i a l energy PL i s the excess . i n t e r f a c i a l concentration of component i dpi i s the change i n the chemical p o t e n t i a l of component i This reduces to r* - -H. at a.chosen i n t e r f a c e p o s i t i o n where the excess concentration of the solvent atom, i s zero. By replacing,the chemical p o t e n t i a l jixx by RT In a^, the s i m p l i f i e d form of the adsorption equation i s obtained P - : RT 3 l n a 2 where a 2 i s the . ^ a c t i v i t y of component 2 R i s the gas constant T i s the absolute temperature Where the solute obeys Henry's law the mole f r a c t i o n may be used i n place of the a c t i v i t y , i . e . f a = - C 2 ^ Y RT £ C 2 . where C 2 i s the mole f r a c t i o n of component 2. - 6 -Since i t i s possible to determine experimentally the d i r e c t i o n • and magnitude of change.of the i n t e r f a c i a l energy, i.e.^ d ^ ; i t i s also possible to determine whether surface adsorption i s occurring. Thus the conditions present at the i n t e r f a c e can be examined and r e l a t e d to other properties,, i n t h i s thesis, the p r e c i p i t a t i n g form. C. • Review of Previous Work Since l i t t l e work.has been done i n which surface energies are r e l a t e d to the graphite form,. i t i s necessary to consider the.two i n i t i a l l y as separate parameters. This section w i l l deal f i r s t with the surface tension data reported f o r Fe-C alloys,, including, the e f f e c t of various a l l o y i n g elements, and secondly-with the graphite form and i t s r e l a t i o n s h i p to composition and s o l i d i f i c a t i o n conditions. . The t h i r d and f i n a l section w i l l review, the data reported i n which graphite form and surface energy have been r e l a t e d . 1. Surface.Tension Measurements Considerable interest.has recently been directed to obtaining surface tension values f o r materials of e i t h e r high p u r i t y or p r e c i s e l y known composition. This, has been necessitated by the poor r e p r o d u c i b i l i t y of the e a r l y work. .Quantitatively comparable data i s now obtainable due to the appreciation of the marked e f f e c t of minor concentrations of,surface active materials. The e f f e c t of minor elements i s e s p e c i a l l y important i n i r o n and i t s a l l o y s since two of the major contaminants are S and 0, both of which are very surface a c t i v e . Only, that data recently reported w i l l be considered, as good r e p r o d u c i b i l i t y i s attained. - 7 -I t has been shown that the surface tension of Fe-C a l l o y s i s independent of the carbon concentration over the range 0 to 4.5 w t . ^ 2 , ^ ~ ^ . • : 13 Dyson ^ has established that sulphur additions lower the y ^y of l i q u i d i r o n and predicts. 1920 dynes/cm f o r the ^ ^y of sulphur-free, pure i r o n i n agreement with published values f o r pure i r o n and i r o n -" 2,11,12,14 carbon a l l o y s . Although carbon i s not surface active i n pure Fe-C alloys, i t s presence does influence the y ^ . o f Fe-C-S a l l o y s . To compare the r e s u l t s .2 of several i n v e s t i g a t i o n s Keverian p l o t t e d the ^ versus a c t i v i t y of sulphur as shown i n Figure l a . •Although'the e f f e c t of carbon on the S a c t i v i t y 15 i s not evident i n t h i s p l o t , Figure l b . shows the data, of Kozakevitch p l o t t e d i n a s l i g h t l y , d i f f e r e n t manner clearly, i l l u s t r a t i n g ' t h e e f f e c t of the carbon. -Additions to i r o n of elements which are not surface active,.. such as N i , produce a change.in the surface tension of the a l l o y as a l i n e a r f u nction of the atomic per cent of the a l l o y i n g , a d d i t i o n " ^ . 17 Kaufman and Whalen have reported y values f o r ternary Fe-1.5$>C-Ni a l l o y s having a wide range of Ni additions. The carbon had l i t t l e e f f e c t on the change of " ^ L V with Ni additions. A s i m i l a r e f f e c t i s expected f o r Fe-C a l l o y s containing small additions of Mn. No quantitative r e s u l t s have been published concerning the e f f e c t 18 of Ce additions on the surface tension of pure i r o n . However, Minkoff has predicted a decrease i n ^ L V with additions of Ce. I t i s a well established f a c t that Ce i s a strong sulphide former and with additions of Ce to i r o n 2 19 containing S, the primary a c t i o n of the Ce i s to remove the sulphur ' . - 8 -0.0001 0.001 0.01 c. ACTIV ITY oi S U L F U R Figure l a . Comparison of Surface Tension Data With Respect to S A c t i v i t y (Keverian ) Effect of Sulfur on the Surface Tension of Liquid Iron-Carbon Alloys at 1450°C (2642°F). Sulfur, w/o Figure l b . Kozakevitch's'Data Showing the E f f e c t of C and S, (Kozakevitch^) -9 -p Keverian has shown that additions of Ce to an i r o n containing sulphur cause an increase i n ^ y . 2. • S o l i d i f i c a t i o n of a ;.Hypereutectic Iron An extensive review., of the s o l i d i f i c a t i o n and g r a p h i t i z a t i o n •20 PI of cast irons has been compiled by Boyles ,,Morrogh and Williams and 22 25 Loper and Heine > . -Although t h i s t h e s i s deals .with the simple Fe-C system i n the hypereutectic C range containing only minor additions of S, Ni,-Mn and Ce and not a.cast i r o n , the s o l i d i f i c a t i o n c h a r a c t e r i s t i c s are very s i m i l a r ^ . .The'main a d d i t i o n to the Fe-C system to produce a,cast i r o n i s S i , the major e f f e c t of which i s to create a range over which the eutectic s o l i d i f i e s and to s t a b i l i z e the g r a p h i t i c form of carbon. .Figure 2 . . i l l u s t r a t e s - t h e Fe-C phase diagram and contains the eq u i l i b r i u m , . s o l i d i f i c a t i o n conditions f o r both the graphite and the Fe 3C system. • In cooling a hypereutectic l i q u i d below the l i q u i d u s temperature proeutectic graphite (kis'h graphite) forms i n the melt. With decreasing temperature t h i s form w i l l develop and may. f l o a t to the surface due to , 2k i t s lower s p e c i f i c g r a v i t y . At the eu t e c t i c a r r e s t temperature a.eutectic of austenite and graphite s o l i d i f i e s on a-spheroidal c r y s t a l l i z a t i o n front c a l l e d a e u t e c t i c c e l l . These c e l l s are generally nucleated.by the k i s h graphite already present. .The ends of the growing,flake graphite remain i n contact with the surrounding l i q u i d . . The sequence of development i s shown i n the sketches of Figure 3. ATOMIC PERCENT CARBON - 11 -K i s h Graphite L Melt J ~l K i s h M Graphite with Austenite Above E u t e c t i c Arrest E u t e c t i c Graphite with Austenite Just Below. E u t e c t i c Arrest J - Figure 3. Graphite.Development-Above and Below the Eut e c t i c A r r e s t On completion of the eut e c t i c s o l i d i f i c a t i o n the structure consists of i r r e g u l a r k i s h graphite flakes and smaller eutectic flake graphite, the matrix being austenite. With decreasing temperature to the.eutectoid, the s o l u b i l i t y of carbon i n austenite decreases producing some proeutectoid graphite which i s usually, deposited on.the flakes already present. Below the eutectoid temp-erature, the austenite decomposes to e i t h e r C>(, plus graphite or ^  plus Fe 3C, depending on the r e l a t i v e s t a b i l i t i e s of the two systems. Generally the Fe 3C transformation i s predominant as the d i f f u s i o n rate of carbon i s r e l a t i v e l y low at-these temperatures. No observable changes occur as the structure i s cooled to room, temperature. Increasing, the cooling rate produces a f i n e r , randomly oriented eutectic graphite, type D i n the A-.S..T.M. Graphite Form D e s i g n a t i o n ^ . - 12 -a. E f f e c t s of A l l o y Additions, on the Graphite Form i . Sulphur Garber and Williams have reported that increasing the sulphur content to 0.028 wt..$ increases the size and. amount of the primary flake graphite and decreases the amount of undercooled D-type eutectic graphite. A coarse flake existed at 0.028 and p e r s i s t e d as the predominant.form up to 0.1 wt.$>. A t r a n s i t i o n from flake to mesh to compact aggregate to free carbide occurred with increase i n the sulphur content up to 0.6 wt.$>. While observing the e f f e c t of S additions, Garber a l s o noted a carbon deposit on the surface of the ingots, increasing i n amount with increasing S. He interpreted t h i s e j e ction.of carbon from the melt as being a surface phenomenon i n which graphite was not wetted by the melt. 20 ..Boyles has shown.that sulphur i s concentrated i n the eutectic l i q u i d during-the formation of the primary dendrites (hypoeutectic iron) and during f r e e z i n g of the e u t e c t i c i s further concentrated i n the eutectic c e l l boundaries. This sulphur i s f i n a l l y p r e c i p i t a t e d as FeS inclusions..' i i . .Manganese 27 Williams has shown that increasing the manganese content of Fe-C a l l o y s increases the tendency f o r the structure to s o l i d i f y white. , T . . ,28 .111. .Nickel S o l u b i l i t y of carbon i n molten i r o n i s lowered as the nickel.content i s increased, 0.2$> f o r a kfy Ni a d d i t i o n . An increase occurs i n the eutectic temperature, 25°F f o r a h'jo Ni addition,. reducing the tendency f o r the. e u t e c t i c to s o l i d i f y with Fe 3C as the stable phase. - 13 -N i c k e l i s r e a d i l y soluble i n s o l i d i r o n , enlarging the temperature-composition range i n which austenite i s stable. This r e s u l t s i n a lowering of the c r i t i c a l transformation temperature of austenite,. about kO°F f o r ' each <$> Ni added. It i s d i f f i c u l t to discuss the e f f e c t s of s p e c i f i c additions when explaining the cast i r o n - s t r u c t u r e . . I t s u f f i c e s to say that the observed microstructure;' i s a r e s u l t of the s p e c i f i c composition and cooling rate of the a l l o y . b. . E f f e c t of Cooling Rate on Structure 29 Morrogh has g r a p h i c a l l y i l l u s t r a t e d the e f f e c t - o f cooling rate on.the r e l a t i v e s t a b i l i t y of the austenite-graphite, austenite-Fe 3C transformation (Figure h). Below this temperature white iron . can solidify 'p- Temperature of solidification of white iron C O O L I N G R A T E Figure k. Relative S t a b i l i t i e s , of the Graphite and Carbide as Affected By the Cooling Rate (Morrog - With increasing cooling rates the temperature at which the graphite eutectic forms becomes progressively lower. In Figure k, 1X corresponds to the e q u i l i b r i u m cooling conditions below which the y - g r a p h i t e . t r a n s i t i o n occurs, whereas below -T 2, t h i s being the melting point of the white i r o n - Ik -e u t e c t i c , the ^-Fe 3C w i l l predominate. . Increasing the cooling, rate causes the e u t e c t i c t r a n s i t i o n temperature to follow a-curve of form XU. At a cooling rate and transformation temperature equal to W, white i r o n w i l l be the eu t e c t i c second component.• . With a furt h e r increase i n the cooling rate the eutectic s o l i d i f i c a t i o n temperature decreases slightly-according to WZ. The tendency f o r an i r o n to s o l i d i f y white i s a l s o a f f e c t e d by the composition - S i and Mn increase.: t h i s tendency while Ni decreases i t . In a d d i t i o n , superheating w i l l cause a melt to undercool thereby increasing the Fe 3C s t a b i l i t y . 3. S o l i d i f i c a t i o n of a Hypereutectic Nodular Iron Since no information i s a v a i l a b l e on the e f f e c t of adding Ce to a pure Fe-C a l l o y , i t i s necessary to r e s t r i c t our discussion to an Fe-C^Si a l l o y . ..When Ce i s added to such a melt, small graphite n u c l e i appear above the l i q u i d u s temperature, t h e i r presence having been established 22 2^5 5^0 ^ 51 by r a p i d quenching te s t s ' ' ' . ..These n u c l e i have only been observed i n irons i n which the graphite p r e c i p i t a t e s i n the spheroidal form. .Loper and Heine c have developed a schematic representation of the temperature range of nucleation and growth f o r the various graphite forms (Figure 5). • With decreasing temperature the n u c l e i develop into l a r g e r spheroids. These are separated from the l i q u i d by a t h i n s h e l l of austenite. The iiiickness of t h i s s h e l l remains constant up to the eu t e c t i c s t a r t temperature , although the nodules grow i n s i z e . Over the eutectic s o l i d i f i c a t i o n range the nodule siz e continues to increase as does the surrounding a u s t e n i t i c s h e l l . - 15 -2000 1500 G R O W T H T E M P E R A T U R E R A N G E t SPHEROIDS J f L A K E SHAPES F I L M , L A C Y , COMPACT 2 0 J O P E « C I N T C A R B O N 40 Figure 5- . Nucleation Range of the Various Graphite Forms (Loper and Heine^ 2) For growth of the nodule to continue, carbon must d i f f u s e through the austenite s h e l l and i r o n must d i f f u s e i n the opposite d i r e c t i o n . With increasing s h e l l thickness the d i f f u s i o n time increases, impeding growth. The d r i v i n g force necessary f o r the reaction to proceed i s supplied by a decrease i n the temperature. . Such a s o l i d i f i c a t i o n process requires a greater eutectic s o l i d i f i c a t i o n - r a n g e , being approximately twice that f o r a comparable grey . 22 iron •Although some nodules remain dormant during the e u t e c t i c s o l i d i f i -c a t i o n no s a t i s f a c t o r y explanation has been developed to explain t h i s e f f e c t . - Subsequent cooling below.the eutectic to the eutectoid generally r e s u l t s i n p r e c i p i t a t i o n of the excess carbon on the graphite present. I t has often been reported that supercooling i s a requirement f o r 1 j the formation of spheroidal graphite ' . However, i n the experiments previously discussed, the graphite nodules were present above the e u t e c t i c s o l i d i f i c a t i o n temperature and thus were not associated with supercooling. The widening of the eutectic s o l i d i f i c a t i o n range i s a r e s u l t of and not the cause of s o l i d -i f i c a t i o n i n the spheroidal form. - 16 -32 Morrogh has i l l u s t r a t e d the development c h a r a c t e r i s t i c s of a nodule, as shown i n Figure 6. Figure 6. Growth C h a r a c t e r i s t i c s of a Graphite Nodule (Morroglr ) The nodule i s e s s e n t i a l l y a r a d i a l development of the b a s a l plane of the 33 hexagonal graphite . k. Relationship Between I n t e r f a c i a l Energy and Graphite Form The change from the flake to the spheroidal form has been r e l a t e d 2,3,18 to an increase i n the graphite-melt i n t e r f a c i a l energy . I t i s thought that such an increase would necessitate a higher d r i v i n g force f o r s o l i d i f i -p cation to occur, acting as a b a r r i e r to nucleation. Keverian showed that Ce additions to an Fe-C-S a l l o y increased the surface tension, r e f l e c t i n g the desulphurizing power of Ce. However no associated increase i n the graphite-melt i n t e r f a c i a l energy could be determined. Such an approach implies that nodular graphite i s r e l a t e d to supercooling. This could not account f o r the presence of n u c l e i above the eutectic temperature. - 17 -•D. S e s s i l e Drop Technique It i s obvious that i f one wishes t o - e s t a b l i s h the interface conditions present during g r a p h i t i z a t l o n , one must examine the graphite-melt i n t e r f a c e . • However, i t i s not possible t o measure d i r e c t l y the surface energy of such an i n t e r f a c e . Using.the techniques a v a i l a b l e one i s able, at best, to determine the d i r e c t i o n and magnitude of change of t h i s parameter. The approach used i n t h i s work i s r e l a t e d to the shape of a l i q u i d drop resting.on an i n e r t base plate.- This i s known as the s e s s i l e drop technique and permits evaluation of the surface tension of the l i q u i d , y and the contact angle through the dropj0. The experimental d i f f i c u l t i e s and errors inherent i n t h i s approach are outlined i n Appendix I. The shape of" a l i q u i d drop on a h o r i z o n t a l , i n e r t surface i s determined by the balance between the surface tension which attempts to create a s p h e r i c a l drop, i . e . , the lowest surface area/unit volume, and the g r a v i t a t i o n a l force which t r i e s t o lower the p o t e n t i a l energy of the mass by f l a t t e n i n g the. l i q u i d . The equation of the s e c t i o n a l outline of such a drop i s a second order d i f f e r e n t i a l which has been numerically solved to four places of decimal by Bashforth and Adams-^. By use of t h e i r tabulated solutions i t i s possible to determine Y^y a n ( ^ ^ e c o r r t a c " t angle 0. It i s necessary to measure1 the parameters x, x 1, z , z 1 shown i n Figure 7 . From these parameters and Bashforth and'Adams' tables, two further parameters, jit and b can be obtained (as shown i n the thesis of 35 D. J. Rose ) from which Figure 7- The S e s s i l e Drop Parameters of Interest For Y and 0 Determination LV - 19 -Y = g d b 2  a LV /5 m2 where g i s the g r a v i t y constant d i s the density m i s the magnification of the drop.from.which the parameters were taken and 0, the i n t e r i o r contact angle, can be determined. The f a c t that both YIN a*id.0 can be measured as independent parameters is. a d i s t i n c t advantage i n t h i s experimental procedure. By applying the values obtained fory^y and 0, and changes in-these values, to Young's Equation, Y = Y - V" cos 0 ..LS *SV "LV t h i s being a balance of the h o r i z o n t a l components of the surface forces shown i n Figure 8^ and by.having a knowledge of,, or by making c e r t a i n assumptions f o r ^ gy, the d i r e c t i o n and magnitude of change of YsL c a n be determined. E. Choice.of System and Aim of Investigation The complexity- of commercial cast i r o n s " r e s t r i c t s t h e i r use i n any, fundamental i n v e s t i g a t i o n . To reduce the many composition variables i t i s necessary to examine simple binary,.or at most, ternary a l l o y s . To study g r a p h i t i z a t i o n therefore, the pure Fe-C binary i s the obvious choice. However, as t h i s system may contain the metastable carbide i t i s a l s o necessary to employ conditions which ensure the s t a b i l i t y of the free graphite form. This was accomplished by. a i r cooling the carbon saturated puron i r o n i n a reduced pressure of 10 5 mm Hg. Since changes i n the primary graphite shape were to be r e l a t e d to the graphite-melt i n t e r f a c i a l energy present during g r a p h i t i z a t i o n , i t was necessary to maximize•these changes to ensure t h e i r detection. The t r a n s i t i o n from the flake to the nodular form was thus examined. - 2 0 --•It has been reported, that a nodule occurs at an ea r l y stage i n i t s growth i n contact with the melt, and i s a r a d i a l development of the basal plane of the hexagonal graphite system. - Thus, to determine the i n t e r f a c i a l conditions present during the formation of a nodule, the graphite basal plane-melt i n t e r f a c e had to be included i n the system under in v e s t i g a t i o n . P y r o l y t i c graphite i s composed of p a r a l l e l , misoriented-layers 36 of the graphite basal plane-' . Thus by melting Fe-C binary a l l o y s on a p y r o l y t i c graphite p l a t e the melt-graphite basal plane i n t e r f a c e could be studied. To ensure that no reaction occurred at t h i s i n terface •y complying with those conditions necessary f o r the s e s s i l e drop a p p l i c a t i o n , the Fe-C a l l o y s were carbon saturated. In addition, since i t was necessary that the energy parameters be obtained during g r a p h i t i z a t i o n , the a l l o y had to contain a greater amount of carbon than that required f o r saturation at the melting temperature. Thus, the binary Fe-C a l l o y was saturated with C at 1 5 0 0 ° C and quenched from t h i s temperature t o r e t a i n the carbon content. Since i t i s only possible to determine the d i r e c t i o n and magnitude of change of the s o l i d - l i q u i d i n t e r f a c i a l energy i t was necessary to make solute additions to the basic a l l o y . .The elements Ce,- S, Ni and Mn were chosen f o r the following reasons: .- Ce was employed as the spheroidizing agent to e f f e c t the change from the fl a k e to the nodular form. - Sulphur additions were made since the presence of, or rather the removal of sulphur has been associated with nodule formation. - N i c k e l and manganese were used, because both are sulphide formers, although much weaker than Ce, and both are generally present i n commercial cast^ i r o n s . - 21 -The o r i g i n a l plan was to study the e f f e c t of sulphur additions and additions of sulphur plus Ce, Ni or Mn on the surface energy and graphite form. However, preliminary experiments indicated that the examination of additions of the single elements to the Fe-C system would be more p r o f i t a b l e . - 22 -I I . EXPERIMENTAL ^. • Materials Used S e s s i l e drop experiment were conducted, using carbon-saturated puron i r o n as the basic a l l o y , Ce, S, Ni and Mn as addition agents, and p y r o l y t i c graphite as the base p l a t e . The Fe-C a l l o y was prepared by induction heating puron iron, i n a spectrographic grade graphite c r u c i b l e to 1500°C i n a vacuum of 1 0 " 5 mm Hg. This temperature was held f o r 10 minutes to ensure completion of the reaction, the power was shut o f f and the sample was allowed t o co o l . Crucibles 0.25" X 0.20" were machined from t h i s a l l o y , the bottom surface being bevelled to ensure an advancing i n t e r f a c e upon melting, and the center being d r i l l e d to hold a l l o y additions. Drops of approximately 0.5 gms were obtained by t h i s procedure. Master a l l o y s were prepared to ensure better c o n t r o l of the add i t i v e s . Ni and Mn master a l l o y s were prepared from 99-9$ metals,, these being added to puron i r o n and melted under 10~ 5 mm pressure i n spectrographic grade graphite c r u c i b l e s . The Ce master a l l o y was prepared using 99-9$ Ce and puron i r o n , the melting being c a r r i e d out i n a sealed spectrographic grade c r u c i b l e , held under s i m i l a r vacuum conditions. The S master a l l o y was prepared by heating puron i r o n i n a spectrographic grade graphite c r u c i b l e to 1050°C under a flow of H 2S. The analyses of the materials used and the master a l l o y s prepared are reported i n Table I. P y r o l y t i c graphite base plates 5/8" X 5/8" were cut from - 3 / l 6 X k X 5" sheets supplied by the General E l e c t r i c Laboratories. D e t a i l s con-cerning the production and properties of p y r o l y t i c graphite are recorded i n Appendix I I . TABLE I. Analyses of Materials Used and Alloys Prepared M a t e r i a l or A l l o y A l .Cr Cu Ce Fe Mg Mn Mo Ni .Si T i V C S Faron Iron ft 0.005 0.0008 <0.002 N.D. - Matrix <6.0008 <0.002 <0.002 <0.004 <^0.001 0.0005 0.002 0 . 0 6 8 < 0 . 0 1 0.0005 <0.0001 0.0004 <0.02 Matrix 0.0001 <0.0005 0.001 0.0008 0.0003 0.002 0.001 0.082 ( 0 . 0 1 Spectrograph!' c Grade Graphite 0.0005 <0.0001 used f o r molds 0.0004 < 0 . 0 2 f o r preparing a l l o y s : 0.1 0.00005^0.0005 0.0008 0.0002 0.0009. 0.005 0.002 Matrix ^ 0 . 0 1 Fe-C A l l o y 1 0.0002^0.0001 0.0008 <"0.02 Matrix 0.0002 <0.0005 0.001 0.0008 0.0003 0.003 0.001 5-4 < 0.01 Fe-C A l l o y 4 0.0002<0.0001 0.0006 <'0.02 Matrix 0.0001 (0.0005 0.002 0.03 0.02 0.002 0.002 5.49 < 0 . 0 1 Fe-C A l l o y 5 O.OOOJ^O.0001 0.001 <0.02 Matrix 0.0003 <Co.0005 0.002 0.01 0.01 0.003 0.001. 5-57 < 0 . Q 1 Master A l l o y s Fe-S Fe-C-Ce Fe-C -Mn Fe-C-M 18.0 IO.87 42.3 5,7 0-53 5.25 5.20 0.034 P y r o l y t i c Graphite 0.0008<p.0001 0.0008 0.00005 0.0001 <0.0005<(0.002 0.0002 0.0005 0.00005 ^0.0005 Matrix 0.01 ft Analysis supplied with material, others being obtained from Coast Eldr i d g e Engineers. A l l m e t a l l i c s not l i s t e d were undetected. ro 1 - 2k -B. Apparatus The s e s s i l e drop experiments were conducted i n the induction •' apparatus described i n d e t a i l i n a thesis by D. J . Rose^. A molybdenum susceptor 5/8" X 0.005" X 3" was suspended i n the center of a 65 mm O.D. vycor tube. The samples were placed i n the center of the susceptor, no r a d i a t i o n shields being required. - A Lepel (Model T-10-3) high-frequency induction generator supplied the power to the furnace and temperatures were measured at ^5° to the furnace a x i s . A Hartmann and Braun disappearing filament o p t i c a l pyrometer was employed, the readings being taken through a mirror which could be rotated i n t o p o s i t i o n between the end of the furnace and the photographing lens. By comparing these temperatures with values simultaneously obtained using a W-WRe thermocouple f i t t e d i n t o the p y r o l y t i c graphite sample a temperature c o r r e c t i o n of + 55° w a s observed over the temperature range of i n t e r e s t . A vacuum of 10 mm Hg was maintained f o r a l l of the t e s t s . The drop shape was recorded using a. B e l l and Howell 8 mm movie camera combined with a lens assembly which permitted photographing the complete image at the f i l m size and at a distance of about 2 l / 2 f e e t . The apparatus including the v e r t i c a l c o i l employed to prepare the master a l l o y s i s shown i n Figure 9-C. Experimental.Procedure Experiments of 20 minutes duration were conducted, the e f f e c t of time a f t e r melting, temperature and a l l o y a d d i t i o n being recorded. a n d contact angle data were obtained from p r i n t s of the projected images magnified approximately 10.times. - 25 -Figure 9. Equipment Used f o r A l l o y Preparation and S e s s i l e Drop Experiments 26 -The graphite form was obtained from polished sections of .the s o l i d i f i e d drops - the samples were mounted i n 828 epon and polished with 6 fi. and 1 p. diamond paste. Much care was exercized i n handling the materialsto avoid contamination. The base plates were rinsed i n acetone, dipped into concentrated HC1, washed, i n al c o h o l and drie d just p r i o r to t h e i r use. During and a f t e r washing, a l l materials were handled by metal tweezers. A s i m i l a r cleaning cycle was followed f o r the i r o n c r u c i b l e s . When additions were made, the material was placed i n the c r u c i b l e following the cleaning-schedule, the c r u c i b l e diameter and weight was recorded, the materials then being placed i n the experimental apparatus. When a vacuum of 1 ji was obtained, a p i c t u r e was taken f o r magnification determination and hydrogen gas was introduced to the system. . This f l u s h i n g was repeated several times to ensure the removal of any gaseous contaminants. A pressure of 500 mm of Hg was f i n a l l y held and the materials were heated to red heat,, the ensuing hydrogen f l a s h i n g removing the surface oxides. The system was then pumped down to 10~ 5 mm Hg and the temperature was slowly increased to the melting point of the a l l o y (fc£ 1280°C). Photographs were taken at t h e . s t a r t . o f melting and p e r i o d i c a l l y , through the heating c y c l e , the time being recorded. • A l l samples were quenched from l600°to ensure s i m i l a r cooling conditions and hence comparable microstructures. Analyses of the s o l i d i f i e d drops were obtained to guard against any serious contaminations occurring during the experiment. - 27 -I I I . RESULTS •A. S e s s i l e Drop Results . 1.. Basic Iron-Carbon A l l o y ... 1 The parameters x, z, x x and z were obtained from the enlarged negatives and the surface tensions and contact angles were determined, the r e s u l t s being l i s t e d i n Appendix-III. Density values were obtained by 38 considering the drop to be >C saturated at each temperature and using the 39 reported r e l a t i o n s h i p between temperature, density and carbon concentration The average and contact angle f o r the Fe-C alloy-is•shown i n Table I I . An estimation of the standard d e v i a t i o n - f o r three t e s t s i s a l s o included to i l l u s t r a t e the range of r e s u l t s i n any. one t e s t , the c a l c u l a t i o n s being included i n Appendix IV. The e f f e c t of time and temperature on the contact angle i s i l l u s t r a t e d . i n Figure 10. Only those 0 values f o r temperatures le s s than 1345°C are p l o t t e d since above t h i s temperature s i g n i f i c a n t wetting of the base occurred, as shown i n the photographs included i n Figure 10. As the contact angle approaches 90° i t becomes v i r t u a l l y , impossible to obtain the desired z parameter. Surface tensions were only determined from high angle drops f o r t h i s reason, the equilibrium angle f o r temperatures up to 1345°C being s u f f i c i e n t to permit the parameter measurement. No consistent v a r i a t i o n of Yjjj- with time or contact angle change was observed,-the. data being a v a i l a b l e i n Appendix I I I . Table III i l l u s t r a t e s the pronounced e f f e c t of ± 0.01" v a r i a t i o n i n the z parameter on the r e s u l t i n g "Y^y Figure 11. shows the wetting c h a r a c t e r i s t i c s of puron i r o n at li+15°C as compared to carbon saturated puron i r o n at 1400° and l600°C. - 28 -TABLE.II. Average Surface Tension and. Contact Angle of the Fe-C, • Fe-C-Ni and Fe-C-Mn A l l o y s Exp. Average ± 1 <T No.. of Temp. Approx. No. o'r.v Calculations °C Eq u i l i b r i u m (dynes/cm) Averaged Angle Fe-C A l l o y s 14 1163 150 29 1325 126 19 1074 116 26 1325 128 20 a) S t a t i s - 1079 120 20 1280 -t i c a l .b). E f f e c t 1064 10 1280 -of Time 27 1206 5 1290 132 28 1197 4 1335 122 29 1234 4 1345 129 35 1116 7 1335 12'9 I I 5 2 Max. 957 to 105 1290 to 128 Average Spread 1307 1345 Fe-C-Ni A l l o y (O.85 wt...# Ni) . ^5 1135 8 1285 118 Fe-C-Mn A l l o y (I . 6 5 wt.# Ma) 1261 8 1330 127 .TABLE I I I . E f f e c t of * 0.01" V a r i a t i o n i n the x and z Parameters on V LV e.g.. Seq 1^380 of Experiment 20 x/z ^ L V x z V a r i a t i o n (dynes/cm) I.O65 O.977 1.090 1021 _ z + 0.01" I.O65 O.987 1.079 1153 + 132 z - 0.01" I.O65 O.967 1.101 900 - 121 - 30 -Figure 11. Wetting C h a r a c t e r i s t i c s of a) Fe-C at l600°C 0^90° ( l e f t ) b) Fe-C at l400°C Q ~ 115° c) Puron i r o n at l 4 l 5°C 0 C=75° (right) 2. E f f e c t of Ni and Mn Additions Although separate Ni and Mn additions were made, 0 to 0.85$> Ni and 0 to I .65 wt.$ Mn, no s i g n i f i c a n t changes i n V of"0 were noted, the data pertaining to the maximum additions being reported i n Figure 10 and Table I I . 3. E f f e c t of Sulphur Additions The surface tension and contact angle were d i f f i c u l t to obtain f o r these a l l o y s . With the ad d i t i o n of sulphur, the s o l u b i l i t y of graphite i n ir o n i s decreased. The excess graphite was p r e c i p i t a t e d out on the surface of the drop thereby d i s t o r t i n g the true drop parameters. Although i t was known that sulphur had t h i s e f f e c t on carbon i t was thought that the excess graphite would p r e c i p i t a t e onto the primary graphite present within the structure. Figure 12 i l l u s t r a t e s the e f f e c t of sulphur on the drop s i l h o u e t t e , plate c) showing the sectioned drop and the act u a l drop parameters as compared to the graphite outline noted i n plate b). In t h i s case parameter measurements were taken from the s o l i d i f i e d drop and an approximate surface tension was calculated. This surface graphite p r e c i p i t a t i o n i s no doubt the same carbon deposition noted by G a r b e r ^ i n h i s sulphur experiments. - 31 -Figure 12. E f f e c t of Sulphur on Drop S i l h o u e t t e - Experiment 12 a) At melt ing b) A f t e r carbon p r e c i p i t a t i o n c) Same sample sect ioned to show o u t l i n e of drop w i t h respect t o surface g r a p h i t e . D i f f i c u l t y was a l s o experienced i n g e t t i n g the sulphur i n t o s o l u t i o n i n the b a s i c Fe-C a l l o y before v a p o r i z a t i o n of the FeS master a l l o y , the p a r t i a l pressure of a l l sulphur forms over FeS at 660°C being O.58 atmospheres-^7, No b a s a l at tack i . e . ? a d h e r e n c e cf the drop to the p l a t e , was noted f o r those a l l o y s which e x h i b i t e d surface graphite p r e c i p i t a t i o n . This e f f e c t was used t o determine whether sulphur had been d i s s o l v e d i n t o the Fe-C a l l o y , and ^ c a l c u l a t i o n s were only made on those t e s t s which showed no b a s a l a t tack . Table IV contains the V values f o r four tes ts which obviously contained some sulphur . The table includes the amount of sulphur added, the per cent sulphur analysed i n the drop, the contact angle , and the average p r o p e r t i e s of the Fe-C a l l o y . Since i t was not p o s s i b l e to reproduce a given sulphur concentrat ion and since sulphur contents of l e s s than 0.01 wt.$> could not be analysed the values cannot be q u a n t i t a t i v e l y compared to K e v e r i a n ' s data . However, a decrease i n ^j^y a n d an increase i n 0 w i t h i n c r e a s i n g sulphur i s observed, consis tent w i t h K e v e r i a n ' s f i n d i n g s . - 32 -TABLE IV. E f f e c t of Sulphur Additions on V • LV and Contact Angle. Experiment Number wt.ft S added wt.# S analysed Average ^ L V Equilibrium 4 12 1.86 0.022 338 (only an approximat i on) 165 36 0 .30 <b.oi 801 141 38 0.01 <0.01 1115 152 39 0.035 <0.01 891 145 Average Pe-C Data - < 0 . 0 1 1152 128 4 . E f f e c t of Ce Additions ' Upon melting the c r u c i b l e containing the Ce a l l o y a d d i t i o n , complete s o l u t i o n of the a d d i t i o n d i d not occur. Instead some p o r t i o n of i t . f l o a t e d on the apex of the molten drop, i t s siz e decreasing with increasing temperature. Silhouettes from Experiment 31 a r e included i n Figure 13 and show the e f f e c t of increasing temperature. This surface material acts as an a d d i t i o n a l force tending t o f l a t t e n the drop hence changing t h e ^ ^ y observed. . L i t t l e change was noted i n the contact angle with increasing temperatures up to l600°C,•Figure lk. Because a high angle was maintained, i t was po s s i b l e to determine surface tensions at the higher temperature where extraneous surface force was minimized. 1 The r e s u l t s are reported i n Table V. To check the e f f e c t of the extraneous force.; a drop to which 0.04 wt.$> Ce had been added was melted and the shape parameters recorded. This same drop was taken from the system, the surface deposit was removed - - 3 4 -145 Legend:. Experiment 3 1 ( 0 . 0 5 # C e ) Experiment 3 2 ( 0 . 0 1 # C e ) - © -Experiment 3 3 ( 0 . 0 0 5 ' / 0 C e ) - Q -H bo X. 4 1 3 5 140 -p | ISO o ° 125 —1300 o { X X IQ \%oo 1600 I Temperature (°C) Figure 1 4 . Contact Angle Versus Temperature f o r Ce Tests TABLE V. - E f f e c t of Ce Additions on V and 0 Q LV Exp. No. wt.$ Ce Added ..wt.$ Ce Analysed Temperature Range °C Average y LV 0 3 0 0 . 0 5 0 . 0 5 "bottom 0 . 0 2 top 1 4 4 5 - 1 6 2 0 6 1 1 140 3 1 0 . 0 2 5 0 . 0 5 1 3 0 5 - 1 6 3 0 8 1 3 1 3 8 5 2 0 . 0 1 < 0 . 0 2 1 5 2 0 - 1 6 4 5 7 5 4 1 3 7 3 3 0 . 0 0 5 0 . 0 3 1 3 1 5 - 1 6 5 0 8 7 6 , . 1 3 8 . 48 0 . 0 5 0 . 0 5 1 3 0 5 - 1 4 0 5 864 1 5 6 5 0 0 . 0 4 not analysed I6O5 5 5 7 1 3 6 5 1 0 . 0 4 0 . 0 5 bottom 0 . 0 2 top 1 6 0 0 6 7 0 . 1 3 9 • and the t e s t was repeated. . The data-obtained i s included in-Table V, Experiments 5 0 and 5 1 - I n experiment 5 1 & symmetrical drop shape was not obtained u n t i l a temperature of 1 5 5 0 ° C was reached, i n d i c a t i n g that complete remelting.did not occur below t h i s temperature. - 3 5 -Although the Ce data was c a l c u l a t e d over a wide temperature range no consistent change with increasing temperature was noted. Average i n t e r f a c i a l energies and changes i n t h i s parameter (neglecting the temperature e f f e c t ) are reported i n Table VI. TABLE VI. Average I n t e r f a c i a l Energy Changes A l l o y Average (dynes'/cm) 0 YlS ^SV ^LV cos (180-0) I n t e r f a c i a l Energy Difference ft Fe-C I I 5 2 128 709 basis of comparison Fe-C-Ni 1135 118 533 - 176 , Fe-C-Mn 1 2 6 l 127 758 + if'9 Fe-C-S Exp. 12 ( 0 . 0 2 2 ^ ^ 3 3 8 165- 326 - 383 Exp. 36(<0.01 wt.# s) 801 . 141 622 , - 87 Exp. 38(<0.01 wt.# S) 1115 152 1033 + 324 Exp. 39(<0.01 wt.f0 S) 891 145 •730 + 21 Fe-C-Ce Exp..30 (-0.05 wt.$ Ce) 611 14.0 468 - 241 Exp.,31 (0.025 vt.# Ce)8l3 138 604 - 105 Exp. 32 (-0.01 wt.$ Ce) 754 137' 550 - 159 Exp. ,33. (-0.005 wt-$ Ce)876 138 650 - 59 Exp. 50 (-0.04 wt.$ Ce) 557 136 401 - 308 Exp. 51 (-0.04 wt,$ Ce) 67O 136 506 - 203 ft Neglecting.temperature effects.. and assuming no change i n ^Qy' : - 36 - ; B. . R e s u l t s of M e t a l l o g r a p h i c Examination of the S o l i d i f i e d Drops 1. Fe-C A l l o y A wide range of primary g r a p h i t e forms p e r s i s t e d over the r e l a t i v e l y s m a l l volume of the drop. The top e x h i b i t e d a l a r g e amount of w e l l developed primary g r a p h i t e , w h i le the bottom of the drop contained a compact form of primary g r a p h i t e , and a much f i n e r D-type e u t e c t i c g r a p h i t e . The general s t r u c t u r e i s i l l u s t r a t e d i n Figure 15. The compact gr a p h i t e does not have the smooth surface of a nodule. Instead, i t resembles the center of a r o s e t t e . . The primary graphite has acted as the n u c l e i f o r the e u t e c t i c graphite p r e c i p i t a t i o n , e x p l a i n i n g the l a r g e g r a p h i t e - f r e e regions surrounding the k i s h f l a k e s . • P l a t e c) shows the f l a k e s which have developed at the i n t e r f a c e , the base a c t i n g as the n u c l e a t i n g agent. . These f l a k e s are e s p e c i a l l y w e l l developed when the drop i s h e l d at the m e l t i n g temperature. The drops adhered to the base p l a t e even when s o l i d i f i e d from the m e l t i n g temperature and the i n t e r f a c e appeared very i r r e g u l a r . This would i n d i c a t e that some b a s a l a t t a c k was o c c u r r i n g . To check t h i s e f f e c t a sample was melted, h e l d f o r : l / 2 hour at t h i s temperature, then allowed t o s o l i d i f y . . Upon removing the drop from . the base, s m a l l m e t a l l i c c r y s t a l s remained on the p l a t e s u r f a c e , as shown i n Figure 16. These c r y s t a l s were analyzed u s i n g powder X-ray techniques and. found t o be e i t h e r r ^ - i r o n or a mixture of - i r o n and Fe 3C - the only • h i g h i n t e n s i t y l i n e f o r Fe 3C i s 2.01A°as compared t o 2.02 A 0 f o r the highest i n t e n s i t y , l i n e ofcA-iron. .Upon examining the drop, p e a r l i t e was present at the i n t e r f a c e . The s t r a i g h t l i n e s noted on the c r y s t a l surface were thought t o be cleavage steps. - 37 -Figure Pp. Fe-C Drop - Experiment Ik a) Structure near apex of drop X 150 b) Etched i n N i t a l X kOO c) Base region of drop X 150 d) Interface C h a r a c t e r i s t i c s X 400 - 38 -Figure 16. M e t a l l i c C r y s t a l s Remaining on Base Plate A f t e r Removal of Fe-C Drop X 210 Some well developed primary flakes were also present at the drop i n t e r f a c e i n d i c a t i v e of the nucleating p o t e n t i a l of the base and the occurrence of primary g r a p h i t i z a t i o n at the melting temperature. 2. E f f e c t of Ni and Mn Additions Figures 17 and 18 i l l u s t r a t e the structure of the 0.85% Ni and 1.65$ Mn a l l o y s r e s p e c t i v e l y . A graphite d i s t r i b u t i o n s i m i l a r to that of the Fe-C a l l o y i s noted, although the graphite i s s l i g h t l y coarser i n both instances. 3. E f f e c t of Sulphur Additions The graphite form changed markedly with even small additions of sulphur. In the a l l o y s containing 0.039$ sulphur and 0.022$ sulphur the graphite flakes were very large extending to the graphite covered surface with no D-type eutectic graphite being noted. F i gure 17. Structure of Drop Containing 0.85$ Ni a) Top of drop X I5O b) Etched X kOO c) Bottom region of drop X 1 5 0 e) Bottom region of drop X 4 0 0 - Uo -Figure 18. Structure of the 1.65$ Mn Drop a) Top of drop X 150 b) Top etched X kOO c) Bottom of drop X 150 d) Interface X kOO -kl -Figure 19. Structure of High Sulphur A l l o y s a) 0.039$ sulphur showing the large f l a k e s , no D-type eu t e c t i c graphite and free carbide i n the p e a r l i t i c matrix X 100 b) 0.022$ sulphur showing the large flakes and compact graphite forms X kOO c) Top of drop b) showing the large flakes extending to the surface and free carbide i n matrix X kOO d) Bottom of same drop showing the very i r r e g u l a r surface of the drop, the C£l80° contact angle and the graphite form. X 35 - k2 -Figure 2 0 . Structure of A l l o y Containing from. 0.005 to 0.01$ S a) Large flakes present near bottom of drop and D-type eut e c t i c graphite X U00 b) Etched showing the a s s o c i a t i o n of the l a r g e r flakes with quenched l i q u i d (carbide). X kOO c) Center of drop showing the f l a k e and compact graphite, the p e a r l i t i c matrix and the c e n t r a l free carbide X 35 d) Bottom of drop, showing the compact graphite X kOO - k} -A compact graphite form was also present, the general structure f o r the two a l l o y s being depicted i n Figure 19. Figure 20 shows the structure of an a l l o y containing less than 0.01 wt.$ sulphur but more than the sulphur l e v e l of the basic Fe-C a l l o y -no wetting or adherence to the base plate being observed and the drop surface being darkened by the presence of graphite. The large flakes were again noted and were located near the base of the drop as shown i n plate a) and. plate b). The upper region of the drop contained a compact graphite form and D-type eu t e c t i c graphite as shown i n plage c ) . A sharp t r a n s i t i o n existed between the flake and compact form and the massive free carbides, as depicted i n plate d). The v a r i e t y of graphite forms noted indicates pronounced sulphur segregation,However, the small si z e of the drops prohibited any a n a l y t i c a l check. k. E f f e c t of Ce Additions When Ce additions were made, the general form of the quenched drop was quite d i f f e r e n t . The surface collapsed i n c e r t a i n areas i n d i c a t i v e of the greater shrinkage associated with the nodular graphite, the surface of an a l l o y containing 0 .05 wt.$> Ce being depicted i n Figure 21 . Figure 21 . Collapsed Surface of Drop Containing 0.05 wt.$ Ce - kk - . . The small button of material apparently not soluble i n the molten drop, was examined a f t e r quenching. The surface was brownish i n c o l o r and upon sectioning and p o l i s h i n g the center was found to contain small i n c l u s i o n s , as shown i n Figure 2k plate b). Since these di d not have the same color or form as the graphite i n the adjacent drop i t was thought that they were sulphide i n c l u s i o n s , , e x p e c i a l l y since the primary a c t i o n of a spheroidizing agent i s the removal of sulphur as a sulphide. The sulphides being l e s s dense would f l o a t to the top. To check t h i s p o s s i b i l i t y the sectioned sample was placed i n the e l e c t r o n probe and a Ce scan was conducted. Table ..VII shows the data obtained and comparative figures f o r the 0.5 wt.$> Ce master a l l o y and the basic Fe-C a l l o y ^ Although i t was hoped that any Ce segregation within the drop could be determined by use of the probe, the small d i f f e r e n c e i n the count rate between the 0.5 wt.$> Ce master a l l o y , the Ce-free Fe-C a l l o y and the range of r e s u l t s obtained f o r any one p o s i t i o n indicated that the concentration d i f f e r e n c e s expected would be undetectable. A small surface button was crushed and examined using X-ray powder techniques. Only the l i n e s were noted. This i s explainable as the amount of material i s very small and the i n c l u s i o n s are contained i n the i r o n matrix. As i n the a l l o y s previously,examined, a wide range of graphite shapes p e r s i s t e d across the drop volume. The structure offour samples w i l l be considered in d e t a i l as these depict the range of shapes observed. - 45 -TABLE VII. -Probe Analysis on Section of A l l o y Containing 0.05 wt.$ Ce (Beam current 0.09 ^ i a , 20 kv,.Reading the Ce Lg l i n e at 7 1 . 6 ° ) - P o s i t i o n on Sample Counts/min. Average Near top of drop 94, 104, 85, 70, Sk, 80, 72, 64, 85, 95 84 Center of drop 84, 99, 107, 86, 98, 100, 81, 79, 75, 84 89 Near base of drop 101, 93, 85, 84, 71, 103, 96, 92, 85, 93 90 Top deposit on drop 1159, 606, 500, 800, 761 765 Fe-C A l l o y (No Ce addition) 103, 90, 102, 84, 87, 92, 100, 95, 86, 89 93 Fe-C-Ce Master A l l o y - (0.5 wt.# Ce) 157, 1^0, 171, 159, 138, 161, 135, 1^3, 129, 150 148 Figure 22 i l l u s t r a t e s the structure of a 0.005 wt.$ Ce a l l o y (analysed 0.03 wt.$). Plates a) and b) show the graphite at the top of the drop, plate c) the t r a n s i t i o n from the flake through the dense rosette to the f i n a l nodular form present near the base of the drop, arid p l a t e d.) the nodules and round-tipped graphite flakes present at the i n t e r f a c e . The matrix i s p e a r l i t e , showing up as white a f t e r l i g h t p o l i s h i n g , f r e e carbides being d i s t r i b u t e d throughout. Figure 23 shows the structure of a 0.04 wt...$ Ce a l l o y (analysed average 0.02 wt.$, 0.02 on top, 0.05 on bottom). More graphite i s present near the top of the drop. The s t a r - l i k e rosettes, p l a t e s a,), b) and c ) , decrease i n number i n progressing towards the base of the drop, plate d). Some dense nodules were present at the lower boundary of the rosette forms, plates e) and f ) . The graphite i n the lower region was sparsely d i s t r i b u t e d , - 46 -Figure 22. Graphite Structure of Experiment 33 (0.005 wt.$ Ce added, analysed 0.03$). a) Top of drop X 35 (the white intermediate region i s p e a r l i t e ) b) Top of drop X 400 c) Center to bottom of drop X 35 d) Interface X 400 - ^7 -Figure 23. Structure of A l l o y Containing Ce (0.04 wt.$ added^analysed 0.02 top - 0.05 bottom) a) Top of drop X 35 b) Top of drop X k00 c) Top of drop etched i n 2$ N i t a l X 35 d) Side of drop showing t r a n s i t i o n region X 35 e) Graphite i n t r a n s i t i o n region X 400 f ) Structure etched i n N i t a l X 400 - kQ -spheroidal i n form, and surrounded by a s h e l l of transformed austenite, plate f ) . . Figure 2k shows-the structure of a 0.05 wt.$ Ce a l l o y . .Plate a) depicts the heavy concentration of nodules at the top. of the drop, Plate b) shows the sulphide i n c l u s i o n s present i n the undissolved material at the drop apex. Place c) and plate d) represent the graphite shapes present i n the c e n t r a l region of the drop, with plate e) i l l u s t r a t i n g the sparsely populated base region and the l a y e r of transformed austenite associated with-the drop periphery. The graphite form contained within t h i s l a y e r i s shown i n plate f ) . This layer i s a l s o present'in the base region of Figure 23, again accompanying the dense nodules. .In Figure 2k, where the nodules are poorly developed, no p e r i p h e r a l l a y e r of transformed austenite i s present. A l l three drops were quenched.from approximately l600°C and thus should have experienced the same cooling rates. Since i t was not possible to check Ce. segregation i n the quenched drop by the probe technique, 5 mg samples of cuttings were taken from the top and bottom of two drops and analysed . spectrographically. Table VIII records the concentration differences observed. TABLE VI I I . -Ce Concentration at Top and Bottom of Drop Experiment wt Ce wt.$> Ce Number Added Analysed  30 0.05 0.02 top O.O5. bottom 51 . 0.0k 0.02 top 0.05 bottom - 4 9 -• , - e a) Top of drop X 35 1 ."9*. *. Figure 24 Structure of 0,05$ Ce a l l o y (0.05 added, analyzed 0 . 0 5 , 0 . 0 2 top and 0.05 bottom) b) Sulphide inclusions i n surface button X 400 c) Graphite form i n t r a n s i t i o n region X 400 d) Structure c) etched i n N i t a l X 400 ie) Structure of lower drop showing the compact graphite and the outer layer of transformed austenite x 150 f) Graphite i n the outer l a y e r X 400 - 50 -•An average f i n a l analyses of the drops i s shown i n Table IX. • TABLE. IX. Average•Spectrographic Analyses A f t e r Test A l Cr Gu Mg Mn . Mo Ni S i T i V 0.0002 0.0001 0.0006 0.0002 0.0005 0.003 0.02 0.02 0.0Q2 0.002 To permit comparison of the s t r u c t u r a l changes associated with major a l l o y additions, the structures of the master a l l o y s are shown i n Figure 25. The master a l l o y s can be compared as the cooling rates are s i m i l a r . The Fe-C (5.0$ C) a l l o y i s depicted i n plate a), coarse primary graphite, some compact graphite, and D-type eu t e c t i c graphite being noted. The Ni a l l o y (10.87 $Ni, 5.2$ C) i s shown i n plate b), a much coarser graphite flake being observed and only small regions of p e a r l i t e contained i n the matrix. The Mn (18.0$ Mn, 5.25$ C) a l l o y i s i l l u s t r a t e d i n p l a t e c ) . .The carbide s t a b i l i z i n g power of the Mn i s evident when examining t h i s structure. .The Ce master a l l o y (O.53 $ Ce, 5.7$ C) i s shown i n plate d). Several large, dense nodules have developed. However, i n general the nodules are very small and w e l l d i s t r i b u t e d throughout the carbide matrix. Some carbon deposition on the small nodules has occurred as a s h e l l of transformed austenite surrounds each nodule. . These cannot be considered as n u c l e i f o r t h i s reason. The sulphur master a l l o y i s not included as i t was a .eutectic mixture of FeS and FeS 2 and hence contained no free graphite. - 51 -- 52 -C. • Thermodynamic Cal c u l a t i o n s Because the surface tension of the Fe-C a l l o y s i s markedly af f e c t e d by oxygen contamination, i t was necessary, to determine the per UO cent oxygen expected i n the melt under the conditions employed. E l l i o t t has examined the equ i l i b r i u m reaction [ C ] F e + [ 0 ] i n F e ^ C 0 ( g a s ) and has shown that the equilibrium oxygen content at l600°C i s approximately 0.0065$ a"t carbon saturation at 1 atmosphere pressure ( e s s e n t i a l l y CO)... This was determined from the reaction: 1/2 o2 ^— [oL . _ ' f i n Fe & F ° = -27,930 - O.57 T = -28,998 (at 1600°C). The oxygen p a r t i a l pressure was determined from UO - l o g P02 at 1 atmosphere t o t a l pressure = I5.2 P02 = 6.3 x io" 1 6 From A F ° = - RT In o f , F e [POs] 1/ 2 r n l = 0.00006 L 0 J $ i n Fe Corr e c t i n g this, using:the a c t i v i t y c o e f f i c i e n t of oxygen i n carbon saturated i r o n at 1600°C (c) -2 i . e . , l o g f 0 = I X 10 0 i n Fe = = 0.006 wt. $ Repeating t h i s c a l c u l a t i o n f o r a lower pressure, i . e . 0.01 atm.CO - l o g P02 at carbon saturation i s approximately 19 from - 53 -extrapolation of E l l i o t t ' s data .'• l og [OL . „ = ' - 6 J . 2 $ i n Fe and using ' f Q = 10 , 70 0::.in carbon saturated iron = 1 0 " 4 ' 1 2 = 7.6 X 1 0 " 5 In the system i n • this: thesis; the pressure was maintained at 10~ 5 mm or 1 0 " 8 atmospheres. The equilibrium concentration of oxygen i n the melt would thus be expected to be very low. The p a r t i a l pressure of oxygen associated with molybdenum oxide was calculated as follows: M o 0 2 ( s ) ^ M O ( s ) + 0 2 ( g a s ) 4 1 , A F ° = 137,000 - .39.4 T at 1600°C = 63,200 1 -8 . . P0 2 = 4.17 X 10 atmospheres Since some FeO may be introduced to the system the associated p a r t i a l pressure of oxygen was a l s o determined. FeO,, . ^ = Fe. + l / 2 0 2 41 '(1) *ST- " ( i ) • ^ " 2 ( g a s ) A F ° = 56,830 - 11.94 T at 1600°C = 34,430 . . - P0 2 = 0.3 X 10 atmospheres. Since i t i s believed that CeS i s formed with Ce additions to the Fe-C a l l o y the thermodynamics of t h i s reaction was checked. The reaction of i n t e r e s t i s : ... C(, .$ i n C saturated Fe) ' + .... 'S.<(.$ i n C saturated Fe)"^ •;. C e S(pu.re) - 54 -The following free energy equations have been used: 39 a) Ce s + 1/2 S 2 g CeS a J y AF° = -133,400 ••+ 20T b) Ce g — ^ Ce 39 1 = 2200 - 2.0 T c) Ce, ^ Ce / r f . „ x ; v . 1 (% m Fe) . Assuming an i d e a l s o l u t i o n f o r lack of appropriate data A F ° = RT In O.5585 = -11C0.T C 140.13 d) 1/2 S 2 S,, . . ; ' ^ g ^ ($ i n Fe) AF° = -.31,520 + 5.27 T 5 9 ^ F° f o r the formation of cerium sulphide from the elements in-.an i r o n melt = A F° - 4 F £ - A F ° - ^ F ° = -104,080 +27.7 T Thus i n an i r o n a l l o y at l800°K (1527°C) A F ° = -5^,080 c a l . a n d -6.57 l o g K = 6.57. I f s o l i d CeS i s present, [$Ce][$S] = 10 . Thus i n an i r o n a l l o y i n which excess Ce (beyond that required to form CeS) i s present, tne f i n a l S a c t i v i t y w i l l be extremely low. .For example, i n a l i q u i d i r o n containing 0.005$ S and 0.05$. Ce, the excess Ce concentration w i l l be approximately 0.03yo. I f , as already assumed, Ce forms an i d e a l s o l u t i o n with , - 5 . 0 5 i r o n , the eq u i l i b r i u m S a c t i v i t y (1$ standard s t a t e ) , w i l l be 10 .The e f f e c t of C saturation on the a c t i v i t y c o e f f i c i e n t of Ce i n d i l u t e s o l u t i o n i n l i q u i d i r o n i s not known and therefore i d e a l i t y must be assumed. . Under the same conditions of C saturation l og f i s about 0.7 s 6 and the equilibrium :S concentration i n the a l l o y w i l l be of the order of 10 f - 55 -•IV. DISCUSSION AND CONCLUSIONS The wide range of values obtained i n any one t e s t i s indicative, of the errors inherent i n the experimental approach and includes the apparatus l i m i t a t i o n s and the a c t i o n of extraneous forces which d i s t o r t the drop form. The greatest single error i s probably r e a l i z e d i n measuring the z parameter. Table I I I shows that a v a r i a t i o n of-.* 0.01" i n t h i s parameter can account f o r a o^y change of * 1J0 dynes/cm, t h i s being approximately the same as the calculated standard deviation. Such a measurement l i m i t a t i o n could a r i s e from a lack of sharp-ness i n the o r i g i n a l negative,. t h i s e r r o r being magnified i n obtaining the desired images. I t i s possible that e l e c t r i c a l l y , induced o s c i l l a t i o n s , mechanical v i b r a t i o n s or movements r e l a t e d to the spreading action could contribute to t h i s e f f e c t . In a d d i t i o n any movements from.the o r i g i n a l p o s i t i o n would a l s o change the magnification. The drop shape could a l s o be d i s t o r t e d by an extraneous force or unsymmetrical wetting a c t i o n . There i s a l s o an inherent d i f f i c u l t y involved i n obtaining the z parameter. Because the Fe-C drops are bonded to the base plate a f t e r cooling from the melting temperature and because the r e s u l t i n g i n t e r f a c e i s quite i r r e g u l a r the p o s s i b i l i t y of a reaction at t h i s i n t e r f a c e a r i s e s . This would a l s o a f f e c t the r e p r o d u c i b i l i t y of the r e s u l t s and require an explanation as the Fe-C a l l o y s were i n i t i a l l y carbon saturated. • The structure of the a l l o y s indicated that primary g r a p h i t i z a t i o n occurred at the melting temperature, l o c a l i z e d , large flakes developing at the i n t e r f a c e . . The upper region i n the drop.contained a heavier, more developed primary graphite. . This was r e l a t e d to a.lower cooling rate and a f l o a t i n g of primary graphite from the basal region. - 56 -Under "equilibrium" conditions a f l u x of carbon atoms i s being transferred between the graphite and the melt. Since i n the lower areas of the drop l i t t l e primary graphite i s present, a f l u x between the. melt and the base p l a t e r e s u l t s . This would account f o r the interface r e a c t i o n even though the Fe-C a l l o y was i n i t i a l l y carbon saturated. Because t h i s reaction does not s e r i o u s l y a l t e r the drop shape and because no a d d i t i o n a l compounds are formed, the s e s s i l e drop, approach i s s t i l l v a l i d . The average for the Fe-C a l l o y s i s i n q u a l i t a t i v e agreement with Kozakevitch's d a t a 1 ^ which predicts a,-; value of 1100 to 1200. dynes/cm f o r a sulphur content of approximately 0.005 wt.$, 4 . 5 wt-.$ C and a temp-erature of l450°C. .However, the s e n s i t i v i t y l i m i t a t i o n b i n the S analyses ( i . e . , values ^ 0.01$ could not be determined) precludes a quantitative comparison. The average contact angle of 128° f o r 1290 to 1335°C compares 2 favorably with a value of 123-° found i n Keverian's work , the difference being a t t r i b u t a b l e to the lower S content of h i s a l l o y s (0.0005$) a n d his. use of a randomly oriented graphite surface. Small additions of Wi d i d not s i g n i f i c a n t l y change the surface energy c h a r a c t e r i s t i c s i n agreement with the data reported,by Kaufman and Whalen 1^ f o r a 1.5$ C a l l o y . This would indicate that no atomic i n t e r -actions occur between the Ni and C atoms. No changes were noted with manganese additions.up. to 1 . 6 5 w t . $ . I t i s not possible to place any emphasis on the sulphur data due to i t s poor r e p r o d u c i b i l i t y . However, the general decrease i n ^ T „ • LiV - 5 7 -and increase i n contact angle with sulphur additions i s i n agreement 2 with Keverian's data and the s t r u c t u r a l changes are s i m i l a r to those reported by .Garber and Williams 1. I t i s generally, believed that the graphite-melt i n t e r f a c i a l energy i s reduced with sulphur additions. In t h i s work i t was observed that the presence of sulphur caused excess carbon to be p r e c i p i t a t e d at the drop surface, although i t was expected that i t would p r e c i p i t a t e , onto the primary graphite already present within the drop. This may indicate an increase i n the graphite-melt i n t e r f a c i a l energy. However, the surface energy data was i n s u f f i c i e n t to t e s t t h i s hypothesis. . The a d d i t i o n of Ce to the Fe-C a l l o y apparently decreased the ^^V" 18 s/ as predicted by Minkoff . However, the Q values were obtained at a higher temperature than the Fe-C values. . Since i t was not possible t o determine the temperature e f f e c t , a true comparison of the values cannot be made. Although s p e c i f i c values cannot therefore be assigned to the i n t e r f a c i a l energy differences t h i s d i f f e r e n c e was noted to increase with increasing Ce content. Such a change indicates that Ce i s being adsorbed to the graphite-melt i n t e r f a c e , a negative change i n ~^^* implying a p o s i t i v e change i n Y*z from: _ I 2 RT C 2 The importance of Ce i n obtaining the nodular form has been established. . The nodules are only w e l l developed i n the lower region of the drop where the Ce content i s the highest. I t i s possible that a flux of Ce atoms i s required to ensure the development of the nodule, t h i s Ce being adsorbed onto the graphite surface. - .58 -Although the inclusions noted i n the "button" remaining on the drop surface could be CeS, the amount observed does not seem consistent with the very low S content of the a l l o y . In a d d i t i o n , the top and the bottom Ce analyses indicated that Ce was only removed from the top of the drop. Since a Ce depletion of i n excess of four times the weight of sulphur i s required to form CeS then sulphur was also only removed from t h i s region, f u r t h e r decreasing the possible volume of CeS. As an a l t e r n a t i v e explanation these i n c l u s i o n s could be r e l a t e d to the small graphite nodules present i n the Ce master a l l o y . The f a c t that the Ce content i s extremely high i n t h i s region would imply that Ce has been p r e f e r e n t i a l l y adsorbed on the i n c l u s i o n s . This would be consistent with the data previously considered. These inc l u s i o n s are.much c l o s e r packed i n the "button" than are thei-nodules i n the master a l l o y . Hence a higher Ce content•would be expected. I t was not possible to d i f f e r e n t i a t e between these two theories as the volume of the i n c l u s i o n s was very small making. X-ray analysis unsuccessful.• I t has been found that the marked change i n the graphite form i n progressing from the top to the bottom of the Fe-C-Ce drops i s associated with a change i n the Ce content. . The structure of the other a l l o y s indicates that the v a r i a t i o n i s p r i m a r i l y r e l a t e d to e i t h e r a high rate of cooling in t h e i n t e r f a c e region or a decrease i n the nucleating p o t e n t i a l of t h i s region r e s u l t i n g i n supercooling. Cooling rate considerations are contained i n Appendix V. Although i t i s not possible to e s t a b l i s h the l i n e s of heat flow i t i s apparent that a higher rate of cooling i n the i n t e r f a c e region i s quite p o s s i b l e . - 59 -Such considerations must a l s o apply to the Ce a l l o y s . I f i t i s accepted that a nodule has a surrounding s h e l l of austenite above the eutectic temperature than the nucleating surface f o r austenite i s already present and hence no e u t e c t i c supercooling would be expected. However as fewer nodules are present i n the basal region i t i s , l i k e l y the com-binations of e f f e c t s which leads to the,f i n e r structures observed. .The contact angle i n the Ce t e s t s d i d not change from 1300 to 1600°C. In the development o f a nodule the graphite i s surrounded by a s h e l l of austenite. I f the experimental analogy i s complete then the base plate-melt i n t e r f a c e i s analgous to the nodule-melt i n t e r f a c e and. hence an austenite l a y e r should develop. Because t h i s i s a s o l i d s h e l l l i t t l e e f f e c t from increasing the temperature would be expected. However, i f the main j u s t i f i c a t i o n f o r the presence of the a u s t e n i t i c s h e l l i s the requirement that an average carbon content.be maintained then a l a y e r of austenite at the i n t e r f a c e would not be expected. In progressing.from the flake to the nodular form, only small changes i n the i n t e r f a c i a l energy were noted. The shape was more dependent on the Ce content and the p o s i t i o n within the drop i . e . , the cooling rate and carbon deposition c h a r a c t e r i s t i c s . . I t i s important to note that t r a n s i t i o n stages e x i s t i n changing from the flake to the nodular form. . This would imply that i t i s not simply a nucleation problem but i s a l s o dependent on the s o l i d i f i c a t i o n conditions. The f a c t that the flakes f i r s t become rounded at the t i p s i s generally associated with a point d i f f u s i o n e f f e c t . The second stage i s a compact rosette shape, t h i s being a fur t h e r increase i n the surrounding area per - 60 -u n i t volume of p r e c i p i t a t e . The f i n a l nodular form has a maximum sphere of influence. ..Such a t r a n s i t i o n does not require a spheroidal n u c l e i . Rather, with increase i n the cooling rate i n progressing towards the base of the drop, the d i f f u s i o n distance of the p r e c i p i t a t i n g carbon i s decreased^a greater sphere of influence and hence greater surface per u n i t volume r e s u l t i n g to permit the carbon deposition. In general.the data i n d i c a t e s that the f i n a l graphite form i s more dependent on the growth conditions than on the i n t e r f a c i a l energies. The i n t e r f a c i a l energy i s probably only of majorvimportance when dealing with the nucleating shape, the. f i n a l form being a r e s u l t of the rates of deposition on the various c r y s t a l faces. - 61 --V. RECOMMENDATIONS FOR FUTURE WORK -A s i m i l a r i n v e s t i g a t i o n using i r o n of a much higher p u r i t y and master a l l o y s having, the. desired compositions would eliminate several of t h e . d i f f i c u l t i e s experienced i n t h i s work. I f drops of approximately two grams were used the r e p r o d u c i b i l i t y would be much improved. The i n c l u s i o n of f a c i l i t i e s permitting.the degassing of the. base plate p r i o r to the t e s t would also a i d i n t h i s respect. Although the s e s s i l e drop technique can y i e l d valuable information a more f r u i t f u l approach would be to study-the growth k i n e t i c s and the development morphology of the various graphite forms. Information of t h i s nature i s required before shape transformations can be completely understood. - 62 -. VI. APPENDICES APPENDIX I. Experimental D i f f i c u l t i e s and Errors Inherent i n the S e s s i l e Drop;Approach Although the sessile- drop technique seems simple, many hazards b e f a l l the unwary. To impart some, appreciation f o r these d i f f i c u l t i e s •k several of the experimental, problems w i l l be b r i e f l y discussed . j.Sample Contamination 1. Sample contamination i s probably the most important single f a c t o r . .Special care must be taken to eliminate any contaminating source. Where oxidation i s a problem, as with i r o n , i t i s necessary to eliminate oxygen from the system and to remove, i f possi b l e , any. oxide contamination from.the material being melted. . Use of a titanium or molybdenum susceptor although-the l a t t e r i s les s e f f e c t i v e , aids i n reducing the oxygen p a r t i a l pressure i n an.induction u n i t . To ensure that no oxide contamination i s present i t may. be necessary to resort to use of an i n e r t atmosphere. However, since the values obtained are only representative of the conditions employed, information from such experiments may. be les s u s e f u l . -Some problems may a l s o a r i s e from contamination of the plate surface by the i n e r t gas. • I f po s s i b l e , i t i s recommended, that the base plate and apparatus be degassed at a high vacuum and at a temperature above that to be.used. This requires that the sample be transportable to the heating section following the degassing operation. . To prevent contamination i t i s a l s o necessary to trap, out d i f f u s i o n pumps and any source of o i l or grease. - 6 3 . -2. Problems Inherent i n the Drop Shape Approach .The drop sample w i l l be i n a state of equilibrium only when i t s vapour pressure i s l e s s than that of the system. However, when the equilibrium vapour pressure of the melt i s greater than the vacuum main-tained by the system, the metal w i l l continuously vaporize. Although such a condition cannot be considered an equilibrium condition,.only a s l i g h t change i n drop dimensions should.result. • I f the equilibrium pressure were s i m i l a r to the vacuum maintained t h i s would not be a serious problem. As i n any wetting experiment, much emphasis i s placed on the cond-i t i o n of the surface and on the p o s s i b i l i t y ' of v a r i a t i o n i n the contact angle when dealing with an advancing as opposed to a receding i n t e r f a c e . • k2 B a r t e l l and Wooley have shown that f o r an advancing.interface the contact angle depends on the previous surface treatment, whereas f o r a receding i n t e r f a c e the angle i s dependent on the c h a r a c t e r i s t i c s of the wetted surface,- both being correct angles f o r the s p e c i f i c conditions i nvolved. The p o s s i b i l i t y that- the contact angle may vary around the drop al s o a r i s e s . . This a f f e c t can be reduced, by taking several measurements around- the. drop. The accuracy of the technique i s a l s o dependent on the volume 1+3 of the drop, t h i s being a function of x/z. Baes and Backs have shown that an optimum range f o r x/z i s 1 . 1 5 "to 1 . 7 - 6k -The greatest d i f f i c u l t y i n obtaining.the desired parameters i s experienced i n determining the distance from the maximum drop diameter to the apex, i.e.,the distance z. . This i s e s p e c i a l l y true f o r small drops having a high surface tension since the shape approaches that of a sphere, and f o r drops having a contact angle approaching 90 • Bashforth has included a technique where by. using successive approximations an accurate determination of t h i s parameter can be made. However, many mathematical manipulations are necessary before t h i s i s a workable solut i o n . 3_ Equipment Design Any errors i n the o p t i c a l system used to record the drop shape w i l l r e s u l t i n poor r e p r o d u c i b i l i t y . This e f f e c t can be minimized by avoiding the need f o r enlargement of the image. Any uncertainty i n the magnification w i l l markedly a f f e c t the r e p r o d u c i b i l i t y since the square of t h i s parameter i s i n v e r s e l y proportional . Image d i s t o r t i o n s may a r i s e due to temperature induced: r e f r a c t i o n e f f e c t s . The magnitude of t h i s e f f e c t can be determined by photographing an object of known size under i d e n t i c a l temperature and pressure conditions. Considering the d i f f i c u l t i e s involved i t i s c e r t a i n l y to the c r e d i t of those i n v e s t i g a t o r s who are able to obtain reproducible r e s u l t s . - 65 -APPENDIX I I . Production and- Properties of P y r o l y t i c Graphite 36,- kk, 45 P y r o l y t i c graphite . l i k e that employed f o r the base pl a t e i s produced by cracking a hydrocarbon gas onto a f l a t surface maintained at approximately 2000°C. .The r e s u l t i n g dense deposit- i s composed of carbon atoms arranged i n two dimensional hexagonal networks aligned p a r a l l e l to the deposition plane. - Adjacent layers e x h i b i t random orientations preventing the material from having the three dimensional c h a r a c t e r i s t i c s of a graphite single c r y s t a l . . This c r y s t a l anisotropy i s t r a n s f e r r e d to the bulk properties of the material, a high e l e c t r i c a l and thermal cond u c t i v i t y being observed f o r d i r e c t i o n s p a r a l l e l to the basal plane whereas the material behaves as an i n s u l a t o r i n the d i r e c t i o n perpendicular to the plane. The macrestructure of a de p o s i t - i s determined by the roughness of the p r e c i p i t a t i n g surface. Growth nucleates at s p e c i f i c l o c a l e s , a r a d i a l type of development ensuing. The end r e s u l t i s the c o n i c a l growth v i s i b l e under p o l a r i z e d l i g h t , the structure of the material used being shown i n Figure 26. The surface of the material has a "pimpled" texture as a r e s u l t of t h i s development. - 66 -Figure 26. Section Through the P y r o l y t i c Graphite Pol a r i z e d l i g h t X 100 - 67 -APPENDIX I I I . S e s s i l e Drop Data Time A f t e r Start Mag., of Temp. x z x1 z1 t ~ fo-ot Melting Photo °C C inches^ .(dynekycm) Fe-C A l l o y Experiment No. 14 at melting 12.88 1325 1.232 1.125 0.893 1.870 791 145 + 1 see. . 1.230 1.150 0.917 1.860 1126 140 + 2 1.235 1.155 1134 + 3 1.240 •1.165 1164 + k 1.235 1.170 1438 + 5 1.242 1.173 0.937 I .865 1379 138 + 6 1.242 1.163 1060 + 7 1.240 1.155 1076 + 8 1.240 1.150 909 + 9 1.247 1.160 0.945 1.863 1103 139 + 10 1.250 1.160 1034 + 11 1.257 1.153 . 916 + 12 1.247 1.170 1248 + 13 . 1.240 1.160 1164 + 14 1.247 1,175 0.972 1.848 1364 135 + 15 1.244 1.165 1164 + 16 1.247 1.170 1295 + .17 1.241 1.150 897 + 18 1.257 1.180 1318 + 19 1.261 1.175 1144 + 20 1.256 1.172 1174 + 21 .1.262 1.183 1.007 1.840 1242 133 + 22 1.250 1.170 .1184 + 23 1.250 1.150 909 + 2k 1.250 .1.170 .. 1184 + 25 1.260 1.163 1.005 1.837 1006 + 26 1.260 1.180 1199 + 27 1.257 1.185 1.015 1.815 . 1405 132 2 min.25 sec. .1.257 1.169 1.073 I .696 1126 127 k min.10 sec. 1335 1.257 1.183 1.068 I .708 1354 126 Experiment No. 19 at s t a r t 11.40 1325 1.030 0.940 721 + 1 sec. 1.035 O.965 O.685 1.635 979 150 + 2 1.030 O.965 1032 + 3 1.030 O.960 970 +4 ' 1.032 O.97O O.702 1.640 1123 148 + 5 1.034 O.965 989 + 6 1.032 O.970 1120 + 7 1.035 0.970 1070 continued. - 6 8 -Time A f t e r S t a r t of Melting Mag., of Photo Temp. °C . X z X 1 t inches") (dynes/cm) 0 . + 8 sec. .  1 1 . 4 0 1325 1.032 O.98O O.695 1.632 1370 146 + 9 1.032 O.93O 1370 •+ 10 1.032 O.965 1031 . + 11 .1.035 O.97O 1071 + 12 • 1.035 O.965 979 + 13 1.035 0.97] 1072 + 1 4 1.035 O.965 994 .+ 15 1.035 0.975 1170 + 16 1.032 . O.97O 1122 + 17 1.035 O.97O 1039 • + 18 1 . 0 4 0 O.97O 1006 + 19 1.035 0.975 0,707 1.630 1167 146 + 20 1.032 O.965 1033 + 21 .i . o 4 o O.965 922 + 22 1.035 O.965 0.720 1.620 979 145 + 23 1.037 O.978 1213 + 24 1.033 O...96O 0.740 -1.695 941 144 2 min.. 12 sec. . 1.035 O.967 0.813 I . 0 7 0 1024 135 3 min..kQ sec. 1.037 0.975 0.861 • I . O 6 3 1150 129 Experiment No..20 (Melting conducted on nucleating surface of plate) + 16 sec. 10.35 1280 1.053 0.975 0.715 1.695 1262 150 + 17 1 . 0 6 8 0.975 964 + 18 1.062 O.988 1231 + 19 I . O 6 5 0.993 1282 . + 20 I . O 6 5 O.98O 0.712 1.675 1052 151 + 21 1.070 O.97O 889 + 22 1.060 O.985 1210 + 23 I . O 6 7 0.977 1002 +: 24 I . O 6 7 0.975 0.710 1.675 971 152 + 25 I . O 6 5 0.973 968 + 26 1.062 O .988 1231 + 27 1.065 0.975 - 993 + 28 1.062 O .983 O . 7 I 5 1.675 1 0 4 4 1 4 9 + 29 I . O 6 5 O .99O 1212 + 30 I.O65 O .985 l l 4 o •+.?1 1 . 0 6 9 - O .98O 1014 + 32. •I.O65 O .978 0.694 1.675 1031 152 + 33 I . O 6 7 0 , 9 8 0 1033 + .34 I . O 6 5 0.977 1021 + 35 I .070 0.973 0.725 I . 6 7 O 917 151 + 42 I . O 5 5 0.955 0.730 I . 6 O 5 917 149 3 min. 1.050 O.967 0.735 I .585 I O 9 8 1 4 8 3 min. 2 sec. •1.050 O.97O 0.735 1.582 1151 147 4 min. .1.050 0.954 O.752 1.570 934 147 4 min.,1 sec. 1 . 0 4 7 O .96O 0.752 1-575 1070 1 4 5 5 min. .1.052 O.962 O .76O 1.570 I O 8 5 145 . 5 min..1 sec. I . O 5 O O.965 0.757 1.575 1071 144 9 min. 1.050 O.957 0.795 1.535 964 l 4 l 9 min. 1 sec. 1.052 O.965 0 , 8 0 0 . 1.550 1036 l 4 o 10 min. 2 4 sec. 1330 I . O 5 5 O.965 • 0 , 8 4 0 1.520 1019 136 continued. - 69 -Time A f t e r Start of Melting Mag. of Photo Temp. . °C X z x 1 L inches') Z± li LV , (dynes/cm c0 ) Experiment No..27 + 20 sec. . 12.90 1290 .1.600 1.445 I . I 6 7 2,385 1200 146 + .30 I . 6 O 7 1.445 I .170 2.380 I I 8 7 146 2 min. 18 sec. . I . 6 O 5 1.455 1.260 2.320 1300 138 3 min.. 48 sec. 1.612 1.454 1.335 2.287 1220 132 5 min..48 sec. I . 6 7 O 1.485 1.467 .2.245 1125 127 6 min. 36 sec. 1375 1.740 I . 6 O 5 1.660 2.090 110 9 min. 42 sec. 1420 1.765 . 1.640 •1.662 2.090 , 111 10 min. 48 sec. 1415 1.757 1.635 1.650 2.090 111 Experiment No. 28 + 1 sec. + :30 1 min. 2 min. 12 sec. Experiment No. 29 + 1 sec. + 48 2 min. 3 min .Experiment No..55 + 20 sec. 2 min. 3 min. 5 min. 7 min. 14 min 30 min 42 sec. 30 sec. 30 sec. 12 sec. 11.04 1335 10.28 1345 I5. .8O 1335 1.285 1.282 1.305 1.327 1.535 1-555 .1.550 1.547 I.589 1.632 1.628 1.622 1,620 1.618 1.615 1.142 1.175 I . . I9O 1.205 1.320 1.355 1.360 1.355 1.480 1.500 1.504 1.490 1.498 504 1.498 Fe-C-Ni (0.85$ Ni) O.885 1.035 1.147 1.197 1.115 1,300 1.355 I .345 1.281 1.361 1.360 1.352 .I.36I 1-357 1.356 I . 9 6 O 1.790 1.720 1.695 2.170 2.060 I .985 1.955 2, 2. •2, 2, 2. 2, 2, 320 275 250 260 265 255 250 1105 1260 1210 1212 1080 1250 1310 1295 1220 1025. 1110. 1010 1100 1210 .1140 150 134 125 122 152 133 129 129 132 131 130 131 129 130 129 Experiment No. 45 + 2 1 sec. 13,52 1285 I .586 1.375 1.279 2.165 87O 139 + 42- 1.610 ,1.435 1.381 2.135 .1129 128 3 min. .I.656 1.490 .1.505 • 2,000 • 1321 120 4 min. .1.655 1.485 1.535 2.-005 1274 118 6 min. .1.659 1.485 1.542 2.010 1232 117 8 min. 1.662 1,490 1.547 2.005 1258 118 •12,2 min. 1.687 1.470 1.565 2.010 942 118 19 min. 1.675 1.480 1.555 I .985 1051 118 continued. 70 Time A f t e r S t a r t -Mag., of Temp. of Melting Photo °C z x J (inches !> (dynes/cm) Fe-C-Mn ( 1.65$ Mn) Experiment- No... 43 1 min..24 sec. 12.02 1295 1.810 1.587 1.365 2.515 1302 145 5 min.,50 sec. 1.847 1.595 1.545 -2.435 1205 133 6 min. I .865 : 1.610 1.585 2.360 1233 133 8 min. 1330 I . 8 7 O •1.645 1.640 : 2.345 1452 127 9 min. 50 sec. - 1365 • 1.860 1.605 1.655 2.310 1190 126 11 min. .1385 1.860 1.598 1.655 2.300 •1145 126 12.7 min. • 1^ 30 I .827 1.585 1.655 2.325 1185 122 14.1 min. . 1455 1.831 1.615 1.657 2.310 1380 122 Fe-C-S Experiment No.. 12•(Data taken from s o l i d i f i e d drop) . + 1 1 min. 10.32 1555 0.950 0.800 0.615 1.255 338 165 Experiment No..36 1 min. 30 sec. 9-57 1295 I .257 1.035 0.915 1.720 630 156 1 min. 31 sec. 1.257 1.040 638 32 1.260 1.057 710 33 1.257 1.051 695 34 1.257 1.050 690 35 I .257 1.035 631 36 1.255 1.055 0.920 1.705 631 155 4 min. 1320 I .250 1.100 0.976 1012 141 4 min.l sec. 1.247 1.105 1075 2 1.242 1.095 1019 3 1.247 I . 0 9 0 967 4 1.245 1.090 975 5 1.242 1,090 O .98O 980 141 7 min. 1340 .1.265 I . O 8 5 1.080 828 132 7 min. 1 sec. 1.255 1.060 738 2 1.260 1.070 767 3 I .256 1.055 706 4 1.255 I .070 782 5 I .256 I . O 6 5 758 6 1.255 • 1.075 1.072 807 152 Experiment No.. 58 .+• 30 sec. 1 min.. 54 sec. 4 min. 30 sec. 6 min. 30 sec. 8 min..42 sec. 10 min..42 sec. IO.56 1335 1.250 I . 2 5 O 1.255 1.247 1.255 .1,250 1.125 1.125 1.130 1.135 1.140 1.140 0.845 0.843 0.840 0,835 0.837 0.837 1.840 1,860 .1.870 I . 8 9 0 1.875 1.880 ,1040 1040 1059 1183 1162 1205 152 153 153 152 153 152 continued. 71 Time A f t e r S t a r t Mag. of Temp X z — : 1 X s 1 i LV (0 of Melting Photo. • . °c Cinches "i N (dynes/cm) Experiment No..39 + 48 sec. 9-55 1295 1..192 1.015 0.912 1.688 704 146 1.190 1.025 O.887 1.720 780 149 1.207 1.055 0.920 .1.690 930 145 1.205 I . O 5 5 1.710 928 1.195 I . O 6 5 1.700 1063 1.902 1.060 1.725 970 1.207 1.050 0.931 1.695 875 143 1 min. 30 sec. 1.205 I . O 5 5 O.917 1.680 928 145 1.205 1.035 1,685 ,794 1.205 1.040 1.700 812 1.202 1.030 •1.715 758 1.205 1,045 1.700 794 1.200 1,035 1.768 800 1.205 1.040 0.902 1.685 813 146 2 min. 18 sec. 1305 . 1.205 1.050 0.917 1.700 869 145 • 4 min. 1285 1.197 I . O 6 5 O .9O5 1.700 1075, 143 6 min. .1.200 1.055 0.902 1.700 945 145 8 min. 1.195 1.060 O.895 1.720 1015 145 10 min. 1.195 I . O 6 5 0.910.. 1.705 1082 142 Experiment No.. 30 Fe-C-Ce 5 min. 36 sec. 12.70 1445 1 .711-1.455 1.357 2.345 792 i 4 l 10-min. .1530 1.735 1.385 1.417 2.185 510 142 12 min. .1620 I .705 1.400 1.405 2.155 • 590 1^ .0 16 min. .1605 1.702 1,380 1.400 2.140 55O l 4 l Experiment No.. 51 3 min. 8.68 1305 1.202 1.045 1.000 1.535 104 0 138 6 min.. 30 sec. 1375 1.210 1.034 1,012 1.520 907 136 11 min. 1447 1.215 1.005 1.015 1.485 704 138-13 min. .48 sec. 1485 1.205 O .97O 1.016 1.470 580 138 19 min. 48 sec. 1615 1.210 0.995 1.055 1.445 650 131 20-min. 54 sec. 1630 1,194 1.030 1.060 1.445 885 127 22 min. 1630 - 1.192 1.035 I . O 6 5 1.437- 930 125 •Experiment No. 52 13 min. 48 sec. . 8.55 1520 1.010 0.895 O.817 1.420 860 138 16 min. 12 sec. -1635 1.019 O .87O O.825 I . 3 7 O 615 138 17 min. 18 sec. 1640. 1.024 0.900 O .83O 1.370 795 138 18 min. 42 sec. 1645 1.010 O.885 O.827 I . 3 8 O 745 136 Experiment No. 33 48 sec. 8.45 1315 1.135 " 0 . 9 8 3 0.919 1.545 940 139 2 min. 1323 1.141 O.980 0.935 1.540 895 139 8 min. 54 i sec. 1455 1,190 1.000 '0.975 1.565 775 139 l 4 min. 42 sec. 1535 1,156 • 0.995 0.945 • 1.510 880 138 19 min. 36 sec. i64o 1.160 1.000 1.022 1.450 875 128 22 min. 30 sec. 1650 1.127 0.980 1.012 1.380 .980 125 continued. Time A f t e r Start Mag. of Temp. of Melting Photo °C z x-1-tinches) - 72 -(dynes/cm) Experiment Mo. 48 (Melting c a r r i e d out on the nucleating .surface) 1 min. 6 sec. 11.75 1305 1.578 1.360 1.060 2.280 915 160 3 min. . 1305 1.567 1.335 1.075 2 . 2 6 0 830 157 4:min.. 18 sec. . 1405 1.590 1,360 1,110 2 . 2 7 O 855 156 5 min..30 sec. . 1405' 1.585 1.370 1.020 2.273 855 157 Experiment No. 50 10 min. 12.64 1605 1.597 1.325 1.400 1.915 578 130 11 min. 1-595 1.330 1.405 1.910 594 130 12 min. 1.600 1.297 1.402 1.895 500 131 Experiment No. 51 12 min. 30 sec. 12.35 • 1600 1.620 1,360 1.300 2.095 660 142 13 min. 3 0 -sec. 1.625 1.370 ,1.345 2.085 680 136 - 73 -APPENDIX IV. S t a t i s t i c a l Analysis of Three Fe-C Tests In each case the drops were taken at 1 second i n t e r v a l s . Experiment l 4 Sequence Xxv ( * L V " 1 1 5 7 ) (VLV - 1 1 5 7 ) * ' 1 - 1 2 1126 - 31 961 -24 1134 - 23 529 - 3 6 1164 + 7 49 - 48 1438 +281 78961 - 60 1379. +222 49284 - 72 1060 . - 97 9490 - 84 1076 - .81 6561 - 96 909 -248 61504 -108 1103 -.5* 2916 -120 1034 -123 15129 -132 916 -24l 58081 -Ikk 1248 + 91 8281 -156 ' 1164 + 7 49 -168 1364 +207 42849 -180 1168 + 11 . 121 -192 1295 +138 19044 -20k • 897 -260 67600 -216 1318 +161 25921 -228 1144 - 13 169 -240 1177 + 17 289 -252 1242 + 85 7225 -264 1184 + 27 729 -276 909 -248 61504 -288 1184 + 27 729 -:300 1006 -151 22801 -312 1199 . + 42 1764 -324 1405 +248 61504 .31,240 603,963 - 7^ -Experiment 19 Sequence " ( ^ ^ - 1 0 7 3 ) ( -1073)" - 12 979 - 9 4 8836 - .24 1032 - 4 l 1681 - 3 6 970 -103 10609 -48 1123 + 50 .2500 - 60 989 - 84 7056 - 72 1120 + 47 2209 - 84 ; 1070 - 3 9 - 96 1370 +297 88209 -108 1370 +297 88209 -120 1031 - 42... 1764 -132 1071 - 2 4 -144 979 - 9h 8836 -156 1072 - 1 1 -168 9 9 4 - 79 6241 -180 1170 + 97 9409 -192 1122 + 49 2401 -204 1039 • • --34 1156 -216 1006 + 67 4489 -228 1167 + 94 8836 -240 1033 - .40 1600 -252 922 -151 22801 -264 979 -9k 8836 -276 1213 +140 196OO -312 941 -132 17424 25,762 322,716 - 75 -Experiment 20 "Serine! ( X L V " 1 0 7 9 ) ( I L V ^ 0 7 9 ' ^ 1.-190 1262 +181 32761 -200 •964 -115 13225 -210 1231 +152 23104 -220 1282 +203 41209 -230 1052 - 27 729 -240 889 -190 36100 -250 1210 +131 17161 -270 1002 - 77 59?9 -280 971 -108 11664 -290 968 •,111 12321 -3OO 1231 +152 23104 -310 993 - 86 7396 -320 1044 + 35 1225 -330 . 1212 +133 17689 -340 , l l 4 o + 62 • 3844 -350 .1014 - 65 li225 -360 1031 - 48 .2304 -370 1033 - .46 2116 -380 1021 - 58 3364 • -390 917 -162 26244 21,580 285,714 Results o f • S t a t i s t i c a l Treatment Experiment Number ( Mean dy^es^cm) Standard Deviation (dynes/cm) * 16s Exp. Theor. Normal ^ Distn. * 2<r . Exp. • 1° Theor. 14 1157 150 . 63 68.2 100 95-46 19 IO73 116 79 68.2 92 • 95-46 20 1079 120 55 68.2 100 95-46 - 76 -• APPENDIX V. Cooling,Rate Considerations Because the drop samples show a much f i n e r . s t r u c t u r e i n the basal region i t i s necessary to consider the possible cooling conditions present. One would.at f i r s t expect a slower cooling,rate and hence coarser structure i n t h i s region due to the large heat content of the base. The loss of heat by r a d i a t i o n to the surroundings .can be approximated by examining the following model, the dimensions being s i m i l a r to those used. 5 The surroundings are considered t o be at a constant low temperature - t h i s i s approximately, true as the molybdenum susceptor loses i t s . h e a t extremely r a p i d l y and i s black within 2 seconds. The drop and base plate are considered; to be at the same temp-erature at.the instant the power i s removed. The. drop surface w i l l . radiate heat mainly.in the d i r e c t i o n to the black surroundings. - 77 -The.actual radiating.area, w i l l he the upper h a l f of the sphere and the small band below the center l i n e . .This angle below the center i s : t a n " 1 0 = 1 s i n £ 0° = 0.137$ . 2 . 5 . ! . 0 = 7 - 8 5 B -Area of a d d i t i o n a l r a d i a t i n g s t r i p 2 f f r X (1) (7.85' X 2 ^ ) .360 = . < 8 . 6 The surface area involved, c o n s i d e r i n g - i t as a spheroidal drop, i s .<( j f d 2 + 0 . 8 . 6 2 (upper h a l f ) •+• (band below the center) = 7 - 1 5 The plate surface w i l l radiate energy mainly i n the d i r e c t i o n shown." . Radiating Area = 5 X 5 - ^ ( 1 ) = 21.86 Emissivity. of pure i r o n from 1000°C t o 1500°C i s approximately O.56 (Metals Handbook). .Emissivity of the graphite plate i s iSs . 0 . 9 (Chemistry and Physics Handbook). - 78 -. The r a t i o of the heat radiated, by the drop surface to that radiated by the graphite base plate i s = oSO.36 ( T 4 - T g ) 7 U 5 = 0.131 CJN0.9 ( T 4 - T 0 4 ) 21.86 where i s the Stefan's constant T i s the temperature of the r a d i a t i n g body To i s the temperature of the surface to which the heat i s r a d i a t i n g . i . e . , approximately. l / 8 as much heat i s radiated by the drop surface. The thermal conductivities, of the materials are: 37 - pure i r o n at 800°C , O.318 joules/sec/cm /°C/cm (This value w i l l decrease with increasing temperature) - p y r o l y t i c graphite " i n the basal plane d i r e c t i o n , i.e p a r a l l e l to the s u r f a c e ^ 2 joules/sec/cm 2/°C/cm \ to the s u r f a c e ^ 0.02 joules/sec/cm 2/°C/cm Thus, i t i s quite possible that the d i r e c t i o n of maximum heat flow is from the drop and along the graphite surface, being emitted e s s e n t i a l l y by r a d i a t i o n . .This would account f o r the higher cooling rate i n the ba s a l area and- the r e s u l t i n g .finer.' structure. - 79 -VII. BIBLIOGRAPHY 1. Keverian, J . , Taylor,• R.F., and- Wulff, J . , Am. Foundryman 25, 85, (1953). . 2. Keverian, J . and Taylor, H.F., Trans. Am. Foundrymen's Soc. 65, 212, • (1957). 3 . Milman, B.C ., • Liteinoe--Proizv. 6, 11,(1958). . 4. White, • D-.W.G., .Canada Department of Mines, and Technical Surveys Internal.Report No.. PM-M-62-4 (May 1, 1962). 5. U h l i g , H.H., i n American Society f o r Metals, "Metal Interfaces". Cleveland, Ohio, The Society (1952), p. 312. 6. Mehl, R.F.,in American I n s t i t u t e of Mining,-Metallurgical and Petroleum Engineers,- I n s t i t u t e of Metals Div., "The; S o l i d i f i -c a tion of Metals and'Alloys", N.Y.,. A.I.M.E. (1951), p. 24. 7. - Hollomon, J . H., and Turnbull, D., i n American i n s t i t u t e of Mining, M e t a l l u r g i c a l and Petroleum Engineers, I n s t i t u t e of Metals Div., "The S o l i d i f i c a t i o n of Metals and A l l o y s " , N.Y., - A.I.M.E., (1950), p.- 1. 8. Turnbull, D.,J. Chem. Phys. 20, 411, (1952). .9. Turnbull, D., and Fisher, J.C., J . Chem.. Phys. 17, 71, (1949). 10. Gibbs, J . . W i l l a r d . , "The C o l l e c t e d Works of J . W i l l a r d Gibbs", New Haven,. Yale Univ,,Press (1948). 11. A l l e n , B.C. and Kingery, ,W .D.,-Trans . A.I .M.E .. 215_, 30,(1959). 12. . Kozakevitch, P. and Urbain, G., Rev. Met. 5_8, 401, 517. and 931,(196l) 13. Dyson, B.F.,. Trans. A.I.M.E. ,227_,. IO98, ( I 9 6 3 ) . 14. Whalen, T.J., Kaufman,S. M. and Humenik,,M., J r . , Trans. Am. Soc. .Metals 5_5_, .3, (I962) . .15. Koxakevitch,,P., Chatel, - S U r b a i n , G. and Sage, M. .Rev. Met.. 52, 139,(1955). 16. Kingery,-W.D. and Humehick,. M.j;. J r . , J . Phys.. Chem. 5_7^  ,359, (1953) • • 17. Kaufman, S. M. and Whalen, T.J., Trans. A.I.M.E. 230, 791, (1964). 18. . Minkoff,. I., Trans. .Am. Foundrymen's Soc. 70, l8> (1-962). .19. Voronova, N.A., and-Mogilevtsev, 0.A.,,Metal. S c i . Heat Treat. Metals (USSR) ,< E n g l i s h Trans. J_, 459, (I963). .20. Boyles, A., "The Structure of Cast Iron", Cleveland, Ohio,- American Society f o r Metals (1947). - 80 -21. Morrogh, H. and Williams,, W.. J.,. J . Iron S t e e l Inst. 155, 521 (1947). 22. Loper,.C. R., J r . , and Heine,. R.- W., Trans. Am.. Foundrymen's Soc. 69_, 583 (1961) . 23. . Loper, : C . R. and Heine,. R.- W., Trans.. Am.-Soc.. Metals, 5_6, 135 ( I 9 6 3 ) . .24. . Carden,R.L.BCIRA j . , 1 0 , 325 (I963). 2 5 . • AES-ASTM Graphite Flake C l a s s i f i c a t i o n i n Grey Cast Iron. ASTM Designation:;A 2^7-47, .26. . Garber, S., J . Iron S t e e l Inst. l 8 l , 291 (1955). 27. .Williams,,W. J.,- J . Iron S t e e l Inst. 164, 1+07 (1950), 2 8 . .Form, G. W. and Wallace, J.. F.,.Trans. Am. Foundrymen's Soc. JO, llkO (1962). 29. Morrogh, H . T r a n s . Am. Foundrymen's Soc. JO, 449 (1962) . 3 0 . • S c h e i l , - E. and Schobel, J.D., Fonderie 19_2, 73 (1962). 3 1 . Loper, C .R.,. J r . , Trans. Am.. Foundrymen, s Soc. J_0, 963 (I962). 3 2 . Morrogh, H., BCIRA J . ,5_, 12, 655 (1955). 3 3 . Strauss, H. E., Von Balchelder, F.W., and S a l k o v i t z , E.I., J.•Metals 10, 2 4 9 ( 1 9 5 1 ) . 3 4 . Bashforth,.F. and Adams, J.C., "An Attempt to Test the Theory of C a p i l l a r y Action", London, Cambridge Univ.. Press (1883) . .35. Rose, D. J.,M.A.Sc.' Thesis, U n i v e r s i t y of B r i t i s h Columbia, 1962. .36. Guentert, O.J., J . P h y s . Chem. 37_, 4 , 884 ( I 9 6 2 ) . .37 . .Smithells,. C.J., "Metals Reference Book", 3d ed. London, Butterworths (1962), v. 2, p. 644. 3 8 . Darken, S. L. and Gurry, R.W., "Physical Chemistry of Metals", N.Y., McGraw-Hill (1953). 3 9 . E l l i o t t , J.F., and G l e i s e r , M., "Thermochemistry f o r Steelmaking", Reading, Mass. Addison-Wesley Pub. Co. ( i 9 6 0 ) , 40. E l l i o t t , J.F., ed. "The P h y s i c a l Chemistry of Steelmaking; proceedings", N.Y., Technology Press, of M.I.T. and Jonn Wiley ( I 9 5 8 ) . 4 1 . American I n s t i t u t e of Mining and M e t a l l u r g i c a l Engineers, Iron and S t e e l Div. "Basic Open Heartn Steelmaking", 2d ed. N.Y., A.I.M.E. (1951) . 42. B a r t e l l , F.E. and Wooley, A.D., J . Am. Chem. Soc. 5_5_, 3518 (1933). - 81 -kj>. Baes, O.F. and Kellogg, H.H., J . Metals 5_, c43 (1953). kk. Harvey, J . , Clarkiy D. and Eastabrook, J.N., Royal A i r c r a f t Establishment Technical Note No. Met. Phys. 361 (1962). 45. Diefendorf, R.J. and Stober, E.R., Metals Progr. 8 l , 103 ( I 9 6 2 ) . kb. Bradshaw, W. and Armstrong, J.R., " P y r o l y t i c Graphite, i t s Hign Temperature Properties", Lockheed A i r c r a f t Co. Technical Documentary Report No. ASD-TOR-b3-195 (1963) . 47. K i r k a l d y , J.S. and Purdy, G.R., Private Communication ( 1963) . 

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