Artifactitious observations of the dragging of particles by grain boundaries
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1 F. L. Arnoldand J. S. Prestley:Mod. Castings, 1961,vol 39, pp. 129-37. 2. P. B. Crosleyand L. F. Mondolfo:Mod. Castings, 1966,vol. 49, No. 3, pp 89100. 3. T Kawasakl:J Japan Foundrymen "sSoc., 1969,vol 41, pp. 22-28. 4. R K. Wdlardsonand A. C Beer"Semiconductors and Semimetals, vol.4, p. 51, AcademicPress,New York and London,1968
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Artifactitious Observations of the Dragging of Particles by Grain Boundaries K. T. AUST, E. F. KOCH, C. S. TEDMON, J r . , AND D. A. VERMILYEA
Fig. 3--Optical micrograph showing the growth of germanium crystals on AlAs (left), and the AsK electron-microprobe image of the same area (right). f o r m s only one compound with a l u m i n u m , AlAs, which h a s the ZnS-type s t r u c t u r e with the l a t t i c e c o n s t a n t v e r y c l o s e to that of g e r m a n i u m . In addition, the fact that the liquid s o l u b i l i t y of a r s e n i c into a l u m i n u m b e c o m e s a p p r e c i a b l e only at high t e m p e r a t u r e s 4 i s a d v a n t a g e o u s for c o n t r o l l i n g the s i z e and the d i s t r i b u t i o n of the compound c r y s t a l s as the n u c l e a t i o n site for g e r manium. In the e x p e r i m e n t , 1 g of m e t a l l i c a r s e n i c i s added to 200 g of an A1-70 wt pct Ge alloy m e l t e d i n a h i g h p u r i t y a l u m i n a c r u c i b l e at 680 ~ or 800~ and the m e l t s a r e then cast into g r a p h i t e mould p r e h e a t e d at 140~ The s a m p l e t r e a t e d at 800~ exhibited the d r a s t i c a l l y r e f i n e d s t r u c t u r e a s shown in Fig. 2; the n u m b e r of 2340-VOLUME1, AUGUST1970
A S H B Y and C e n t a m o r e have shown that the ability of a m i g r a t i n g g r a i n boundary in copper to d r a g s m a l l oxide p a r t i c l e s is dependent upon, a m o n g other f a c t o r s , the v i s c o s i t y of the oxide p a r t i c l e . 1 As the v i s c o s i t y of the oxide i n c r e a s e d , g r a i n b o u n d a r y d r a g g i n g of p a r t i cles b e c a m e m o r e difficult and in the l i m i t of a m a t e r i a l with v e r y high v i s c o s i t y , A12Oa, the p a r t i c l e s were i m m o b i l e . T h i s l a t t e r r e s u l t is in c o n t r a d i s t i n c t i o n to the r e p o r t e d o b s e r v a t i o n of the d r a g g i n g of c r y s t a l l i n e CrazC6 by g r a i n b o u n d a r i e s in a u s t e n i t i c s t a i n l e s s steel. 2 F u r t h e r , it is w e l l - k n o w n that g r a i n boundary c a r b i d e s often p r e c i p i t a t e in a u s t e n i t i c s t a i n l e s s s t e e l s with very c o m p l e x m o r p h o l o g i e s , 3'4 and should be difficult to drag. Since CrzaC8 is a quite r e f r a c t o r y c a r bide, the r a t e of s e l f - d i f f u s i o n within c a r b i d e p a r t i c l e s at t e m p e r a t u r e s ca 900~ would be v e r y low, so that the v i s c o s i t y should be high and d r a g unlikely. T h e s e f a c t o r s , coupled with the obvious i m p o r t a n c e of p o s s i ble g r a i
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