Nucleation in undercooled Sn-Sb alloys
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232~
/
I~
Sn
4.8
17.5 wl~
Sb
SB
Fig. 1--Part of the Sn-Sb phase diagram in the region of the periteetic reaction SbSn + L ~ c~. The composition of the alloys undercooled are x (hypoperitectic) and y (hyperperitectic).
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240"C
Nucleation in Undercooled Sn-Sb Alloys d
G. L. F . P O W E L L , G. A. C O L L I G A N , AND A . W. U R Q U H A R T
IN r e c e n t
p a p e r s , l - s the a u t h o r s h a v e shown that the u n d e r c o o l i n g of bulk s a m p l e s (40 g) of h y p o e u t e c t i c and h y p e r e u t e c t i c a l l o y s a s a function of c o m p o s i t i o n is a method of d e t e r m i n i n g the n u c l e a t i n g e f f i c i e n c y of one p h a s e of the e u t e c t i c f o r the o t h e r . The method is s o m e w h a t s i m i l a r to that a p p l i e d by Sundquist and Mondolfo 4 to 100 to 300 pm d r o p l e t s of e u t e c t i c a l l o y s . One o b v i o u s a d v a n t a g e of a l a r g e r s a m p l e is that it f a c i l i t a t e s m e t a l l o g r a p h y and e n a b l e s the w h o le t h e r m a l h i s t o r y of the c o o l i n g s a m p l e to be r e c o r d e d r a t h e r than i s o l a t e d n u c l e a t i o n t e m p e r a t u r e s . A n o t h e r a d v a n t a g e of the method 1-s is that n u c l e a t i o n e f f e c t s due to u n i n t e n t i o n a l a d d i t i o n of i m p u r i t i e s can be e l i m inated. T h e u n d e r c o o l i n g of bulk s a m p l e s a s a function of a l l o y c o m p o s i t i o n c a n a l s o be a p p li e d to p e r i t e c t i c s y s t e m s to i n v e s t i g a t e n u c l e a t i o n c a t a l y s i s . H o w e v e r , f o r p e r i t e c t i c s the i n t e r p r e t a t i o n is s o m e w h a t l e s s d e f i n i t e b e c a u s e of the d i f f e r e n c e s in p h a s e c o m p o s i t i o n s f o r t h e a l l o y s i n v o l v e d . T h i s p a p e r r e p o r t s the u n d e r c o o l i n g b e h a v i o r and r e l a t e d m i c r o s t r u c t u r e s of bulk s a m p l e s of Sn-Sb a l l o y s as the c o m p o s i t i o n s of the s a m p l e s a r e changed f r o m one s i d e of the p e r i t e c ti c c o m p o s i t i o n to t h e o t h e r . Th e e x p e r i m e n t a l method a p p li e d to the i n v e s t i g a t i o n of n u c l e a t i o n b e h a v i o r in p e r i t e c t t c s y s t e m s is e x -
G. L. F. POWELL, formerly Research Associate, Thayer School of Engineering, Dartmouth College, Hanover, N. H., is now with the Australian Mineral Development Laboratories, Frewville, S. A. Australia. G. A. COLLIGAN and A. W. URQUHART are Associate Dean and Ph.D. Candidate, respectively, Thayer School of Engineering, Dartmouth College. Manuscript submitted June t 5, 1970. 918-VOLUME 2, MARCH 1971
246~
0
Perltectlc Temperature
I 1 rain. ,
TIME
Fig. 2--Curve A-cooling curve for hypoperiteetic composition (x in Fig. 1). Curve B-cooling curve for hyperperitectic composition (y in Fig. 1).
p l ai n ed with r e f e r e n c e to F i g . 1. A s a m p l e containing 40 g of tin and 2 g of
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