The chromium-platinum constitution diagram
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weight percent 7inr
Fig. 4--Density composition plots for zinc and tin alloys, at 2460C and at their liquidus temperatures.
a l l o y tn the s y r i n g e w a s 7.5 wt p c t Zn, which Is the c o m p o s i t i o n m i d w a y b e t w e e n the o v e r a l l a l l o y c o m p o s i t i o n and the ZnSn e u t e c t t c . The t r a c e r a l l o y was i n j e c t e d when the tip of the s y r i n g e had j u s t r e a c h e d the 7.5 wt p c t liquidus t e m p e r a t u r e , c o r r e s p o n d i n g to about 25 p c t weight s o l i d at t h a t point in the c a s t i n g . A t y p i c a l m a c r o s t r u c t u r e of a s p e c i m e n , which was quenched d u r i n g growth, i s shown in Fig. 2. The f i g u r e shows the s h a p e and f o r m of the e u t e c t l c and d e n d r i t i c f r o n t s d u r i n g the f r e e z i n g p r o c e s s . S a m p l e s w e r e c o o l e d a t d i f f e r e n t r a t e s b y changing the a i r c o o l ing p r e s s u r e . The a u t o r a d t o g r a p h s for the d i f f e r e n t
F r o m the a u t o r a d i o g r a p h s , Fig. 3, it can be s e e n t h a t g r a v i t a t i o n a l f l u i d flow o c c u r s and t h a t the d i r e c tion of m o t i o n is in p a r t u p w a r d s in the p a r t i a l l y s o l i d r e g i o n . T h i s i s the d i r e c t i o n to be e x p e c t e d f r o m the d e n s i t y m e a s u r e m e n t s . It should b e noted that flow in m o s t o t h e r a l l o y s y s t e m s , w h e r e the d e n s i t i e s of the c o m p o n e n t m a t e r i a l s a r e v e r y d i f f e r e n t , would b e e x p e c t e d to be m o r e p r o n o u n c e d than the flow found in t h e s e e x p e r i m e n t s . The d e n s i t y of p u r e tin (6.84 g / c u c m at 420~ 6 i s a l m o s t i d e n t i c a l to that of p u r e z i n c (6.66 g / c u c m at 420~ e. So that l i t t l e change in d e n s i t y is to be e x p e c t e d with change in c o m p o s i t i o n in t h i s a l l o y . The a u t o r a d t o g r a p h s , Fig. 3, a l s o show that t h e r e i s s o m e flow within the p a r t i a l l y s o l i d r e g i o n t o w a r d the e u t e c t t c i n t e r f a c e , a s i s to be e x p e c t e d due to the v o l u m e c o n t r a c t i o n a s the r e m a i n i n g liquid f r e e z e s / C o n c u r r e n t e x p e r i m e n t s on m a c r o s e g r e g a t i o n s i n d i c a t e t h a t the m a c r o s e g r e g a t t o n in t h e s e a l l o y s i s t h a t e x p e c t e d f r o m the g r a v i t a t i o n a l fluid motion. 1. R. J. McDonaldand J. D. Hunt: Trans. TMS-AIME, 1969,vol.245, pp. 199397. 2. R. J. McDonaldand J. D. Hunt:Met. Trans., 1970,vol. 1, pp. 1787-88. 3. R. Mehrabian,M. A. Keane,and M. C. Flemings:Met. Trans., 1970, vol. 1, pp. 1209-20. 4. R. Mehrabian,M. A. Keane,and M. C. Flemings:Met. Trans., 1970,vol. 1, pp. 3238-41. 5. D. J. Hebditch:D. Phil.Thesis,Universityof Oxford. 6. C. J. Smithells:MetalsReferenceBook,4th ed., 1967, pp. 689. 7. M. C. Flemingsand G. E. Nereo:Trans. TMS-AIME, 1967,vol.
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