Phase stability diagrams for complex alloys
- PDF / 228,386 Bytes
- 2 Pages / 612 x 792 pts (letter) Page_size
- 66 Downloads / 232 Views
Phase Stability Diagrams for Complex Alloys R. O. WILLIAMS
/ B IN(/ /
While a p h a s e d i a g r a m c o m p l e t e l y d e s c r i b e s the p h a s e e q u i l i b r i a in an a l l o y s y s t e m , i t s r e p r e s e n t a t i o n b e c o m e s i n c r e a s i n g l y difficult a s the n u m b e r of c o m ponents i n c r e a s e s . S p e c i f i c a l l y , a f o u r - c o m p o n e n t s y s t e m r e q u i r e s a t h r e e - d i m e n s i o n a l c o n s t r u c t i o n to r e p r e s e n t the p h a s e e q u i l i b r i a a t a single t e m p e r a t u r e . A s a w k w a r d a s t h i s m a y be, a f i v e - c o m p o n e n t s y s t e m cannot be r e p r e s e n t e d at a l l . The p u r p o s e of t h i s note i s to d e m o n s t r a t e that, by r e s t r i c t i n g our attention to a single c o m p o s i t i o n , it i s p o s s i b l e to c o m p l e t e l y r e p r e s e n t the p h a s e e q u i l i b r i a in a s i m p l e , t w o - d i m e n s i o n a l d i a g r a m s o m e w h a t ukin to a b i n a r y phase d i a g r a m . The c h a r a c t e r of the d i a g r a m i s not changed a s the n u m b e r of c o m p o n e n t s i n c r e a s e s , although the c o m p l e x i t y in t e r m s of t h e n u m b e r of p h a s e s m a y i n c r e a s e . We p r o p o s e to c a l l such diagrams "alloy-phase-stability diagrams" or "stability d i a g r a m s " . In our p r o p o s e d s t a b i l i t y d i a g r a m , we would s i m p l y r e p r e s e n t the a t o m f r a c t i o n of e a c h p h a s e a s a function of t e m p e r a t u r e . To i l l u s t r a t e such a d i a g r a m , we have c o n s t r u c t e d one in Fig. 1 f o r the c o m p o s i t i o n AB~ f o r the b i n a r y s y s t e m shown in F i g . l ( a ) . We s e e that at T1 the t3 p h a s e s t a r t s to f r e e z e ; the amount of /3 p h a s e i n c r e a s e s c o n t i n u o u s l y until the e u t e c t i c t e m p e r a t u r e , T 2 is r e a c h e d . At t h i s t e m p e r a t u r e a l l the r e m a i n i n g liquid, of e u t e c t i c c o m p o s i t i o n , f r e e z e s . The amount of e u t e c t i c liquid i s given by the length of t h i s h o r i z o n t a l line c. W i t h d e c r e a s i n g t e m p e r a t u r e , the r e l a t i v e a m o u n t s of c~ and /3 r e m a i n a p p r o x i m a t e l y c o n s t a n t . We have a l s o i n d i c a t e d the c o m p o s i t i o n of the a and /3 p h a s e s with the dotted l i n e s . Since t h i s d i a g r a m only c o n t a i n s the i n f o r m a t i o n in the p h a s e d i a g r a m , we have n e i t h e r c r e a t e d nor d e s t r o y e d i n f o r m a t i o n about the c o m p o s i t i o n in q u e s t i o n . F o r a b i n a r y s y s t e m , a s t a b i l i t y d i a g r a m p r o v i d e s no a d v a n t a g e o v e r the p h a s e d i a g r a m . But f o r a t e r n a r y s y s t e m the s t a b i l i t y d i a g r a m m o r e s a t i s f a c t o r i l y r e p r e s e n t s the t e m p e r a t u r e d e p e n d e n c e of the e q u i l i b
Data Loading...
