The constitution of the system Al-Ti-B with reference to aluminum-base alloys
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is w e l l known 1-3 that m i n o r a d d i t i o n s of t i t a n i u m to a l u m i n u m r e s u l t in s i g n i f i c a n t g r a i n r e f i n e m e n t by p a r t i c l e s of the compound A13Ti. It i s a l s o known 3 that if m i n o r a d d i t i o n s to a l u m i n u m contain both t i t a n i u m and b o r o n the g r a i n r e f i n i n g a c t i o n i s much i m p r o v e d . T h e s e t e r n a r y a l l o y s of A 1 - T i - B contain the c o m p o u n d s A13Ti, A1B2, a n d / o r TiB2 o r a s o l i d s o l u t i o n (A1Ti)B2, it b e i n g s u p p o s e d by s o m e 4 that the l a t t e r compound, TiB2, i s then the n u c l e a t i n g agent f o r a l u m i n u m . On the o t h e r hand, it h a s been shown 5 how in r e l a t i v e l y c o n c e n t r a t e d t e r n a r y a l l o y s , e.g. A1-5 wt pet Ti, ! wt p c t B, the A13Ti i s a c t i v e a s a n u c l e a n t while m o s t of the f i n e r TiB2 [or (A1Ti)B2] p a r t i c l e s do not n u c l e a t e a l u m i n u m and a r e p u s h e d d u r i n g s o l i d i f i c a t i o n to i n t e r d e n d r i t i c r e g i o n s . In o r d e r to r e s o l v e t h e s e s e e m i n g l y c o n t r a d i c t o r y s t a t e m e n t s , an a t t e m p t h a s been m a d e to d e t e r m i n e the constitution of t h i s c o n t r o v e r s i a l s y s t e m , A 1 - T i - B , in the r e l e v a n t a l u m i n u m c o r n e r . A p r o v i s i o n a l d i a g r a m h a s been p u b l i s h e d by M a r cantonio and Mondolfo 6 and i s b a s e d on m i c r o s c o p i c a l and X - r a y d a t a but d o e s not i n c l u d e d i r e c t e v i d e n c e about the l i q u i d u s b o u n d a r i e s . T h e p r i n c i p a l p r o b l e m i s that the compound TiB2 [ o r (A1Ti)B2] h a s a v e r y high m e l t i n g point 7,s so that the l i q u i d u s s u r f a c e f o r t h i s compound(s) i s e x c e p t i o n a l l y s t e e p in the a l u m i n u m r i c h c o r n e r of the s y s t e m . In the p r e s e n t w o r k , d i r e c t and d i f f e r e n t i a l t h e r m a l a n a l y s e s have b e e n u s e d to d e t e r m i n e a p p r o x i m a t e l y t h e s h a p e and p o s i t i o n of t h i s s u r f a c e , and, h e n c e , the s o l u b i l i t y of TiB2 in m o l t e n aluminum base alloys. EX PE R1MENTAL A l l o y s w e r e p r e p a r e d f r o m A . I . A . G . Super Raffinal a l u m i n u m containing
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