Rapid melting and solidification of a surface layer
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s o l i d i f i c a t i o n v a r i a b l e s of t h r e e s u b s t r a t e m a t e r i a l s : a l u m i n u m , i r o n , and n i c k e l . S e v e r a l s t u d i e s have p r e v i o u s l y b e e n c a r r i e d out to effect of high c o o l i n g r a t e s , 10 5 to 10 x~ K / s on q u a n t i t a t i v e l y d e s c r i b e heat flow in a s e m i i n f i n i t e the s t r u c t u r e of s o l i d m a t e r i a l s f o r m e d f r o m t h e i r s u b s t r a t e m a t e r i a l s u b j e c t e d to high i n t e n s i t y r a d i a m e l t s has r e c e i v e d i n c r e a s e d a t t e n t i o n e v e r s i n c e tion. An a n a l o g c o m p u t e r p r o g r a m was d e v e l o p e d by Duwez and his c o w o r k e r s p u b l i s h e d r e s u l t s of t h e i r Cohen 6 to i n v e s t i g a t e the t e m p e r a t u r e d i s t r i b u t i o n s in i n v e s t i g a t i o n s on s p l a t cooling. ~'2 A l a r g e n u m b e r of the m o l t e n s u r f a c e l a y e r and the s o l i d s u b s t r a t e d u r i n n o v a t i v e b a t c h and continuous t e c h n i q u e s for p r o ing m e l t i n g of a s e m i i n f i n i t e solid s u b j e c t e d to a s t e p duction of l a b o r a t o r y and c o m m e r c i a l q u a n t i t i e s of f u n c t i o n heat input. T he t h e r m a l p r o f i l e s thus genr a p i d l y s o l i d i f i e d m a t e r i a l have s i n c e b e e n developed. e r a t e d w e r e s u b s e q u e n t l y u s e d by o t h e r i n v e s t i g a t o r s In g e n e r a l , t h e s e t e c h n i q u e s involve q u e n c h i n g of a to estimate average cooling rates during solidification liquid on a high c o n d u c t i v i t y s u b s t r a t e . D e t e r m i n a of n o n c r y s t a l l i n e s t r u c t u r e s . 5 O t h e r r e s e a r c h e r s 7 tion of e x a c t c o o l i n g r a t e s d u r i n g s o l i d i f i c a t i o n of c r y s have u s e d the p o i n t s o u r c e heat flow e q u a t i o n s p r o t a l l i n e and n o n c r y s t a l l i n e s t r u c t u r e s i n t h e s e p r o p o s e d by R o s e n t h a l 8 for b e a d - o n plate welding. One c e s s e s has r e q u i r e d e s t i m a t e s of heat t r a n s f e r coeffidifficulty with a l l t h e o r e t i c a l c a l c u l a t i o n s , i n c l u d i n g c i e n t s b e t w e e n the liquid and the s u b s t r a t e . Two n o t e that p r e s e n t e d h e r e , is that not a l l i n c i d e n t r a d i a t i o n worthy a t t e m p t s have b e e n made to d i r e c t l y m e a s u r e is a b s o r b e d b y the s u b s t r a t e - r e f l e c t i v i t y v a r i e s with heat t r a n s f e r coefficients d u r i n g s p l a t cooling, s,4 Howpower density, substrate material, surface condition e v e r , it is q u e s t i o n a b l e w h e t h e r t h e s e v a l u e s can be (e.g., oxide l a y e r ) , and is d i f f e r e n t for p r i m a r y p h a s e s used in c a l c u l a t i o n of cooling r a t e s in o t h e r r a p i d s o l i and i n c l u s i o n s . N e v e r t h e l e s s , it was b e l i
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