An improved piston-and-Anvil technique for quenching liquid metals

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An Improved Piston-and-Anvil Technique for Quenching Liquid Metals P . RAMACHANDRARAO, D. BANERJEE, AND T. R. ANANTHARAMAN

DURINGthe

l a s t decade a n u m b e r of t e c h n i q u e s have been developed for q u e n c h i n g liquid m e t a l s and alloys at cooling r a t e s a s high as 105 to 10 a deg C p e r sec. I-7 A s p e c i a l f e a t u r e of all these t e c h n i q u e s has b e e n the e x t r a c t i o n of heat by conduction. To d e r i v e the m a x i m u m benefit of conduction cooling, the liquid m e t a l is g e n e r a l l y s p r e a d into a thin film and b r o u g h t into v e r y close contact with a highly conducting s u r f a c e . Though the above conditions can be satisfied in a n u m b e r of methods, the ' g u n ' and ' p i s t o n - a n d - a n v i l ' t e c h n i q u e s a m o n g them have so f a r proven e x t r e m e l y popular. However, each of t h e s e two techniques i s c h a r a c t e r i z e d by s p e c i a l a d v a n t a g e s a s well as d i s a d v a n t a g e s . The gun technique g i v e s a f a s t e r cooling r a t e (107 to 10e deg C p e r sec), 7 but i t s product is a highly porous o r flaky foil of v a r y i n g t h i c k n e s s , u n s u i t a b l e for even e l e c t r i c a l r e s i s t i v i t y m e a s u r e m e n t s , let alone m e c h a n i c a l t e s t i n g . In all available v a r i a t i o n s of the p i s t o n - a n d - a n v i l t e c h nique, the liquid d r o p e i t h e r m o v e s u n d e r the force of g r a v i t y o r is e j e c t e d by a positive gas p r e s s u r e at n e g ligible velocity. U n d e r these conditions the t h i c k n e s s of the foil is g r e a t e r than in the gun technique and the foil is also m o r e u n i f o r m in c r o s s - s e c t i o n , but the Cooling rate gets r e d u c e d m a i n l y b e c a u s e of the slow fall of the m e t a l d r o p l e t to l 0 s to 108 deg C p e r sec.3 In addition, as pointed out by Duwez, ~ this method is somewhat of a ' h i t - a n d - m i s s ' type in which as many as 75 pct of the foils m a y have to be r e j e c t e d . The p r e s ent c o m m u n i c a t i o n d e s c r i b e s what m a y be c o n s i d e r e d an advantageous c o m b i n a t i o n of the gun and p i s t o n - a n d anvil t e c h n i q u e s . Fig. l(a) is a line d i a g r a m of our q u e n c h i n g a p p a r a tus. It is m a i n l y c o m p o s e d of the shock tube of the gun technique, a p r e s s u r e switch, f a c i l i t i e s to hold the m o l ten m e t a l at the d e s i r e d t e m p e r a t u r e , and the p i s t o n a n d - a n v i l s o l i d i f i c a t i o n s e t - u p . The c o n s t r u c t i o n a l d e t a i l s of the shock tube, f u r n a c e and the m o l t e n m e t a l c o n t