An x-ray investigation of precipitation effects in brass containing nickel and aluminum
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An X-Ray Investigation of Precipitation Effects in Brass Containing Nickel and Aluminum W. S. RADZINSKI AND F. H. COCKS
ALTHOUGH
the age h a r d e n a b i l i t y of b r a s s c o n t a i n ing joint additions of n i c k e l and a l u m i n u m has b e e n known for many y e a r s , 1 the d e t a i l s of the p r e c i p i t a t i o n r e a c t i o n s in this s y s t e m s t i l l r e m a i n unknown. A r e cent 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 i s study, h o w e v e r , has shown that two e x o t h e r m i c r e a c t i o n s o c c u r d u r i n g age h a r d e n i n g in the C u - Z n - N i - A 1 s y s t e m . 2 F o r a solution h e a t - t r e a t e d a l l o y having the c o m p o s i t i o n 20.6 wt pct Zn-6.8 wt pct N i - 2 . 2 wt pct A l - b a l a n c e Cu, t h e s e e x o t h e r m i c m a x i m a a r e found to o c c u r n e a r 475 ~ and 625~ r e s p e c t i v e l y , for h e a t in g at a r a t e of 15~ p e r min. An X - r a y i n v e s t i g a t i o n of the e f f e c t of t h e s e p r e c i p i t a t i o n r e a c t i o n s on m a t r i x i n t e r a t o m i c s p a c i n g has now b e e n c a r r i e d out, so that c h a n g e s in the l a t t i c e p a r a m e t e r of the m a t r i x a ll o y m a y be c o r r e l a t e d both with o b s e r v e d h a r d n e s s c h a n g e s and with c a l c u l a t e d kinetic data on the p e r c e n t c o m p l e t i o n of each exothermic reaction. The X - r a y d e t e r m i n a t i o n of the l a t t i c e p a r a m e t e r i n v o l v e d the following c o n s i d e r a t i o n s : if a p o w d e r e d s p e c i m e n is p r e p a r e d i n i t i a l l y , it is found that d u r i n g heat-treatment marked dezincification occurs, causing s u b s t a n t i a l c h a n g e s in the m e a s u r e d l a t t i c e p a r a m e t e r . On the o t h e r hand, if the p o w d e r e d s p e c i m e n is p r e p a r e d a f t e r h e a t - t r e a t m e n t is c o m p l e t e , then r e s i d u a l s t r a i n e f f e c t s p r o d u c e s u f f i c i e n t b r o a d e n i n g to r e n d e r the d e t e r m i n a t i o n of the peak p o s i t i o n i n a c c u r a t e . In the p r e s e n t c a s e , t h e s e e f f e c t s w e r e s u r m o u n t e d by using a s o l i d bulk s p e c i m e n whose g r a i n W. S. RADZINSKI and F. H. COCKS are Staff Scientist and Senior Scientist, respectively, Tyco Laboratories, Inc., Bear Hill, Waltham, Mass. Manuscript submitted November 12, 1969. 1458-VOLUME 1,MAY 1970
s i z e was a p p r o x i m a t e l y of 9.7 x 10 TM c m . Any p r e f e r r e d o r i e n t a t i o n of the g r a i n s t r u c t u r e would affect the r e l a t i v e line i n t e n s i t i e s but not peak positions. By g r i n d i n g and p o l i s h i n g the s u r f a c e with 5-p a l u m i n a a f t e r aging, s p e c i m e n induced line b r o a d e n i n g was s u b s t a n t i a l l y e l i m i n a t e d . P e a k p o s i t i o n s w e r e then found by d e t e r m i n i n g the r e l a t i v e d i f f r a c t e d i n t e n s i t y by
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