Hydrogen embrittlement in a Phosphor-Bronze alloy

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Hydrogen Embrittlement in a Phosphor-Bronze Alloy J A M E S M. P O P P L E W E L L

AND J A M E S A. F O R D

T h e p h e n o m e n o n of h y d r o g e n e m b r i t t l e m e n t h a s l o n g been associated with ferrous materials. However, copp e r a l l o y s h a v e n o t b e e n r e p o r t e d s u s c e p t i b l e to t h i s f o r m of e m b r i t t l e m e n t e x c e p t t h r o u g h t h e s p e c i a l h i g h temperature reaction: C u 2 0 + H~ ~ Fig. 9--Ti-6 Me-2 Sn-4 Z r - 6 A1 thinned by ion milling. (a) O r t h o r h o m b t c m a r t e n s i t e has been r e t a i n e d in the thin foil; and (b) selected a r e a diffraction r e v e a l s (111) twinning in m a r t e n s i t e plate. twinned on {lll}a,. T h u s , t h e a p p l i c a t i o n of ion t h i n n i n g t o m a r t e n s i t i c s a m p l e s a l s o a p p e a r s to b e u s e f u l s i n c e it p e r m i t s t h e d e t a i l s of t h e b u l k p h a s e to b e r e tained for study in thin foils. F i n a l l y , it i s a p p r o p r i a t e t o p r e s e n t o n e p o s s i b l e e x p l a n a t i o n f o r t h e s u p p r e s s i o n of s p o n t a n e o u s r e l a x a t i o n i n i o n - t h i n n e d f o i l s . It h a s a l r e a d y b e e n s h o w n t h a t a g e n e r a l m o t t l e d a p p e a r a n c e i s c h a r a c t e r i s t i c of i o n thinned foils and it was suggested that such mottling was due to radiation damage from the ion beam. This t y p e of r a d i a t i o n d a m a g e h a s b e e n o b s e r v e d b y t r a n s mission electron microscopy in several ion-irradiated m e t a l s in w h i c h t h e d a m a g e w a s s h o w n to b e d e f e c t c l u s t e r s . 5 - 7 If the m o t t l i n g i s a c t u a l l y d u e to s m a l l d e feet clusters, then such clusters can inhibit the format i o n a n d m o t i o n of the p l a n a r f e a t u r e s w h i c h c h a r a c t e r i z e t h e s p o n t a n e o u s r e l a x a t i o n in t h e s a m e w a y t h a t i r r a d i a t i o n - i n d u c e d c l u s t e r s h a v e b e e n s h o w n to a c t a s 2600-VOLUME 5, DECEMBER 1974

2Cu + H 2 0

Ineffective deoxidation causes Cu20 formation in the g r a i n b o u n d a r i e s w h i c h r e a c t s w i t h h y d r o g e n to f o r m water vapor resulting in severe grain boundary emb r i t t l e m e n t . l - 5 R e c e n t l y , we h a v e o b s e r v e d a n o t h e r f o r m of h y d r o g e n e m b r i t t l e m e n t in c o p p e r a l l o y C . D . A . # 5 1 0 " d u r i n g s t r e s s c o r r o s i o n t e s t i n g in m o i s t a m m o *Alloy C. D. A. #510 nominal composition: - Sn - 4.7 pet, P - 0.2 pet + rem Cu. Alloy C. D. A.#638 nominal composition: - AI - 2.8 pet, Si - 1.8 pet, Co 0.4 pet + rem Cu. nia. R was found that electro-tin plated samples exhibited much more rapid crack propagation rates than d i d u n p l a t e d s a m p l e s . A n o t h e r a l l o y C . D . A . # 638* tested at the same time did not show the same effect. Stress corrosion samples were prepared as U-bends f r o m 50 p c t c o l d