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Failure stress, psi

Pct TD

1 2 3 4 5 6

32,050 23,200 40,225 42,150 59,300 57,800

97.4 97.7 98.5 98.7 99.7 99.9

S p e c i m e n s w i t h t h e h i g h e s t p c t T D e x h i b i t e d the l a r g e s t failure stress, as expected. All s i x s p e c i m e n s w e r e o b s e r v e d to f a i l in a n e x p l o s i v e m a n n e r p r i m a r i l y a l o n g the d i r e c t i o n of l o a d i n g r a t h e r t h a n a t a p p r o x i m a t e l y 45 d e g to t h i s d i r e c t i o n a s w o u l d b e e x p e c t e d f o r a b r i t t l e m a t e r i a l . It t h u s a p pears that the stresses in the longest specimen direction exceeded the critical resolved shear stress value t o c a u s e t h i s m o d e of f a i l u r e . M o r a n e f o u n d t h a t s i n g l e c r y s t a l s of MgCu2, a c u b i c L a v e s p h a s e , f a i l e d a l m o s t explosively with complete specimen disintegration between room temperature and 400~ a n d b e t w e e n 450 ~ a n d 600~ t h e MgCu2 s p e c i m e n s w e r e f o u n d to f a i l b y s e v e r e v e r t i c a l c r a c k f o r m a t i o n . T h u s , no s h e a r f a i l u r e f o r MgCuz e v e n up to 600~ w a s f o u n d . S i n c e H o Z n z i s r e l a t e d to MgCu2 b y a s l i g h t a t o m i c r e a r r a n g e m e n t , i t i s not s u r p r i s i n g t h a t t h e m o d e of f a i l u r e of t h e HoZn2 s p e c i m e n s r e s e m b l e s r a t h e r c l o s e l y t h a t f o r MgCu2.

Oxide Dispersion Strengthening in Sintered Aluminum Products, SAP NIELS HANSEN OXIDE d i s p e r s i o n s t r e n g t h e n i n g i n A1-A1 o x i d e products, deformed in tension has been satisfactorily a c c o u n t e d f o r i n p r o d u c t s c o n t a i n i n g 0.2 to 4.7 wt p c t A1 o x i d e . ~ O x i d e d i s p e r s i o n s t r e n g t h e n i n g w a s f o u n d by recrystallizing extruded products but this method is only possible in low-oxide products. For products, e.g., commercial SAP, with a higher oxide content it i s p r o p o s e d , on b a s i s of t h e f i n d i n g 2 t h a t s u b g r a i n boundary strengthening and oxide dispersion strengthe n i n g a r e s u p e r i m p o s e d , to d e r i v e f i g u r e s f o r t h e o x i d e s t r e n g t h e n i n g b y r e d u c i n g t h e s t r e n g t h of e x truded products by a subgrain-boundary strengthening contribution. T h i s i n d i r e c t a p p r o a c h i s a p p l i e d to f o u r S A P m a t e r i a l s in the e x t r u d e d c o n d i t i o n i n o r d e r to s t u d y t h e e f f e c t of t h e oxide p h a s e p a r a m e t e r s on the t e n s i l e f l o w s t r e s s a t r o o m t e m p e r a t u r e a n d a t 400~ The NIELS HANSEN is Head, Metallurgy Department, Danish Atomic Energy Commission Research Establishment, RisS, Roshilde, Denmark. Manuscript submitted May 15, 1969. METALLURGICAL TRANSACTIONS

M e t a l l o g r a p h i c e x a m i n a t i o n of a p o r t i o n of s p e c i men no. 6 just below the fracture surface revealed a m a r k e d c h a n g e in t h e t w i n s t r u c t