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T H E limited ductility g e n e r a l l y observed in b e r y l l i u m r e s u l t s from the lack of an active slip s y s t e m with a s l i p component p a r a l l e l to the " C ~' a x i s . At t e m p e r a t u r e s below about 200~ the ductility is f u r t h e r r e s t r i c t e d by the formation of bend p l a n e s , g e n e r a t e d by b a s a l s l i p , which lead to cleavage and b r i t t l e f r a c t u r e . 1-3 Elongations at r o o m t e m p e r a t u r e in p o l y c r y s t a l l i n e b e r y l l i u m under uniaxlal tension a r e t y p i c a l l y 1 to 5 pct. Thus, extensive ductility in b e r y l l i u m can probably only be achieved under conditions where deformation modes other than slip contribute s u b s t a n t i a l l y to the total d e formation. Superplastic behavior (other than that induced by i n t e r n a l s t r e s s , as in t h e r m a l cycling through phase t r a n s f o r m a t i o n s ) is g e n e r a l l y attributed to the unique p r o p e r t i e s of a g g r e g a t e s of v e r y fine g r a i n s at t e m p e r a t u r e s above half the absolute melting point. Fine g r a i n s , stable at high t e m p e r a t u r e s , a r e commonly found in eutectic or eutectoid alloys and only r a r e l y in single phase m a t e r i a l s . 4 In polyphase m a t e r i a l s , it a l s o a p p e a r s n e c e s s a r y for s u p e r p l a s t i c behavior that the p h a s e s be p r e s e n t in n e a r l y equal amounts and have about the s a m e ductility. 4 Diffusion bonding work, r e p o r t e d e l s e w h e r e s on c a s t and w a r m r o l l e d ("ingot s h e e t " ) b e r y l l i u m with a 16 ~m g r a i n s i z e , e s t a b l i s h e d that extensive c o m p r e s s i v e d e f o r m a t i o n of this m a t e r i a l was p o s s i b l e without s i g n i f i cant change in grain s i z e or shape. This investigation of p o s s i b l e s u p e r p l a s t i c i t y in b e r y l l i u m was undertaken as a r e s u l t of these o b s e r v a t i o n s . EXPERIMENTAL TECHNIQUE Coupons were made by a diffusion bonding process described elsewheres from ten sheets of 0.64 mm (0.025 in.) thick beryllium foil, and sheet-type, pinloaded tensile bars were machined from the coupons. The foil was prepared by can rolling a cast ingot, followed by bare rolling to the final thickness. The resulting laminate was about 0.33 cm (0.13 in.) thick and had a grain size of about 16 ~m. The laminates produced are isotropic in the plane of the sheet and have a maximum basal texture of about 4.5 times random. 5 A chemical analysis of this material is given in Table I. The difference in oxygen content by the two analysis techniques is probably real. Neutron activation samples CLINTON R. HEIPLE is Senior Research Metallurgist,Dew Chemical USA, Rocky Flats Division,Golden, Colo. 80401. Manuscript submitted March 6, 1972. METALLURGICALTRANSACTIONS

the bulk of the m a t e r i a l , including the finely d i s p e r s e d oxide found along the bond i n t e r f a c e s . The s p a r k e m i s sion s p e c t