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strains (varying s t r e s s fields) within t h e s e regions of " g o o d crystal." With r e g a r d t o this last p o i n t , it is of interest t o note that X - r a y diffraction provided some of the f i r s t d i r e c t evidence for dislocations in t e r m s of the existence of nonuniform strains over s m a l l distances. 5 T h e r e have been numerous X - r a y diffraction studies of cold worked m e t a l s d u r i n g the p a s t twenty years; however, t h e s e have been concerned for the most part w i t h cold worked powders which, although providing g e n e r a l structural information, do not p e r m i t examination of structure-property relations. With regard t o solid polycrystalline materials, a r e c e n t study of an a - C u - G e alloy deformed by explosive loading at various shock pressures established the existence of certain e m p i r i c a l relations between the yield strength of the m a t e r i a l and the substructural p a r a m e ters (mean free path and nonuniform strain) d e t e r mined by X - r a y diffraction.6 It will be shown here that t h e s e same relationships apply t o pure Cu deformed by r o l l i n g at room temperature. T h e s e observations on pure Cu are important because it is well known that Cu tends t o form a dislocation cell structure on deformation and that the cell size is relatively constant above a certain v a l u e of strain. However, despite the fact that the cell size (or mean free path) r e m a i n s constant, the strength continues t o i n c r e a s e as a function of strain.%8 As will be shown h e r e , this further i n c r e a s e in strength can be related t o an i n c r e a s e in the l e v e l of the nonuniform strains associated with the dislocation substructure and it is therefore possible t o establish the importance of the nonuniform strains independent of the effects of the mean free path. Finally, the process of dynamic recovery at high strains in pure Cu will be shown to be a consequence of the collapse of the nonuniform strains, most likely as a r e s u l t of stress-induced rearrangement of dislocations through c r o s s slip a n d / o r c l i m b . The delay of the onset of dynamic recovery by the addition of 95 ppm Sn t o the Cu and the fact that it does not o c c u r in OFHC Cu also follow from the behavior of the nonuniform strains. E X P E R I M E N T A L PROCEDURE Copper rod ~1.0 cm in diam and 99.999+ pct pure was used as the base m a t e r i a l for these experiments. A Cu-0.01 a t . pct Sn alloy was prepared by arc m e l t ing an appropriate amount of Cu with a m a s t e r alloy VOLUME 8A, JANUARY 1977-45

of Cu-12.5 a t . pct Sn prepared from the pure Cu and 99.999+ pct Sn. The alloy was remelted s e v e r a l t i m e s t o promote homogenization and then g i v e n a f i n a l homogenization a n n e a l at 1050°C. Chemical analysis showed the alloy to contain 95 + 5 ppm Sn. Specimens of both the Cu and the Cu-Sn alloy were prepared by r o l l i n g the m a t e r i a l into s t r i p s 0.38 cm thick and recrystallizing at 500°C for 30 m