STRENGTHENING IN HEAVILY DEFORMATION PROCESSED CU-20-PERCENT NB

Strengthening in heavily deformation processed Cu-20% Nb was compared with predictions from barrier and nonhomogeneous deformation models of hardening. A barrier model of strengthening, where the difficulty in propagating plastic flow across Cu-Nb interfaces controls strengthening, or a nonhomogeneous deformation model of strengthening in plastically deforming two phase structures, where the high density of dislocations generated to maintain compatibility between the Cu and Nb phases controls strengthening, were both in good agreement with the observed increases in strength with increasing deformation processing. Both models predict the observed Hall-Petch relation with Nb filament spacing. They also predict dislocation densities that continuously increase over the range of strains induced during deformation processing by wire drawing or rolling. This is in contrast to experimental observations indicating that the dislocation density in Cu-20% Nb is independent of the degree of deformation processing and that it is about the same as that measured in similarly deformation processed pure Cu.