The work-hardening of copper-silica

Abstract

Abstract A study by transmission electron microscopy of plastic relxation at undeformable spherical silica particles in a matrix of copper which has undergone plastic deformation leads to an understanding of the dislocation processes involved. The major process is the formation of dipoles of prismatic loops, either of primary Burgers vector, or of secondary Burgers vector. A full account is given of the systems of secondary dislocations which operate. The secondary dislocations form a tangle or plastic zone which hardens the crystal locally. The local hardening has two consequences: the crystal as a whole is strengthened because of the stress required to make primary dislocations cut the tangle; and further plastic relaxation is impeded, giving rise to local elastic stresses and a back stress. The observations enable one to estimate the magnitude of the elastic stresses, and explain (to within a factor of two) the strain hardening, the Bauschinger Effect, the strain for the onset of plastic cavitation, and certain observations by Wilson (1965) of the internal stresses in deformed two-phase alloys. The observations also cast light on the slip-line spacing, although further work is required to explain this completely.