Characterization of thermally activated dislocation mechanisms using transient tests

Two methods of repeated transient tests, namely relaxation and creep, are shown to be ideal techniques for the characterization of plastic deformation processes. They yield similar information about a microscopic activation volume, which is the signature of the operating dislocation mobility mechanism. Microstructural parameters are also obtained, the values of which are different in creep and stress relaxation. They characterize work-hardening during the transient and dislocation exhaustion rates respectively. The equations describing the transients and the assumptions involved are presented. Experimental results on Ni3Al polycrystals illustrate the possibilities of both tests and support the above assumptions. In particular, crystals which work-harden exhibit high dislocation exhaustion-rates, as shown by comparison of Ni3Al with TiAl, Ge and Cu. The respective contributions to the strain-rate of the mobile dislocation densities and velocities can also be estimated.