Characterising thermally activated dislocation mechanisms

Various methods based on mechanical tests have been developed through the years for investigating dislocation mobility. The measured experimental quantities are the strain-rate sensitivity of the stress or thermodynamic parameters, such as the activation volume and energy, which are considered as characteristic parameters of dislocation mobility. However, these parameters are generally determined by assuming that, during the mechanical test, the dislocation microstructure remains constant, a condition which is not frequently satisfied. We show that a careful examination of the transient test kinetics, such as repeated load relaxations and repeated creep tests performed on the Ni3Al intermetallic compound, can provide useful information concerning microstructural evolutions, in particular on the mobile dislocation densities and the internal stress variations. Correlations are found between dislocation exhaustion rates and work hardening coefficients.