Characterising thermally activated dislocation mechanisms

Various methods based on mechanical tests have been developed through the y ears for investigating dislocation mobility. The measured experimental quan tities are the strain-rate sensitivity of the stress or thermodynamic param eters, such as the activation Volume and energy, which are considered as ch aracteristic 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 frequ ently satisfied. We show that a careful examination of the transient test k inetics, such as repeated load relaxations and repeated creep tests perform ed on the Ni3Al intermetallic compound, can provide useful information conc erning microstructural evolutions, in particular on the mobile dislocation densities and the internal stress variations. Correlations are found betwee n dislocation exhaustion rates and work hardening coefficients. (C) 2001 El sevier Science B.V. Ail rights reserved.