Deformation by creep or by stress-relaxation involve similar thermally activated phenomena. In particular our microstructural observations on the Al-Al2Cu lamellar composite illustrated the importance of the interphase accommodation mechanisms, specially movements of linear defects at the phase boundaries.
Our experimental results have shown that the asymptotic stress measured in stress-relaxation tests takes the same value as the threshold stress limiting the steady state creep domain. From this finding we develop a simple Bingham rheological model in which a temperature dependent threshold stress is combined with a generalized Dorn viscosity law. The model correlates satisfactorily the results of both steady state creep tests and the results of stress-relaxation tests.
The calculated activation energy and stress exponent are compared with the values deduced from physical models of deformation accommodation through grain boundary sliding. The preexponential factor of the viscosity law is discussed with reference to its dependence on the dislocation substructure.