A MECHANICAL INTERPRETATION OF THE ACTIVATION-ENERGY OF HIGH-TEMPERATURE DEFORMATION IN 2 PHASE MATERIALS

The deformation of two phase materials is analyzed and a mechanical mo del is derived for calculating the apparent activation energy of how. The latter is expressed in terms of the individual activation energies of the two constituent phases. The model is used to account for the o bservation that the activation energy for two phase flow is generally much higher or much lower than the flow activation energies of the ind ividual phases. This is because the apparent activation energy of the aggregate includes an additional term that depends on the rate of chan ge with temperature of the volume fractions of the two phases. The pre dictions of the model are compared to experimental results and are sho wn to be in good agreement with them. The present mechanical approach demonstrates clearly that the apparent activation energy for the flow of a two phase material is not, in general, related to a specific mech anism since an additional mesoscopic term is involved.