A mechanical interpretation of the activation energy of high temperature deformation in two phase materials

The deformation of two phase materials is analyzed and a mechanical model 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 observation that the activation energy for two phase flow is generally much higher or much lower than the flow activation energies of the individual phases. This is because the apparent activation energy of the aggregate includes an additional term that depends on the rate of change with temperature of the volume fractions of the two phases. The predictions of the model are compared to experimental results and are shown 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 mechanism since an additional mesoscopic term is involved.