Colossal anelasticity in polycrystals deforming under conditions of diffusional creep

Since diffusional creep viscosity depends strongly on the grain size, a variability in the grain size in a polycrystal can generate significant internal stresses. Upon unloading, the non-uniform internal stresses recover, leading to anelastic strains. The anelastic strains can be very large, approaching 100 times the elastic strains. We solve the case of bimodal viscosity in closed form to highlight the features of this type of anelasticity. The results are compared to the anelastic behavior of two-phase superplastic alloys. In such alloys the spatial variability in the diffusional viscosity can arise from the variability in the activation energy of grain boundary diffusion, which, because of its Arrhenius nature, can produce a much higher degree of variability than the grain size.