Analysis of Coble creep in cylindrical and cubic crystals

AbstractAn analysis is made of the rate of creep by the stress induced diffusion of vacancies along surfaces or grain boundaries of crystals of cylindrical and cubic shape, developed from the original proposal by Coble of the significance of this creep mode. It is shown that complete analytical solutions can be obtained, satisfying all physical conditions of the problem. The creep rate ε by this mechanism at a temperature T in a cylinder of length L and diameter D subjected to a stress σ along its axis is given by ε = 64D8g wσΩ/kTLD2[1 + (4L/3D)], where Dg is the, self-diffusion coefficient in a layer at the surface or grain boundary of width w, Ω is the atomic volume and k is Boltzmann's constant. In the case of a cube of side L subject to stress σ perpendicular to a pair of faces, the creep rate ε = 16DgwσΩ/kTL3.MST/251