The Influence of Alumina Dispersions on the Diffusion-Creep Behaviour of Polycrystalline Copper

Abstract

AbstractThe creep behaviour of powder-compacted copper and copper containing 0.5, 1.0 and 1.5 vol.-%alumina has been investigated in the range where the stress-directed lattice diffusion of vacancies is expected to control. Addition of alumina particles is shown to change the initial flow characteristics from Newtonian, where the creep rate έ is proportional to the applied stress σ, to Bingham type, where έ is proportional to an effective stress σέ. This effective stress is defined by σέ = σ − σ0, where σ0 is a threshold value that increases linearly with volume fraction of alumina and below which no deformation occurs. The proportionality constant between έ and σE is shown to be identical to that between έ and σ and is given by the Nabarro-Herring equation as BΩD/d2 kT, where B is a numerical constant, Ω the atomic volume, D the lattice self-diffusion coefficient, D the grain size, and kT has its usual meaning. Above the threshold stress, creep rate decreases with strain and this curvature is more pronou...