The Inhibition of Diffusion Creep by Precipitates

AbstractIt has been demonstrated repeatedly that diffusion creep is inhibited when a second phase is present in a polycrystalline sample. It is proposed that this inhibition is due to the precipitates affecting adversely the ability of the high-angle grain boundaries to absorb or emit vacancies. During strain, precipitates are collected at those boundaries which are parallel to the tensilestress axis and this results in the diffusion-creep rate falling continuously. A simple model is presented which assumes that deformation can proceed only by the generation of dislocations in the matrix adjacent to the intergranular precipitates. The derived relationship between strain (e) and time (t) is e = (α/β) (1 – exp – J3t), where α and β are constants for a given specimen and test condition. The diffusional strain predicted from this equation was found to be in reasonable agreement with that observed in a creep specimen of a magnesium – 0.55 wt.-% zirconium alloy. The theoretical model can also be applied to the ...