A dislocation network theory of Harper-Dorn creep—I. Steady state creep of monocrystalline Al

Abstract

A recently developed dislocation network theory of high temperature creep is modified for consistency with the equally recent experimental observation that the dislocation link length distribution that develops during Harper-Dorn (H-D) creep of monocrystalline Al deformed in compression at 920 K contains no segments that are long enough to glide or climb freely. H-D creep is therefore a phenomenon in which all the plastic strain in the crystal is generated by the process of stress-assisted dislocation network coarsening, during which the glide and climb of dislocations is constrained by the requirement that the forces acting on individual links are balanced by the line tension of the links. It is not possible to test all the predictions of the theory because not all the required input information is available. In particular, the kinetic law governing the growth rate of individual links is not known. Nonetheless, using an established and well-known equation as a first guess, it is possible to simulate the experimentally observed distribution of dislocation link lengths with reasonable semiquantitative accuracy. In other respects, especially regarding the steady state creep rate, the theory is in excellent agreement with the experimental results.