AN EXAMINATION OF THE METALS DEFORMING BY HARPER-DORN CREEP AT HIGH HOMOLOGOUS TEMPERATURES

At low stresses and high homologous temperatures, metals exhibit Newtonian viscosity with a stress exponent of 1. This behavior is attributed to either Harper-Dorn creep arising from a dislocation process or Nabarro-Herring creep resulting from the stress-directed diffusion of vacancies. By analysing experimental data where the occurrence of Harper-Dorn creep is unambiguous, a relationship is derived for the transition between the two processes. It has been suggested recently that several experiments, using the zero creep technique on wires and foils, are consistent with Harper-Dorn creep. Using the transition relationship, it is demonstrated that these experiments are instead within the regime of Nabarro-Herring creep.