The role of Harper–Dorn creep at high temperatures and very low stresses

Creep experiments were conducted on single crystals of very high purity aluminum to evaluate the validity of the Harper–Dorn region of flow which occurs at very low stresses and high homologous temperatures. The results confirm the existence of a different flow process under these conditions but with a stress exponent closer to ∼3 rather than 1. Measurements show that the dislocation density within this low stress region varies with stress in a manner consistent with the behavior anticipated from an extrapolation of data reported in the regime of conventional power-law creep at high stresses. All of the experimental results are in reasonable agreement with earlier published data, including with the original data of Harper and Dorn when their results are plotted without incorporating a threshold stress.