New observations on high-temperature creep at very low stresses

Creep tests were conducted in compression to evaluate the flow behavior of aluminum at very high temperatures and low stresses. The experiments used two types of specimens: single crystals of 99.999% purity and oligocrystalline samples of 99.97% purity. Results obtained for the single crystals lie consistently between the conventional region of Harper-Dorn creep and the anticipated behavior based on an extrapolation of conventional 5-power creep. Using etch pit studies with the single crystals, it is shown there is no evidence for subgrain formation and the measured dislocation densities are consistent with data extrapolated from the conventional 5-power region. The creep results on single crystals suggest the stress exponent is close to similar to 3 at low stresses. It is demonstrated these results are consistent with earlier data including the results of Harper and Dorn when their data are plotted in terms of the true applied stress without incorporating a threshold stress. (C) 2009 Published by Elsevier B.V.