HIGH-TEMPERATURE DEFORMATION IN A Ta-W ALLOY

摘要

High-temperature deformation was investigated in a Ta-2.5 wt W commercially available tan- talum alloy, at temperatures in the range of 1523-1723 K and at a stress range extending from 35 MPa to 210 MPa. The experimental data, which cover several orders of magnitude of strain rate, show that the stress dependence of creep rate is high and that the temperature dependence of creep rate is higher than that for self diffusion in tantalum. An analysis of the experimental data indicates that a threshold stress for creep exists, and that the temperature dependence of the threshold stress is much stronger than that at- tributable to the shear modulus. By considering the effect of the threshold stress and its temperature depen- dence on creep plots, it is demonstrated that the true creep characteristics of Ta-2.5 wt W are consistent with those reported for solid-solution alloys at high stresses. In particular, the creep behavior of the alloy exhibits a transition from a region controlled by viscous glide to a high-stress region related to the break- away of dislocations from solute-atom atmospheres. An examination of creep substructure in Ta-2.5 wt W reveals the presence of interaction between moving dislocations and dispersion particles. It is suggested that such an interaction provides the most likely source of the threshold stress for creep in the alloy.