High-temperature deformation in a Ta-W alloy

High-temperature deformation was investigated in a Ta-2.5 wt% W commerciall y available tantalum 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 stre ss 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 stron ger than that attributable to the shear modulus. By considering the effect of the threshold stress and its temperature dependence on creep plots, it i s demonstrated that the true creep characteristics of Ta-2.5 wt% W are cons istent with those reported for solid-solution alloys at high stresses. In p articular, the creep behavior of the alloy exhibits a transition from a reg ion controlled by viscous glide to a high-stress region related to the brea kaway of dislocations from solute-atom atmospheres. An examination of creep substructure in Ta-2.5 wt% W reveals the presence of interaction between m oving dislocations and dispersion particles. It is suggested that such an i nteraction provides the most likely source of the threshold stress for cree p in the alloy. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Scien ce Ltd All rights reserved.