✍ Scribed by Z. Lin; E.J. Lavernia; F.A. Mohamed
No coin nor oath required. For personal study only.
AbstractÐHigh-temperature deformation was investigated in a Ta±2.5 wt% W commercially 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 stress dependence of creep rate is high and that the temperature dependence of creep rate is higher than that for self-diusion 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 attributable to the shear modulus. By considering the eect of the threshold stress and its temperature dependence 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 breakaway 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.
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