Atomistic simulations and theoretical modeling of dislocation slip and yield response of industrial tantalum alloys

Abstract

Dislocation core structure, critical resolved shear stress (CRSS) and mobility of ½<111> screw and edge dislocations in BCC Ta-8%W alloy was studied using molecular statics and dynamics simulations at 5 and 300 K. Two EAM potentials are available to study the Ta-W system - Johnson-Zhou and Chen potentials. Both potentials give good estimates of edge dislocation mobility in Ta and Ta-8%W. However, the Johnson-Zhou potential predicts a considerably higher CRSS for screw dislocations in pure Ta as compared to experiments. Thus, only the Chen potential is used to study solid solution strengthening in Ta-8%W alloy. The CRSS for Ta-8%W alloy with Chen potential was estimated to be 600 MPa and 300 MPa for screw dislocations at 5 and 300 K, respectively. Edge dislocations exhibit twinning-anti twinning asymmetry in CRSS given the asymmetry in atomic disregistry and dislocation misfit across the glide plane. The simulation results for screw and edge dislocation mobility were found to be in good agreement with the CRSS values from the analytical model of Rao and Suzuki for screw dislocations and the model of Maresca and Curtin for edge dislocations. The study of stability and expansion of shear dislocation loops revealed that theoretical results for loop stabilizing stress from Scattergood and Bacon's equation agreed with results from direct atomistic simulations. The current work predicts that screw dislocations control the experimental yield behavior of the Ta-8at%W alloy at all temperatures. The CRSS for Ta-8%W alloy is a result of solid solution strengthening due to randomly dispersed W solutes in Ta.