The behavior of 12⟨111⟩ screw dislocations in W–Mo alloys analyzed through atomistic simulations

Abstract

Analyzing plastic flow in refractory alloys is relevant to many different commercial and technological applications. In this study, screw dislocation statics and dynamics were studied for various compositions of the body-centered cubic binary alloy tungsten–molybdenum (W–Mo). The core structure did not appear to change for different alloy compositions, consistent with the literature. The pure tungsten and pure molybdenum samples had the lowest plastic flow, while the highest dislocation velocities were observed for equiatomic, W0.5Mo0.5 alloys. In general, dislocation velocities were found to largely align with a well-established dislocation mobility phenomenological model supporting two discrete dislocation mobility regimes, defined by kink-pair nucleation and migration and phonon drag, respectively. Velocities were observed to increase with temperature and applied shear stress and with decreasing kink-pair formation energies. The 50 at. % W alloy was found to possess the lowest kink-pair formation energy, consistent with its higher dislocation velocity. Furthermore, molybdenum segregation to the dislocation line was found to be thermodynamically favorable specifically at low temperatures and was observed to significantly delay the onset of dislocation glide and then generally enhance dislocation velocities thereafter. This behavior was explained by examining the energy landscape of dislocation glide. Furthermore, a segregation/de-segregation phase transition was observed to occur around 2500 K beyond which no preferential segregation to the dislocation was found. Overall, our findings suggest strong dependencies of plastic flow in W–Mo alloys on composition and elemental segregation, in agreement with the available literature, and may provide useful information to guide the design of next generation structural materials.