Critical temperatures for ductile to brittle transition and athermal strength in refractory metals

The plasticity of body-centered cubic metals exhibits a strong temperature dependence, governing both their yield behavior and their transition from brittle to ductile fracture. While it is well established that strength and toughness in bcc metals undergo distinct transitions at critical temperatures, the underlying mechanisms—particularly how dislocation structure, interactions, and glide modes govern these changes—are not fully understood. In this work we employ phase field dislocation dynamics to simulate glide kinetics of long screw dislocations and dislocation loops in five refractory body-centered cubic metals: Mo, Nb, Ta, V, and W. This mesoscale approach to dislocation modeling provides a parameter-free, cross-material framework that enables direct, mechanistic comparison of temperature-dependent glide. Analysis reveals that critical stress–temperature data collapse onto a single master curve after a simple normalization by measured quantities, yielding a compact descriptor for pure bcc metals. This universal scaling provides a direct, predictive link between the fundamental kinetics of screw dislocation glide and macroscopic properties of body-centered cubic metals. Loop expansion simulations reveal that the screw-to-edge mobility ratio increases approximately linearly with temperature and yet remains less than unity across all systems. Loop aspect ratio is found to correlate with bulk elastic anisotropy (Zener ratio). Notably, screw-to-edge mobility contrast in Nb is larger than expected from elastic anisotropy alone, highlighting that core-controlled kinetics amplify the effects of elastic anisotropy. Together, these findings establish a mechanistic connection from tabulated material properties to temperature-dependent glide, clarifying why different body-centered cubic refractories exhibit distinct strength and toughness transitions.