Screw-controlled strength of BCC non-dilute and high-entropy alloys

The impressive mechanical properties of single phase BCC High Entropy Alloys (HEAs) has renewed interest in understanding the mechanisms controlling strength in BCC alloys. Theory and simulation of strengthening of screw dislocations in HEAs shows that screw dislocations become spontaneously kinked along their length to lower the total energy due to solute/screw interactions. Dislocation motion then mainly occurs via two mechanisms, lateral kink migration and breaking of cross-kinks due to kink formation on different glide planes. Existing kink migration models, in spite of successes in capturing some experiments, are based on several invalid assumptions. Here, a new theory for the kink migration in HEAs is developed based on recent understanding in dilute alloys, leading to a fully derived analytical model for the kink migration energy barrier as a function of applied stress and kink spacing. Results emerge to be quantitatively close to those presented in recent theory by Maresca and Curtin but are on much firmer theoretical basis. A revised version of the Maresca-Curtin screw strengthening theory that incorporates the new kink migration model is compared to experiments on non-dilute Fe-Si, Nb-Mo, and Nb-W alloys and shows broad agreement as a function of temperature and composition, establishing the quantitative accuracy of the new theory.