Deformation Mechanisms and Activation Parameters in RMPEA Micropillars Across the Temperature Spectrum—From Cryogenic to High Temperature

Refractory multi-principal element (RMPE) alloys possess remarkable strength retention at elevated temperatures, making them attractive for extreme structural environments. Several promising single-phase alloys demonstrate an intermediate temperature strength regime that is quasi-athermal, motivating studies that aim to link the temperature-dependent mechanical behavior to dislocation behavior in these concentrated BCC alloys. To elucidate the relationships between strength, dislocation plasticity, and thermal activation, in situ single crystal micropillar compression experiments are conducted in the SEM on a newly developed RMPE alloy (Hf-Mo-Nb-Ta-Ti) deformed along two different crystallographic directions at both cryogenic and elevated temperatures. At each testing temperature, the specimens are subjected to various strain rates allowing for the extraction of activation parameters, with post-mortem TEM used to evaluate resulting dislocation structures. The obtained results, supported by phase-field dislocation dynamics (PFDD) simulations, are analyzed within the framework of thermally activated deformation mechanisms and the origins of the quasi-athermal strength observed at intermediate temperatures, bolstering the understanding of defect dynamics in high temperature multi-component alloys.