Atomic mechanism of cyclic healing effect in dual-phase metastable high entropy alloy

Abstract

While many experiments and simulations on the high entropy alloy have focused on the deformation mechanisms under monotonic loading, the cyclic deformation behaviors remain largely elusive. In this work, the cyclic deformation behaviors of the dual-phase metastable high entropy alloy Ta0.5HfZrTi were investigated using molecular dynamics simulations with special focus on the interaction between phase boundaries and dislocations. Unlike the monotonic loading, the complex dislocation network formed in the growth of the martensite can be dramatically modified with different cyclic loading patterns. Both cyclic growth and cyclic healing effect were observed in simulations with different loading patterns. As the minimum strain reduces, the isolated dislocations and the unpinned partial dislocation on the stacking fault are found compressed and absorbed by the phase boundaries with the repeated straining. This cyclic healing effect is in distinct contrast to conventional cyclic straining hardening mechanisms with the increased dislocation density in metals and in agreement with the recent experimental observation of absent strain hardening effect in the cyclic response conduced on the metastable HEA recently. The present study provides a platform to probe an atomic-level understanding of the fundamental mechanisms in fatigue of dual-phase metastable HEAs.