Chemical short-range-order induced multiscale strengthening in refractory medium entropy alloys

High/medium entropy alloys (H/MEAs) are generally possible to exhibit chemical short-range order (SRO). However, the complex role of SRO on mechanical properties from nano-scale to meso-scale is still challenging so far. Here, we study the strengthening mechanism and deformation behavior in a model body-centered-cubic HfNbTa MEA by using atomic-scale molecular dynamics, micro-scale dislocation dynamics, and meso-scale crystal plasticity finite element. The SRO inhibits dislocation nucleation at the atomic scale, improving the flow stress. The SRO-induced ultrastrong local stress fluctuation greatly improves the micro-scale dislocation-based strength by the significant dislocation forest strengthening. Moreover, the Ta-rich locally ordered structure leads to an obvious heterogeneous strain and stress partitioning, which forms a strong strain gradient in the adjacent grain interiors and contributes to the strong back-stress-induced strain hardening.