A hierarchical multiscale crystal plasticity model for refractory multi-principal element alloys

Refractory multiple principal elemental alloys (RMPEAs) show the excellent combinations of mechanical properties and oxidation resistance, are considered the most promising as the structural materials for aerospace industries and gas turbine. However, the quantitative contribution of microstructure on the strength and deformation mechanisms remains challenging at micrometer scale. In this work, we capture the lattice distortion and chemical short-range order (CSRO) using atomic simulation, and introduce them into the hierarchical multiscale model to study the strengthening mechanism and plastic behavior in the body-centered cubic HfNbTa RMPEA. The results show that the ultrastrong local stress fluctuation greatly improves the dislocation-based strength, causing the significant dislocation forest strengthening in the annealed state. The dislocation slip would be suppressed for raising the strength and increasing the difficulty of the plastic deformation in the annealed HfNbTa. Thus, the existence of the CSRO structure effectively enhances the strength, in a good agreement with the experiment. The inhomogeneous degree of the stress distribution become more serious at the high strain, responding well to the plastic deformation of the high-strength HfNbTa. 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 in the annealed HfNbTa. Our findings give an insight into exploring MPEAs with desired mechanical properties via tailoring CSRO by utilizing thermomechanical processing.