Unveiling the nanoscale strengthening mechanism of short-range order in CoCuFeNiPd high-entropy alloys: A hybrid MD/MC simulation study

Short Range Order (SRO) is the core unit of the microstructure in CoCuFeNiPd high entropy alloys (HEAs), which directly affects strength and plasticity. However, its strengthening mechanism at the nanoscale remains unclear. This study employed the hybrid MC/MD simulation method to investigate the effects of crystallographic orientation and SRO on the indentation mechanical response and phase transformation behavior of CoCuFeNiPd HEAs. The findings indicate that the phase transformation mechanism of HEAs varies with changes in orientation. Dislocation slip dominates in the [110] and [111] orientations. In the [001]-orientation, the phase transformation primarily follows the FCC-BCC-HCP. During the initial deformation stage, the premature nucleation of the BCC phase accelerates the yielding process. The [111]-orientation achieves exceptional hardness by forming a robust and immobile dislocation network. The SRO effect causes phase transformation to primarily occur in the atomic aggregation regions of Co-Fe-Pd, inhibiting dislocation propagation and maintaining high indentation hardness. Consequently, the introduction of SRO significantly enhances the hardness of CoCuFeNiPd HEAs in all directions. The generalized stacking fault energy calculations reveal that the potential strengthening mechanism is the SRO-induced increase in stacking fault energy, which effectively suppresses dislocation slip and nucleation, thereby mitigating surface damage. These results provide significant insights for engineering and optimizing HEAs with superior mechanical performance.