Variation of chemical ordering induced by grain boundaries in multi-principal element alloys

Cr segregation at grain boundary (GB) of Multi-principal element alloys (MPEAs) is extensively observed and holds significance in physical processes, e.g., oxidation, but its atomic-level mechanism is still debated. Here, correlations among atomic-level volume, electronegativity, charge transfer, and atomic stress, are systematically investigated in equiatomic CrFeCoNi alloys, both with and without GBs. The correlations slightly disturbed in GBs inadequately elucidate the discrepancy of Cr short range ordering (SRO) in the interior grain and at GBs. High excess free volume inherent in GBs, distinguishing from the interior, is a crucial factor, driving Cr enrichment by means of the mitigation of electron loss and the alleviation of very high tensile stress. The stress mechanism in conjunction with the electronegativity of element and the characteristics of GB structure, not only adapts to Cr segregation in CrFeCoNi, but also to other element of low electronegativity within considered alloys.