Mechanism of elemental segregation around extended defects in high-entropy alloys and its effect on mechanical properties

Abstract

Elemental segregation around extended defects is common in high-entropy alloys (HEAs) composed of multi-principal elements, which profoundly impacts their mechanical properties. In HEAs, the driving force for segregation usually competes with chemical short-range ordering (CSRO) formation, making it challenging to elucidate the segregation mechanisms. In this study, we systematically investigate the chemical composition changes around extended defects, including dislocations, stacking faults, and grain boundaries (GBs) in CoNiCrFe HEAs, to explore the chemical-structure-mechanical relationship utilizing hybrid Monte Carlo and molecular dynamic (MC/MD) simulations and theoretical analysis. We find a pronounced Cr enrichment and Co/Ni/Fe depletion around all defects considered in this work. A correlation between the degree of structural disorder and the chemical segregation/depletion phenomenon in the proximity of extended defects has been uncovered. Our results show that due to the extreme chemical complexity in HEAs, CSRO inevitably contributes to the elemental rearrangement and affects segregation. Consequently, the segregation behavior in HEAs is mainly controlled by interactions between different atomic pairs, and the segregation entropy also plays a dominant role. By decoupling the strengthening contribution from elemental segregation and CSRO, we demonstrate and highlight that the strengthening in HEAs can be modulated by elemental segregation. The positive impact of element segregation on interfacial properties - improved ultimate tensile strength and elongation, has been evidenced through experimental comparisons of CoNiCrFe with different Fe additions. This work elucidates the mechanism of heterogenous elemental distributions in HEAs where elemental segregation and CSRO coexist, paving the way for manipulating their mechanical properties by modulating the compositional variations.