Defect-induced inhomogeneous atomic environments in complex concentrated alloys

Abstract

The multiple elements in equal ratios in complex concentrated alloys (CCAs) favor the formation of local atomic environments like segregation or chemical ordering observed in recent experiments. Such special local atomic environments may pin dislocations on the slip plane, resulting in a higher flow stress for the escape of dislocations and hence a dynamic strain aging (DSA) effect in the form of stress drop. Here, Monte Carlo molecular dynamics (MC/MD) simulations are used to elucidate the atomic atmospheres around dislocations and stacking faults in the NiCoCr alloy system and quantitatively determine the stress drop effect. Increased chemical ordering and segregation around stacking faults and dislocation cores are observed, but detailed analysis shows that atomic segregation around stacking faults (Suzuki atmospheres) contributes the most to stress drop, compared with segregation around dislocation cores (Cottrell atmospheres) and enhanced ordering (Fisher) effects. The MD simulated stress drops are in good agreement with theoretically predicted and experimental values. This work fills an important gap in the understanding of the DSA effect in H/MEAs.