Enhanced strength-ductility synergy via high dislocation density-induced strain hardening in nitrogen interstitial CrMnFeCoNi high-entropy alloy

Abstract

• Nitrogen addition induced a remarkable increase in strength but only a negligible decrease in uniform elongation of CrMnFeCoNi HEA. • First-principles calculations were carried out to analyze the effect of nitrogen on generalized stacking fault energy ( γ usf , γ isf , and γ utf ) and twinning. • The pinning effect of nitrogen on dislocations contributed to the increased dislocation density and thus the higher strain-hardening rate. The present work demonstrates that nitrogen doping inhibits the formation of deformation twins in a CrMnFeCoNi high entropy alloy, while significantly increasing the strength without sacrificing much ductility at 77 K. Microstructural characterization and first-principles calculations were employed to unveil the role of interstitial nitrogen atoms in obtaining such an excellent combination of strength and ductility at 77 K. It is found that nitrogen addition increases generalized stacking fault energy (GSFE) and reduces twinning. However, the pinning of dislocations by nitrogen atoms effectively suppresses dislocation cross-slip and dynamic recovery and in turn, promotes the accumulation of dislocations. The high dislocation density induces a high strain hardening capacity and improves uniform elongation, which compensates for the ductility loss accompanied by solid solution strengthening. The effect of nitrogen doping enriches the design concept of high- and medium-entropy alloys, providing an economical and effective strategy to develop ultra-high-performance alloys that are suitable for cryogenic applications.