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

The present work demonstrates that nitrogen doping inhibits the formation of deformation twins in a CrMnFeCoNi high entropy alloy, while significantly increases the strength without sacrificing much duc-tility 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.(c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

This study demonstrates that nitrogen doping can suppress the formation of deformation twins in a CrMnFeCoNi high entropy alloy and significantly enhance its strength at 77 K without sacrificing much ductility. Microstructural characterization and first-principles calculations uncover the role of interstitial nitrogen atoms in achieving this excellent combination of strength and ductility. The addition of nitrogen increases the generalized stacking fault energy and reduces twinning, while the pinning of dislocations by nitrogen atoms effectively inhibits dislocation cross-slip and dynamic recovery, thereby promoting the accumulation of dislocations. The high dislocation density contributes to high strain hardening capacity and improved uniform elongation, compensating for the ductility loss caused by solid solution strengthening. The effect of nitrogen doping enriches the design concept of high- and medium-entropy alloys and provides an economical and effective strategy for developing ultra-high-performance alloys suitable for cryogenic applications.