Insights into microstructures and mechanical properties of gigapascal-strength nitrogen-doping equiatomic VCoNi multicomponent alloys attained via annealing heat treatment

Abstract

This study systematically investigates the effects of high-concentration nitrogen doping on microstructure evolution and mechanical properties of equiatomic VCoNi multi-component alloys (MCAs) treated using different annealing conditions. The results suggest that after a 900 °C annealing, the nitrogen content in the matrix promotes vanadium nitride formation through preferential VN bonding. This depletes vanadium in the matrix, substantially facilitating κ-phase precipitation. Such nitrides exhibit a progressive tendency of dissolution into the alloy matrix with increasing annealing temperature and duration. Specifically, the 1000 °C-annealed specimen achieves exceptional strength-ductility synergy, namely a yield strength of ∼950 MPa, ultimate tensile strength of ∼1.3 GPa, and ∼ 26 % fracture elongation. This performance enhancement mainly originates from multiple strengthening effects caused by the introduction of nitrogen atoms. Furthermore, local chemical ordering (LCO) are also found in this 1000 °C-annealed specimen, which promotes planar dislocation slip behavior and generates high-density planar dislocation arrays in the alloy. This fact effectively accommodates plastic strain, facilitating the strength-and-ductility synergy. The present work provides meaningful perspectives for interstitial strengthening mechanisms and tailoring heat treatment processes in MCAs for real applications.