Study on Microstructure and Properties of FeCoNiCr0.8Al0.2 High‐Entropy Alloy by Multigradient Plasma Nitriding Process

This study explores the microstructure and properties of FeCoNiCr 0.8 Al 0.2 high‐entropy alloy (HEA) under multigradient plasma nitriding. The effects of adjusting the nitriding temperature, duration, and gas pressure on the microstructure and properties of the nitrided layer were characterized. The results show that a nitrogen‐enriched strengthening layer, composed mainly of Fe 4 N, CrN, and AlN, was successfully formed on the alloy surface after nitriding. Nitriding duration exhibited the strongest correlation with case depth, reaching up to 36 μm. In terms of mechanical properties, the nitriding process considerably enhanced the surface hardness. Higher nitriding pressure led to a deeper hardened layer with a more gradual hardness gradient, along with notably improved tribological performance. Under the optimized condition of 550°C × 8 h × 100 kPa, the hardness reaches 2.3 times that of the substrate (603.96 HV), and the wear loss was reduced by a≈93%. The friction coefficient stabilized, accompanied by a transition in the wear mechanism from severe spalling and abrasive wear to mild abrasive and oxidative wear. This work demonstrates that multigradient plasma nitriding can effectively strengthen the surface of FeCoNiCr 0.8 Al 0.2 alloy, providing an important experimental basis and theoretical guidance for developing high‐performance surface‐strengthened high‐entropy alloys and expanding their engineering applications.