Plasma nitriding is successfully employed in treating AlxCoCrFeNi high-entropy alloys (HEAs) with finely-divided Al content (i.e.,x values in molar ratio,x =0.1-0.8) to develop wear-resistant structural materials.Nitridation greatly removes the Al from the matrix that completely deplete the Ni-Al enriched phase,forming nanoscaled nitrides (AlN and CrN) precipitations near the surface.Nitriding promotes the hard-ness of present alloys with values widely ranging from 276 HV to 722 HV.Interestingly,the higher content the Al,the smaller thickness the nitrides layer,but the higher hardness due to the increased amount of hard nitrides phases and volume fraction of BCC phase.Significantly,plasma nitriding considerably improves the wear resistance of AlxCoCrFeNi HEAs by 4-18 times.