Effect of Mo on microstructure and sliding wear performance of CoCrFeNiMox high entropy alloy coatings by laser cladding

The CoCrFeNiMo _x (x = 0, 0.5, 1, 1.5 in molar ratio) high-entropy alloys (HEAs) coating were prepared on AISI1045 steel by laser cladding. The microstructure, hardness and tribological properties were investigated through x-ray diffraction, scanning electron microscopy (SEM), microhardness tester and reciprocating tribometer. The result shows that the coating is metallurgically bonded to the substrate and exhibits columnar and equiaxed grains microstructure consisted of main face-centered cubic (FCC) solid solution and few body-centered cubic (BCC) struture when x≤ 1.0. The (Fe, Cr, Mo)-riched σ phase shows up in the CoCrFeNiMo _1.5 FCC matrix due to excess Mo addition. CoCrFeNiMo _x HEA coatings shows an obvious increase of surface hardness from 261 HV _0.2 to 793 HV _0.2 by increasing the Mo content to 1.5 in the molar ratio, and exhibited the most excellent wear resistance among all the compositions designed in this work. The wear resistance of the CoCrFeNiMo _1.5 alloy coating is about 2.2 times higher than that of the coating without Mo. The wear mechanism changes with increasing Mo content, though abrasive wear is a common mechanism, more adhesive wear occurred at low Mo content but few oxidation and fatigue wear occured at high Mo content.