Abstract: MoS₂ modified Fe-Cr-Mo-Si alloy coating was prepared on 40Cr steel substrate by laser cladding technology. The effect of defocusing amount on macro morphology, microstructure, microhardness and friction and wear resistance of the composite coating was studied. The results show that with the increase of defocusing amount, the smoother the composite coating surface, the better metallurgical bonding between the composite coating and the substrate. The upper part of the composite coating is fine equiaxed crystal, the middle is dendrite, and the bottom is columnar and plane crystal grown perpendicular to the fusion line. The grain size of equiaxed crystal decreases with the increase of defocusing amount. With the increase of defocusing amount, the hardness value of composite coating increases accordingly, and the highest microhardness value appears in the upper part of the composite coating when the defocusing amount is 2 mm, up to 696.1 HV0.5, about 3 times of that of the substrate (230.6 HV0.5). Under the same wear condition, the average friction coefficient and wear loss of composite coating decrease with the increase of defocusing amount. When the defocusing amount is 2 mm, the minimum wear loss is 0.010 g, which is only 21.7% of that of the Fe based coating. The wear mechanism of composite coating is abrasive wear and adhesion wear. With the increase of defocusing amount, the smaller the wear degree of the composite coating surface, the better the wear resistance.

Key words: laser cladding, defocusing amount, MoS₂, Fe-Cr-Mo-Si alloy coating, microstructure, friction and wear