Effect of aging treatment on microstructure and properties of VN alloy reinforced Co-based composite coatings by laser cladding

Laser cladding VN alloy reinforced Co-based composite coatings on the mild steel was aging treated at 550 °C, 650 °C and 750 °C, respectively. Effects of aging temperature on the phase compositions, microstructure, microhardness, and wear resistance of the composite coatings with and without heat treatment had been investigated systemically. The results showed phase compositions of the composite coatings were not affected after aging treatment at 550 °C and 650 °C, and σ-FeV phase was not detected after aging treatment at 750 °C. The volume fraction of Cr23C6 and VN was gradually increased with the increasing of aging temperature. The number of short rod-shaped dendrites and equiaxed grains in the composite coatings was gradually increased as aging temperature increased, the distribution of the equiaxial grains was more uniform, and the dislocation density was reduced. Compared with the composite coatings without aging treatment, the microhardness and wear resistance of the composite coatings were both firstly decreased after aging treatment at 550 °C and 650 °C, then gradually increased with the increase of aging temperature, and the increase was 9.9% and 10.7%, respectively, for aging treatment at 750 °C. The wear mechanism of three composite coatings were all the abrasive wear.