Microstructure and thermal fatigue resistance of Co-based alloy coating on H13 steel by laser cladding

Thermal fatigue failure is easy to occur on H13 steel surface under working condition, the Co-based coating was fabricated by Nd:YAG laser on H13 steel. Microstructure, distribution of elements and composition of phases were investigated by means of optical microscope(OM), scanning electron microscope(SEM), energy dispersive spectrometer(EDS) and X-ray diffraction(XRD).The effect of thermal fatigue on microhardness of Co-based coating and quenching-tempering H13 steel was tested by microhardness tester. The results show that: From bottom to the surface of Co-based coating, planar crystal, cellular crystal, dendrite crystal and equiaxed crystal were observed; Co-based alloy coating is mainly composed of -Co and M23C6, M2O3 and M3O4(M=Fe, Co, Cr)are produced on the surface of coating after thermal cycling; Microhardness of Co-based coating which could reach 706HV0.2, decreased gradually. After 1000 thermal cycles, the microhardness decreases of Co-based alloy coating and H13 steel are 24.4% and 37.7%, respectively; The surface of the Co-based coating has no thermal cracks, while that of H13 steel has a large number of thermal cracks; Cr2O3 oxide film is formed on Co-based alloy coating, which makes thermal fatigue resistance of coating better than that of H13 steel.