The difference of composite coating and Cr coating: The base layer of the composite coating has good bonding strength with the base material, and the internal stress of the coating layer is small, but the composite layer is easy to fall off, and the service life is limited by the thickness of the composite layer; however, the hardness of the coating is high, the wear resistance and the processability are good. However, the bonding strength is relatively low, but the coating thickness is large and the service life is high. The order of microhardness of the coating is from Cr to Ni, Cr, NiCo, Ni-NiCo, NiFe, Ni-NiFe, Ni, and the performance remains stable at temperatures up to 200-300 °C.