Differences in hardness and microstructure of laser cladding M2 coatings

Abstract

The M2 coatings on medium carbon steel were prepared using a laser cladding process, and the microstructure and microhardness of the coatings were studied. The results show that the microhardness of the coating shows an increasing trend from the coating top to the bonding interface. The microhardness is 694 HV1 at the surface of the coating, which reaches 836 HV1 in the bottom regions of the coating. The wear rate of the coating is 0.32 mm3/N·m, which shows lower wear rate and better wear resistance. The coating microstructure is also different, and the coating consists of overlapping and non overlapping regions. The microstructure of overlapping region is a dendritic solidified crystalline structure encapsulated on α - Fe phase primary crystals with a dispersed carbide. The microstructure of non overlapping zone is composed of columnar crystal zone, basket crystal zone, and dendritic zone from the bottom of the coating to the surface, respectively, with the carbides distributed along the grain boundaries in the form of a network. Near the coating interface, needle-like high-carbon martensite forms in the coating. The carbides in the coating are relatively coarse.