Microstructure, mechanical properties and reciprocating wear properties of diamond grits-reinforced NiCrBSi composite coatings on 42CrMo

Abstract

In this study, diamond grits-reinforced wear-resistant NiCrBSi composite coatings with diamond exposed to the air (Sample I) and embedded in the coating (Sample II) were prepared on 42CrMo steel by vacuum cladding technique. Moreover, a post-heat treatment was performed to restore the weakened substrate. The surface morphology, interfacial microstructure, mechanical properties and reciprocating wear properties of the coated samples, as well as the post-heat-treated samples, were investigated. Besides, the wear mechanism was discussed. On both the coatings, flaky and prismatic structure and rectangular precipitates around diamond grits were chromium carbides. The cross-sectional morphology and EDS results showed that a metallurgical bonding interface was developed by the apparent element diffusion between the cladding layers and the 42CrMo steel substrates, which was beneficial for ensuring their bonding strength. Both the NiCrBSi/diamond composite coatings could significantly improve the wear resistance of 42CrMo steels. The wear resistance of Sample I and Sample II were 7.7 times and 5.3 times heavier than that of the original substrate, respectively. The abrasive, adhesive, and oxidative wear occurred during the friction-wear tests, in which the abrasive wear was dominant. In addition, the dominant wear mechanism of 42CrMo steel was adhesive wear. After the post-heat treatment, the weakened properties of 42CrMo steel were restored due to the phase transformation from lath martensite and ferrite to lamellar pearlite and ferrite. Further, the treated 42CrMo steel achieved higher properties than the original substrate and retained the excellent wear properties of the surface composite coating.