The collaborative effect of carbon-borides and the redistribution of Ni, Cr and Mo on the corrosion and wear resistance of NiCrMoCB coatings

Abstract

A kind of NiCrMo coatings added in different contents of B and C used B4C as the precursor, had been designed and fabricated by laser cladding in this study. The phases, microstructure, microhardness, fracture features, and wear and corrosion resistance were thoroughly analyzed. The results showed that due to the addition of B4C, the phases changed from fcc-centered cubic (FCC) + σ phase to FCC + carbon-borides, and the eutectic structure appeared in the interdendritic regions. Most noteworthy, there was coherent relationship between the (Cr, Mo)23(B, C)6 and FCC phase. With the increase of B4C content, the microhardness of the coatings increased significantly. This factor, together with the eutectic structure, further enhanced the wear resistance of the coatings. Due to the existence of the eutectic structure, the coating maintained ductile fracture + brittle fracture. Furthermore, the formation of carbon-borides also improved the corrosion resistance, instead of causing deterioration, because of the coherent relationship of (Cr, Mo)23(B, C)6 and FCC phase together with no severe segregation of Cr and Mo around interdendritic regions, which reduced the possibility of galvanic corrosion, playing the role of synergistic improvement to the wear resistance and corrosion resistance of the coatings.