Influence of WC grain size on the microstructure and wear property enhancement of 18Ni300 coatings

Abstract

18Ni300-based cladding layers with micro/nano WC additives were fabricated via plasma transferred arc welding (PTA) technology. This work investigates the influence of WC grain size on microstructure evolution and wear performance. The comparative investigation of the microstructure results indicates that the nano-WC particle-reinforced 18Ni300 coating sample shows more fine grains and nanoparticles. These nanoprecipitates are Ni3Mo and WC, which are uniformly distributed in the martensite matrix. The in-situ precipitation forms Ni3Mo precipitates in the maraging matrix, which is triggered by the intrinsic heat treatment effect of PTA. The hardness of the 5 wt% nano-WC/18Ni300 composite exhibits the highest value (395.8 ± 10.7HV0.3), which is 12.41 % higher than that of the original 18Ni300 coating (352.1 ± 12.1HV0.3). Meanwhile, the nano-WC-reinforced 18Ni300 coating shows the highest wear resistance, which is approximately 2.5 times higher than the original 18Ni300 cladding layer. It could be concluded that the refining and strengthening effects of nano-WC addition on the microstructure and wear resistance of the 18Ni300 coating were superior to those of micro-WC. Molecular dynamics simulation results indicate that melting begins at the surface of nano-WC and then proceeds to the solid core as the temperature rises from 300 K to the melting point. Meanwhile, the nano-WC particles have a more sensitive diffusion tendency with the matrix than the micro-WC particles. This diffusion of the surface atoms can generate solid bonding with the surrounding atoms in their matrix and promote the agglomeration and in situ precipitation of Ni3Mo, finally synergistically improving the wear resistance of the nano-WC-reinforced composite.