Wear resistance and self-lubrication of electrodeposited Ni-SiC:MoS2 mixed particles composite coatings

Abstract

Ni-based mixed particles composite coatings were designed to achieve superior wear resistance by combining hard carbides and solid lubricants as a reinforcing particles mix. Pure nickel and single-particles composites were electrodeposited in the same conditions for benchmarking. A pre-study was carried out to optimise the current density to avoid loss of process efficiency due to hydrogen evolution. The production process was also improved by employing ultrasounds to avoid porosity and dendritic growth in the metal caused by conductive MoS2 particles. The presence of MoS2 particles led to nanocrystallinity in the nickel matrix, confirmed by electron backscatter diffraction (EBSD) maps and transmission electron microscopy (TEM). The microstructural changes and codeposition in the different composites were correlated to microhardness and pin-on-disc tests. An extremely high hardness was observed in the mixed particles composite (≈1110 HV) due to the combined effect of the nanocrystalline matrix and high codeposition rate (≈15 vol% SiC and ≈8 vol% MoS2). The codeposition of MoS2 particles provided a self-lubrication capability to the coating, reducing the friction coefficient compared to pure Ni from 0.15 to 0.07. The wear rate was reduced more than 12 times by the mixed reinforcement compared to pure Ni and more than 6 times compared to Ni-SiC.