Fabrication and effect of heat treatment on the microstructure and tribology properties of HVOF-sprayed CoMoCrSi coating

Abstract

A type of CoMoCrSi coatings were fabricated by using HVOF technique, and the microstructures, mechanical properties and tribological behaviors at room temperature (RT) of the coatings annealed at 800 °C for different time were investigated in detail. Annealed CoMoCrSi coatings exhibited better crystallization and more compact microstructures compared to as-sprayed coatings. The porosity of the annealed coatings reduced to 0.32–0.2%, and adhesive strength increased to 63.8–68.5 MPa, both of that were all reached at an equivalent level with the variation of the annealed time. The surface microhardness could be enhanced from 902.8 HV0.3 for the as-sprayed coating to 1237.6 HV0.3 for the coating annealed for 10 h, which could be attribute to more compact microstructures and hard nano-sized Cr2O3 layer, that resisted indentation effectively. With the increasing of sliding distance at room temperature, the friction coefficients of the annealed coatings reached at 0.39–0.4, and the wear rates decreased to 0.88–1.59 × 10–6 mm3 N−1 m−1, demonstrating enhanced tribological performance of the CoMoCrSi coating after heat treatment. Numerous metallic oxides, i.e., Cr2O3 played a critical role in sustaining and anti-wear, and oxides, i.e., Co3O4, MoO3, and CoMoO4 transferred to the Al2O3 pair surface and formed a continuous transfer film during the friction test at RT, which directly reduced friction and leading to a low friction coefficient and wear rate.