Influence of Heat Treatment on Corrosion Resistance of High-Velocity Oxygen-Fuel Sprayed WC-17Co Coatings on 42CrMo Steel

The influence of heat treatment from 500 to 1100 °C on the 5 wt.% H 2 SO 4 solution-induced corrosion resistance of high-velocity oxygen-fuel sprayed WC-17Co coatings on 42CrMo steel was investigated, by using x-ray diffractometer (XRD), scanning electron microscopy (SEM)-energy-dispersive spectrometer (EDS), and polarization curve methods. XRD analysis showed decrease in W 2 C phase intensity with recrystallization of amorphous Co and generation of new Co 3 W 3 C and Co 6 W 6 C phases with heat treatment. Porosity distribution did not follow a particular pattern; it initially increased and then decreased with increasing temperature. Corrosion resistance sequence of the as-sprayed and heat-treated coatings in 5 wt.% H 2 SO 4 solution was C-5 > C-9 > C-A > C-7 > C-11. Furthermore, microstructure and phase structure of heat-treated coatings revealed the formation of different discontinuous plate-like oxide films on the surface of the heat-treated coatings which indicated the vital effect of binder structure on the corrosion resistance.