Characterization and Wear Behavior of a Coated Sol-Gel Layer on WC/Co Coatings Deposited by HVOF

Tungsten carbide powders have been known as one of the hardness and wear resistance materials. The combinations of carbide with soft metals such as cobalt as a binder are widely used to improve the wear resistance, toughness and prevent brittle failure. In this research, WC-12Co powders were deposited on steel substrate by high velocity oxygen fuel (HVOF) spraying. Due to the existence of pores and microcracks in the coatings, the corrosion and wear resistance properties of the coatings could be improved by sealing the porosities and cracks via a post deposition treatment. A thin layer of Al2O3 were deposited on the HVOF thermally sprayed WC-Co coatings by Sol-Gel method. The phase composition of coatings was investigated by X-Ray Diffraction (XRD) analysis and the morphology and microstructure of the coatings as well as their thicknesses were investigated by Scanning Electron Microscopy (SEM) followed by image analysis. To study the wear resistance of the coatings a pin on disk wear tester was used. The results showed that the coefficient of friction was reduced from 0.6 to about 0.3 after sealing. The wear rates of the sealed coatings were decreased from 5.5x 10-3 in the as-sprayed coatings to 3.4 x 10-3.in the sealed coatings. The wear resistance of coatings after the sol-gel sealing process was improved due to the filling of the pores and cracks as well as formation of the aluminum and cobalt oxides on the surface during wearing test.