Wear evaluation of plasma sprayed oxide and carbide coatings

Wear of plasma sprayed Cr2O3, TiO2, Cr3C2-NiCr and WC-Co coatings have been evaluated with a block-on-ring arrangement under dry and lubricated conditions. The results indicated that the wear of the coatings was interpreted in term of subsurface grain fracture which was related to the special microstructure of the coatings such as size, shape and distribution of pore as well as crack. Among the four kinds of coating, Cr2O3 coating possesses the lowest wear coefficient. Water accelerated cracking and fracturing and deteriorated the wear resistance of both Cr3C2-NiCr and TiO2 coatings. Ethanol reduced the wear of Cr3C2-NiCr coating, which was attributed to the formation of a smooth surface film mainly consisting of Cr2O3. Wear of Cr2O3 coating against an Al2O3 ball at high temperature has been also produced. The wear of Cr2O3 coating against Al2O3 ceramics decreased with increase in temperature and load. The reaction between Cr2O3 coating and Al2O3 ceramics at high temperature and the formation of a protective film consisting of Cr2O3, Al2O3 and SiO2 glass on the surface of Cr2O3 coating improved the wear resistance of Cr2O3 coating.