Tribological behavior of various plasma-sprayed ceramic coatings

For comparing tribological behaviors of plasma-sprayed ceramic coatings, a series of friction and wear experiments has been carried out under oscillating sliding condition on four kinds of coatings: WC-12%Co, Cr3C2-25%NiCr, Al2O3-20%TiO2 and Cr2O3. Each one was rubbed against itself under dry friction at low and high temperature, as well as under lubricated conditions at high temperature. The experimental results indicated that there were two main wear mechanisms, plastic smearing and adhesive tearing, in the worn coatings. Plastic smearing corresponded to a lower average friction coefficient and wear rate, while adhesive tearing corresponded to higher values. The adhesive tearing caused much more wear than plastic smearing. The adhesion tendency between contacting surfaces depended on the properties of coating materials. An ah-synthetic oil as lubricant to contact surfaces at 400 degrees C displayed various lubrication effects on the tested coatings, depending on the compatibility of coating material with the lubricant and coating porosity. WC-12%Co and Cr2O3 coatings showed better tribological behaviors than two other coating materials.