Abstract   Al₂O₃ coatings with different porosity were deposited by atmospheric plasma spraying. The tribological properties of coatings against copper alloy were evaluated with a block-on-ring and ring-on-ring configuration under severe dry friction conditions at room temperature. Microstructure of coatings were observed using SEM. Some therm-physical properties of the coatings were measured. Results showed that dense coating exhibits cracking failure in two severe sliding conditions, one is in a block-on-ring testing with a normal load of 500N and a sliding velocity of 0.84 m/s, the other is in a ring-on-ring testing with a load of 1106N and sliding speed higher than 26.8 m/s. This failure phenomenon is explained in terms of the higher residual stress and thermal conductivity of the plasma sprayed dense Al₂O₃ coating.

Keywords: Plasma spraying; Al₂O₃; friction and wear; failure mechanism