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The tribological behavior of 5 wt% copper oxide-doped tetragonal zirconia polycrystal composite has been investigated while it slides against an alumina counterface under high temperature conditions. The effects of load (1, 2.5, and 5 N) and velocity (0.05 and 0.1 m/s) on the wear mechanism have been investigated. The results were compared with undoped zirconia at 595°C. A coefficient of friction (COF) of 0.35 and a specific wear rate less than 10 À6 mm 3 /Nm were obtained at 595°C when copper oxide was added to zirconia. Further, it has been observed that a self-lubricating layer is formed at the interface. Scanning electron microscopy and X-ray photoelectron spectroscopy have been used to investigate the formation of the self-lubricating copper-rich layer at the interface between the disk and counterface materials. The formation of a self-lubricating layer, as well as the wear mechanisms at different operational conditions (load and velocity) are discussed. It appears that plastic deformation of copper-rich phase at higher temperature is responsible for the decrease in friction and wear. J ournal materials. The particle size of 3Y-TZP and CuO powder were 64 nm and 74 lm, respectively. The processing route and mechanical properties were described in detail elsewhere. 20,22 Cold-pressed 5CuO-TZP samples were sintered at 1500°C for 8 h with heating and cooling rate of 2°C/min.The sintered density was measured by immersion in mercury using the Archimedes' method. The sintered disks were polished to a surface roughness (R a ) of <50 nm using a diamond paste. The polished disks were ultrasonically cleaned in ethanol and then annealed at 850°C for 2 h. For comparison, undoped 3Y-TZP and 0.8 mol% (0.5 wt%) 0.5CuO-TZP were prepared and sintered at 1400°C and 1500°C for 2 h, respectively.

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