Dry-sliding self-lubricating ceramics: CuO doped 3Y-TZP

Dense 8 mol% CuO doped 3Y-TZP ceramics prepared by pressureless sintering at 1500 °C exhibits a good wear-resistance (specific wear rate k < 10⁻⁶ mm³ N⁻¹ m⁻¹) and promisingly low friction (coefficient of friction f = 0.2–0.3) when sliding against an alumina ball under unlubricated conditions. It was recognized that a self-lubricating mechanism is the most important contribution to the reduction of friction. During operation of the tribosystem, a soft interfacial patchy layer is generated in the contact area. As confirmed by calculations, based on a deterministic friction model, this soft interfacial patchy layer reduces friction. It was demonstrated that the presence of copper oxide is important for the formation of such an interfacial layer. The mechanism of the transition from mild to severe wear was also investigated. Detachment of a top layer in the wear track was proven to be the main reason for this tribological change.