The synergistic effects of CaF2 and Au lubricants on tribological properties of spark-plasma-sintered ZrO2(Y2O3) matrix composites

The synergistic effects of CaF2 and Au lubricants on tribological properties of spark-plasma-sintered ZrO2(Y2O3) matrix composites have been studied from room temperature to 800 °C in sliding against an alumina ball. The composite with solid lubricants of Au and CaF2 exhibits a friction coefficient of 0.36–0.50 and a wear rate of 1.67 × 10−6–3.55 × 10−6 mm3/Nm over the entire temperature range studied. At low temperatures, the metallic gold within the composite is extruded from the matrix, and well spread onto the worn surface to form a self-lubricating film during wear process. With the increase of temperature, a smooth CaF2 lubricating film containing metallic gold lubricants is gradually generated on the worn surface. These self-lubricating films are partially transferred to the coupled ball, and greatly reduce friction and wear of ZrO2(Y2O3) matrix composites. The worn surfaces and transfer films formed during wear process have been characterized to identify the synergistic lubrication behavior of CaF2 and Au lubricants at different temperatures.