Effects of Co₃O₄ Addition on Friction and Dry Sliding Wear Characteristics of 8 mol% Yttria-Stabilized Cubic Zirconia

The aim of the present study was to investigate the influence of Co₃O₄ additive on the microstructure, wear, and tribological properties of 8 mol% yttria-stabilized cubic zirconia (8YSZ) using a pin-on-disk tribometer, surface profilometer, hardness tester, and a scanning electron microscopy system. Specimens were produced by doping 1-15 wt.% Co₃O₄ in 8YSZ using a colloidal process, sintering at 1500 °C for 1 h, and subsequent annealing at 1500 °C for 10 and 50 h. Microstructural analysis showed that Co₃O₄ dissolved partially in 8YSZ, with the undissolved Co₃O₄ precipitating as a secondary phase at the grain boundaries. Further, the addition of Co₃O₄ enhanced the grain size. Wear tests were carried out using an Al₂O₃ ball as the counterface against ceramic disk under dry sliding friction conditions at room temperature (24 °C). The wear volume of 8YSZ decreased from 0.30 to 0.11 mm³ as a result of the addition of 15 wt.% Co₃O₄. Additionally, friction coefficient of the 8YSZ significantly reduced from 0.55 to 0.17 at the beginning stage of the sliding after the addition of 15 wt.% Co₃O₄. This was because Co₃O₄ creates a thin lubricating layer on the friction surface. In addition, the undoped and Co₃O₄-doped 8YSZ specimens exhibited abrasive wear under the dry sliding friction conditions, owing to the formation and propagation of microcracks, which resulted in the removal of material from the surface. The specific wear rate of 8YSZ decreased with increasing the Co₃O₄ content. Thus, the addition of Co₃O₄ to 8YSZ improves its wear resistance and surface topography.