Behavior of CuO as solid lubricant inside ZTA matrices

Abstract

This investigation delves into the behavior of copper oxide (CuO) as a solid lubricant inside zirconia toughened alumina (ZTA) ceramic composites. The investigation starts with the preparation of ZTA through co-precipitation followed by powder metallurgy to develop CuO (1.5 wt. %)/ZTA composites. In all cases, hot isotactic pressing is applied for densification. The fully densified samples are thoroughly mirror-polished to investigate the mechanical and tribological properties. A 1.8% reduction in micro-hardness and 6% improvement in fracture toughness are observed with incorporation of CuO into the ZTA matrices. The analysis reveals that the presence of ionic copper at the grain boundary leads to the formation of copper-rich phases, causing a decrease in hardness. However, the softer CuO particles contribute to crack bridging and crack deflection, enhancing fracture toughness. Subsequent investigation into the tribological properties highlights the positive influence of the softer CuO phases acting as a secondary component within the ZTA matrix. A significant enhancement of 39.34% in the Coefficient of Friction (COF) is achieved by incorporating CuO into the ZTA matrix. This improvement can be attributed to the formation of a patchy layer through smearing and squeezing actions on wear debris during sliding. The uniform patchy layer results in smoother and more polished surfaces, leading to an improvement in both the COF and specific wear rate. Further wear analysis reveals various phenomena contributing to surface wear, including pullout of grain particles, micro-fracture, high abrasions, and laminar removal of grains. Overall, the introduction of CuO proves to be beneficial, showcasing improved mechanical and tribological properties in the developed composites, with application in dies, inserts, sparkplugs, etc.