Role of CuO in Al2O3-B2O3 Composites: In Situ Phases, Density, Hardness, and Wear Resistance

The aim of this study was to develop a novel set of Al2O3-B2O3-CuO composites and evaluate their tribological performance at varying humidity (10-95% relative humidity) levels. First, the Al2O3-B2O3 composites were prepared using cold press sintering by varying the amount of B2O3 (5-20 wt%). The results revealed that an increase in B2O3 content in the composites increased the amount of aluminum borate in situ phase during sintering. The presence of the aluminum borate phase in the composite enhanced the hardness and wear resistance, whereas the humidity-sensitive alumina phase reduced friction at higher humidity levels. Next, CuO (5 wt%) was added to the Al2O3-B2O3 composites to form Al2O3-B2O3-CuO composites. These composites showed an increase in the percentage relative density by 16-37% and hardness by 1.2-1.9 times. Subsequently, the tribological performance was improved significantly. The underlying mechanism for improved wear resistance was discussed using the crystal-chemical approach and polarization theory to guide the design of these novel Al2O3-B2O3-CuO composites.