Control of tribological properties of alumina-based composite by formation of in situ phases

The mechanical, and endurance need of space applications surpassing the available friction and wear reducing technologies, demanding novel materials. An alumina self-lubricating composite is developed by the formation of in situ phases (boron oxide and aluminum borate) by conventional powder metallurgy route. Four different compositions are used to control amount of in situ phases. Additionally, the composition used in the study also adds in achieving liquid phase sintering and densification. The composites were characterized using X-ray diffraction to confirm the phases present, and strength was measured in terms of microhardness The X-ray diffraction results revealed the formation of boron oxide and aluminum borate. Sliding tests on the composites were carried out using alumina balls at different loads to investigate the friction and wear performance. The wear resistance and hardness were increased with aluminum borate concentration. However, the friction results showed a strong dependency on the boron oxide and aluminum borate concentration. More specifically, at low load, lowest coefficient of friction was observed for the composite with maximum boron oxide and minimum aluminum borate concentrations. At high load, the low friction was shown by composite with minimum boron oxide and maximum aluminum borate. The mechanisms for friction and wear behavior at different loads are explained.