Abstract
Mo5Si3 reinforced silicon nitride composite was fabricated by sintering a Mo-solution infiltrated porous silicon nitride at 1850°C in N2 atmosphere; silicon nitride containing solid lubricant particles of MoO3 at the surface layer was developed by oxidizing a Mo5Si3-Si3N4 composite at 700°C in air. The mechanical properties and the tribology behavior of Mo5Si3-Si3N4 composite were evaluated. It was found that the Mo5Si3 dispersed at grain boundary of silicon nitride, the average diameters of Mo5Si3 particles being in the range 0.2 to 0.6μm. The flexural strength of the Mo5Si3-Si3N4 composite was 881MPa, which was higher than that of unreinforced silicon nitride by about 20%, because of the Mo5Si3 sub-micron particles reinforced the grain boundaries of silicon nitride. The friction coefficient of silicon nitride depended on the stress conditions and the shape of the pin. When increasing the spherical radius of the pin from 5 to 18mm, the friction coefficient of the Mo5Si3-Si3N4 composite decreased and the wear mechanism shifted from adhesive-abrasive wear to a complex type of adhesive-abrasive and abrasive wear mechanism. The formation of MoO3 on the surface layer of Mo5Si3-Si3N4 after oxidation treatment lowered the friction coefficient, the friction coefficient of oxidized Mo5Si3-Si3N4 composite being 0.46 in the dry friction condition. Due to the self-lubricant effect of MoO3, the friction coefficient of oxidized Mo5Si3-Si3N4 composite was lower than that of conventional silicon nitride by about 25%.
