Fabrication and wear behavior of Mo5Si3 particles reinforced Si3N4 composite

Mo5Si3 reinforced silicon nitride composite was fabricated by sintering a M o-solution infiltrated porous silicon nitride at 1850 degreesC in N-2 atmos phere; silicon nitride containing solid lubricant particles of MoO3 at the surface layer was developed by oxidizing a Mo5Si3-Si3N4 composite at 700 de greesC in air. The mechanical properties and the tribology behavior Of Mo5S i3-Si3N4 Composite were evaluated. It was found that the Mo5Si3 dispersed a t grain boundary of silicon nitride, the average diameters Of Mo5Si3 partic les being in the range 0.2 to 0.6 mum. The flexural strength of the Mo5Si3- Si3N4 Composite was 881 MPa, which was higher than that of unreinforced sil icon nitride by about 20%, because of the Mo5Si3 sub-micron particles reinf orced 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 18 mm, the frict ion coefficient of the Mo5Si3-Si3N4 composite decreased and the wear mechan ism shifted from adhesive-abrasive wear to a complex type of adhesive-abras ive 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%.