Effect of microstructure on the wear resistance of silicon nitride

Commercial silicon nitride powder was hot pressed in the presence of additives (5 wt% Al2O3, 2 wt% Y2O3) to complete density. The resulting microstructure showed elongated β-Si3N4 grains with no trace of any remaining α-Si3N4. The microstructure of the samples was altered by changing the hot pressing schedules. Mechanical properties such as Young's modulus, hardness, fracture strength and fracture toughness were measured for samples with different microstructures. Wear tests were conducted on a reciprocating pin-on-disc apparatus with paraffin oil as a lubricant. The wear on the silicon nitride pin increased as the hardness of the samples decreased. Further, the low hardness samples showed a considerable amount of fracture on the surface. Modification of the composition to 5 wt% Y2O3, 2 wt% Al2O3 and 5 wt% Al2O3, 5 wt% Y2O3 changed the mechanical properties of the samples. However, the wear behavior was similar to that of the samples tested originally i.e., as hardness decreased, wear of the pin increased, providing additional evidence for the proposed wear mechanism by plastic deformation