The influence of intergranular phases on the tribological performance of sialons

The wear behavior of couples consisting of sialons and iron-based alloys has been investigated using different experimental methods such as fretting tests at room temperature and at 500 °C, pin-on-disk tests, diffusion couple experiments, and drilling field tests. The room temperature fretting wear behavior appears to be a complicated process involving both the formation of transfer layers and tribo-oxidation of the materials, and the resulting extent of wear seems to correlate with hardness. An increase in the fretting test temperature to 500 °C causes a thick iron oxide layer to form. This oxide film prevents the sialon from being worn and lowers the coefficient of friction. The pin-on-disk tests show even more markedly than the fretting experiments that the sialons tend to wear more against 42CrMo4 steel than against GG25 cast iron. In addition, the diffusion couple experiments show that the sialons react more with 42CrMo4 steel than with GG25 cast iron, and they also indicate that the amount of chemical interaction between the sialons and 42CrMo4 steel increases with the amount of intergranular phase. During the drilling of GG25 cast iron, on the other hand, it appears that the tribological performance of the sialons correlates with the hardness of the sialons, which is influenced by the amount and nature of the intergranular phases in the sialons.