Tribological Behavior of Si3N4-hBN Ceramic Materials against Stainless Steel under Dry Friction Condition

The main objective of this paper is to study the tribological behavior of Si3N4-hBN composites sliding on stainless steel. Unlubricated wear tests were carried out on a MMU-5G type pin-on-disc wear tester. The results showed that the addition of hBN to Si3N4 resulted in a marked decrease of friction coefficient, from 0.95 for Si3N4 against stainless steel to 0.03 for Si3N4-30%hBN against stainless steel. Wear coefficients were below 10-4 mm3/Nm for all materials tested and decreased sharply with increasing volume fraction of hBN, e.g. nearly zero for Si3N4-20%hBN pin. The materials and worn surfaces as well as wear debris were characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). Furthermore, the tribofilms were analyzed by using electron probe microanalysis (EPMA), laser scanning microscope (LSM), X-ray photoelectron spectroscopy (XPS). The analysis indicated that, under unlubricated condition, a tribo-oxide film containing B2O3, SiO2 and Fe2O3 was formed on the wearing surface. The tribofilm with a certain thickness protected both Si3N4-hBN pin and stainless steel disc, and lubricated the wear surfaces.