EFFECTS OF HUMIDITY AND SLIDING SPEED ON THE WEAR PROPERTIES OF SI3N4 CERAMICS

The wear properties of two kinds of Si3N4 exposed to high and low humidity are examined experimentally at various sliding speeds. Bearing steel is used as the disk material under pin-on-disk-type sliding conditions. The wear rates of the pressureless sintered plus hot isostatically pressed Si3N4 are slightly lower than those of pressureless sintered Si3N4. It is observed that adsorbed moisture and the sliding speed markedly affect the wear properties of Si3N4. The highest wear rate is obtained with a high humidity and low sliding speed. As the sliding speed increases, the wear rates are decreased and the effect of the humidity on the wear rates of the Si3N4 is reduced. Three suggestions are made to explain the high wear rate of the Si3N4 pin specimen at a high humidity. One suggestion is the effect of the material property change caused by the adsorbed water molecules. Another is the plowing action of the hard particles of Fe2O3 formed as a result of the oxidation of the bearing steel disk. The other suggestion is the corrosion effect at the Si3N4 surface. An increase in the sliding speed is supposed to reduce the effect of the humidity on the wear rate of Si3N4 by raising the temperature of both the bearing steel disk and the Si3N4 pin specimen. Measurement of the temperature of the disk surface shows a significant change with sliding speed.