EFFECT OF SINTERING AIDS ON TRIBOLOGICAL CHARACTERISTICS OF SI3N4 CERAMICS AT 120-DEGREES-C IN WATER

The effect of sintering aids on the tribological behavior of three kinds of hot-pressed Si3N4 ceramics sliding on itself in water was investigated at 120 degrees C under saturated vapor pressure of 0.1 MPa. At lower sliding speeds, the friction coefficients and specific wear rates of MgO+Al2O3-doped Si3N4 (SN-1- were larger than those of Y2O3+Al2O3-doped materials (SN-2 and SN-3), and the wear behavior for all samples was mainly controlled by the reaction to produce NH3. These phenomena are probably caused by the contact stress on the asperities formed by the dissolution of the grain boundaries, because the intergranular layers for the SN-1 sample were easier to dissolve than those for the other samples. At higher sliding speeds above 0.4 m s(-1), the friction coefficients and specific wear rates decreased in order of SN-3, SN-1 and SN-2. The wear properties were governed by the oxidation and microfracture of the Si3N4 substrate and may be related to the Aat oxide film formed on the worn surface of SN-1 and the inferior oxidation resistance of Y-10(SiO4)(6)N-2 existing as the secondary phase in SN-3.