Reciprocating friction and wear of two silicon nitride-based ceramics against type 316 stainless steel

Reciprocating ball-on-flat tests were conducted to assess the relative friction and wear behavior of two silicon nitride (Si3N4)-based materials under lubricated conditions. One of these ceramic materials was produced by a commercial supplier and is designated NT-451. The other was an experimental ceramic composite with a composition of 4.2 wt.% Y2O3 (sintering aid), 2.1 wt.% Al2O3 (sintering aid), 8.5 wt.% SiC whiskers, 39.1 wt.% TiC, with the balance Si3N4. The standard slider (ball) material was type 316 stainless steel. Tests were conducted with two liquid lubricants at room temperature and at 170°C. The first lubricant was a commercial 30-weight viscosity diesel oil and the second was a special oil formulation to which silver compounds had been added. Steady state kinetic friction coefficients (μ) for both ceramics lubricated with both oils averaged approximately 0.12 at room temperature. At elevated temperature, μ ranged from about 0.06 to 0.16, depending on the lubricant. Lubricated wear rates of the ceramic materials tended to be lower for the composite (3×10−8 mm3/N m) than for the NT-451 (1.5×10−7 mm3/N m). Likewise, the wear of the stainless steel was lower against the composite than against the NT-451 (1×10−7–5×10−7 and 0.5×10−6–3×10−6 mm3/N m, respectively). These results suggest that silicon nitride materials can be made more compatible (in terms of wear and friction) with metallic counterfaces in reciprocating wear situations by the judicious selection of additions. No clear and significant effects of Ag particles in the oil were observed in the friction or wear data for either ceramic-stainless steel couple.