Tribology of Si3N4 containing in-situ grown Si2N2O processed from oxidized α - Si3N4 powders

Silicon nitride ceramics containing in-situ grown Si2N2O were prepared from oxidized silicon nitride powders by hot isostatic pressing (HIP) at 1500 °C and 1700 °C in a nitrogen gas environment under 20 MPa for 3 h. In case of systems sintered at 1700 °C, the volume fraction of the silicon oxynitride (Si2N2O) increased, and the β - Si3N4 phase decreased with the increase of oxidation time. The tribological behavior of the materials was studied by the ball-on-disc method under dry sliding conditions at room temperature under an applied load of 5 N with a sliding speed of 0.05 m/s using Si3N4 ball as a tribo-partner. For the systems sintered at 1700 °C, the coefficient of friction (COF) values were between 0.8 and 0.76 at the start, and started decreasing with the increasing sliding distance, at 1000 m of sliding distance the values were between 0.65 and 0.6. The lowest COF value was measured for the system with unoxidized α-Si3N4 powder sintered at 1700 °C with the value of 0.65. The lowest wear rate, 1.224 x 10-4 mm3/N•m, was measured for the system with 10 h oxidized α-Si3N4 powder sintered at 1500 °C. Fractographical analyses of the wear track revealed that the main wear mechanisms were abrasive wear with grain pull-out, micro-cracking, and debris formation together with tribo-film formation.