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 degrees C and 1700 degrees C in a nitrogen gas environment under 20 MPa for 3 h. In case of systems sintered at 1700 degrees C, the volume fraction of the silicon oxynitride (Si2N2O) increased, and the beta - 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 degrees 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 alpha-Si3N4 powder sintered at 1700 degrees C with the value of 0.65. The lowest wear rate, 1.224 x 10-4 mm3/N center dot m, was measured for the system with 10 h oxidized alpha-Si3N4 powder sintered at 1500 degrees 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.

Automated summary

The study prepared silicon nitride ceramics containing in-situ grown Si2N2O through hot isostatic pressing at 1500 and 1700 degrees C in a nitrogen gas environment. In the tribological study, materials sintered at 1700 degrees C showed a decrease in friction coefficient with increasing sliding distance, with the system sintered with unoxidized alpha-Si3N4 powder at 1700 degrees C having the lowest COF value.