Fabrication of Silicon Nitride Nanoceramics and their Tribological Properties

Abstract

Si2N2O secondary phase‐free, fully dense nano‐Si3N4 ceramics (≥97% of theoretical density) were developed by combining carbothermal reduction treatment and spark plasma sintering (SPS), and their tribological properties were investigated by subjecting to self‐mated sliding under unlubricated conditions. Commercially available Si3N4 nanopowder was used as a starting material and phenolic resin was used for carbothermal reduction, which was conducted at 1450°C for 10 h. Fully densified Si2N2O phase‐free Si3N4 ceramics with a wide range of grain size from 90 nm to 1.5 μm were fabricated by varying SPS temperature from 1550° to 1750°C. The microstructure of the developed Si3N4 ceramics was changed from nano equi‐axed at 1550°C to large elongated bimodal grain morphology at 1700° or 1750°C. The frictional behavior was not dependent on the microstructure, but the wear rate was strongly influenced such that it decreased by an order of magnitude (from 9.7 × 10−5 to 0.88 × 10−5 mm3/N·m) with decreasing grain size. The dominant wear mechanism was changed from the delamination of tribochemical layer for the ceramics with nano equi‐axed grain microstructure to the fracture and grain pull‐out for the ceramics with duplex microstructure.