Physical and Mechanical Properties of Ceramics Based on Si₃N₄ of Various Dispersion with 3% Y₂O₃–Al₂O₃

This article focuses on the process of producing ceramics based on the commercial Si₃N₄ powder of various dispersions (<5 μm and <1 μm) by spark plasma sintering (SPS). The powder mixtures of 97 wt % Si₃N₄ + 3 wt % additive of the Y₂O₃–Al₂O₃ composition are synthesized by the Pechini method. The SPS technology is used to obtain ceramic samples of ∅20 mm. The sintering is carried out in a vacuum at a heating rate of 50°C/min and a load of 70 MPa until the end of the shrinkage. The microstructure and phase composition of the ceramic samples are investigated. Mechanical properties are measured: Vickers hardness, Palmquist fracture toughness, and flexural strength according to the B3B (ball-on-three-balls test) method. Tribological tests are also carried out. It is established that the lower the dispersion of the powder mixtures based on Si₃N₄, the lower the end temperature of shrinkage. The relative density achieved is 96%. Ceramic materials based on Si₃N₄ powder with the dispersion of <1 μm are difficult to machine; they have the hardness of 19.0 ± 0.7 GPa and the crack resistance of 5.1 ± 0.4 MPa m^1/2. The flexural strength of the ceramics evaluated by the B3B method depends on the dispersion of Si₃N₄ powder; it is more than two times higher for the ceramics based on the commercial Si₃N₄ powder with the dispersion of <1 μm.