2016 年 57 巻 9 号 p. 1593-1596
Combustion-synthesized Y-α-SiAlON and Ca-α-SiAlON powders were consolidated by spark plasma sintering (SPS) at 1300–1450℃ for 10 min, and the mechanical properties of the consolidated bulk samples were investigated. XRD analysis revealed that α-SiAlON partially transforms into β-SiAlON during the SPS and a bulk mixture of α/β-SiAlON was obtained. The fraction of β-SiAlON increased with the increase in sintering temperature and the α to β transformation ratio was higher for Y-α-SiAlON than for Ca-α-SiAlON. The hardness of the consolidated bulk increased with sintering temperature, and after reaching a maximum at 1350℃, the hardness gradually decreased with temperature in both the Y-α-SiAlON and Ca-α-SiAlON. The increase in hardness with temperature arises from the increased density of the sintered body, while the decrease in hardness results from grain growth due to an increase in temperature. The fracture toughness tended to increase with temperature and did not show a maximum for either α- or β-SiAlON, although the Y-α-SiAlON always exhibited a greater toughness than the Ca-α-SiAlON. The greater toughness of the Y-α-SiAlON is attributable to its higher fraction of transformed β-SiAlON, because the elongated shape of the β-SiAlON leads to the prevention of crack propagation.
