Lu_2Si_2O_7コートした窒化ケイ素の耐酸化性及び強度保持性

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Silicon nitride (Si_3N_4) coated with lutetium disilicate (Lu_2Si_2O_7) layer through the intermediate silica (SiO_2)-rich phase was fabricated by reaction sintering after dip-coating. The Lu_2Si_2O_7 layer with a thickness of 3-29 μm was formed on Si_3N_4 substrate. It was relatively dense with several pores, and strongly jointed to the substrate through the intermediate phase. Oxidation resistance and strength retention of the coated Si_3N_4 were investigated and compared with those of the uncoated Si_3N_4. Apparent activation energy for oxidation at 1300-1500℃ in air increased up to 523.1 kJ/mol with increasing thickness of the coating layer, which was about 1.7 times higher than that of the uncoated Si_3N_4 (310.3 kJ/mol). After long-term cycling oxidation at 1500℃ for up to 1000 h in air, the total weight gain decreased by up to 51%, indicating that oxidation resistance improved by about 100%. The improvement was attributed to the protection of the substrate from an oxidative environment by the Lu_2Si_2O_7 layer and underlying SiO_2-rich phase. Flexural strength of the coated Si_3N_4 was not deteriorated before and after the cycling oxidation at 1500℃ for up to 1000 h in comparison with that of the uncoated Si_3N_4. However, the high-temperature strength at 1400-1500℃ in air was a little less than that of the uncoated Si_3N_4. The deterioration was attributed to the softening of amorphous SiO_2 phase, which existed in the intermediate phase (between the Lu_2Si_2O_7 layer and substrate) and inside the substrate.
社団法人日本セラミックス協会の論文
2004-07-01

Lu_2Si_2O_7コートした窒化ケイ素の耐酸化性及び強度保持性

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