炭素蒸着法で作製したin-situ生成Si_3N_4-SiCナノ複合体の機械的特性に及ぼす酸素量の影響

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The purpose of the present work is to propose a toughening method of Si_3N_4 ceramics by forming a nanocomposite grain-boundary phase of SiC nanoparticles in the weak grain-boundary phase. The SiC nanoparticles are formed by in-situ reaction between an oxide phase on the surface of Si_3N_4 powder and carbon, which is coated on Si_3N_4 powder by thermal decomposition of methane(CH_4)gas. The surface oxygen content can increase by an oxidation process or decrease by washing process. The sintered bodies are obtained by hot-pressing at 1800℃ for 1h in N_2 atmosphere under 30 MPa of applied pressure. By increasing the carbon content, both of the fracture toughness and the bending strength first increase, then reach the maximum value at the same amount of carbon, and decrease. TEM observation showed that the precipitated SiC particles dispersed in the grain-boundary phase, at the Si_3N_4-Si_3N_4 interface and inside of the Si_3N_4 grain. The precipitated SiC content depends on the coated carbon and surface oxygen content on the Si_3N_4 powder surface. The reacted carbon content shifts to higher carbon content as oxygen content increases. When the reacted carbon content increases, the resultant SiC content also increases. Therefore, the carbon content at which the fracture toughness and bending strength exhibit the maximum values increases with increasing the surface oxygen content. A surface oxidized Si_3N_4 powder is generally regarded as an inferior powder;however, the oxidized powder can be used to produce high quality Si_3N_4 ceramics by applying the present carbon coating method.
社団法人日本セラミックス協会の論文
1995-11-01

炭素蒸着法で作製したin-situ生成Si_3N_4-SiCナノ複合体の機械的特性に及ぼす酸素量の影響

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