A series of silicon carbide-based ceramics with different sintering additives were liquid-phase sintered to high densities. Yb2O3 in combination with AlN was used as the additive, instead of the commonly used Y2O3–AlN, to improve the refractoriness of the secondary phase. Thermo-chemical decomposition of AlN was sufficiently suppressed with the use of nitrogen overpressure and reasonable weight loss was achieved in the different additive containing SiC ceramics without a reactive powder bed. Use of the heavier rare-earth element modified the liquid phase formed during sintering and reduced the phase transformation controlled grain growth rate, compared with Y2O3 doped materials. It also permitted microstructure tailoring through post-sintering heat treatments in nitrogen. Materials with self-reinforced microstructures, formed as a result of anisotropic grain growth, were obtained. Improved fracture toughness (4.5–5 MPa/m1/2) and good flexural strength retention up to 1400°C were also observed.
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Document Type: Research Article
Institute for Problems in Materials Science, National Academy of Sciences of Ukraine, Kiev, Ukraine
Instituto de Pesquisas Energéticas e Nucleares, São Paulo, SP, Brazil
Publication date: May 1, 2005