Effects of Elemental Additives on Densification, Microstructure, Strength, and Thermal Conductivity of Silicon Carbide Ceramics

Abstract

Effects of elemental additives on the densification, microstructure, strength, and thermal conductivity of hot-pressed SiC ceramics were investigated. The addition of Be, B, and Al gave up to 98% of theoretical density, whereas other additives had only a slight effect on densification. The microstructure, flexural strength, and thermal conductivity of dense SiC ceramics varied considerably depending on the additive used. For example, SiC ceramics with added Al had fine grains −2.3 μm in size and high flexural strength, ≅ 940 MN/m2. On the other hand, those with added Be or B had larger grains ≅ 5.7 and ≅4.2 in size and lower flexural strengths ≅400 and ≅ 290 MN/m2, respectively. Moreover, with added Be an extremely high thermal conductivity, ≅ 260 W/m·K, was obtained; this value is much larger than those for SiC ceramics with B or Al additions.