Effects of AlN Content and Sintering Atmospheres on the Thermal Conductivity of Hot-Pressed SiC Ceramics

In pursuit of high thermal conductivity of SiC ceramics, this article reports the effects of AlN and sintering atmospheres on the thermal properties and microstructure evolution of SiC ceramics. Dense SiC ceramics with different contents of AlN additive were fabricated through hot-press sintering at 1950°C in Ar/N2 atmosphere under a pressure of 40 MPa for 3 h. The results showed that the thermal conductivity of samples without AlN addition was 53.5 W.m−1.K−1 when sintered in Ar and 50.3 W.m−1.K−1 when sintered in N2. The SiC ceramics with 4 wt% AlN sintered in Ar showed abnormally large grains and exhibited the highest thermal conductivity of 121.7 W.m−1.K−1 among all the samples. The sample with 2 wt% AlN sintered in N2 exhibited a thermal conductivity of 108.6 W.m−1.K−1; the thermal conductivity deceased with the increasing AlN content afterwards. Such a decreasing trend of thermal conductivity was attributed to the ascending 2Hss content and smaller grains of ceramics. There existed an optimal content of AlN and a proper sintering atmosphere for perfecting the microstructure and the thermal conductivity of SiC ceramics.