Millimeter wave-HIP combined sintering of AIN ceramics and their thermal conductivity

With the aim to improve the thermal conductivity of yttria dispersed AIN ceramics through a short time and low temperature treatment under nitrogen atmosphere, millimeter wave (MMW) heating was combined with post-HIP treatment. Relative density increased by post HIP treatment over 1600°C on previously MMW heated samples even with the same temperature. The thermal conductivity exceeded over 170W/m°K when treated through MMW-HIP combined sintering with 1700°C+ 1700°C treatment by 0.5 h+0.5 h. This valued had been attained through the MMW treatment alone at 1800 °C for 2 h under 3 wt% hydrogen mixed nitrogen atmosphere. The optimal dispersion amount was 3 wt% in the MMW-HIP combined sintering while that was 5 wt% in the MMW sintering alone. The relative density has been saturated at the first MMW heating over 1700°C. On the other hand, thermal conductivity increased with the treatment temperature both in first MMW and post HIP. No significant pressure dependence can be seen in the thermal conductivity with this experimental condition.