Abstract
The effect of reducing atmosphere on yttria dispersed AlN ceramics sintered by millimeter wave-HIP combined sintering was investigated. The specimens were sintered by millimeter wave (MMW) heating under nitrogen reducing atmosphere containing 3 vol% hydrogen followed by post-HIP treatment at 1700°C for 0.5 h under nitrogen pressure of 190 MPa. The relative densities to the theoretical one saturated at the first MMW heating over 1700°C. Thermal conductivities of AlN ceramics sintered by MMW heating under heavily reduced atmosphere with nitrogen were higher than that through MMW heating under normally reduced atmosphere. The thermal conductivity increased with decreasing the yttria additive amount and with increasing the sintering temperature. The optimized yttria dispersion amount was 1 wt% in the MMW heating at 1800°C for 0.5 h. Relative density and thermal conductivity increased by post-HIP treatment. The optimized yttria dispersion amount shifted from 1 wt% to 3 wt% after post-HIP treatment.
