Effect of YF3 on densification behavior and thermal conductivity of AlN ceramics with Y2O3–YF3 additives under reducing atmosphere

The effect of yttrium fluoride (YF3) on the densification behavior, microstructure, phase composition and thermal conductivity of aluminium nitride (AlN) ceramics with yttrium oxide (Y2O3) and YF3 additives were studied. Since YF3 provided liquid phases and promoted densification at a lower temperature, the sintering temperature required to reach the full density of AlN samples decreased with the increase in YF3 content. Appropriate addition of YF3 could improve the thermal conductivity of AlN ceramics, but the values of thermal conductivity decreased as YF3 increased further. It is attributed to the ability of YF3 to react with oxygen impurity was worse than that of Y2O3. Moreover, the reducing atmosphere significantly affected the phase composition, and the oxygen content in grain boundary phases decreased at 1750 °C and 1800 °C. Therefore, the proper proportion of Y2O3–YF3 additives could simultaneously improve densification and the thermal conductivity of AlN samples at a low sintering temperature.