Phase and microstructure optimization of grain boundary oxides and its effect on the thermal conductivity of Y2O3-doped AlN ceramics

Abstract

AlN green bodies with variable O and C contents were employed to fabricate Y2O3-doped AlN ceramics of different grain-boundary phase compositions and microstructures via debinding in air and N2, respectively. The microstructural evolution and grain-boundary oxide migration and their effects on the properties of the ceramics were explained. Finally, modified models were built to predict the thermal conductivity of these AlN ceramics with complex microstructures. During sintering, the oxide melt migrates to the ceramic surface driven by the differences between the surface energy and solid/liquid interface energy of the melt. The phase compositions and distributions of the grain-boundary oxides vary with sintering temperature. In addition, the amorphous layers were detected experimentally. All of these factors have great effects on ceramics properties. AlN ceramics were shown to have a thermal conductivity as high as 221.64 W/(m·K), which agrees with the value predicted via modified models.