Preparation of nanocrystalline AlN ceramics by spark plasma sintering

AlN ceramics were prepared by spark plasma sintering (SPS) using the pure nano-AlN powders and the nano-AlN powders doped by 3% Y₂O₃ (mass fraction) as the raw materials. The relative density, microstructure, mechanical properties, and thermal conductivity of two types of AlN ceramics were studied. The results show that, both the pure nano-AlN powders and the nano-AlN powders doped by Y₂O₃ can obtain the AlN ceramics with the relative density above 99% prepared by SPS at 1500 ℃ for 5~60 min under 40~60 MPa. When the sintering pressure is 50 MPa, the average grain size of the AlN ceramics is the smallest, which is 176 nm and 190 nm, respectively. The hardness and bending strength of the AlN ceramics are obviously improved by the grain refinement. When the sintering time is extended from 5 min to 60 min, the grain size of the AlN ceramics is increased to 1.71 μm and 1.73 μm, respectively. The grain growth leads to the decrease of hardness and bending strength of the AlN ceramics, but improves the thermal conductivity. It is found that the addition of Y₂O₃ sintering agent can effectively improve the comprehensive properties of the AlN ceramics under the same SPS sintering process.