Structure and properties of AlN ceramics prepared with spark plasma sintering of ultra-fine powders

The AlN powders with grain size about 100 nm were synthesized by low-temperature carbon thermal reduction method. The synthesized powders without any additives could be completely densified through spark plasma sintering (SPS) technique above 1470 °C in vacuum under the pressure of 40 MPa. The properties of AlN ceramics sintered at different temperature and pressure were investigated. The results indicated that the density of SPS sintered AlN ceramics decreased with the reduction of sintering pressure and temperature. The grain size of the sintered samples reduced from about 1 μm to 200 nm as the sintering pressure and temperature decreased from 40 MPa and 1600 °C to 30 MPa and 1500 °C. No inter-granular phase was found in the microstructure of sintered samples, which resulted in a strong grain bond and consequently improved the mechanical properties especially the fracture toughness. Moreover, the effects of the grain size and porosity on the mechanical properties of the sintered samples were also discussed.