Novel fabrication process of AlN ceramic matrix composites at low temperatures

Abstract A novel processing method to fabricate AlN-MgO-MgAl ₂ O ₄ composites has been developed, using non-sintered, porous, aluminum nitride (AlN) preforms infiltrated with a magnesium alloy in two directions, downward and upward, at relatively low temperatures (650°C, 800°C, 950°C). Microstructural, phase, and chemical analyses show that at 950°C and 135 min holding time, a continuous network of ceramic phases can be achieved successfully. Magnesium oxide and spinel phases (MgAl ₂ O ₄ ) are formed in-situ, when nitrogen gas is used. Due to the formation of a magnesium nitride layer on the surface of the non-sintered aluminum nitride, the infiltration mechanism proceeds effectively. No metallic phases are observed in the samples processed at 800°C and higher: these samples show high electrical resistivity ranging from 6.73×10 ⁸ to 2.10×10 ¹¹ Ωcm. Thermal diffusivity, heat capacity and density have been measured using the nano-flash method, differential scanning calorimetry and Archimedes technique, respectively. The effects of residual porosity and holding time on the thermal conductivity have been studied. Maximum thermal conductivity and density at room temperature are 96 W/(mK) and 2.45 g/cm ³ , respectively.