Use of post-heat treatment to obtain a 2H solid solution in spark plasma sintering-processed AlN-SiC mixtures

Dense aluminum nitride-silicon carbide (AlN-SiC) solid solutions with a 2H structure were fabricated by the post-heat treatment of dense AlN-SiC composites fabricated by spark plasma sintering (SPS). The changes in the relative density, microstructure, and phases present were investigated for the compositions of 25 mol% AlN-75 mol% SiC (AlN 25), 50 mol% AlN-50 mol% SiC (AlN 50), and 75 mol% AlN-25 mol% SiC (AlN 75). The AlN-SiC composites fabricated by the SPS were dense ceramics with fine microstructures and composed of 2H and 6H AlN-SiC solid solutions. The AlN 50 samples heat treated at 2200°C and the AlN 75 samples heat treated at 2100°C were also dense ceramics and composed of only the 2H AlN-SiC solid solution. In contrast, the AlN 25 samples heat treated at 2200°C were porous ceramics and composed of several AlN-SiC solid solutions (2H, 4H, 6H, and 15R), and the AlN 75 samples heat treated at 2200°C were decomposed into an Al melt. Dense AlN-SiC solid solutions composed of only the 2H phase can be obtained by controlling the heat-treatment temperatures, except for the AlN 25 sample.