Microstructure and mechanical properties of heat-treated silicon carbide-aluminum nitride solid solutions

Nanophase-structured composites were fabricated by heat treating hot-pressed 2H-wurtzite SiC-AlN solid-solution specimens of 25, 50, and 75 mol% AlN within the spinodal decomposition zone. Heat-treatment conditions were 1750°C for 150 h, in flowing nitrogen gas. The hot-pressed specimens contained 2H-wurtzite equiaxed grains, and the grain size increased with AlN content. Lattice parameters followed Vegard's law. Nanoprecipitates with typical modulated tweed-type structures were observed along the [21̄1̄0] zone axis and were orthogonal to the {011̄2} planes that make angles of 46.70°, 46.90°, and 47.11° to the [0001] for the three compositions. The microhardness, flexural strength, and fracture-toughness values of the heat-treated specimens were not significantly different from the hot-pressed values.