Microstructure and toughening of SiC-AlN ceramics induced by seeding with α-SiC

The microstructure and toughening of SiC-AlN ceramics from powder mixtures of beta-SiC, AlN and alpha-SiC by hot-pressing were studied in the 1870 to 2030 degrees C temperature range. The reaction of AlN and beta-SiC(3C) powders causing transformation to the 2H (wurtzite) structure appeared to depend on the hot-pressing temperature and the seeding with alpha-SiC. For the compositions of 49 wt% AlN/49 wt% SiC with 2 wt% alpha-SiC and 47.5 wt% AlN/47.5 wt% SiC with 5 wt% alpha-SiC heated at 2030 degrees C for 1 h, complete solid solutions with a single phase of 2H could be obtained. An appreciable amount of alpha-SiC seeding could develop columnar inter-grains of the 4H phase and the stable 2H phase with a relatively uniform composition and grain size distribution. The seeding effect of alpha-SiC on the phases present and compositional microstructures with columnar inter-grains was investigated in detail. The mechanical properties of the hot-pressed solid solutions were evaluated in terms of fracture toughness and Vickers hardness.