Physico-Chemical Investigation of Component Interactions of the Si ― Al ― O ― N ― Ti System in the Region Si3N4 ― AlN ― Al2O3 ― SiO2 ― TiN ― TiO2. Part 1. Subsystems Si3N4 ― Al2O3, Si3N4 ― TiN, and Al2O3 ― TiN

Abstract

Using the methods of differential thermal and x-ray diffraction analysis an investigation was made of component reactions in the Si ― Al ― O ― N ― Ti system, particularly between the compounds Si 3N4 ― Al2O3, Si3N4 ― TiN, and Al2O ― TiN under conditions approximating those used in the hot pressing of composites. It was established that in the reaction of Si3N4 with Al2O3, β-sialon, SiO2, AlN, and the intermediate reaction products (mullite and X-phase) are formed. In the reaction of Si3N4 with TiN, as a result of the decomposition of Si3N4 at 1650-1900°C titanium disilicide is produced, which forms eutectics with free silicon and residual TiN at 1320 and 1280°C, respectively. The reaction of Al2O3 with TiN similarly leads to the formation of a eutectic between Al2O3 and spinel at 1850°C. The presence of eutectic liquids in the specimens after sintering promotes densification of the material, and improves certain of its mechanical properties.