Sialon ceramic matrix composites
The present study has been performed on β'-sialon matrix reinforced with either carbon fiber, metals or TiN components. The study describes the optimum methods of fabrication of these composites and also investigates their mechanical and electrical properties. In carbon fiber/sialon system, reaction between the fiber and the matrix has been identified and overcomed by applying high densification rate and low temperature sintering. Samples containing 10-20V% fiber was hot pressed to almost theoretical density at temperatures 1500-1550°C. In metal reinforced sialon matrix composites there is always a reaction between the metal and the sialon to form metal silicide liquid at relatively low temperatures, which is found to be helpfull in decreasing the maximum densification temperature. Sialon reinforced by 15V% Ni powder is pressureless sintered to over 95 % of the theoretical density at temperature of 1450°C. Reaction in such composites can be controlled by increasing the sintering heating rate and the amount of silicon metal dissolveed into the metal particles (which strongly influences the composites mechanical properties) can be controlled by a two stage heat treatment sintering particularly in the stainless steel/sialon system. The addition of TiN to sialon matrix resulted in processing with no troubles of chemical incompatibility and composites with attractive mechanical properties. Density of almost theoretical was achieved in the addition of 10-30V%TiN to sialon. The crack type investigations on sialon and sialon matrix composites shows that the cracks are of Palmqvist type. The indentation fracture toughness of the composites mentioned above is dependant on the reinforced phase type, volume fraction and sintering temperature. In fiber/sialon composites fracture toughness of 4 7.9 MNm⁻³/² was achived by hot pressing 15V% carbon fiber/sialon composites. In metal/sialon composites, however, fracture toughness of 13 MNm⁻³/² is achieved, whilst the indentation fracture toughness of 30V%TiN reinforced sialon composites is 8.9 MNm⁻³/². The electrical conductivity of these composites is strongly dependant on the reinforced phase volume fraction and most importantly on the particles size of the conductive phase. However, resistivity of 0.5 Ω. cm is achieved in the addition of 20V% carbon to the sialon matrix. In metal/sialon systems resistivity of 3.37 Ω. cm is achieved in 20V% Ni/sialon composite whilst 30V%TiN is required to create a resistivity of 443 Ω. cm in such composites.