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Effect of Processing Methods on Purity, Structure of Interfaces and High Temperature Strength of MoSi2 and MoSi2-SiC Composites

The effect of processing methods on the purity and structure of MoSi2 grain boundaries and MoSi2-SiC interfaces and their elevated temperature mechanical properties have been investigated. The processing techniques involve formation of MoSi2 by in-situ reaction, hot pressing of elemental Mo and Si powders and conventional hot pressing of commercial grade Starck MoSi2 powders. The SiO2 contents of the hot pressed products have been found to be sharply different, depending on the processing methods and the composition of the raw materials used. Transmission electron microscopy (TEM) examination has shown that reaction-hot-pressed MoSi2 based materials possess atomically abrupt grain boundaries (matrix) and interfaces (MoSi2-SiC composites), which are free of amorphous layers, while Starck MoSi2 contains globular SiO2 particles. Compression tests in the range of 1100°-1300°C have shown that the reaction-hot-pressed MoSi2 and MoSi2-SiC composite have superior properties. The mechanisms of high temperature deformation and serrated flow behaviour have been investigated using TEM of deformed specimens.