Effects of carbon additions on MoSi2 microstructure and properties

Carbon as a second-phase particulate addition to a MoSi2 matrix has been investigated for possible improved mechanical property effects. MoSi2 with 0, 1, 2 and 4wt%C was fabricated using hot pressing and containerless hot isostatic pressing at temperatures of 1400, 1600 and 1800°C. These processing conditions showed the formation of an in-situ SiC phase and the ternary Nowotny phase C less than or equal 1Mo less than or equal 5Si3, which affected the microstructure and fracture behaviour of the materials. Microindentation techniques were used to evaluate the hardness and fracture toughness of the MoSi2 and C-MoSi2 materials. Increasing the processing temperature increased the hardness due to in-situ SiC formation as a result of carbon reaction with silica, although only modest improvements in fracture toughness were observed.