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 4 wt% 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<1Mo<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.