Effect of carbon addition on the creep of molybdenum disilicide composites

The effect of carbon addition on the creep deformation behavior of molybdenum disilicides was examined. It is shown that with the addition of carbon, the amorphous silica phase present at the grain boundaries is reduced to SiC, which forms particulates at the grain boundaries. These particulates (a) inhibit further coarsening of grains and (b) serve as reinforcements to enhance creep resistance. Since creep deformation rates are extremely sensitive to grain size in these materials, to observe reinforcement effect the creep rates need to be compensated for the grain size effects. On the basis of the grain size compensated creep rates, it was found that an addition of 2 wt.% carbon is as effective as 20–30 vol.% reinforcement of SiC. The effect of particulate reinforcement on creep of MoSi2 is examined after compensating for grain size effects. It is shown that (a) volume fractions greater than 20% are needed to have a noticeable effect of reinforcement, and (b) among all reinforcement examined so far SiC provides the best reinforcement.