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A Review of Creep of Silicides and Composites
Published online by Cambridge University Press: 25 February 2011
Abstract
A review of creep behavior of molybdenum disilicides and their composites is presented. Creep rates of these silicides are compared with those of other high temperature materials such as superalloys, ceramic-ceramic composites, intermetallics including aluminides (nickel and titanium), berylides (vanadium and niobium), and refractory metals(molybdenum and tungsten). Creep rates of silicides are shown to be very sensitive to grain size even in the power-law creep regime with grain size exponent of the order of five and above. In addition, the results show that with increase in volume fraction of reinforcements there is a decrease in creep rates for volume percentages less than 25%. To achieve significant improvement in creep strength volume percentages of reinforcements greater than 25% are required. This weakening effect at low volume percentages is related to accompanying decrease in grain size with the addition of reinforcements. Addition of carbon to MoSi2 eliminated the silica present at grain boundaries and converted it to SiC. The SiC thus formed, inhibited grain growth during hot pressing. Thus although addition of carbon enhanced creep resistance, its effect is masked by the accompanying decrease in grain size. Thus, grain size plays a dominant role in the creep of molydisilicide composites. It is shown that among all the materials molybdenum disilicides possess very high creep resistance comparable to ceramic-ceramic composites.
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- Copyright © Materials Research Society 1994
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