ENGINEERING ASPECT OF CREEP DEFORMATION OF MOLYBDENUM DISILICIDE

Molybdenum disilicide (MoSi2) is a promising candidate material for structural application in gas turbine engines. Investigation of creep deformation of MoSi2 indicated that for high temperature use, the creep strength of MoSi2 needs to be improved. Alloying and addition of reinforcing phases have been shown to reduce creep rate significantly. The compositions studied include polycrystalline as well as single crystal MoSi2, SiC whisker and particulate reinforcements, alloying with WSi2 and addition of ductile phases of niobium particles. For all the composition, a stress exponent of between 3 and 4 was observed indicating a dislocation-recovery mechanism of creep. The temperature dependence of creep rates gave activation energy of 306 and 346 kJ mol-1 for polycrystalline MoSi2 in compression and tension respectively. A value of 251 kJ mol-1, however, is observed for single crystal MoSi2 compressed roughly along [210] direction. The significance of these parameters is analyzed.