Creep behavior of mullite short fiber reinforced ZL109 alloy composites athigh temperature

The creep behavior of Al2O3. SiO2 fiber reinforced ZL109 composites has bee n investigated at four temperatures ranging from 553 to 623 K. The results show high stress exponent and high apparent creep activation energy. A good correlation between the normalized creep rate and normalized effective str ess means that the true stress exponent of minimum creep strain rate of the composite is very close to 5, and the minimum creep strain rate is matrix lattice diffusion controlled. The threshold stress decreases with increasin g temperature linearly and disappears at a temperature close to 623 K. It i s assumed that the long range internal back stresses generated in creep red uce the load transfer to fibers and the interaction between dislocations an d strengthening precipitates decreases at high temperature. At a high tempe rature where the long range internal back stresses is very close to the app lied stress, the threshold stress disappears.