High-temperature deformation of mullite and analysis of creep curves

The creep behavior of mullite was studied under different stresses and in the temperature range 1200-1450 degreesC, and an analysis of creep curves was proposed. The study of creep behavior of mullite at high temperatures clearly indicates that this material exhibits concurrent creep and slow crack growth. An effective transition stress exists at each temperature. The analysis takes account of the total creep curve; in particular, the primary and stationary stages. It is now possible to determine by extrapolation the steady-state creep rate for specimens that break in the transient domain during tests. Thus, one can verify the influence of the stress on the steady-state creep rate over a wide stress range. On the other hand, this analysis clearly indicates the existence of two values of the activation energy around 1300 degreesC; this suggests a change of creep mechanism at this temperature.