Silicon carbide-based ceramics can be rapidly densified above approximately 1850 °C due to a transient liquid phase resulting from the reaction between alumina and aluminum oxycarbides. The resulting ceramics are fine-grained, dense, and exhibit high strength at room temperature. SiC hot pressed at 1875 °C for 10 min in Ar was subjected to creep deformation in bending at elevated temperatures between 1500 and 1650 °C in Ar. Creep was thermally activated with an activation energy of 743 kJ/mol. Creep rates at 1575 °C were between 10−9/s and 10−7/s at an applied stress between 38 and 200 MPa, respectively, resulting in a stress exponent of ≍1.7.
Dense, polycrystalline AIN samples of grain size between 1.8 and 19 pm were fabricated by hot-pressing. Bar-shaped samples were subjected to creep in four-point bending under static loads in nitrogen atmospbere. The outer fiber stress was varied between 20 and 140 MPa and the temperature between 1650 and 1940 K. Steady-state creep was established in each of the tests. The steady-state creep rate, de/dt was proportional to d d -" where the stress exponent, n, was between 1.27 and 1.43 and grain-size exponent, m, between -2.2 and -2.4. The activation energy for creep ranged between 529 and 625 kJ/mol. Both round (r type) and wedgeshaped (w type) cavities were observed in electron micrographs of the deformed samples. No noticeable change in the dislocation density was observed. Contribution of cavitation to the creep rate was estimated using an unconstrained cavity model. Based on this study it is concluded that the dominant mechanism of creep in polycrystalline AIN is diffusional. [
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