High-temperature plasticity of SiC sintered with Lu2O3-AlN additives

SiC ceramics containing Lu –AlN sintering additives were gas-pressure sintered, and creep testing in four-point bending geometry was performed at temperatures between 1200 °C and 1500 °C in air. Compared with the more conventional additive system Y –AlN, the creep resistance of the Lu -containing ceramics is higher. In particular, strain rates down to 6 ⨯ 10 s were measured after 60 h at both 1300 °C/300 MPa and 1400 °C/100 MPa; in no case was steady-state creep reached. Annealing the ceramics at 1950 °C for extended periods of time led to significant changes in the amount and distribution of intergranular phases. However, in contrast to earlier work using Y –AlN additives, the influence of annealing on the creep resistance was negligible. Compliance testing as a function of temperature was conducted in order to monitor the softening behavior of materials with different additive compositions. In favorable cases, the drop in stiffness was only 12% up to a test temperature of 1450 °C.