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

Abstract

Abstract SiC ceramics containing Lu2O3–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 Y2O3 –AlN, the creep resistance of the Lu2O3-containing ceramics is higher. In particular, strain rates down to 6 ⨯ 10–10 s–1 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 Y2O3 –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.