High-temperature plasticity of SiC sintered with Lu ₂O ₃-AlN additives : Dedicated to Professor Dr. Fritz Aldinger on the occasion of his 65th birthday

Abstract

SiC ceramics containing Lu ₂O ₃–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 ₂O ₃–AlN, the creep resistance of the Lu ₂O ₃-containing ceramics is higher. In particular, strain rates down to 610 ⁻¹⁰s ⁻¹ were measured after 60h at both 1300°C/300MPa and 1400°C/100MPa; 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 ₂O ₃–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.