Creep and visco-elastic behaviour of LPS-SiC sintered with Lu2O3-AlN additive

Using AlN and Lu2O3 as sintering additives, three different SiC ceramics were liquid-phase sintered and subsequently annealed. Creep testing in four-point bending geometry was performed at temperatures between 1200 and 1500 °C in air under stresses ranging from 50 to 300 MPa. Grain boundary sliding accomodated by grain boundary diffusion along with some creep cavitation were found to be possible creep mechanisms. A comparative study in reference to the additive system Y2O3-AlN demonstrates significantly improved creep resistance of the Lu2O3-containing ceramics. In particular, the strain rates ranged from 1 × 10−10 to 1 × 10−8 s−1, with stress exponents of 1.4 ± 0.3, for the creep conditions detailed above. High-temperature compliance testing was also conducted from room temperature to 1450 °C in order to understand the visco-elastic behaviour of these materials. Excellent visco-elastic behaviour was observed even at 1450 °C as compared to other LPS-SiC with YAG or Y2O3-AlN additive system. Up to 1450 °C, the stiffness drop was only 7-10%.