Gas pressure sintering of SiC sintered with rare-earth-(III)-oxides and their mechanical properties

The sintering behaviour of LPS-SiC and the influence of the size of the rare-earth cations on the secondary phase characteristics were investigated with different rare-earth oxide additions. In all cases, the most important sintering mechanism was found to be the solution-reprecipitation process. This fact was corroborated by TEM and EDS analyses. Post-sintering annealing resulted in devitrification of the secondary phases coupled with anisotropic grain growth due to the phase transformation from β-SiC to α-SiC. Improved fracture toughness of the annealed materials was attributed to crack deflection by the elongated grains. SEM microstructural analyses were performed in order to elucidate structure-property relationships. A comparative study in reference to the additive system Y2O3-AlN demonstrates significantly improved high-temperature properties of the Lu2O3-containing SiC ceramics.