Aqueous colloidal processing of SiC with Y3Al5O12 liquid-phase sintering additives

The aqueous colloidal processing of SiC with Y₃Al₅O₁₂ liquid-phase sintering additives was investigated for two different additive systems, one the mixture of Y₂O₃ and Al₂O₃ in a 3:5 molar ratio and the other directly Y₃Al₅O₁₂. The investigation involved the study of the colloidal stability of the different components, and the comparison of the rheological behaviour of concentrated suspensions of SiC, SiC + 3Y₂O₃:5Al₂O₃, and SiC + Y₃Al₅O₁₂ as a function of the sonication condition, dispersant content, and solid loading. This allowed appropriate conditions for the preparation of well-dispersed, single-phase, and multi-component concentrated suspensions of SiC to be identified. It was found that the multi-component suspensions have better rheological behaviour than the single-phase ones, and that in terms of rheology and slip casting the Y₃Al₅O₁₂ additives are more functional than the conventional 3Y₂O₃ + 5Al₂O₃ additives. It was also demonstrated that the Y₃Al₅O₁₂ additive is as effective as the 3Y₂O₃ + 5Al₂O₃ additive in densifying SiC via liquid-phase sintering, with there existing no differences either in the microstructure or in room-temperature mechanical properties (hardness, toughness, and fracture mode). Implications of interest for the wet-shaping of complex SiC parts are discussed.