Colloidal Processing and Mechanical Properties of SiC with Al₂O₃ and Y₂O₃

Abstract

A 30 vol% aqueous suspension of SiC/Al₂O₃/Y₂O₃ (1/0.02/0.016 volume ratio) system was consolidated by filtration through gypsum mold. The green compact was hot-pressed at 1700–1900°C under a pressure of 39 MPa in an Ar atmosphere. The sintering mechanisms were discussed based on the analysis of shrinkage curves of SiC/Al₂O₃/Y₂O₃ compacts during hot-pressing. The hot-pressing at 1800–1900°C gave dense SiC ceramics (>99% theoretical density) with average four-point flexural strengths of 554–658 MPa, fracture toughness of 4.2–5.3 MPa·m^1⁄2 and Vickers hardness of 20–25 GPa. The Weibull modulus of the SiC hot-pressed at 1800°C was in the range from 4.6 to 7.0. The processing in the heterocoagulation region (pH 5.0) for the SiC and sintering additives gave the highest mechanical properties after the hot-pressing.