Colloidal processing and mechanical properties of SiC with Al2O3 and Y2O3

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 1700-1900degreesC 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 1800-1900degreesC 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 1800degreesC 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.