Densification behavior of monolithic SiC fabricated by pressureless liquid phase sintering method

As a preliminary investigation of process development for SiC fiber-reinforced SiC matrix composites (SiCf/SiC composites) via a pressureless liquid phase sintering (PLPS) method, the manufacturing process parameters of monolithic SiC fabricated with/without very low pressure during the sintering under high temperature (1850 and 1900 °C) were optimized. Two kinds of sintering additive system (only Al2O3 and Al2O3–Y2O3 mixtures) can be achieved full densification corresponding to 99% of the theoretical density without high pressure during the sintering. Monolithic SiCs of both sintering additive systems applied with prepressure of 20 or 40 MPa possessed the flexural strength and porosity comparable to those of conventional liquid-phase sintered SiC with high pressure during the sintering. The low pressure (0.63 MPa) during sintering reduced the densification in particular for the materials sintered with just Al2O3. The additions of BN particles led to a gradual decrease in mechanical strength with an increase in porosity