Fabrication Of BAS/SiC Ceramic Matrix Composites And Its Microstructure And Mechanical Properties

BAS/SiC, BSAS/SiC and BAS/(Si3N4-SiC) composites were synthesized by hot-press sintering and spark plasma sintering method. Crystalline phases and microstructure observations were characterized by X-ray techniques, SEM, TEM and HRTEM method. Room-temperature mechanical properties of the composites were measured by a three-point bend and single-edge-notch beam method. Fracture mode, strengthening and toughening mechanisms of the SiC matrix composites were studied. Oxidation behavior and toughening mechanisms at high temperature of the composites were also studied.BAS was first introduced to the sintering of SiC ceramics. The results showed that BAS could serve as an effective liquid sintering aid to promote densification of SiC grain during sintering process, and could entirely crystallize to high melting hexacelsian. SiC grains are homogenously distributed in the continuous BAS matrix. With increasing the sintering temperature and BAS content, the densities of the composites increase. The excellent mechanical properties were obtained for the BAS/SiC composites. The flexural strength and fracture toughness of 40wt.%BAS/SiC composites HP-ed at 1900oC was up to 597MPa and 7.0 MPa·m1/2, respectively, and its room-temperature flexural strength can maintain to 1200oC. The strength and toughening mechanisms were realized by crack propagation, crack bridging and SiC pullout of the BAS/SiC and BSAS/SiC composites.The densites of the composites were increased with Sr instead of Ba of the BAS phase partly. Microstructure of the BAS/SiC and BSAS/SiC composites hardly affect by BAS content, which indicates the growth of SiC grains are controlled by interface reaction. TEM observation indicated that no reaction layers or armosphere layers were observed, there was no reaction between SiC particles and BAS phase. SiC grains are compatible with BAS phase.Excellent oxidation resistance was obtained at high temperature for BAS/SiC composites. It was found that the oxidation rate of the composites followed a simple parabolic growth law. The weight change of 40wt.%BAS/SiC was 0.31mg/cm2 after oxidation at 1200oC maintaining 8h.Fully dense BAS/(Si3N4-SiC) composites were successfully fabricated by SPS method. The addition ofβ-Si3N4 particles increased the mechcanical properties of the BAS/SiC composites. the flexural strength and fracture toughness of the 30wt.%BAS/(20Si3N4+50SiC) omposites were up to 659MPa and 6.7MPa·m1/2, respectively, comparing with 527MPa and 5.5MPa·m1/2 of 30wt.%BAS/SiC composites, which induced good strengthening and toughening effect of self-reinforces rodβ-Si3N4 particles of the composites.