Oxidation behavior and damage mechanism of SiCf/SiC minicomposites with multilayered (BN/SiC)n interfacial coatings at 1200 ℃

Abstract

ABSTRACT SiCf/SiC minicomposites with multilayered (BN/SiC)n interfacial coatings were fabricated via chemical vapor infiltration and precursor infiltration pyrolysis methods. Oxidation behavior, mechanical properties, and interfacial self-healing mechanism of minicomposites at 1200°C were comparatively studied. In dry air, SiC matrix at edges of composites was oxidized to glassy SiO2, thereby sealing the pores between fibers and matrix, healing microcracks, and preventing the diffusion of oxygen into the material. Results of thermogravimetric–differential thermal analysis proved that glassy borosilicate formed at 910°C and 1050°C in minicomposites with BN/SiC and multilayered (BN/SiC)2 coatings. In water/oxygen atmosphere at 1200°C, there existed an equilibrium between the generation of SiO2 and gaseous Si(OH)4. Uncoated sample and minicomposite with single BN coatings were simultaneously eroded by oxidizing atmosphere in directions perpendicular and parallel to fiber axis. Microholes formed due to BN volatilization were gradually healed by glassy borosilicate in minicomposites containing SiC layers, improving interface self-healing capability of composites. After oxidation in water/oxygen atmosphere for 100 min, minicomposites with multilayered (BN/SiC)2 coatings retained relatively high fracture strength and strain, which were 499.0 MPa and 1.05%, respectively.