Fracture Behavior of Si<sub>3</sub>N<sub>4</sub>/SiC-Chopped-Fiber Composites with SiO<sub>2</sub> at the Grain Boundary

Abstract

Si3N4/SiC-chopped-fiber composites with various amounts of SiO2 at the grain boundary were fabricated by hot isostatic pressing (HIP). The SiC fibers (average diameter 130μm) were chopped with high aspect ratio and randomly dispersed in the matrix. Emphasis was placed on characterizing the fracture properties of the composites in comparison with the Si3N4 matrix material. A carbon layer of about 3μm, deposited on the surface of the fibers, was found to be very suitable for enhancing the pull-out process during fracture extension. As a result, catastrophic fracture from notches or pre-existing cracks could be avoided and the work of fracture (WOF) of the composite materials displayed values about 7-8 times higher than that of the matrix (i.e., ≈80J/m2). However, some physical limitations mainly related to the stereological arrangement of the fibers in the matrix, made the critical stress intensity for crack propagation (KIC) of the composites almost the same as that of the matrix, independently of the presence of the SiC fibers and the added amount of SiO2.