Microstructure-property relationships of SiC fibre-reinforced magnesium aluminosilicates—II. Mechanical properties and failure characteristics

Abstract

Interfacial frictional shear stresses, flexural properties and failure mechanisms are reported for two magnesium aluminosilicates unidirectionally reinforced with Nicalon SiC fibres. Composites A and B were hot-pressed at 1500 and 920°C, respectively. High values of interfacial frictional shear stresses inferred from Marshall's analysis of the micro-indentation technique could be attributed in part to the presence of compressive radial stresses at the fibre-matrix interfaces. Although both composites failed non-catastrophically in symmetrical four point bend testing at room temperature, the failure modes were different. Extensive matrix microcracking, fibre failure and then fibre pull-out were commonly observed in composite A. Failure modes in composite B included the formation of a limited number of matrix cracks, the failure of fibres in the matrix crack front and progressive delamination. Our observations demonstrate that the mechanical properties, the interfacial frictional shear stresses and the failure mechanisms of both composites are governed by their microstructural features, in particular the chemistry and structure of the matrix-fibre interfacial region.