Graphite-fibre/carbide-matrix composites - III. Fracture behaviour of composites with a boron-carbide matrix

Results of two experimental series of fabricating and testing C/B4C composi tes are presented. The two fabrication routes used, both based on powder me tallurgy, differ from each other by the method of control of the blending s tage of the process. This was done either by noting when the appearance of the mixture reached about the same level of homogeneity, independent of fib re volume fraction, or by controlling the mixing time and obtaining mixture s with variable homogeneity and fibre-length distribution. The usual presen tation of experimental data as dependence of strength on fibre volume fract ion has little physical meaning when one deals with short-fibre composites produced by a powder-metallurgy route. To obtain a basis for modelling the fracture processes, one needs to describe in sufficient detail the formatio n of the microstructure accompanied by two competing processes, these being an increase in microstructural homogeneity and a reduction in fibre length . It is also shown that in the particular system under consideration the fi bre/matrix interface strength can change non-monotically with increase in t he temperature and time of the sintering process. (C) 1999 Elsevier Science Ltd. All rights reserved.