Effect of preparation parameters on the properties of unidirectional SiC-fibre-reinforced MAS and BMAS glass-ceramics

The objective of this paper is to investigate the possibilities of fibre-reinforced glass-ceramics based on cordierite (MAS, magnesium alumino-silicate) and barium-osumilith (BMAS, barium magnesium alumino-silicate) and to find optimum preparation conditions with respect to mechanical properties, particularly high strength and toughness values. The prepregs were prepared by the sol-gel slurry method, the composites by application of the most effective densification conditions via the molten and high-viscosity state and by crystallisation under various temperature/pressure/time programmes. Best properties were obtained in the BMAS system with 14 wt% BaO at a relatively low SiC-fibre content of 20 to 30 vol% (strength: 534MPa, work of fracture: 16 kJ m(-2)). Higher values of strength were obtained with a predominant glass phase (up to 900 MPa) but these composites have only low application temperatures. Here, the optimum fibre concentration is much higher (about 50 vol%) than in the crystallised composites. The lower optimum fibre content of the predominantly crystallised composites is a consequence of a different phase composition and microstructure of the matrix compared with that without the presence of fibres under the same thermal and pressure conditions. (C) 1997 Elsevier Science Limited.