Effect of fabrication parameters on the microstructural quality of fibre-foil titanium metal matrix composites

The microstructure of fibre-foil Ti-6Al-4V (composition in weight per cent) and IMI 834 matrix metal matrix composites (MMCs), and corresponding foil- bonded alloys, are investigated in relation to fabrication parameters. High er fabrication temperatures are required in IMI 834 MMCs, which results in a thicker interfacial reaction layer than in Ti-6Al-4V MMCs. The matrix mic rostructure in all materials is predominantly a with intergranular beta, as a result of the slow cooling rate. MMCs reinforced with SM1240 fibres exhi bit boron precipitates along foil bond lines, owing to diffusion during con solidation. Fabrication using fibre mats with 7.1 fibres per millimeter (FP M) results in an excellent microstructure in (Ti-6Al-4V)-SM1240. The larger diameter of the SM1140 + fibre compared with SM1240 means that (Ti-6Al-4V) -SM1140 + requires FPM significantly below 7.1 in order to produce acceptab le microstructural quality. The higher residual stresses in IMI 834 MMCs re sult in cracking of the matrix and fibre-matrix interfacial region when a F PM of 7.1 is used. Acceptable microstructural quality is observed in IMI 83 4 MMCs when the FPM of fibre mats is reduced to 6.3. Interfibre cracking in IMI 834-SM1140 + is enhanced by a higher matrix microhardness than the oth er materials. This high hardness may be caused by a high matrix carbon cont ent. (C) 1997 British Crown.