Fibre uniformity and cavitation during the consolidation of metal-matrix composite via fibre-mat and matrix-foil diffusion bonding

Fibre uniformity is important for ensuring overall mechanical properties of a composite. The conditions for achieving uniform fibre distribution in solid-state consolidated composites are quantitatively analysed. It is shown that the uniformity is influenced by initial fibre spacing, fibre packing and foil thickness before consolidation and matrix flow during consolidation. A graphical technique is presented to determine optimum pre-consolidation arrangement of fibres and foils for a given volume fraction. Residual cavities in partially bonded composites are observed in both hexagonally and rectangularly packed fibre arrays. Foil bending is mainly the cause for the cavities found in the former case, whereas in the rectangular array an ear defect is observed after an intermediate stage of bonding and is believed to be responsible for the voids which form during matrix flow in this case. The initiation of the ear defect is determined by matrix volume incompressibility and quantitatively analysed with respect to different conditions of the flow constraint imposed during consolidation. These predictions are compared favourably with experimental results.