Novel MMC microstructure with tailored distribution of the reinforcing phase

Saffil short fibre agglomerates with diameters of 0.4 mm to 1 mm have been prepared using a tumbling technique. These were packed and infiltrated with molten 6061 Al alloy to make a metal matrix composite (MMC) with a novel microstructure in which the composite spheres are randomly distributed in the fibre-free aluminium matrix. In parallel, a commercial preform made of identical Saffil alumina short fibres and having the same fibre volume faction was used to prepare a conventional MMC by the same technique. Microstructural observation indicates that, within the composite spheres, the local volume fraction of fibre decreases from the outer layer to the centre region. The energy absorption during fracture was estimated by using a three point loading test on notched samples and was compared with that for conventional MMCs. Preliminary results suggest that this novel MMC possesses higher energy absorption capability and hence better damage tolerance. The fracture surfaces were examined by scanning electron microscopy in order to inform these experimental results.