USE OF SPRAY TECHNIQUES TO SYNTHESIZE PARTICULATE-REINFORCED METAL-MATRIX COMPOSITES

In an attempt to optimize the structure and properties of particulate-reinforced metal-matrix composites, a variety of novel synthesis techniques have evolved over the last few years. Among these, the technique of spray processing offers a unique opportunity to synergize the benefits associated with fine particulate technology, namely microstructural refinement and compositional modifications, coupled with in situ processing, and in some cases, near-net shape manufacturing. Spray technology has resurrected much interest during the last decade and there now exists a variety of spray-based methods. These include spray atomization and deposition processing, low-pressure plasma deposition, modified gas welding techniques and high velocity oxyfuel thermal spraying. Spray processing involves the mixing of reinforcements with the matrix material under non-equilibrium conditions. As a result, these processes offer an opportunity of modifying and enhancing the properties of existing alloy systems, and also developing novel alloy compositions. In principle, such an approach will inherently avoid the extreme thermal excursions, and the concomitant macrosegregation associated with conventional casting processes. Furthermore, the spray processing technique also eliminates the need to handle fine reactive particulates associated with powder metallurgical processes. In this paper, recent developments in the area of spray synthesis or processing of discontinuously reinforced metal-matrix composites are presented and discussed with particular emphasis on the synergism between processing, microstructure and mechanical properties.