Summary and Future Direction

Friction stir processing (FSP) has emerged as an effective tool for grain refinement and microstructure modification. It has now been also demonstrated that FSP is an attractive method to process composites. A wide range of reinforcements that include ceramic and metallic particles, carbon nanostructures have been incorporated in metallic matrices by FSP. This process has proved its potential in fabricating both bulk and surface composites. Nanocomposites and hybrid composites have been also fabricated by FSP. Different approaches such as groove filling, drill-hole, powder metallurgy and FSP combination, and in situ method have been followed to process a variety of composites. A major concern in fabricating the metallic matrix composites (MMCs) has been the inhomogeneity of particle distribution. A number of tool designs have emerged in order to distribute the particles uniformly. It has also been demonstrated how the process parameters affect the microstructure and properties of the processed composites. Both single-pass and multi-pass FSP have been explored and they have been found that the particle distribution generally improves with the number of passes. FSP has been also found useful in homogenizing the microstructure of as-cast and other MMCs that suffer from microstructural inhomogeneity such as particle clustering.