Heterostructured metal matrix composites for structural applications: a review

Metal matrix composites (MMCs) with homogeneous structures (i.e., reinforcements with a uniform size are randomly dispersed in the metal matrix with a uniform grain size distribution) exhibit a strength-ductility/toughness tradeoff, which greatly hinders their engineering applications. Heterostructured metal matrix composites (HSMMCs) are regarded as an emerging class of MMCs consisting of heterogeneous zones with dramatically different attributes in the metal matrix, reinforcement and interface, relative to their conventional homogeneous counterparts, endowing them with the excellent combination of strength and ductility/toughness. These superior mechanical properties are enabled by activating extra strengthening and intrinsic/extrinsic toughening mechanisms induced by heterostructures. In the review, particular emphasis is given to the design principles of HSMMCs from the view of toughening mechanisms. The classification criteria of heterogeneity design are proposed based on the constituents of MMCs, including matrix heterogeneity, reinforcement heterogeneity, interface heterogeneity, and combined heterogeneity (a combination of two or more constituents aforementioned). In the combined heterogeneity design, the matrix & reinforcement heterogeneity design is specially named architecture design due to the orderly spatial arrangement of matrix and reinforcement. We then examine each of the diverse heterostructures, particularly, their fabrication methods, mechanical properties and strengthening & toughening mechanisms in the HSMMCs. Afterwards, we review the typical structural applications of MMCs in aerospace, aviation and transportation. Finally, directions for future research in the field of HSMMCs are proposed.