Towards overcoming hetero-deformation-induced hardening and strain localization Trade-off: A review of micro/nano hybrid-reinforced composites

Particle-reinforced metal matrix composites (PRMMCs) often suffer from high stress concentration regions due to incompatibility between hard reinforcements and the soft matrix. Reinforcement hybridization is a promising strategy; however, traditional hybrid MMCs with homogeneous/random microstructures typically exhibit a strength-ductility-toughness trade-off, limiting their practical applications. In heterogeneous microstructures, deformation incompatibility between hard and soft domains—accommodated by geometrically necessary dislocations (GNDs)—generates hetero-deformation-induced (HDI) hardening, which is considered the key factor behind their exceptional mechanical properties. This review examines micro/nano hybrid reinforcements in MMCs to optimize heterogeneity, enhancing HDI hardening effects while mitigating stress concentrations. We explore architectured micro/nano hybrid composites as a promising toughening strategy, demonstrating how the synergy of micro- and nano-reinforcements in tailored architectures can transform conventional composites into strong, tough materials. Key topics include typical architectures, mechanical property characterization, strengthening/toughening mechanisms, and theoretical insights for future advancements in this emerging class of MMCs. Additionally, we highlight the new concept of the trade-off between HDI hardening and strain localization in heterostructures.