Tensile behavior and strengthening mechanisms in a submicron B4C-reinforced Al trimodal composite

The physical and mechanical characteristics of cryomilled Al 5083-boron carbide (Al-B4C) metal matrix composites (MMCs) render them both scientifically interesting as well as technologically important. Trimodal architectures (containing three components, nano/ultrafine grains, coarse grains and ceramic reinforcements) allow for multiple degrees of freedom in the design of the microstructures that can be engineered, for example, to achieve combinations of strength, ductility and damage resistance that are not attainable with conventional materials. Various manufacturing strategies have been formulated to fabricate trimodal MMCs. Among these, cryomilling, which involves mechanical milling in a cryogenic liquid slurry (e.g., nitrogen), has been widely studied because in addition to minimizing recovery during the formation of nanocrystalline grains, it facilitates the incorporation of reinforcement particles in the metal matrix. In this study, novel trimodal composites reinforced with faceted, submicron (~500 nm), commercially-available B4C with varying volume fractions of coarse grain phase (0-30%) were fabricated. Within this class of engineering materials ultimate tensile strengths of 620-760 MPa and tensile elongations of 1.8-3.7% are observed. The microstructural features are investigated in depth, the strengthening mechanisms quantitatively evaluated and the mechanisms for enhancing strength and/or ductility are discussed.