"Lattice Strain Matching"-Enabled Nanocomposite Design to Harness the Exceptional Mechanical Properties of Nanomaterials in Bulk Forms

Enhanced Plastic Stability: Achieving High Performance in a Al6xxx Alloy Fabricated by Additive Manufacturing

Additive manufacturing (AM) facilitates the creation of materials with unique microstructural features and distinctive phenomena as compared to conventional manufacturing methods. Among the various well-fabricated AM alloys, aluminum alloys garner substantial attention due to their extensive applications in the automotive and aerospace industries. In this work, an Al6xxx alloy is successfully fabricated with outstanding performance. A nucleation agent is introduced to diminish the susceptibility to cracking during the AM process, thereby inducing a heterogeneous microstructure in this alloy. However, the introduction of ultrafine grains induces plastic instability, evidenced by the presence of Lüders band. This work investigates the evolution of the Lüders band and the strategy to reduce their undesirable effect. The heterogeneity destabilizes the band propagation and thus deteriorates the ductility. Through a T6 heat treatment, the local Lüders strain decreases from 10.0% to 6.2%, leading to a substantial enhancement in plastic stability. With the increase in grain growth and the enlargement of coarse grain regions, the mismatch between the local and macroscopic Lüders strain disappears. Importantly, the strength and the thermal conductivity are concurrently increased. The findings demonstrate the significance of ensuring plastic stability to achieve improved strength-ductility trade-off in AM alloys with heterogeneous microstructures.

Toughening Ceramic-Based Composites by Homogenizing the Lattice Strain at Phase Boundaries

Ceramic-based composites generally have low fracture toughness, and toughening these materials without sacrificing their hardness has been a big challenge. This study presents an approach for toughening ceramic-based composites by modulating the strain partition and stress distribution in phase-boundary regions. A new concept of homogenizing the lattice strain to achieve high fracture toughness in ceramic-based composites is proposed based on the collective lattice shear of martensitic phase transformation. The strategy was demonstrated by ZrO₂-containing WC-Co ceramic-metal composites as a prototype. The crystal planes along the WC/ZrO₂ martensitic transforming phase boundaries exhibited significantly larger and uniform lattice strains compared with conventional dislocation pile-up phase boundaries with highly localized lattice strains. The homogeneous strain and stress distributions across interfaces enabled the composite to have simultaneously high fracture toughness and hardness. The "homogenizing the lattice strain" strategy proposed in this work is applicable to a broad range of ceramic-based composites to achieve superior comprehensive mechanical properties.

Strain Engineering: A Boosting Strategy for Photocatalysis

Whilst the photocatalytic technique is considered to be one of the most significant routes to address the energy crisis and global environmental challenges, the solar-to-chemical conversion efficiency is still far from satisfying practical industrial requirements, which can be traced to the suboptimal bandgap and electronic structure of photocatalysts. Strain engineering is a universal scheme that can finely tailor the bandgap and electronic structure of materials, hence supplying a novel avenue to boost their photocatalytic performance. Accordingly, to explore promising directions for certain breakthroughs in strained photocatalysts, an overview on the recent advances of strain engineering from the basics of strain effect, creations of strained materials, as well as characterizations and simulations of strain level is provided. Besides, the potential applications of strain engineering in photocatalysis are summarized, and a vision for the future controllable-electronic-structure photocatalysts by strain engineering is also given. Finally, perspectives on the challenges for future strain-promoted photocatalysis are discussed, placing emphasis on the creation and decoupling of strain effect, and the modification of theoretical frameworks.