Diamond is not only the hardest material in nature, but is also an extreme electronic material with an ultrawide bandgap, exceptional carrier mobilities, and thermal conductivity. Straining diamond ...can push such extreme figures of merit for device applications. We microfabricated single-crystalline diamond bridge structures with ~1 micrometer length by ~100 nanometer width and achieved sample-wide uniform elastic strains under uniaxial tensile loading along the 100, 101, and 111 directions at room temperature. We also demonstrated deep elastic straining of diamond microbridge arrays. The ultralarge, highly controllable elastic strains can fundamentally change the bulk band structures of diamond, including a substantial calculated bandgap reduction as much as ~2 electron volts. Our demonstration highlights the immense application potential of deep elastic strain engineering for photonics, electronics, and quantum information technologies.
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•Dual-phase strengthening mechanism-inspired microlattice metamaterial was designed.•The metamaterial's strength, stiffness and energy absorption ability were enhanced.•Large-scale ...metamaterial was 3D printed and applied to a micro aerial vehicle (MAV).•The MAV shows greatly increased flight duration with considerable weight reduction.
The rapid advancement in CAD and 3D printing technology have brought the rise of mechanical metamaterials which inspired from nature and have optimized microstructural features to exhibit superior mechanical properties over conventional materials for various structural applications. Here, by adopting dual-phase strengthening mechanism in crystallography, we proposed a microlattice strengthening strategy which incorporates stretching-dominated octet-truss (OCT) units as the second phase particles into the diagonal planes of the bending-dominated body-centered cubic (BCC) lattice matrix, to form an anisotropic OCT-BCC lattice. The OCT-BCC dual-phase microlattice possess superior specific compressive strengths that are ~300% and 600% higher than BCC microlattices along its horizontal direction and longitudinal direction, respectively, accompanied with a significant increase in stiffness and energy absorption as well. Moreover, a large-scale OCT-BCC lattice metamaterial with dimensions up to 5.0 cm × 2.0 cm × 1.0 cm was successfully manufactured and integrated into a micro aerial vehicle (MAV). The metamaterial-integrated MAV has an airframe that is ~65% lighter than its bulk counterpart, resulting in a significant increase (~40%) in flight duration. This work not only provides an effective metamaterial enhancement design strategy, but also promotes the practical application of large-scale 3D printed metamaterial in the field of micro unmanned aerial vehicle.
A series of NiCoCrSix (x = 0, 0.1, 0.2, 0.3) medium-entropy alloys were synthesized to investigate the effect of Si addition on the microstructures, mechanical properties and helium irradiation ...resistance of the NiCoCr-based alloys. The microstructures and the phase evolution of these alloys were examined using electron microscopy as well as the existing models. The results show that the alloys exhibit a single face-centered-cubic structure when the Si content is in the range of 0–6.25 at.%, whereas phase decomposition occurs as the Si content further increases (∼9 at.%). Comparing with NiCoCr, NiCoCrSi0.2 exhibited improved strength without sacrificing the ductility. The yield strength and ultimate tensile strength increased from 438 to 599 MPa and 921 to 1032 MPa, respectively, whilst the ductility kept as high as ∼50%. Our analysis indicates that the increased strength is mainly ascribed to the grain boundary strengthening. The large ductility is primarily due to the low stacking fault energy and shear modulus of the NiCoCrSi0.2 alloy, which makes mechanical twinning in small grains accessible and provides a steady strain-hardening rate in a wide strain regime. Besides, the enhanced compositional complexity and local lattice distortion induced by the introduction of Si can improve the helium irradiation resistance of NiCoCr, resulting in reduced average bubble size.
•Microstructure,mechanical properties and helium irradiation resistance of NiCoCrSix MEAs were investigated.•Enhanced strength was obtained in NiCoCrSi0.2 without the sacrifice of ductility.•Comparing with NiCoCr, NiCoCrSi0.2 exhibits improved helium irradiation resistance.
Abstract
Hollow micro/nanolattices have emerged in recent years as a premium solution compared to conventional foams or aerogels for mechanically robust lightweight structures. However, existing ...hollow metallic micro/nanolattices often cannot exhibit high toughness due to the intrinsic brittleness from localized strut fractures, limiting their broad applications. Here, we report the development of hollow CoCrNi medium-entropy alloy (MEA) nanolattices, which exhibit high specific energy absorption (up to 25 J g
−1
) and resilience (over 90% recoverability) by leveraging size-induced ductility and rationally engineered MEA microstructural defects. This strategy provides a pathway for the development of ultralight, damage-resistant metallic metamaterials for a myriad of structural and functional applications.
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•The promoting effect of pre-precipitated δ phase on deformation twinning and recrystallization behavior of Inconel 718 superalloy during hot compression was studied ...systematically.•The promoting effect on the formation of deformation twins was attributed to the lower stacking fault energy (SFE) and the local stress concentration.•A novel heteroepitaxial recrystallization (HERX) mechanism was found based on inverse precipitation.
The delta (δ) processing strategy is an efficient heat treatment to refine and homogenize the grain microstructure of Inconel 718 superalloy (IN718). However, the microstructure becomes complicated by the effect of pre-precipitated δ phases, due to the coupling of precipitations, high temperature, and loading stress. The present study aims to clarify the effect of δ phases on the microstructure evolution of IN718, especially the promoting effect on deformation twins (DTs) and dynamic recrystallization (DRX) behavior. The results show that the promoting effect of δ phases on the formation of DTs was attributed to the lower stacking fault energy (SFE) caused by the precipitation of δ phases and the local stress concentration caused by the distribution of δ phases. The area fraction of DRX grains in the compressed δ-containing specimen was 21% higher than that in the compressed δ-free specimen, which was associated with the discontinuous dynamic recrystallization (DDRX) nucleation stimulated by the single δ phase and the continuous dynamic recrystallization (CDRX) nucleation promoted by the distribution of δ phases. Furthermore, a novel heteroepitaxial recrystallization (HERX) mechanism was found based on inverse precipitation from the undissolved δ phase to γ matrix phase grains with a crystallographic orientation relationship of (0_10)102δ//(__111)011HERX.
Abstract
The universe abounds with solid helium in polymorphic forms. Therefore, exploring the allotropes of helium remains vital to our understanding of nature. However, it is challenging to ...produce, observe and utilize solid helium on the earth because high-pressure techniques are required to solidify helium. Here we report the discovery of room-temperature two-dimensional solid helium through the diamond lattice confinement effect. Controllable ion implantation enables the self-assembly of monolayer helium atoms between {100} diamond lattice planes. Using state-of-the-art integrated differential phase contrast microscopy, we decipher the buckled tetragonal arrangement of solid helium monolayers with an anisotropic nature compressed by the robust diamond lattice. These distinctive helium monolayers, in turn, produce substantial compressive strains to the surrounded diamond lattice, resulting in a large-scale bandgap narrowing up to ~2.2 electron volts. This approach opens up new avenues for steerable manipulation of solid helium for achieving intrinsic strain doping with profound applications.
The effect of Sn on the formation of -component dislocation loops was investigated by the combination of in situ ion irradiation and density functional theory calculations. The size of -component ...dislocation loops in Zr-1Nb-1Sn is smaller than that in Zr-1Nb, whereas the number density in Zr-1Nb-1Sn is about three times that in Zr-1Nb. We demonstrate that alloying Sn in Zr can decrease vacancy formation energy to impact the thermal stability of 〈c〉 loops and enhance vacancy diffusional anisotropy to inhibit the loop growth by promoting vacancy diffusion along the basal plane and reducing vacancy diffusion along the non-basal plane.
Designing structured materials with optimized mechanical properties generally focuses on engineering microstructures, which are closely determined by the processing routes, such as phase ...transformations. However, the direct connection between phase transformations and mechanical properties remains largely unexplored. Here, we propose a new concept of generalized stability (GS) to correlate phase transformations with plastic deformations in terms of the trade-off relationship that exists between thermodynamics and kinetics. We then suggest that, to achieve structured materials with excellent strength–plasticity combinations, phase transformations and/or plastic deformations with high GS, thermodynamic driving force (ΔG), and kinetic activation energy (Q), are highly expected. We verify the GS concept against a phase transformation-modulated nanostructured Fe alloy, for which an ultrahigh yield strength of 2.61 GPa and an ultimate compressive strength of 3.32 GPa while having a total strain to failure of 35% are achieved via multiple strengthening and hardening mechanisms. A theoretical analysis, in combination with microstructural characterization, indicates that the desired thermo-kinetic parameter triplets (i.e., high GS-high ΔG-high Q) could be inherited from the phase transformation to the plastic deformation, which ultimately yields good mechanical performance. The proposed concept can be regarded as the first theoretical criterion or a general rule that correlates phase transformation with plastic deformation, and can assist in the rapid selection of phase transformations to facilitate superior mechanical properties.
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The corrosion behavior of recrystallized annealed (RXA) and stress-relieved annealed (SRA) Zircaloy-4 was assessed in 360 ℃ lithiated water for 400 days. SRA Zircaloy-4 with localized corrosion sites ...below the oxide/metal interface exhibits a much faster out-of-reactor corrosion rate than RXA Zircaloy-4. High-density dislocations can enhance the diffusion of oxygen anions along dislocations, promoting the advancement of corrosive reactions and forming localized corrosion sites. Such a mechanism leads to a less uniform crystallography orientation of monoclinic ZrO2 grains at the oxide/metal interface of SRA Zircaloy-4 compared to its RXA counterpart, resulting in higher compressive stress and oxide cracking rates.
•SRA Zircaloy-4 exhibits a faster out-of-reactor corrosion rate than RXA Zircaloy-4.•Localized corrosion sites form below the oxide/metal interface of SRA Zircaloy-4.•Less uniform m-ZrO2 grains form at the oxide/metal interface of SRA Zircaloy-4.•High-density dislocations promote the formation of localized corrosion sites.•High-density dislocations result in higher stress and oxide cracking rates.
In nanostructured alloys, the concurrence of (solid-state) grain growth and phase transition is ubiquitously observed; however, due to the lack of kinetic evidences, the underlying physics of ...concurrence remains scarcely understood. In this study, for nanostructured Fe alloy as a model system, macro- and micro-scale characterizations for the concurrence were carried out using in situ X-ray diffraction and in situ high-resolution transmission electron microscopy (HRTEM). Macroscopically, the grain growth occurs and ceases before the end of phase transition, and microscopically, the concurrence of grain boundary (GB) and phase boundary (PB) migrations was certified as well. These experimental results, together with the ex situ HRTEM and molecular dynamics simulation, uncovered the interaction between GB and PB migrations, i.e., both velocity and direction of the PB migration are influenced when the PB interacts with the GB. On this basis, the concurrence was utilized to produce a new kind of heterogeneous and hierarchical microstructure (i.e., dual-phase bimodal nanostructure). The present findings, yield a deep understanding of the phase transition in nanostructured alloys, and further, demonstrate the potential usage of concurrence in manipulating the nanostructures for the development of nanostructured alloys.
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