To enhance the strength-to-weight ratio of a material, one may try to either improve the strength or lower the density, or both. The lightest solid materials have a density in the range of 1,000 kg/m ...³; only cellular materials, such as technical foams, can reach considerably lower values. However, compared with corresponding bulk materials, their specific strength generally is significantly lower. Cellular topologies may be divided into bending- and stretching-dominated ones. Technical foams are structured randomly and behave in a bending-dominated way, which is less weight efficient, with respect to strength, than stretching-dominated behavior, such as in regular braced frameworks. Cancellous bone and other natural cellular solids have an optimized architecture. Their basic material is structured hierarchically and consists of nanometer-size elements, providing a benefit from size effects in the material strength. Designing cellular materials with a specific microarchitecture would allow one to exploit the structural advantages of stretching-dominated constructions as well as size-dependent strengthening effects. In this paper, we demonstrate that such materials may be fabricated. Applying 3D laser lithography, we produced and characterized micro-truss and -shell structures made from alumina–polymer composite. Size-dependent strengthening of alumina shells has been observed, particularly when applied with a characteristic thickness below 100 nm. The presented artificial cellular materials reach compressive strengths up to 280 MPa with densities well below 1,000 kg/m ³.
In 1903, Alexander Graham Bell developed a design principle to generate lightweight, mechanically robust lattice structures based on triangular cells; this has since found broad application in ...lightweight design. Over one hundred years later, the same principle is being used in the fabrication of nanolattice materials, namely lattice structures composed of nanoscale constituents. Taking advantage of the size‐dependent properties typical of nanoparticles, nanowires, and thin films, nanolattices redefine the limits of the accessible material‐property space throughout different disciplines. Herein, the exceptional mechanical performance of nanolattices, including their ultrahigh strength, damage tolerance, and stiffness, are reviewed, and their potential for multifunctional applications beyond mechanics is examined. The efficient integration of architecture and size‐affected properties is key to further develop nanolattices. The introduction of a hierarchical architecture is an effective tool in enhancing mechanical properties, and the eventual goal of nanolattice design may be to replicate the intricate hierarchies and functionalities observed in biological materials. Additive manufacturing and self‐assembly techniques enable lattice design at the nanoscale; the scaling‐up of nanolattice fabrication is currently the major challenge to their widespread use in technological applications.
Nanolattices are highly ordered three‐dimensional architectures composed of nanoscale constituents, and have, in the recent past, redefined the limits of the accessible material‐property space throughout different disciplines. The exceptional mechanical properties of nanolattices, including their ultrahigh strength, damage tolerance, and stiffness, are reviewed, and their potential for multifunctional applications beyond mechanics, relevant fabrication methods, and future directions are discussed.
The deformation behavior of Chromium (Cr) was investigated with the goal to understand and quantify the thermally-activated dislocation plasticity and the transition to the ...temperature-/rate-independent regime in body-centered cubic (bcc) metals. High-temperature nanoindentation experiments were utilized to characterize the deformation behavior of bcc Cr from room temperature to 673 K. To validate the indentation method itself at elevated temperatures, we systematically studied the temperature-dependent indentation elastic modulus, which clearly shows a discontinuity at the magnetic phase transition at 308 K, which is quantitatively consistent with literature data. We characterized the kinetics of dislocation plasticity by analyzing the strain-rate sensitive behavior of the hardness at different temperatures. The observed signatures of the plastic relaxation mechanisms are discussed in the context of screw dislocation mobility governed by thermally-activated kink-pair nucleation, kink-drift or dislocation-impurity interaction.
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Nanoindentation experiments in the temperature (T) range of 298 and 573 K were performed to determine the activation energy (Q) for the plastic flow in a nanocrystalline CoCrFeMnNi high-entropy ...alloy, which was synthesized using high-pressure torsion. A marked increase in Q from ~0.5 to ~1.8 eV was observed when T is increased from 473 to 523 K, which correspond to ~0.3 and ~0.34 Tm (Tm: melting temperature), respectively. Detailed analysis reveals that this transition is associated with the additional activation of the grain boundary diffusion mechanism in enhancing plasticity.
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Abstract
Increasing demand in automotive, construction, and medical industries for materials with reduced weight and high mechanical durability has given rise to porous materials and composites. ...Materials combining nano‐ and microporosity and a well‐defined cellular macroporous architecture offer great potential weight reduction while maintaining mechanical durability. To achieve predictable mechanical performance, it is essential to apply experimental and computational efforts to precisely describe material structure–properties relationships. This study explores polymer structures with polymerization‐inherited porosity and well‐defined macroporous geometry, fabricated via digital light processing (DLP) 3Dprinting. Pore size and relative density are varied by ink composition and printing parameters to track their influence on the structure stiffness. Simulated stiffness values for the base polymer correspond to the experimentally determined elastic properties, showing Young's moduli of 554–722 MPa depending on the cosolvent ratio, which confirms the structure–properties relationship. Macroporosity is introduced in the form of a 3D tetrahedral bending‐dominated architecture with the resulting specific Young's moduli of 79.5 MPa cm
3
g
−1
, comparable to foams. To merge the gap in stiffnesses, further investigation of structure–property relationships of various 3D–printed lattice architectures, as well as its application to other stereolithography methods to eliminate the negative effects from printing artifacts and resolution limit of the DLP 3D‐printing, are envisioned.
The present study provides fundamental information on the resource recyclability of the interconnect assembly, i.e., the steel interconnector and the nickel meshes, from an end-of-life JÜLICH Solid ...Oxide Cell Stack—F10 design. The interconnector is composed of iron, chromium, and less than 4 wt.% of other alloying elements, mainly cobalt and manganese. Calculated blended compositions with the nickel meshes revealed their potential as a raw material in the production of 4xx, 2xx, or 3xx stainless steels. The melting behavior of the interconnect assembly was investigated under different conditions, i.e., in inert and oxidizing atmospheres, with and without the addition of slag-forming fluxes. The results demonstrated preferential oxidation of chromium in a trivalent state within the stable cubic spinel phase. Finally, the experimental results were compared with the thermodynamic equilibrium calculations based on the available databases (FToxid, SGTE, and SGPS) in FactSage 8.1 software. The calculated tendency to oxidize is in the order of Cr > Mn > Fe > Co > Ni at P(O2) greater than 10−10 bar, validating the experimental results.
In this study, we evaluate the evolution of the interfacial processes in metallic sliding contacts (i.e., aluminum alloys) in terms of their elemental composition, structural changes, and ...nanomechanical properties in order to understand the optimal running-in behavior leading to steady-state low friction and high wear resistance. Two different sliding conditions are used, resulting in low and high long-term friction and corresponding well with the low and high wear rates. Ex situ elemental analysis of these sliding experiments was performed by means of X-ray photoelectron spectroscopy. The mechanical properties were evaluated using nanoindentation and microcompression testing. While the elemental analysis revealed an increased oxide content for the near-surface region of the worn surfaces compared to the unworn material, the oxide content was higher for the experiments that resulted in an unfavorable tribological response (i.e., high friction and high wear). Similarly, the sub-surface grain-refined layer under these conditions was thicker compared to the experiment with a short running-in stage and low steady-state friction and wear. These observations correlated well with the nanoindentation and microcompression results, which show higher hardness and yield stress for the high friction and wear experiment. Correspondingly, low steady-state friction and wear were obtained with the formation of a thin and mechanically stable tribolayer.
Highly nanotwinned (NT) metals have advantages such as high strength, good ductility, favorable corrosion resistance, and thermal stability. It has been demonstrated that the introduction of high ...density NT microstructures can enhance the tribological properties of metals. However, the influence of the microstructure and the composition of NT alloys on the tribological behavior are not clear. In this work, the sliding wear behavior of fully NT materials, specifically Cu-Al and Cu-Ni alloys, are studied by a nanoscratch technique using a nanoindenter. The effects of microstructure and chemical composition on the wear properties are also studied. The results show that the chemical composition has an obvious influence on the wear resistance and microstructural deformation. For NT Cu-Al alloys, the hardness and sliding wear resistance improve with increased Al content from Cu-2wt.%Al to Cu-6wt.%Al. NT Cu-10wt.%Ni alloy shows even better wear resistance than Cu-6wt.%Al. The microstructural analysis shows that NT Cu alloys with higher wear resistance correspond to a smaller deformation-affected zone. The improvement of sliding wear properties of Cu-Al alloys with higher Al content may be ascribed to their decreased stacking fault energy. NT Cu-Ni alloy shows better wear resistance than Cu-Al alloy, this may be related to the formation of intermetallic compounds in Cu-Al system. This study broadens the knowledge about tribological properties of NT materials and provides a potential method to optimize their sliding wear resistance by altering the chemical composition of NT Cu alloys.
High-purity Cu samples containing parallel columns of highly aligned nanotwins with median spacing of 25nm were subjected to tension-compression cyclic loading by a high-throughput cyclic testing ...method. The methodology utilizes gradients in surface strain amplitude of a vibrating cantilever: one along the beam axis, with decreasing strain from the fixed to the free end of the beam, and the other through the foil thickness with decreasing strain from the surface to the neutral axis. Systematic microstructural investigations indicate that nanotwins are not stable under cyclic loading and that the applied strain amplitude has a strong influence on the resulting twin structure. In the highly stressed regions the detwinning process produces a twin free microstructure, allowing for subsequent extrusion and crack formation, and introduces fatal defects into structural parts.
BaCe0.65Zr0.2Y0.15O3-δ (BCZ20Y15) has raised great interest due to its good protonic conductivity and chemical stability. However, the sintering of the material is considerably challenged by its ...refractory nature. In the current work, almost fully densified single-phase BCZ20Y15 with grain sizes exceeding 10 μm was successfully fabricated by sintering at 1500 °C by using calcined powders consisting of naturally separated perovskite phases and 0.5 wt% NiO. The role of NiO as sintering aid was elucidated by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Atom Probe Tomography (APT) methods, concerning global and local material composition. Furthermore, the mechanism leading to the promoted densification and grain growth is elucidated based on current experimental results and a comprehensive review of the literature.
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