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With high resistance against interdiffusion, electromigration, creep and fatigue, single-crystal films of refractory metals are highly desired for applications in opto- and micro-electronic devices. Their fabrication is nevertheless very challenging, primarily due to their high melting points. Requiring no external thermal input, ion-irradiation presents an alternative route for single-crystal films by converting from their polycrystalline counterparts through irradiation-induced selective grain growth. The incomplete poly- to single-crystal conversion is however a common problem which limits the application of this method. Here we use refractory W thin films, the element with the highest melting point, as a model system. We systematically investigate the influences of film microstructure (texture and grain size) and irradiation temperature (77 K and room temperature) on the evolution of selective grain growth under 4.5 MeV Au+ ion-irradiation. We find that the driving force for selective grain growth can be increased by narrowing the texture spread of the films, refining the grain size and decreasing the irradiation temperature. Following this guidance, a complete conversion of a polycrystalline W film into a single crystal is achieved. This study therefore provides insights into the mechanism of selective grain growth and proves that it is an effective technique for microstructure engineering in thin film materials. The concepts can be applied to all crystalline metal films.

Microfabrication of synthetic single crystal diamond using accelerated helium ions beams has significant potential for functional applications, such as high precision optical devices, through tailoring of the optical properties via diamond graphitization. The use of helium ion microscopes (HIM) with nano-scaled focused ion beam spot sizes also allows for precision nano-patterning of the diamond surface through post-exposure selective etching of the generated graphitic phase. Here, single-crystalline diamonds with ⟨100⟩, ⟨110⟩, ⟨111⟩ and ⟨123⟩ orientations are exposed to He ion radiation from a HIM at a range of acceleration voltages and fluences. It is observed that ⟨123⟩ orientation was notably more sensitive to ion irradiation as sp3 bonds transition to sp2 bonds at lower fluence (1015 ions/cm2) compared to other orientations. In situ uniaxial compression of SC diamond micro-pillars revealed the strength of ⟨123⟩-oriented pillars is strongly dependent on the ion fluence, and thus is tunable by ion irradiation. Notably, ⟨100⟩-oriented pillars exhibit a better damage resistance as a small strength degradation due to its higher ion channeling efficiency. The irradiation damage of energetic helium ions on the structure and strength of diamond is therefore highly orientation-dependent. Such results provide the critical knowledge for precise patterning and designing of diamond-based functional structures in nano-fabrication.

Additive manufacturing of metals by 3D printing of polymeric filaments containing high loading of metal powder, subsequent debinding, and sintering offers a potent alternative to the widespread beam-based processes. The polymeric binder is the decisive component for a successful fabrication process. This study presents the development of a multi-component binder system for filament-based 3D printing of 316 L stainless steel in various optimization steps. The binder contains a polyethylene (PE) backbone, which ensures the structural integrity during solvent debinding. A soluble binder component consisting of a thermoplastic elastomer (TPE) and a second PE is used, to reduce the polymer content via solvent extraction prior to thermal debinding. The TPE grants flexibility to the filaments, while the PE allows reduction of the viscosity and increase in stiffness and strength. This enables precise tuning of the rheological and mechanical properties of the filaments. The capabilities of the binder system developed, are demonstrated by the fabrication of 3D plate-lattices. The structures are printed, subjected to a two-step solvent – thermal debinding procedure, and finally sintered. In the compression tests the structures are able to undergo large plastic deformations without fracture, highlighting their potential for energy absorption applications. The main contribution of this work is the development and disclosure of a binder system with two types of soluble polymers. This allows the precise control of the mechanical and rheological properties, as well as the backbone fraction of the binder. Based on the characterization performed, the binder system can be easily modified to adapt for other solid loading materials and fractions, as parameters like stiffness, viscosity, or backbone content can be adjusted precisely., Additive Manufacturing, 49, ISSN:2214-8604

Correlated high-speed nanoindentation and energy-dispersive spectroscopy are applied in a combinatorial investigation of the Ni-Ta system. All seven phases in the system are clearly resolved in the resulting maps, and the mechanical properties and composition ranges for each phase are determined. Good agreement with ab initio calculations is generally observed with some exceptions, most notably NiTa2. This is achieved using a simple correlation method utilizing directly overlaid data matrices to allow compositional labeling of mechanical data. This allows easy data segmentation without requiring complicated statistical deconvolution methods. Without this correlative method, phase deconvolution of the Ni-Ta system would be challenging due to several phases possessing adjacent compositions and mechanical properties. This demonstrates the potential of this new correlative approach for future investigations, particularly those involving complex microstructures and/or compositional variation., Small Methods, 6 (2), ISSN:2366-9608

Thermal management is conventionally the design of microelectronics circuitry to maximize heat extraction and minimize local heating. In this work, we investigate a reverse thermal management problem related to understanding and preventing heat dissipation during the propagation of a self-sustained reaction in Ni/Al reactive multilayers, metastable nanostructures that can release heat through a self-sustained propagating exothermic reaction. While it was recently demonstrated that reactive multilayers can serve as on-chip heat sources for on-demand healing of metal films, they still face challenges of device integration due to conductive heat losses to the substrate or adjacent on-chip components, which act as heat sinks and consequently quench the reaction. Here, we study the impact of different heat sink materials, such as gold, copper, and silicon, on the propagation velocity and temperature of the self-sustained heat wave and show that the propagation can be controlled and even stopped by varying the heat sink thickness. Further, we demonstrate that the introduction of a multilayered Al

Nanocrystalline NbMoTaW high entropy alloys (HEAs) have attracted significant attention due to their superior mechanical properties at elevated temperatures. However, the fracture behavior of nanocrystalline HEAs is still unknown. In this study, the fracture behavior of thin HEA films was investigated using micro-cantilever bending. The nanocrystalline films demonstrated critical stress intensities of ~3 MPa√m, which is significantly higher than previous single- and bi-crystalline values. This work demonstrates the capability of ion beam assisted deposition to strengthen nanocrystalline thin films with only minor losses in toughness.

The mechanical properties of multilayer films consisting of alternating layers of magnesium and niobium are investigated through micropillar compression experiments across a broad range of temperatures. The data collected from the variable temperature micropillar compression tests and strain rate jump tests are used to gain insight into the operative deformation mechanisms within the material. At higher temperatures, diffusion-based deformation mechanisms are shown to determine the plastic behavior of the multilayers. Diffusion occurs more readily along the magnesium–niobium interface than within the bulk, acting as pathway for magnesium diffusion. When individual layer thicknesses are sufficiently small, diffusion can remain the dominant deformation mechanism down to room temperature. Multilayer strengthening models historically rely solely on dislocation-based arguments; therefore, consideration of diffusion-based deformation in nanolaminates with low melting temperature components offers improved understanding of multilayer behavior. acceptedVersion

The effect of the specimen size on the mechanical characteristics of material, a phenomenon commonly referred to as the “size effect”, becomes increasingly important at micron and sub-micron dimensions of the specimen. However, the majority of size effect studies on face-centered cubic (fcc) metals have focused on pure elements, where deformation is accomplished by dislocation glide. In this work, single crystalline Ni – x at. % Co (with x = 0, 30, 50) solid solution micropillars were studied by mechanical testing and transmission electron microscopy (TEM) to elucidate the role of stacking fault energy on the size effect in Ni as a function of Co-addition. In situ strain rate jump (SRJ) microcompression testing allowed the evaluation of strain rate sensitivity and activation volumes for all pillar sizes at different strain rates, spanning over three orders of magnitude. TEM analysis showed that for an increase in Co content up to 50%, the SFE decreased from ~85 to ~28 mJ/m2. We observed all Ni – x at. % Co micropillars to exhibit consistent size effect trends (n=~−0.7), independent of composition and yield criterion, and similar trends between activation volume and different sizes: activation volume increases with grain size/pillar size., Materials Science and Engineering: A, 800, ISSN:0921-5093, ISSN:1873-4936

Many emerging applications in microscale engineering rely on the fabrication of three-dimensional architectures in inorganic materials. Small-scale additive manufacturing (AM) aspires to provide flexible and facile access to these geometries. Yet, the synthesis of device-grade inorganic materials is still a key challenge towards the implementation of AM in microfabrication. Here, we present a comprehensive overview of the microstructural and mechanical properties of metals fabricated by most state-of-the-art AM methods that offer a spatial resolution $\leq$10$\mu$m. Standardized sets of samples were studied by cross-sectional electron microscopy, nanoindentation and microcompression. We show that current microscale AM techniques synthesize metals with a wide range of microstructures and elastic and plastic properties, including materials of dense and crystalline microstructure with excellent mechanical properties that compare well to those of thin-film nanocrystalline materials. The large variation in materials performance can be related to the individual microstructure, which in turn is coupled to the various physico-chemical principles exploited by the different printing methods. The study provides practical guidelines for users of small-scale additive methods and establishes a baseline for the future optimization of the properties of printed metallic objects $-$ a significant step towards the potential establishment of AM techniques in microfabrication.

The development of non-noble nano-porous metal materials is hindered by surface oxidation reactions and from the difficulty to generate long range order pore arrays. Dealloying is a promising route to generate such materials by selective chemical etching of metal alloy materials. This process can generate nano-metal materials with superior plasmonic, catalytic and adsorptive surface properties. Here, the impact of properties of the etching solution on the dealloying process to generate nano-pores across thin film alloys was investigated by in-situ SAXS dealloying experiments. Single phase CuZn alloys were used as model materials to evaluate the influence of the solution temperature on the pore formation kinetics. This novel analysis allowed to visualize the change in surface properties of the materials over time, including their surface area as well as their pore and ligament sizes. The dealloying kinetics at the very early stage of the process were found to be critical to both stable pore formation and stabilization. SAXS in-situ data were correlated to the morphological properties of the materials obtained from ex-situ samples by Rutherford back scattering and scanning electron microscopy., Scientific Reports, 8, ISSN:2045-2322

Intentional breaking of the lattice symmetry in solids is a key concept to alter the properties of materials by modifying their electronic band structure. However, the correlation of strain-induced effects and breaking of the lattice symmetry is often indirect, resorting to vibrational spectroscopic techniques such as Raman scattering. Here, we demonstrate that reflectance anisotropy spectroscopy (RAS), which directly depends on the complex dielectric function, enables the direct observation of electronic band structure modulation. Studying the strain-induced symmetry breaking in copper, we show how uniaxial strain lifts the degeneracy of states in the proximity of the both L and X symmetry points, thus altering the matrix element for interband optical transitions, directly observable in RAS. We corroborate our experimental results by analysing the strain-induced changes in the electronic structure based on ab-initio density functional theory calculations. The versatility to study breaking of the lattice symmetry by simple reflectance measurements opens up the possibility to gain a direct insight on the band-structure of other strain-engineered materials, such as graphene and two-dimensional (2D) transition metal dichalcogenides (TMDCs)., 6 pages, 3 figures, 11 panels, 33 references

Reactive multilayers can be used for energy storage as well as releasing large amounts of heat in a short time. Molecular Dynamics (MD) simulations are used to study the influence of the crystal structure on the reaction front propagation in Al–Ni multilayers. Different microstructures, namely, amorphous, single crystal, columnar grains, and randomly oriented grains of varying size, are investigated. The effect of the microstructure on the propagation speed is studied and compared to existing experimental results. Furthermore, MD simulations allow to study the inter-diffusion of the Al and Ni layers. It is found that crystallinity has a significant impact on the front propagation speed, which is likely related to different diffusion mechanisms. The more disordered the individual layers become, e.g., by increasing the grain boundary density, the higher is the resulting propagation speed.

The fabrication of 3D ink-printed and sintered porous Si scaffolds as electrode material for lithium-ion batteries is explored. A hierarchically-porous architecture consisting of channels (~220 μm in diameter) between microporous Si struts is created to accommodate the large volume change from Si (de)lithiation during electrochemical (dis)charging. The influence of sintering parameters on Si strut porosity and the resulting mechanical and electrochemical properties of the scaffolds are studied experimentally and computationally. Varying sintering temperatures (1150–1300 °C) and sintering times (1–16 h) the open porosity within the Si filaments can be tailored between 46 and 60%. Pore size (3–6 μm) and wall thickness (3–8 μm) can be adjusted to tailor the surface-to-volume ratio. Computational results show that maximum capacity is expected at ~50% Si strut porosity, balancing short diffusion lengths and sufficient volume of active material. Stress concentrations are reduced at higher filament porosities albeit at the cost of energy density. For a filament porosity of 46%, hierarchically porous Si microlattice electrodes display gravimetric and volumetric capacities as high as 2,990 mA h g−1 and 2,860 mA h cm−3, respectively. The simple 3D printing + sintering approach provides further opportunities for optimization of Si electrodes by geometrical freedom.

This paper presents the proof-of-concept for a 4D printed active compliant hinge with a selectively variable stiffness for the deployment and reorientation of satellite appendages. We use 4D printing to create an active compliant hinge capable of bending to a given angular position, holding the position without consuming energy and reorienting itself multiple times in a slow and controlled manner without using rigid mechanisms and, therefore, requiring no lubrication. The deployment and the reorientation of the hinge are achieved by exploiting thermally induced stiffness modulation of one of the constituting materials and two antagonistic shape memory alloy actuators. The hinge is specifically designed for the case study of a 6U CubeSat with two orientable solar panels. In this work, we first explain the working principle of the hinge and propose three different actuation strategies to increase the energy collection of the considered CubeSat. Second, we describe the specific functional and geometric requirements of the hinge, the resulting design and the fabricated functional prototype. The latter is tested in a standard laboratory environment to measure the range of motion, the energy consumption and the actuation time. Finally, the feasibility of the three proposed actuation strategies is evaluated considering the corresponding net increase in collected energy. The results show that the hinge is compatible with the stowing requirements and capable of achieving maximum angular positions larger than 90° in both directions and holding any intermediate position with an accuracy of less than 3°. The three actuation strategies considered lead, in a standard laboratory environment, to an increase in energy generation between 54% and 72%., Smart Materials and Structures, 30 (8), ISSN:1361-665X, ISSN:0964-1726

A combinatorial science approach is utilized to study the microstructural and mechanical properties of metastable copper‑tungsten solid solutions. Lateral compositional gradient (also called composition-spread) samples were deposited by simultaneously sputtering copper and tungsten targets positioned obliquely at opposite ends of a silicon substrate. The chemical composition of the film varies continuously along its length from 12 to 45 atomic % copper and has a nominal thickness of 1 μm. Nanoindentation was performed to measure the hardness and elastic modulus of the film. Grain size and solid solution strengthening models are applied to interpret the hardness of the film, though a simple rule of mixtures is found to give a more satisfactory fit to the data. The elastic modulus of the film is consistently below that predicted by the rule of mixtures. X-ray diffraction revealed plane spacing less than that predicted by Vegard's law as well as three chemical compositions exhibiting enhanced long-range order. Transmission electron microscopy analysis confirms that the film consists of a single metastable body centred cubic solid solution where the lattice spacing and grain size depend on chemical composition.

In this work, the onset strains of fragmentation, the fracture strength, and fracture toughness of amorphous and crystalline Ge2Sb2Te5 (GST) films are determined. Using in situ methods, such as resistance measurements, reflectance anisotropy spectroscopy (RAS), and light microscopy during uniaxial tensile loading, we demonstrate that onset strain of fragmentation and delamination depend on both, crystallographic state of the GST film and the film thickness. We observe that amorphous GST fractures at larger strains than crystalline GST. However, due to its small Young's modulus the fracture toughness KIC of amorphous GST is lower than that of crystalline GST (amorphous: K I C = 0.4 ± 0.2 MPa m0.5; crystalline: K I C = 0.8 ± 0.2 MPa m0.5). The results presented are critically discussed with respect to the potential application of GST films in flexible displays.

With progressing miniaturization of modern electronic devices, interconnects become increasingly smaller. Additionally, as electronic devices move away from rigid substrates toward flexible ones, understanding their mechanical and structural stability is becoming crucial. In this work, a thorough mechanical characterization of copper thin films deposited on flexible substrates was performed with two techniques, namely well-established synchrotron X-ray diffraction (sXRD) and the rather new usage of reflectance anisotropy spectroscopy (RAS) for mechanical characterization of thin films. The comparison of these two techniques shows that RAS can be reliably used for the accurate and prompt yield stress measurements. The acquisition time of RAS is much faster than that of sXRD: 1 second per data point compared to several seconds per data point for sXRD experiments. Moreover, the signal-to-noise ratio of the RAS data is much higher than that of the sXRD. Our results show that yield stress of Cu films increases with the decrease in the film thickness, going from 352 MPa for a 500 nm films to 793 MPa for a 50 nm thick film. Microstructure analyses of the films by electron microscopy allowed correlation of the mechanical behavior of the films to their grain morphologies. We have shown that RAS can supplement sXRD measurements due to a faster acquisition rate which allowed us to analyze the creep behavior of our copper thin film at different strain rates.

Elastic strain is an effective and thus widely used parameter to control and modify the electrical, optical, and magnetic properties of crystalline solid-state materials. It has a large impact on device performance and enables adjusting the materials functionality. Here, we promote a micromechanical strain enhancement technology to achieve ultra-high strain in semiconductors. The here presented suspended membranes enable the accurate control of the strain on a wafer-scale by standard top-down fabrication methods making it attractive for both device applications and also, thanks to the simplicity of the method, for fundamental research. This review aims at discussing the process of strain enhancement and its usage as an investigation platform for strain-related physical properties. Furthermore, we present design rules and a detailed analysis of fracture effects limiting the strain enhancement.

Metals with nanometer-scale grains or nanocrystalline metals exhibit high strengths at ambient conditions, yet their strengths substantially decrease with increasing temperature, rendering them unsuitable for usage at high temperatures. Here, we show that a nanocrystalline high-entropy alloy (HEA) retains an extraordinarily high yield strength over 5 GPa up to 600 °C, 1 order of magnitude higher than that of its coarse-grained form and 5 times higher than that of its single-crystalline equivalent. As a result, such nanostructured HEAs reveal strengthening figures of merit-normalized strength by the shear modulus above 1/50 and strength-to-density ratios above 0.4 MJ/kg, which are substantially higher than any previously reported values for nanocrystalline metals in the same homologous temperature range, as well as low strain-rate sensitivity of ∼0.005. Nanocrystalline HEAs with these properties represent a new class of nanomaterials for high-stress and high-temperature applications in aerospace, civilian infrastructure, and energy sectors.

Most refractory high-entropy alloys (HEAs) are brittle and suffer from limited formability at ambient temperature. Previous studies imply that grain boundaries affect their fracture behavior, but quantitative studies on the fracture properties of body-centered-cubic HEAs are scarce. Here, using in situ micro-cantilever tests, we show that the fracture toughness of a bi-crystal HEA, Nb 25 Mo 25 Ta 25 W 25 , is one order of magnitude lower than that of single crystalline ones. Atom probe tomography of the bi-crystal HEA reveals element segregation and formation of oxides and nitrides at grain boundaries, suggesting that minimizing grain boundary segregation is critical to improving fracture properties in refractory HEAs.

Sample geometries for micro-mechanical testing, e.g. micro-pillars and micro-cantilevers are primarily produced using gallium focused ion beam technology. However, the effects of the gallium ions on the mechanical properties of metals which are embrittled by liquid metal gallium are still unknown. In this work, micro-compression samples from single crystalline and ultrafine-grained aluminum are fabricated using both xenon and/or gallium ions. The different ions have little effect on the yield strength of single crystalline aluminum. However, for the ultrafine-grained aluminum, the strength is reduced with increasing Ga dose, and considerable differences in the deformation morphology and resulting microstructures are observed.

Controlling the grain boundary network of small-scale materials—such as coatings and thin films—is an ambitious goal that would ultimately enable the production of components with tailored properties and improved reliability. In this work we present a new technique—which we term ion-induced grain boundary engineering (iGBE)—to engineer the character distribution and connectivity of grain boundaries in gold films in situ, as they are being deposited. iGBE consists of a repeated sequence of ion-induced material removal and material deposition which results in the selection and growth of crystal grains in twinned relationship. This phenomenon yields a substantial increase in the density and connectivity of Σ3 twin boundaries, which have renowned beneficial effects on the material's resistance to intergranular degradation. We confirm the improved reliability of iGBE microstructures by assessing their resistance to electromigration—one of the most common causes of failure in integrated circuit interconnects. We find that, through iGBE, interconnect lifetime increases by three orders of magnitude at standard operating conditions. Since iGBE is material-insensitive and compatible with standard microfabrication technology, we expect it to have significant impact on microelectronics industry.

Many biological systems consisting of mechanically graded composites can be used to join mechanically different materials like bone, cartilage and mussel. Synthetic routes have so far been unable to achieve both the 3-D nature and the property tuning at micrometer length scales to replicate such systems. Deliberate strengthening of the mismatched surfaces and weak regions could be beneficial for a wide range of applications such as flexible electronics with locally stiff constituents, NEMS and MEMS systems, dental prosthesis having heterogeneous particle distributions resembling to natural tooth and joining mechanically different biological materials such as bone, cartilage and mussel. Dip Pen Nanolithography (DPN) can be a strategy to achieve this goal. In this study, DPN is utilized to locally deposit graded polymer-based composite materials at the micron scale. Spatial resolutions of 3–20 μm are obtained on entire pattern profiles with 6–70 μm width and up to 2 μm height. Colloidal probe microscopy and nanoindentation are used for mechanical characterization. Results show that the hardness and modulus of the gradient nanocomposite patterns can be tuned locally by changing the concentration of the ceramic nanoparticles.

Micro-compression testing of focused ion beam fabricated pillars is a popular technique for mechanical characterization at small scales. However, there are concerns associated with these ion-prepared samples, including irradiation damage from Ga ions and Ga segregation at grain boundaries resulting in liquid metal embrittlement. In this work, this is investigated using strain rate jump nanoindentation and micro-compression of single crystalline and ultrafine-grained aluminum with different grain boundary conditions. The extracted strain rate sensitivity and activation volume are used to study the effects of Ga and Xe ion species from fabrication and testing methods on deformation behavior of aluminum samples. Results show that the measured strain-rate sensitivity of non-equilibrium, ultrafine-grained aluminum is significantly affected by the dosage of Ga. Activation volumes suggest that the dominant deformation mechanism remains consistent despite Ga at the boundaries. Atom probe tomography reveals that Ga was observed to segregate to aluminum grain boundaries up to 2.2 at.% in the FIB prepared sample., Materials & Design, 181, ISSN:0264-1275, ISSN:1873-4197

Zero-index (ZI) materials are synthetic optical materials with vanishing effective permittivity and/or permeability at a given design frequency. Recently, it has been shown that the permeability of a zero-index host material can be deterministically tuned by adding photonic dopants. Here, we apply metal-induced crystallization (MIC) in quasi-random metal-semiconductor composites to fabricate large-area zero-index materials. Using Ag-Si as a model systems, we demonstrate that the localized crystallization of the semiconductor at the metal/semiconductor interface can be used as design parameter to control light interaction in such a disordered system. The induced crystallization generates new zero-index states corresponding to a hybridized plasmonic mode emerging from selective coupling of light to the \r{a}ngstr\"om-sized crystalline shell of the semiconductor. Photonic doping can be used to enhance the transmission in these disordered metamaterials as is shown by simulation. Our results break ground for novel large-area zero-index materials for wafer scale applications and beyond., Comment: 23 pages, 4 figures

An extensive range of metals can be dissolved and re-deposited in liquid solvents using electrochemistry. We harness this concept for additive manufacturing, demonstrating the focused electrohydrodynamic ejection of metal ions dissolved from sacrificial anodes and their subsequent reduction to elemental metals on the substrate. This technique, termed electrohydrodynamic redox printing (EHD-RP), enables the direct, ink-free fabrication of polycrystalline multi-metal 3D structures without the need for post-print processing. On-the-fly switching and mixing of two metals printed from a single multichannel nozzle facilitates a chemical feature size of, Nature Communications, 10 (1), ISSN:2041-1723

Controlling anisotropy in self-assembled structures enables engineering of materials with highly directional response. Here, we harness the anisotropic growth of ice walls in a thermal gradient to assemble an anisotropic refractory metal structure, which is then infiltrated with Cu to make a composite. Using experiments and simulations, we demonstrate on the specific example of tungsten-copper composites the effect of anisotropy on the electrical and mechanical properties. The measured strength and resistivity are compared to isotropic tungsten-copper composites fabricated by standard powder metallurgical methods. Our results have the potential to fuel the development of more efficient materials, used in electrical power grids and solar-thermal energy conversion systems. The method presented here can be used with a variety of refractory metals and ceramics, which fosters the opportunity to design and functionalize a vast class of new anisotropic load-bearing hybrid metal composites with highly directional properties., Scientific Reports, 9 (1), ISSN:2045-2322

Materials with enhanced vibration damping properties are of ever-growing technological interest. The ability of a material to limit mechanical vibrations, indeed, not only may extend its service life, but also reduces its susceptibility to mechanical noise generation. The selection and design of damping structural materials usually aims to maximize the loss coefficient, while sacrificing the stiffness, to achieve the proper vibration damping capability. In this work, we overcome this typical stiffness tradeoff by geometrically confining thin viscoelastic layers between stiff thicker ones in a layered composite, thus enhancing its viscoelastic shear response. The preparation of the composite is guided by a simple design methodology based on the effective properties of its homogenized counterpart. An optimal design window, defined for the viscoelastic volume fraction, directs the manufacturing of the composite. This approach allows to manufacture composites that exhibit enhanced damping properties, with over three orders of magnitude increase of loss coefficient and less than one order of magnitude decrease of stiffness compared to the constituent stiff material. Such materials might find applications in fields where high stiffness is required but a damping component is necessary to avoid the build-up of dangerous vibrational modes: from the aerospace industry to the design of “silent” infrastructures.

Various parameters from fabrication and testing are known to influence the behaviour for microcompression experiments, especially the work-hardening behaviour. In this regard, the most important factor is found to be the availability of unconstrained slip planes. The second-most important factor is the lateral constraint acting on the sample, which usually arises from friction between indenter and pillar in a combination with a laterally stiff indenter setup, which can generate significant grain rotation and deviation from ideal single slip behaviour. The effect of lateral constraints on the strain-hardening rate is demonstrated on single crystals of gold and a novel solution by cyclic loading conditions is suggested, which could provide comparable conditions for different types of indenter hardware. In this work, the cyclic loading method is shown to minimise the influence of lateral constraints and provide more accurate measurements of strain-hardening behaviour than commonly applied microcompre...

Ever since quasicrystals were first discovered, they have been found to possess many unusual and useful properties. A long-standing problem, however, significantly impedes their practical usage: steady-state plastic deformation has only been found at high temperatures or under confining hydrostatic pressures. At low and intermediate temperatures, they are very brittle, suffer from low ductility and formability and, consequently, their deformation mechanisms are still not clear. Here, we systematically study the deformation behaviour of decagonal Al–Ni–Co quasicrystals using a micro-thermomechanical technique over a range of temperatures (25–500 °C), strain rates and sample sizes accompanying microstructural analysis. We demonstrate three temperature regimes for the quasicrystal plasticity: at room temperature, cracking controls deformation; at 100–300 °C, dislocation activities control the plastic deformation exhibiting serrated flows and a constant flow stress; at 400–500 °C, diffusion enhances t...

Decagonal quasicrystals (DQCs), as a class of two-dimensional quasicrystals, are known to be highly anisotropic in most of their physical properties. Here we show that their plastic anisotropy can be considerably reduced, and even eliminated, when they are scaled down to the sub-micrometer regime and deformed at room temperature. The reduced plastic anisotropy might be attributed to both size and temperature dependence of dislocation activities. This finding may shed light on the exploration of new deformation mechanisms for quasicrystal plasticity in an unknown size and temperature regime.

Co-sputtering from confocal sources is a widespread technique for the production of thin film alloys. In this process the substrate is rotated to ensure that the films are homogeneous in thickness and composition. Even though the choice of substrate rotation speed is a critical parameter in such depositions, its influence on the resulting film's homogeneity has not been studied systematically. This work addresses the question from a different angle: the formation of multilayers as a function of substrate rotation speed is investigated. A very simple and widely applicable model is developed to predict the period and the composition of the multilayers as a function of the radial position and the substrate rotation speed. The model is benchmarked with characterization results of an immiscible Cu-56 at.% Ta metastable alloy, which is co-sputtered with varying substrate rotation speed. It is shown that the model can predict the period of the composition modulations very accurately, and its predictive power with respect to the amplitude of the composition modulation is only limited by intermixing due to Cu surface segregation during the deposition process. Multilayers with a minimum period of 1 nm could be prepared in the Cu–Ta system using this method.

Ultrathin Si films in the nanometer range are extensively used for electronic and optoelectronic devices. Their mechanical properties have a high impact on the durability of the devices during lifetime. Here, fragmentation and buckling of 8–103 nm thin amorphous and polycrystalline (poly-) Si films on polyimide substrates have been studied by in situ light microscopy, Raman spectroscopy and resistance measurements. Generally, a smaller film thickness and a compressive residual stress delays the fracture of the film. The fracture strength of poly-Si films is larger compared to that of amorphous Si films while the adhesion to the substrate is better for amorphous Si compared to poly-Si. The onset delamination as a function of film thickness differs for the two phases and is described by two different models. Thin-film models for fracture toughness (amorphous Si: K 1C = 1.49 ± 0.22, poly-Si: K 1C = 3.36 ± 1.37) are applied, discussed, and found to be consistent with literature values.

Tungsten foams with directional, controlled porosity were created by directional freeze-casting of aqueous WO3 powder slurries, subsequent freeze-drying by ice sublimation, followed by reduction and sintering under flowing hydrogen gas to form metallic tungsten. Addition of 0.51 wt% NiO to the WO3 slurry improved the densification of tungsten cell walls significantly at sintering temperatures above 1250 °C, yielding densely sintered W-0.5 wt% Ni walls with a small fraction of closed porosity (

A novel 3D printing method for voxel-by-voxel metal printing is presented. Hollow atomic force microscopy (AFM) cantilevers are used to locally supply metal ions in an electrochemical cell, enabling a localized electroplating reaction. By exploiting the deflection feedback of these probes, electrochemical 3D metal printing is, for the first time, demonstrated in a layer-by-layer fashion, enabling the fabrication of arbitrary-shaped geometries.

In this work a systematic in situ annealing study of sputtered Cu–Ta alloys is reported. Under equilibrium conditions Cu and Ta are completely immiscible, the metastable Cu–Ta alloys hence undergo phase separation upon annealing. Using in situ X-ray diffraction the phase evolution at temperatures

Chocolate consists of cocoa butter, cocoa particles, sugar, and additives, which together determine its taste and optical properties. The optical properties of chocolate play a vital role in consumer perception, representing type and quality in the blink of an eye. Here, we present a comprehensive analysis of the optical properties of white, milk, and dark chocolate, while demonstrating how to craft orange to blue chocolate via a thin food-grade coating. Using Mie theory, we show that chocolate can be treated as a turbid solid, where cocoa butter acts as a glass-like dielectric while all other ingredients contribute to its scattering and absorption. We expect the proposed coating to be easily adapted to other food surfaces to bring color to a broader range of edible products.

Multi-principal element (MPE) alloys, sometimes also known as high entropy, complex concentration or multicomponent alloys, have attracted significant attention due to their remarkable mechanical properties, especially face-centered cubic (fcc) CrCoNi-based alloys. In this study, the size effect and strain rate dependence of the strength of equiatomic ternary (CrCoNi), quaternary (CrFeCoNi), and quinary MPE (CrMnFeCoNi) alloys were investigated using in situ strain rate jump (SRJ) micropillar compression tests. No obvious correlation is found between size dependence of strength and the number of elements in these alloys, but an inverse relation is observed between size effect exponent and the Peierls' stress. The single arm source strengthening model was successfully applied on the entire range of samples from the fcc pure elements to fcc equiatomic MPE alloys. Moreover, the activation volumes (~10 b3 to ~100 b3) are consistent among the MPE alloys, indicating the main deformation mechanism is similar in these alloys: dislocation-solute and dislocation-dislocation interactions., Materials & Design, 193, ISSN:0264-1275, ISSN:1873-4197

High-entropy alloys (HEAs) are evolving multi-component metallic systems, wherein generally five or more principal elements tend to provide strong solid-solution strengthening. In contrast to typical metals and alloys, the deformation mechanisms in HEAs have not been well understood so far. Here, we employ strain rate jump micro-compression testing to study the deformation mechanisms of two face-centered cubic (fcc) (FeCoNiCuPd and CrMnFeCoNi) and two body-centered cubic (bcc) HEAs (VNbMoTaW and NbMoTaW). The size-dependent strength, strain rate sensitivity, and activation volumes of the HEAs are compared with those of pure fcc and bcc metals. Both the fcc and bcc HEA pillars exhibit relatively low size dependence of strength compared to their corresponding pure metals, which can be attributed to the increased lattice distortion. Both the fcc and bcc HEAs exhibit enhanced strain rate sensitivity (SRS) with reducing pillar sizes. The FeCoNiCuPd HEA exhbits slightly lower size depedence of flow stress and a larger activation volume than those of the CrMnFeCoNi HEA (Cantor alloy), which could be associated with the higher dislocation motion resistance by adding palladium atoms with a markedly larger atomic size. The VNbMoTaW HEA also shows slightly lower size depedence of flow stress than that of the NbMoTaW HEA, which could be due to higher Peierls stress by adding the fifth element vanadium. Although there is no significant difference regarding activation volumes between HEAs and their corresponding pure metals, further studies are still needed to give a fundamental understanding of deformation mechanisms in a broad range of HEAs.

Recent studies demonstrate novel metamaterials featuring unique properties by combining origami-inspired designs with additive manufacturing. In particular, the use of flexural hinges endows distinct advantages towards miniaturization and fabrication; however, there are limited applications due to the limited loading and fatigue resistance of the hinges. In this study, we focus on testing and characterizing mechanical properties of flexural hinges so that our findings could have immediate applications in 3D-printed origami structures. We introduce an aramid fiber composite hinge and compare it to a single-material polyamide and a multimaterial photopolymer hinge. We investigate the impact of the materials and geometric design parameters on the load carrying capability and flexural properties. Furthermore, the fatigue behavior of the hinges is characterized, identifying the constitutive mechanisms. We consolidate all the data and findings to construct a comprehensive design parameter – property map, which serves as a guideline for optimizing hinge performance for a given set of required properties., Materials & Design, 191, ISSN:0264-1275, ISSN:1873-4197

In the past two decades, small-scale mechanical testing has become ubiquitous for mechanical measurements, offering new opportunities to quantitatively probe the mechanical behavior of materials. In this study, we applied four different small-scale mechanical testing techniques – conventional and statistical nanoindentation and micropillar compression and splitting tests – to study the mechanical behavior of Al–Cu intermetallics using a diffusion couple. This allowed the determination of the hardness, elastic modulus, yield stress, plastic flow behavior, and the critical stress intensity for fracture for nearly all of the intermetallic phases. A novel statistical indentation phase map plot was introduced, allowing the easy visualization of phases within property space. Hardness and elastic modulus results were found to be in good agreement with more recent studies and DFT predictions, while fracture results suggest the single crystal forms of the intermetallics show superior toughness. This work demonstrates that using small-scale mechanical testing in a combinatorial manner allows the interrogation of intermetallics with large composition ranges in a high-throughput manner with high precision and efficiency.

Nanocrystalline metals generally exhibit exceptionally high strength. However, their susceptibility to grain growth restricts their applications in high temperature environments. The current study presents that nanocrystalline Cu thin films produced by ion beam assisted deposition (IBAD) are able to sustain their as-deposited microstructure and high hardness upon annealing at high temperatures. IBAD-Cu films exhibit a strong (1 1 1) fiber texture, which is caused by the ion beam induced effects of substrate cleaning, preferential damage and preferential sputtering. The microstructure of the IBAD-Cu films is stable at temperatures up to 800 °C (80% of the melting point of Cu). The hardness of the as-deposited IBAD-Cu films can reach a maximum value of 3.85 GPa. Even after annealing, their hardness is still much higher than that of the normally deposited (without ion beam) films as well as their bulk nanocrystalline counterparts before heat treatment. The excellent thermal stability of microstructure is attributed to the formation of nanometer-sized voids and their pinning effect on grain boundary migration. The kinetics of void formation, the contribution of twin boundaries and ion beam induced defects to the hardness are analyzed and discussed. The findings in this study demonstrate that IBAD is an effective method for the stabilization of microstructure and mechanical properties of nanocrystalline metal thin films.

A dense intra-granular dispersion of small secondary Nb(C, N) precipitates in commercial TP347 Nb-stabilized austenitic steel was formed during a short-term hardening heat treatment in the temperature window ΔT=1050–950 °C, starting with isothermal annealing at 1050 °C and followed by continuous cooling from 1050 °C to 950 °C. The precipitates are semi-coherent in cube-on-cube orientation relationship with the austenitic matrix, of characteristic faceted octahedral shape with {111} facets and typically d=15±4.6 nm in size. The experimentally determined volume fraction f=1.4±0.2·10−3 correlates well with thermodynamic calculations. The precipitation gives a significant strengthening of the steel from σy initial ~ 529±42 MPa to σy hardened ~ 703±39 MPa, corresponding to a strength increment Δσy ~ 174 MPa ( ~ 33%) in good agreement with the prediction for Orowan strengthening. The present work is relevant to the exploration of the application potential of short term hardening heat treatments for precipitation strengthening austenitic steels.

W–Cu alloys are typically used for heat sinks, radiation shielding or high performance contact materials. Their immiscibility leads to interpenetrating structures, with typically smallest microstructural length scales on the order of several micrometres. This work focusses on tuning this length scale from the atomic level to the nanometre and submicron range. This is made possible by exploiting the two constituents’ immiscibility in thermodynamic equilibrium as well as the lack of Cu segregation to W grain-boundaries, thus allowing for the growth of the two phases. The system is studied in the complete concentration range and microstructure is related to both mechanical and electronic properties.

Local contact damage as well as cohesive and adhesive failure can limit the lifetime and applicability of hydrogenated diamond-like carbon (DLC) films on metallic substrates. DLC on titanium (Ti) is very interesting for industrial applications (e.g. biomedical applications), while also an excellent model system for the general understanding of hard and brittle films on ductile metallic substrates. Interlayers deposited between the DLC film and the Ti substrate have been shown to affect failure of such DLC coated Ti substrates. In this study, the effect of interlayer structure on contact damage and cohesive and adhesive failure is studied with tantalum (Ta) in its α- and β-phase. In all investigated cases the more ductile α-Ta provides improved results over the hard and brittle β-Ta interlayer. Due to plastic deformation effects, the resistance to contact damage is significantly increased with an α-Ta interlayer. Delamination occurs at the interface between the Ti substrate and the Ta interlayer. Compared to DLC on Ti without a Ta interlayer no enhancement in onset strain of fragmentation and delamination was achieved. A finite-element analysis shows that stress concentrations can be distributed over both interfaces if the Young's modulus of the interlayer material is of the order of the Young's modulus of the DLC.

In metals and alloys, phase separation takes place either by nucleation and growth or by spinodal decomposition. Here, transmission electron microscopy (TEM) and atom probe tomography (APT) are combined in an effort to study phase separation in an immiscible Cu–34 at.% Ta thin film alloy on a nanometer scale. Upon annealing at 400–600 °C the initially X-ray amorphous metastable alloy phase separates and crystallizes into a Cu-rich phase with fcc structure and a Ta-rich phase with β-Ta structure. While the fcc phase crystallizes already upon 10 min annealing at 400 °C, first indications of a crystalline β-Ta phase are observed after 30 min annealing at 400 °C, but this phase does not become fully crystalline at temperatures below 600 °C. Proximity histograms of the APT data show that phase separation is taking place predominantly by diffusion of Cu, which is in accordance with the known relative diffusivities of the materials. An increase in the amplitude of the composition fluctuation and a decrease in the width of the interface between Cu-rich and Ta-rich regions are observed in the proximity histograms as phase separation progresses. These results suggest spinodal decomposition as the mechanism of phase separation.

© 2015 Taylor Francis Size effects in plasticity are mostly studied in metallic systems but they are rarely investigated in ionic crystals. In this study single crystalline KCl and LiF pillars were fabricated by focused ion beam technique and compressed using a flat punch tip in a nanoindenter. The materials were investigated with regards to crystal orientation test temperature pre straining and doping. The results show: (1) [1 1 1] LiF pillars do exhibit size effect with an exponent of -0.38 in contrary to no size effect in [1 1 1] LiF reported in literature; (2) [0 0 1] LiF and [0 0 1] and [1 1 1] KCl have similar size effect exponents of -0.68 -0.71 and -0.65 respectively; (3) the size effect of [1 1 1] LiF pillars is more sensitive to the temperature change than that of [0 0 1] LiF pillars; (4) pre straining of [1 1 1] LiF pillars results in a reduced size effect; (5) the 0.05 mol CaCl2 doping in [0 0 1] KCl slightly increases strength levels and does not change the size effect much. The magnitude of the size effects in ionic crystals can be attributed to the bulk stress level but not the slip systems. In addition a correlation between critical temperatures and size effect slopes is illustrated and the additivity of strengthening mechanisms is critically discussed.

Tungsten thin films have exceptional thermal and mechanical properties, compared to other pure metal coatings, making them indispensable in many contemporary high-tech applications. Their superior properties, however, are strongly dependent on film microstructure, specifically including comprising phases, and hence, the employed deposition parameters, making a thorough process control essential. This study therefore investigates the different material properties of the bcc α and the A15 β phase of tungsten with respect to process parameters. The formation of β-W is mainly dependent on process gas pressure. While all films deposited at elevated pressure consist of β-W, the onset of β formation can already be observed for low pressure deposition, if magnetron power is reduced sufficiently. However, β-W formation for all deposition pressures can be suppressed by applying a substrate bias during deposition, leading to an α-W configuration. This indicates that the alpha-to-beta transition during film growth predominantly depends on adatom energy, rather than solely on the inclusion of residual impurities. Simultaneously, mechanical and electrical performance could be improved, while maintaining a nanocrystalline microstructure.

Friction and wear minimizing coatings are crucial for applications in combustion engines and medical implants. Their performance is typically limited by mechanical failure especially due to local overload. In this work, the contact damage creation, evolution, and final morphology of hydrogenated diamond-like carbon (DLC)-coated titanium (Ti) substrates are investigated. The influence of the DLC film thickness and the elastic–plastic deformation of the Ti on the contact damage are studied by microindentation and static finite-element analysis. Film thickness, indenter radius, and applied load as well as the elastic–plastic deformation of the Ti are shown to significantly affect contact damage. A failure plot is presented with the location of first failure in the DLC and compared to the experimental observation. In addition, a case study with variable fracture toughness of the DLC and its influence on the failure plot is shown. The stress distribution in the DLC follows a transition from a membrane-like to a plate-like deformation behavior upon increasing the DLC film thickness. Thin DLC films reveal increased cracking in the inner zone of the indent, while thicker DLC films reveal pronounced edge cracking. These edge cracks were correlated to pop-ins in force–displacement curves upon microindentation. Finally, a film thickness optimization process is presented for hard and brittle films on soft and ductile metallic substrates.