High-strength, high-conductivity copper/silver-alloyed materials were prepared by cold-spray (CS) manufacturing. For DC high-field application at room temperature, bulk Cu/Ag (5% vol. Ag) alloys with high mechanical properties and high electrical conductivity can be obtained by CS and post-heat treatments. For pulsed-field application at liquid nitrogen temperature, bulk Cu/Ag (5% vol. Ag) alloys serve as precursors for room-temperature wire drawing. The Cu/Ag-alloyed bulk CS deposit presents a high yield strength of about 510 MPa with a corresponding electrical resistivity of 1.92 µΩ·cm (at 293 K). The Cu/Ag-alloyed wires show a very high ultimate tensile strength (1660 MPa at 77 K or 1370 MPa at 293 K) and low electrical resistivity (1.05 µΩ·cm at 77 K or 2.56 µΩ·cm at 293 K). Microstructural studies via STEM allow us to understand this very high level of mechanical strength. The results evidence that materials developed by CS exhibit very high mechanical properties compared to materials prepared by other routes, due to the high velocity of the deposited particles, which leads to high initial deformation rates and specific microstructural features.

Micropillar compression is a method of choice to understand mechanics at small scale. It is mainly studied with electron microscopy or white-beam micro-Laue X-ray diffraction. The aim of the present article is to show the possibilities of the use of diffraction with a coherent X-ray beam. InSb micropillars in epitaxy with their pedestals (i.e. their support) are studied in situ during compression. Firstly, an experiment using a collimated beam matching the pillar size allows determination of when the sample enters the plastic regime, independently of small defects induced by experimental artefacts. A second experiment deals with scanning X-ray diffraction maps with a nano-focused beam; despite the coherence of the beam, the contributions from the pedestal and from the micropillar in the diffraction patterns can be separated, making possible a spatially resolved study of the plastic strain fields. A quantitative measurement of the elastic strain field is nevertheless hampered by the fact that the pillar diffracts at the same angles as the pedestal. Finally, no image reconstructions were possible in these experiments, either in situ due to a blurring of the fringes during loading or post-mortem because the defect density after yielding was too high. However, it is shown how to determine the elastic bending of the pillar in the elastic regime. Bending angles of around 0.3° are found, and a method to estimate the sample's radius of curvature is suggested.

Plastic deformation mechanisms have been investigated in the MAX phase Ti2AlN. Nanoindentation has been used to induce plastic deformation in a single grain, and a Transmission Electron Microscopy (TEM) lamella has been extracted in cross section through the indent by using Focused Ion Beam (FIB) technique. By combining TEM observations and automated crystal orientation mapping (ACOM), highly misoriented domains (HMD) have been revealed below a nanoindentation imprint. Thanks to a careful analysis of the relative crystal orientations between these HMD, {11-22} and {11-21} deformation twins have been identified for the first time in a MAX phase. Complex structures, involving secondary twinning or different {11-22} twin variants have also been characterized.

This study investigates the effect of thermal aging on the microstructure and tensile properties of a 15-15Ti austenitic stainless steel in the baseline operating conditions of a sodium fast reactor, in the range between 400°C and 600°C. Samples that were aged at up to 600°C for 1000 hours exhibit no evidence of material recovery. Thus, after aging heat treatments, micro-hardness measurements do not decrease, and TEM analyses do not show any modification of the dislocation network. However, TEM examinations have indicated a new threshold for the precipitation of nanometric titanium carbides after an isothermal treatment at 500°C for about 5000 hours. Concerning the tensile properties, the aged states present a gain both in strength and in ductility compared to the initial cold-worked state. The large gain in ductility is observed for all of the temperatures tested (between 20°C and 400°C) and occurs concomitantly with an increase in the strain hardening rate of the material. One plausible hypothesis to explain this improvement of the mechanical behaviour relies on the nanometric titanium carbides formed during the aging process. These precipitates could act as obstacles that impede the motion of existing dislocations, thereby contributing an additional strain hardening mechanism, which would lead to greater strength and also delay the onset of strain localization.

Strain and defects in crystalline materials are responsible for the distinct mechanical, electric and magnetic properties of a desired material, making their study an essential task in material characterization, fabrication and design. Existing techniques for the visualization of strain fields, such as transmission electron microscopy and diffraction, are destructive and limited to thin slices of the materials. On the other hand, non-destructive X-ray imaging methods either have a reduced resolution or are not robust enough for a broad range of applications. Here we present X-ray ptychographic topography, a new method for strain imaging, and demonstrate its use on an InSb micro-pillar after micro-compression, where the strained region is visualized with a spatial resolution of 30 nm. Thereby, X-ray ptychographic topography proves itself as a robust non-destructive approach for the imaging of strain fields within bulk crystalline specimens with a spatial resolution of a few tens of nanometers.

Room-temperature deformation mechanism of InSb micro-pillars has been investigated via a multi-scale experimental approach, where micro-pillars of 2 µm and 5 µm in diameter were first fabricated by focused ion beam (FIB) milling and in situ deformed in the FIB-SEM by micro-compression using a nano-indenter equipped with a flat tip. Strain rate jumps have been performed to determine the strain rate sensitivity coefficient and the related activation volume. The activation volume is found to be of the order of 3–5 b 3 , considering that plasticity is mediated by Shockley partial dislocations. Transmission electron microscopy (TEM) thin foils were extracted from deformed micro-pillars via the FIB lift-out technique: TEM analysis reveals the presence of nano-twins as major mechanism of plastic deformation, involving Shockley partial dislocations. The presence of twins was never reported in previous studies on the plasticity of bulk InSb: this deformation mechanism is discussed in the context of the plasticity of small-scale samples.

By exploiting experimentally measured optical properties of Silicon Carbide (SiC) at different temperatures, we recently showed based on a numerical analysis, that when SiC grating is heated, the position of its emissivity peak shifts towards higher wavelength values and its amplitude decreases. This proved the necessity to adapt the parameters of the grating to the temperature of measurements. In this previous article, we performed only numerical simulations for ideal devices. In order to check the validity of these results, we need some verifications from both the experimental and numerical points of view. In the herein study, we milled gratings on the same type of SiC for which the optical properties measurements were conducted. Then, we performed reflectivity measurements as a function of wavelength and temperature, in order to experimentally show the peak shift and to validate our optimized gratings. Hereby, this work provides guidelines for the design of optimized coherent thermal sources for different temperatures based on a combined numerical and experimental analysis. (C) 2021 Elsevier Ltd. All rights reserved.

This study deals with the evolution of strength and microstructure in pure nickel during wire drawing from an initial diameter of 1.74 mm to 30 μm, corresponding to a total true strain of 8.1. Electron backscattering diffraction (EBSD) and X-ray diffraction (XRD) have been used for microstructural characterization. In the later stages of deformation, the fraction of low angle boundaries decreased as did the misorientations within a grain or cell. The dislocation density stabilized at ∼2 × 1015 m−2, and the activation volume decreased from ∼100 b3 at a strain of 1 to ∼ 15 b3 at strains ≳4, where b is the magnitude of the Burgers vector. Cross-sectional EBSD of the wires revealed that a core region had <111> fiber texture, whereas a peripheral shell region had a complex fiber texture due to redundant shear strain. Viscoplastic self-consistent (VPSC) simulations were in good agreement with the crystallographic texture evolution in the wires during drawing. The wire drawing data is compared with other deformation techniques, to provide a broad framework for analyzing microstructure-strength-ductility relationships. At large strains of >2, with an essentially constant dislocation density, the strength can be related solely to Hall-Petch strengthening by a refinement of the transverse grain size.

Plastic deformation in InSb single crystals is governed by the motion of dislocations. Since InSb has a diamond cubic lattice, it possesses two sets of slip planes: a shuffle set and a glide set. Transmission electron microscopy analysis of deformed bulk single crystals shows that, at low temperatures (<20 °C), dislocations have narrow cores, while at higher temperatures, they have extended cores. However, it remains unclear to which slip plane set these dislocations belong. In this paper, by combining experiments and atomic-level calculations, we show that dislocations with narrow and extended cores, respectively, belong to the shuffle and glide sets. The conclusion is reached by calculating the generalized stacking fault energy curves and ideal shear stresses using density functional theory calculations and the intrinsic stacking fault width associated with dislocations using atomistic simulations. It is also found that while the shuffle set dislocations are easier to activate at lower temperatures, dislocations on the glide set become dominant at higher temperatures.

The effect of length scale on mechanical strength is a significant consideration for semiconductor materials. In III-V semiconductors, such as InSb, a transition from partial to perfect dislocations occurs at the brittle-to-ductile transition temperature (~150 °C for InSb). High temperature micro-compression reveals InSb to show a small size effect below the transition, similar to ceramics, while in the ductile regime it shows a size effect consistent with fcc metals. The source truncation model is found to agree with the observed trends in strength with size once the change in Burgers vector and bulk strength are taken into account.

Compression of micropillars is followed in situ by a quick nanofocused X-ray scanning microscopy technique combined with 3D reciprocal space mapping. Compared to other attempts using X-ray nanobeams, it avoids any motion or vibration that would lead to a destruction of the sample. The technique consists of scanning both the energy of the incident nanofocused X-ray beam and the in-plane translations of the focusing optics along the X-ray beam. Here, the approach by imaging the strain and lattice orientation of Si micropillars and their pedestals during in situ compression is demonstrated. Varying the energy of the incident beam instead of rocking the sample and mapping the focusing optics instead of moving the sample supplies a vibration-free measurement of the reciprocal space maps without removal of the mechanical load. The maps of strain and lattice orientation are in good agreement with the ones recorded by ordinary rocking-curve scans. Variable-wavelength quick scanning X-ray microscopy opens the route for in situ strain and tilt mapping toward more diverse and complex materials environments, especially where sample manipulation is difficult.

Strain and defects in crystalline materials are responsible for the distinct mechanical, electric and magnetic properties of a desired material, making their study an essential task in material characterization, fabrication and design. Existing techniques for the visualization of strain fields, such as transmission electron microscopy and diffraction, are destructive and limited to thin slices of the materials. On the other hand, non-destructive X-ray imaging methods either have a reduced resolution or are not robust enough for a broad range of applications. Here we present X-ray ptychographic topography, a new method for strain imaging, and demonstrate its use on an InSb micro-pillar after micro-compression, where the strained region is visualized with a spatial resolution of 30 nm. Thereby, X-ray ptychographic topography proves itself as a robust non-destructive approach for the imaging of strain fields within bulk crystalline specimens with a spatial resolution of a few tens of nanometers.

Physical properties of nano-objects differ from what they are in bulk materials when the size decreases down to the nanometre scale. This behavioural change, named size effect, also applies to mechanical properties and has been evidenced in various materials. For instance, at low temperature, bulk silicon is known to be a brittle material while silicon nano-objects exhibit a ductile behavior. Although mechanical properties of silicon have been intensively studied over the last decades, the origin of this remarkable brittle-to-ductile transition at small scales remains, however, undetermined. In this article, a study of the plastic behaviour of nano-pillars is reported. The main results obtained from the combination of numerical calculations and experimental compression tests followed by atomically-resolved transmission electron microscopy imaging are described. We discuss the possibility for perfect dislocations to dissociate at low temperature and the underrated role of shuffle partial dislocations in plastic deformation of silicon. The formation of unexpected extended defects in the {115} planes with increasing plastic strain, also appears as a key-factor leading to the transition between ductile and brittle regimes at small scales.

Deformation mechanisms of cold drawn and electropolished nickel microwires are studied by performing in-situ monotonous and cyclic tensile tests under synchrotron radiation. X-ray diffraction tests allow probing elastic strains in the different grain families and establishing a link with the deformation mechanisms taking place within the microwires. The measurements were carried out on several microwires with diameters ranging from as-drawn 100 µm down to 40 µm thinned down by electropolishing. The as-drawn wires exhibit a core-shell microstructure with <111> fiber texture dominant in core and heterogeneous dual fiber texture <111> and <100> in the shell. Reduction of specimen size by electropolishing results in a higher yield stress and tensile strength along with reduced ductility. In-situ XRD analysis revealed that these differences are linked to the global variation in microstructure induced by shell removal with electropolishing, which in turn affects the load sharing abilities of grain families. This study thus proposes a new way to increase ductility and retain strength in nickel microwires across different diameters by tuning the microstructure architecture.

Nanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields (> 90T) as they combine both high strength and high electrical conductivity. Multi-scaled Cu–Nb wires are fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured, and nanostructured microstructure exhibiting a strong fiber crystallographic texture and elongated grain shapes along the wire axis. This paper presents a comprehensive study of the effective elastic behavior of this composite material by three multi-scale models accounting for different microstructural contents: two mean-field models and a full-field finite element model. As the specimens exhibit many characteristic scales, several scale transition steps are carried out iteratively from the grain scale to the macro-scale. The general agreement among the model responses allows suggesting the best strategy to estimate the effective behavior of Cu–Nb wires and save computational time. The importance of crystallographical and morphological textures in various cases is discussed. Finally, the models are validated by available experimental data with a good agreement.

A Ti-stabilized cold-worked 15Cr-15Ni steel, called AIM1 (Austenitic Improved Material #1), has been selected as a candidate for the fuel cladding tubes of sodium-cooled fast reactors. This steel exhibits an unusual loss of ductility between 20 and 200 degrees C for both solution-annealed and cold-worked conditions, which is similar to that observed for Twinning Induced Plasticty steels and for the 200 and 300 series stainless steels. Therefore, a multi-scale study has been carried out to determine the deformation mechanisms that are active at different temperatures. Tensile tests have been performed to characterize the macroscopic material behavior, and Electron Backscattered Diffraction and Transmission Electron Microscopy characterization techniques have been used to investigate the meso and micro-scale phenomena, such as the deformation microstructures and the evolution of the lattice defects. The parameters governing the deformation mechanisms have been examined, with particular attention paid to the conditions for mechanical twinning activation. This work required an original study of the variation of Stacking Fault Energy with temperature, based on the measurement of the dissociation extension of dislocation nodes. An increase in the SFE was observed between 20 and 200 degrees C. After reviewing the existing models for predicting twinning, the present study proposes an approach based on the minimization of the total energy of the material to explain why twinning is not favorable at high temperatures. M 20 degrees C, both dislocation slip and twinning are active and efficient mechanisms to release the strain energy. However, at 200 degrees C, only dislocation slip is favorable and is often associated with dislocation cross-slip.

The mechanical properties of materials usually depend on the size of the considered object. Silicon, for instance, undergoes between the macroscopic and nanometer scales, a brittle-to-ductile transition at room temperature. Although essential for the constantly developing Si-based nanotechnologies, the origin of this remarkable behaviour change remains undetermined for several years. The observation of the mechanisms responsible for plastic deformation in nano-objects is indeed highly challenging at the microscopic scale. One needs controlling the deformation while identifying induced individual plastic events at the smallest scale during the first stages of plasticity. This work describes nano-compression experiments on 100 nm-diameter Si nanopillars followed by post-mortem analysis of the deformed specimens through SEM and atomic resolution TEM imaging. The observed plastic deformation disrupts the usual description of low-temperature undissociated-dislocations-mediated plasticity and is comforted by molecular dynamics calculations. These results shed a new light on the transition between ductile and brittle regimes in silicon by introducing the missing link between plasticity and fracture. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Increasing the figure of merit ZT of thermoelectric (TE) alloys is a challenge that is currently attempted through various metallurgy methods, including nanostructuring and dislocation engineering. Microstructures with such a level of complexity raise questions about the mechanical reliability of these new materials. Indeed, despite the values of hardness and elastic modulus known for the clear majority of TE materials, the data on deformation mechanisms are still rare. Focusing on the nanostructured p-type half-Heusler Hf0.44Zr0.44Ti0.12CoSb0.8Sn0.2, our multi-scale study aims to analyze the deformation mechanisms. Experiments conducted at macro-, meso-, and micro-scale are designed to trigger and assess plasticity mechanisms. Compression testing on bulk samples subject to a confining pressure environment and temperature leads to an exclusive brittle failure. The mixed-mode failure mechanisms involve switching between intra- and inter-granular crack propagation, depending on the grain size met by the crack tip. Cube-corner nanoindentation at meso-scale generates cracks and enables fracture toughness estimation, while TEM analysis of the crack tip area confirms no dislocation activity and 3D-Electron Back Scattered Diffraction technique confirms the mixed crack propagation behavior. At micro-scale, micro-pillar compression stress-strain curves and failure mechanisms are comparable with bulk samples testing analysis. These results can be used to provide design guidelines for more crack-resistant TE alloys.

Indium Antimonide (InSb) single-crystalline micro-pillars were mechanically deformed by uniaxial compression loading-unloading cycles up to the beginning of the plastic regime. After deformation, 2D spatially resolved maps were collected via two X-Ray Diffraction (XRD) techniques: polychromatic micro-Laue and monochromatic micro-diffraction. In both techniques, the integrated diffracted intensity shows strong variations inside the pillar. Moreover, the shift and streaking of one spot in polychromatic XRD as well as the lattice strain and tilt components derived from monochromatic XRD reveal that the plastically deformed area is localized on the top of the pillar, in agreement with scanning electron microscopy images. The two XRD techniques are thus providing correlated but yet complementary information.

Investigation of the strain field and defects in crystalline materials is essential in materials characterization, fabrication and design, as they are responsible for distinct mechanical, electric and magnetic properties of a desired material. Therefore, the visualization of strain and its relation to the type and density of defects in the crystal at the nanoscale is required. A domain in which such questions are particularly relevant is the fabrication of nanodevices for microelectronics from semiconductors, such as InSb, that are used as fast transistors, detectors and sensors. Classically, transmission electron microscopy (TEM) provides imaging of the crystalline defects with atomic spatial resolution, but due to the thin sections requirement, sample preparation is invasive and can modify the strain fields to be analyzed. A conventional tool to non-invasively study strain is Laue X-ray micro-diffraction [1], which reveals the strain field in crystalline samples averaged over the direction of the beam propagation with a resolution limited by the beam size. X-ray topography (XRT) [2] has been routinely used for imaging defects based on the diffraction contrast, with the resolution being restricted by the detector pixel size. X-ray coherence methods, such as coherent diffraction imaging (CDI) and ptychography, which are based on measuring the sample's far-field diffraction patterns and using phase retrieval algorithms, permit obtaining high resolution images. If the measurements are performed close to a Bragg peak, the resulting image becomes highly sensitive to the presence of strain [3, 4]. We have recently developed ptychographic topography, in which a crystalline sample is rotated with respect to the incident beam such that a certain atomic plane is in the Bragg condition, as shown in Fig. 1a [5]. A pinhole is then placed after the sample in the forward direction and is spatially translated, providing the sufficient overlapping necessary for ptychographic reconstructions [6]. The diffraction patterns are recorded at each pinhole position with a 2D detector downstream of the pinhole and used simultaneously for the reconstruction of the wave front at the pinhole position. So far measurements were performed in forward direction due to the limited space at the beamline to fulfil the ptychographic detector sampling requirement along the Bragg-diffracted beam direction. Numerical backpropagation then enables one to obtain an image of the sample, which is sensitive to the lattice displacements caused by defects.