Due to the scarcity of “easy slip” systems in hexagonal materials with a hexagonal close-packed structure (hcp), deformation twinning plays a crucial role in determining mechanical properties and texture evolution. In this article, we highlight the current understanding of mechanisms and mechanics of the twinning system $\left\{ {10\bar 12} \right\}\left\langle {10\bar 1\bar 1} \right\rangle $, which is commonly activated in all hexagonal materials for nucleation and propagation of deformation twins, twin–twin interactions, solute segregation at twin boundaries, and the development of constitutive models that account for the fundamental mechanisms of twinning/detwinning. Future directions such as characterizing the three-dimensional shapes of twins, the influence of solute atoms on twin propagation, and the influence of twin–twin junctions on mechanical properties of the hexagonal materials are discussed.

In this study, we report a micropillar stress relaxation technique employing a stable displacement-controlled, in-situ scanning electron microscope indenter, and unusually large micropillars to precisely measure stress relaxation in electroplated nanocrystalline Ni thin films. The observed stress relaxation is significant under constant displacement: even well below the 0.2% offset yield strength, the stresses relax by ∼4% within a minute; in the work hardening regime, stress relaxes by ∼9% in 1 min. A logarithmic fit of the relaxation curves is consistent with an Arrhenius thermal activation of plasticity and suggests an activation volume in the vicinity of ∼10 b 3. The apparent and effective activation volumes diverge at lower strains, particularly in the “elastic” regime. These measurements are compared to similar measurements performed on free-standing thin film tensile coupons. Both methods yield similar results, thereby validating the applicability of pillar compression to capture time-dependent plasticity. To our knowledge, these are the first micropillar stress relaxation experiments on metals ever reported.

The remarkable properties of nanotwinned (NT) face-centered-cubic (fcc) metals arise directly from twin boundaries, the structures of which can be initially determined by growth twinning during the deposition process. Understanding the synthesis process and its relation to the resulting microstructure, and ultimately to material properties, is key to understanding and utilizing these materials. This article presents recent studies on electrodeposition and sputtering methods that produce a high density of nanoscale growth twins in fcc metals. Nanoscale growth twins tend to form spontaneously in monolithic and alloyed fcc metals with lower stacking-fault energies, while engineered approaches are necessary for fcc metals with higher stacking-fault energies. Growth defects and other microstructural features that influence nanotwin behavior and stability are introduced here, and future challenges in fabricating NT materials are highlighted.

The twinning-induced plasticity effect enables designing austenitic Fe-Mn-C-based steels with >70% elongation with an ultimate tensile strength >1 GPa. These steels are characterized by high strain hardening due to the formation of twins and complex dislocation substructures that dynamically reduce the dislocation mean free path. Both mechanisms are governed by the stacking-fault energy (SFE) that depends on composition. This connection between composition and substructure renders these steels ideal model materials for theory-based alloy design: Ab initio-guided composition adjustment is used to tune the SFE, and thus, the strain-hardening behavior for promoting the onset of twinning at intermediate deformation levels where the strain-hardening capacity provided by the dislocation substructure is exhausted. We present thermodynamic simulations and their use in constitutive models, as well as electron microscopy and combinatorial methods that enable validation of the strain-hardening mechanisms.

Tungsten oxide (WO3−x) nanomaterials with controlled morphology and composition were fabricated by thermal evaporation of WO3 and S powders at different temperatures in a vacuum tube furnace. At 850 °C the obtained green particle is still of the same monoclinic WO3 phase as that of the starting powder. At a temperature between 900 and 1100 °C, the resultant dark-blue products are particle-like clusters composed of numerous monoclinic WO2.90 short nanorods, but the clusters became looser and the nanorods grew somewhat longer as the temperature increased. At a temperature between 1150 and 1250 °C, elongated and thoroughly separate purple-red monoclinic W18O49 nanorods were obtained. The growth of the prepared WO3−x nanomaterials was controlled by a gas–solid mechanism. Their photocatalytic degradation on organic contaminants was evaluated by decomposing methylene blue (MB) in aqueous phase under sunlight, in which WO3 particles presented higher photocatalytic activity than its oxygen-deficient counterparts, WO2.90 and W18O49. But the W18O49 nanorods had higher adsorption ability to MB in all the samples.

Twins are domain crystals inside their parent crystals, where they share some of the same crystal lattice points in a symmetrical manner. The formation and growth of twins result in substantial evolution of microstructures and properties in a large variety of metallic materials. Twin boundaries that separate two crystals effectively strengthen the material by impeding mobile dislocations, and increase the ductility and work-hardening capability of metallic materials. The articles in this issue of MRS Bulletin overview the synthesis and mechanical behavior of nanotwinned metallic materials, as well as plasticity dominated by mechanical twinning.

A novel CuWO4/Cu1−x Znx WO4/ZnWO4 hybrid photocatalyst with sandwiched heterojunction structure was prepared by a one-port synthesis with Zn doping into CuWO4. The crystalline structure, optical, and morphological properties as well as photocatalytic performance of the as-prepared hybrid photocatalyst were studied. By adjusting the amount of Zn doped, the optimal doping level was determined to be 0.1 wt% Zn2+. More than 80% photocataytic degradation of rhodamine B was achieved within 20 min over 0.1 wt% Zn2+ doped CuWO4, while only 20% was achieved for the pure CuWO4. The enhancement was proposed to be due to the formation of a CuWO4/Cu1−x Znx WO4/ZnWO4 sandwiched heterojunction. Such tandem type heterojunction was found to be efficient for charge separation compared to traditional single heterojunction, which, in turn, resulted in a significantly enhanced photocatalytic activity. Our finding is also expected to be valuable for the exploration of CuWO4-material as a new group of efficient photocatalysts.

Nanotwins require little energy to form in metals, but their impact on strength and ductility is dramatic. New mechanisms of strengthening, strain hardening, ductility, and strain-rate sensitivity have been observed in nanowires, films, and bulk materials containing nanoscale twins as the twin-boundary spacing decreases. These mechanisms can act in concert to produce interface-dominated nanomaterials with extreme tensile strength and plastic deformation without breaking. This article reviews recent theoretical and experimental understanding of the physical mechanisms of plasticity in nanotwin-strengthened metals, with a particular focus on the fundamental roles of coherent, incoherent, and defective twin boundaries in plastic deformation of bulk and small-scale cubic systems, and discusses new experimental methods for controlling these deformation mechanisms in nanotwinned metals and alloys.

The US Materials Genome Initiative (MGI) has emphasized the need to accelerate the discovery and development of materials to maintain industry competitiveness in new and existing markets. While largely interpreted as an initiative arising from the materials community, it is important to address the coupling of materials with manufacturing and all other relevant aspects of product development in order to maximize its impact. The dual thrusts of Integrated Computational Materials Engineering and the MGI represent a long-term vision of industry, academic, and government stakeholders. The goal is to build a new kind of coupled experimental, computational, and data sciences infrastructure. The emphasis is on high-throughput methods to accelerate historical sequential processes of serendipitous materials discovery and largely empirical materials development by leveraging computation and modern data sciences and analytics. The notion of a materials innovation ecosystem is introduced as the framework in which to pursue acceleration of discovery and development of materials consisting of various elements of data sciences, design optimization, manufacturing scale-up and automation, multiscale modeling, and uncertainty quantification with verification and validation.

Gold nanoparticles have been deposited on the surface of hematite nanorod array photoanode to improve the photoelectrochemical water splitting performance. The Au nanoparticles induce the Fermi level equilibration, the surface catalysis, and the plasmonic enhancement effects in the Au/hematite photoanode. The Fermi level equilibration effect promotes the extraction of photo-generated charge carriers, suppressing the charge recombination. Surface catalysis effect reduces the overpotential for photoelectrochemical water oxidation. In the Au/hematite sample, the Fermi level equilibration and the surface catalysis effect make major contribution to photocurrent enhancement while the plasmonic effect makes a little contribution. In addition, the Au@SiO2 particle has been immobilized on hematite nanorod array surface that has been passivated. In the Au@SiO2/hematite sample, the photocurrent enhancement originating from plasmonic effects is negligible. Both the Femi level equilibration and the surface catalysis effects were excluded due to the isolated Au and hematite while surface passivation is mainly responsible for the photocurrent enhancement.

Transparent high refractive index materials are of the central importance for the development of metasurface in visible range. Titanium dioxide (TiO2) has been considered as a perfect candidate due to its wide band gap and high refractive index. However, till now, it is still quite challenging to fabricate high-quality TiO2 films with high refractive indices and low losses. Here we demonstrate the fabrication of high-quality TiO2 film using an electron-beam evaporation method. We show that the post-annealing conditions play key roles in the microstructure crystallographic and the optical refractive index of the TiO2 films. A predominately oriented TiO2 film has been achieved by annealing at 700 °C in oxygen ambient. The refractive index is as high as 2.4, and the corresponding loss is negligible at 632 nm. Further studies on dielectric antennas show that our TiO2 film can be an ideal platform to fabricate metasurface in visible frequency range. We believe that our research will be important for the advances of all-dielectric metasurfaces.

The influence of temperature and strain rate on hot deformation behavior and microstructure of Cu–10Ni–3Al–0.8Si alloy was investigated. The true stress increased rapidly initially until it approached the peak values. The peak value of true stress and the Zener–Hollomon parameter decreased with the increase of temperature and the decrease of strain rate. The thermal activation energy of the alloy was about 396.57 kJ/mol, the processing map was established and the appropriate compression temperature was between 900 and 950 °C. The 〈001〉 and 〈011〉 fiber texture was the main type of texture. The increase of temperature or strain rate accelerated the formation of 〈001〉 fiber texture. Dynamic recrystallization nucleated and deformation bands formed at 750 °C. Recrystallization was accelerated with the increase of temperature and the decrease of Zener–Hollomon parameter. Both continuous recrystallization resulting from dynamic recovery and dynamic discontinuous recrystallization were softening mechanisms.