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Over the past 3–5 years, the ability to process interface dominant nanolayered bimetallic composites in bulk quantities has opened new opportunities for investigations into structural material behavior under extreme strains. This article reviews the emergence of mechanically stable, predominant bimetallic interface characters during nanomaterial synthesis via Accumulative Roll Bonding, a severe plastic deformation technique. This processing method itself imposes an extreme condition. We show that the interfaces that are naturally selected by this extreme operation remarkably prove to be stable under exposure to other extreme conditions, including elevated temperatures and ion irradiation. Through control of synthesis pathways, interfaces of the desired atomic structure can be manufactured using scalable thermomechanical processing techniques. This, in turn, opens unprecedented new possibilities for designing bulk materials with interface-dominant properties including enhanced strength, deformability, thermal stability, and radiation damage tolerance. [ABSTRACT FROM AUTHOR]

Atomically ordered bimetal interfaces typically develop in nearequilibrium epitaxial growth (bottom-up processing) of nanolayered composite films and have been considered responsible for a number of intriguing material properties. Here, we discover that interfaces of such atomic level order can also emerge ubiquitously in large-scale layered nanocomposites fabricated by extreme strain (top down) processing. This is a counterintuitive result, which we propose occurs because extreme plastic straining creates new interfaces separated by single crystal layers of nanometer thickness. On this basis, with atomic-scale modeling and crystal plasticity theory, we prove that the preferred bimetal interface arising from extreme strains corresponds to a unique stable state, which can be predicted by two controlling stability conditions. As another testament to its stability, we provide experimental evidence showing that this interface maintains its integrity in further straining (strains > 12), elevated temperatures (> 0.45 Tm of a constituent), and irradiation (light ion). These results open a new frontier in the fabrication of stable nanomaterials with severe plastic deformation techniques. [ABSTRACT FROM AUTHOR]

We examine the development of stable bimetal interfaces in nanolayered composites in severe plastic deformation. Copper-niobium multilayers of varying layer thicknesses from several micrometers to 10 nanometers (nm) were fabricated via accumulative roll bonding (ARB). Investigation of their 5-parameter character and atomic scale structure finds that when layer thicknesses refine well below one micrometer, the interfaces self-organize to a few interface orientation relationships. With atomic scale and crystal plasticity modeling, we identify that the two controlling factors that determine whether an interface is stable under high strain rolling are orientation stability of the bicrystal and interface formation energy. A figure-of-merit is introduced that not only predicts the development of the prevailing interfaces but also explains why other interfaces did not develop. Through a suite of nanomechanical and bulk test results, we show that ARB composites containing these stable interfaces are found to have exceptional hardness (∼4.5 GPa) and strength (∼2 GPa). [ABSTRACT FROM AUTHOR]

Abstract: In this work, a silver–copper (Ag–Cu) nanocomposite with 200nm bilayer thickness and eutectic composition was rolled at room temperature and 200°C to nominal reductions of 75% and higher. Initially the material had a random texture and {111} bi-metal interface plane. X-ray diffraction measurements show that the Ag and Cu phases developed the same brass-type (or ‘alloy-type’) rolling texture regardless of rolling reduction and temperature. Transmission electron microscopy analyses of the nanostructures before and after rolling suggest that adjoining Ag and Cu layers maintained a cube-on-cube relationship but the interface plane changed after rolling. Polycrystal plasticity simulations accounting for plastic slip and deformation twinning in each phase were carried out to explore many possible causes for the brass-type texture development: twinning via a volume effect or barrier effect, Shockley partial slip, and confined layer slip. The results suggest that the observed texture evolution may be due to profuse twinning within both phases. Maintaining the cube-on-cube relationship would then imply that neighboring Ag and Cu crystals twinned by the same variant and on a twin plane non-parallel to the original interface plane. Explanations for this unusual possibility for Cu are provided at the end based on the properties of the Ag–Cu interface. [ABSTRACT FROM AUTHOR]

Accumulative roll-bonded Cu/Nb nanolaminates (ARB Cu/Nb) possess high strength, thermal stability, and radiation tolerance arising from a high content of heterophase interfaces at fine layer thicknesses. These properties can be tailored by processing parameters used in the ARB Cu/Nb fabrication process, in which layer thickness, thermal history, and strain pathway determine the interface types and resultant properties found in the material. In this work, we subject ARB Cu/Nb to annealing, and then two different rolling pathways – one where rolling direction is held constant (longitudinal rolling, or LR), and one where rolling direction is rotated by 90° and held constant thereafter (cross rolling, or CR). Rolling is performed on ARB Cu/Nb over a targeted range of layer thicknesses from 193 to 25 nm and resultant bulk textures measured by neutron diffraction are correlated with mechanical properties measured by miniaturized tensile tests. The annealing procedure sharpens texture in both phases. We find that Cu mostly develops the same texture in LR and CR. In contrast, Nb develops a distinct texture along the CR pathway that is distinct from the LR texture. The composite texture of Cu/Nb is thus distinct between LR and CR pathways. This difference in texture development between Cu and Nb as a function of strain after change in rolling direction demonstrates the viability for deliberate pairing of Cu LR and Nb CR textures at a desired layer thickness. For mechanical properties, we find that differences in texture do not result in yield or flow stress differences above a layer thickness of 25 nm. Below a layer thickness of 25 nm, despite similar Taylor factors, yield and flow stress and are significantly different. This indicates texture only influences mechanical behavior at low layer thickness, where interface structure dominates mechanical properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] Novel two phase lamellar composites are fabricated via accumulative roll-bonding. [•] Earlier developed a dislocation density based hardening law for HCP is adapted to BCC. [•] Bulk texture development in the two phases is not affected by the interface. [•] Predictions of texture and deformation mechanisms for the individual phases are reported. [Copyright &y& Elsevier]