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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]

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]

Here we seek to probe and understand the mechanical behavior of grain boundaries in pure Ta as a model bcc material using micropillar compression experiments. Three high angle grain boundaries are chosen with varying crystal orientations. Multiple bi-crystal pillars are prepared containing a single, nearly vertical grain boundary in the approximate center of the pillar and compared against their single crystalline pillar counterparts. The main phenomenon of interest was slip transmission or strain transfer in the bi-crystals which was considered to occur when slip traces aligned across the grain boundary. This occurred in two of the three bi-crystals. These observations were compared against two slip transmission factors, m ' = cos ( ψ ) cos ( κ ) and L R B = cos ( θ ) cos ( κ ) , where ψ , θ , a n d κ are the angles between the slip vectors, slip plane normals, and the intersection of the slip planes with the grain boundary from the slip systems on either side of the grain boundary. Additionally, transmission was compared against the stress-strain response and overall deformation (i.e., sheared boundary) of the bi-crystal. The transmission factors exhibited a consistent behavior with slip transmission occurring for high transmission factors and not occurring for low transmission factors. For example, slip transmission occurred for m ' ≥ 0.85 and did not occur for m ' ≤ 0.46. The engineering stress-strain response and overall deformation behavior did not show correlations with the presence or absence of slip transmission. High angle boundaries in bcc metals are shown to represent a diverse set of responses in bi-crystalline micropillar compression experiments. [ABSTRACT FROM AUTHOR]

Here we investigate the elastic and plastic anisotropy of hexagonal materials as a function of crystal orientation using a high-throughput approach (spherical nanoindentation). Using high purity zirconium as a specific example, we demonstrate the differences in indentation moduli, indentation yield strengths and indentation post-elastic hardening rates over multiple grain orientations. These results are validated against bulk single crystal measurements, as well as data from cubic materials. By varying the indenter size (radius), we are also able to demonstrate indentation size effects in hexagonal materials, including possible signatures of strain hardening due to twin formation in the nanoindentation stress–strain curves. [ABSTRACT FROM AUTHOR]

Nanocrystalline alloys are promising structural materials yet lack thermal stability in many cases. Recent work shows that interface structure has an outsize effect on the thermal behavior of nanostructured alloys. This work focuses on the role of controlled heterophase interface structure in the thermal evolution of model Cu/Nb nanolaminates. We introduce 3D interfaces containing nanoscale heterogeneities in all spatial dimensions between Cu and Nb, forming 3D Cu/Nb. TEM, nanoindentation, and DSC are used in tandem to establish thermal stability and to identify shifts in microstructure as a function of static annealing temperature. 3D interfaces are shown to survive annealing to 300 °C for 1 hr., while 3D Cu/Nb microstructure evolves to form low-density and voided regions correlating to the onset of layer pinch-off between 500 and 600 °C annealing temperatures. A diffusivity- and vacancy energetics-based mechanism is developed to explain void formation driven by 3D interface degradation at elevated temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] Mechanical properties play a central role in drug formulation development and manufacturing. Traditional characterization of mechanical properties of pharmaceutical solids relied mainly on large compacts, instead of individual particles. Modern nanomechanical testing instruments enable quantification of mechanical properties from the single crystal/particle level to the finished tablet. Although widely used in characterizing inorganic materials for decades, nanomechanical testing has been relatively less employed to characterize pharmaceutical materials. This review focuses on the applications of existing and emerging nanomechanical testing methods in characterizing mechanical properties of pharmaceutical solids to facilitate fast and cost-effective development of high quality drug products. Testing of pharmaceutical materials using nanomechanical techniques holds potential to develop fundamental knowledge in the structure–property relationships of molecular solids, with implications for solid form selection, milling, formulation design, and manufacturing. We also systematically discuss pitfalls and useful tips during sample preparation and testing for reliable measurements from nanomechanical testing. [ABSTRACT FROM AUTHOR]

Rolling of Ag–Cu layered eutectic composites with bilayer thicknesses in the submicron regime (∼200–400nm) activated deformation twinning in Cu. Using atomistic simulations and dislocation theory, we propose that the Ag–Cu interface facilitated deformation twinning in Cu by permitting the transmission of twinning partials from Ag to Cu. In this way, twins in Ag can provide an ample supply of twinning partials to Cu to support and sustain twin growth in Cu during deformation. Interface-driven twinning as revealed by this study suggests the exciting possibility of altering the roles of dislocation slip and twinning through the design of heterophase interface structure and properties. [Copyright &y& Elsevier]

3D interfaces are a new type of interface containing nanoscale crystallographic, structural, and chemical heterogeneities in all spatial dimensions. Recently, 3D interfaces have been shown to enhance strength and deformability simultaneously by frustrating shear instability under layer-normal micropillar compression in Cu/Nb nanolaminates. However, quantification of deformed microstructure and effects of loading orientation were not explored in that work. Here, we address these shortcomings by performing post mortem TEM characterization of micropillars compressed at normal and 45° inclination to layers. We find high strength and deformability in both loading geometries and show that 3D interfaces enhance mechanical behavior under multiple loading orientations. In layer-normal compression, post mortem characterization allows for quantification of key quantities correlating well to the severity of shear localization across nanolaminates with different layer thickness and interface type. In 45° compression, TEM results demonstrated no strong plastic instability. This motivated analytical computation of Schmid factors and simulation of slip system activity via crystal plasticity finite element modeling (CPFE). The CPFE model demonstrates that most slip activity occurs non-parallel to layers, indicating that dislocation-3D interface interactions must mediate the observed mechanical behavior of micropillars. This work lays the foundation for further study of 3D interface-driven deformation physics in nanostructured alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

Mechanical properties of thin films are often obtained solely from nanoindentation. At the same time, such measurements are characterized by a substantial amount of uncertainty, especially when mean pressure or hardness are used to infer uniaxial yield stress. In this work we demonstrate that indentation with a pyramidal flat tip (frustum) indenter near the free edge of a sample can provide a significantly better estimate of the uniaxial yield strength compared to frequently used Berkovich indenter. This is first demonstrated using a numerical model for a material with an isotropic pressure sensitive yield criterion. Numerical simulations confirm that the indenter geometry provides a clear distinction of the mean pressure at which a material transitions to inelastic behavior. The mean critical pressure is highly dependent on the plastic Poisson ratio ν p so that at the 1% offset of normalized indent depth, the critical pressure p m c normalized to the uniaxial yield strength σ 0 is 1 < p m c /σ 0 < 1.3 for materials with 0 < ν p < 0.5 . Choice of a frustum over Berkovich indenter reduces uncertainty in hardness by a factor of 3. These results are used to interpret frustum indentation experiments on nanoporous (NP) Copper with struts of typical diameter of 45 nm. An estimate of the yield strength of NP Copper is obtained 230 MPa < σ 0 < 300 MPa. Edge indentation further allows one to obtain in-plane strain maps near the critical pressure. Comparison of the experimentally obtained in-plane strain maps of NP Cu during deformation and the strain field for different plastic Poisson ratios suggest that this material has a plastic Poisson ratio of the order of 0.2–0.3. However, existing constitutive models may not adequately capture post-yield behavior of NP metals. [ABSTRACT FROM AUTHOR]

Experimentally quantifying the mechanical effects of radiation damage in reactor materials is necessary for the development and qualification of new materials for improved performance and safety. This can be achieved in a high-throughput fashion through a combination of ion beam irradiation and small scale mechanical testing in contrast to the high cost and laborious nature of bulk testing of reactor irradiated samples. The current work focuses on using spherical nanoindentation stress-strain curves on unirradiated and proton irradiated (10 dpa at 360 °C) 304 stainless steel to quantify the mechanical effects of radiation damage. Spherical nanoindentation stress-strain measurements show a radiation-induced increase in indentation yield strength from 1.36 GPa to 2.72 GPa and a radiation-induced increase in indentation work hardening rate of 10 GPa–30 GPa. These measurements are critically compared against Berkovich nanohardness, micropillar compression, and micro-tension measurements on the same material and similar grain orientations. The ratio of irradiated to unirradiated yield strength increases by a similar factor of 2 when measured via spherical nanoindentation or Berkovich nanohardness testing. A comparison of spherical indentation stress-strain curves to uniaxial (micropillar and micro-tension) stress-strain curves was achieved using a simple scaling relationship which shows good agreement for the unirradiated condition and poor agreement in post-yield behavior for the irradiated condition. The disagreement between spherical nanoindentation and uniaxial stress-strain curves is likely due to the plastic instability that occurs during uniaxial tests but is absent during spherical nanoindentation tests. [ABSTRACT FROM AUTHOR]

Cu/Nb nanocomposites containing sharp, two-dimensional (2D) interfaces have outstanding strength but limited deformability. In contrast, Cu/Nb with three dimensional (3D) biphase interfaces exhibiting crystallographic, topological, and chemical variations in all spatial dimensions overcomes this limitation by simultaneously enhancing material strength and deformability. While structural characterization of 3D interfaces has been performed to understand their mechanical behavior, three dimensional chemical characterization of such interfaces is lacking. In this work we quantify the local chemistry of 3D interfaces in Cu/Nb nanocomposites using atom probe tomography (APT). Our analysis demonstrates chemical heterogeneities along all spatial dimensions in 3D interfaces, establishes the length scale of such features, and quantifies the morphology of 3D interfaces. 3D interface heterogeneities form by surface diffusion during physical vapor deposition (PVD), suggesting that deposition parameters can be used to control interface structure and provide unique ways to explore processing-structure-property relationships in interface-dominated nanocomposites. [Display omitted] [ABSTRACT FROM AUTHOR]

While bimetallic nanocomposites have demonstrated extraordinary – three to even ten-fold – gains in strength with decreasing layer thickness, their strengths tend to plateau beyond a critical layer thickness. More disappointingly, such increases in strength are almost always accompanied by a decrease in their strains to failure (ductility). In this work we report simultaneous improvements in both strength and mechanical stability of Nb/Mg nanolaminates with decreasing layer thicknesses, a trend seldom reported in nanolaminates consisting of pure metals. Using micro-pillar compression and nanoindentation experiments we show that physical vapor deposited (PVD) Nb/Mg nanolaminates that contain a body center cubic (bcc) Mg pseudomorphic phase demonstrate a >60% increase in strength and a >80% increase in strain to failure over those containing the hexagonal close packed (hcp) Mg phase. Instead of a strength plateau, the hcp-to-bcc phase transition in Mg results in a renewed strengthening regime in the nanolaminate caused by the change to a coherent interface from an incoherent one, along with a concurrent increase in strain-to-failure due to the introduction of a more plastically isotropic bcc material from an anisotropic hcp structure. Using high resolution transmission electron microscopy (HR-TEM) we also demonstrate the presence of a thin layer of bcc Mg at the Nb/Mg interface at larger layer thicknesses when Mg is predominantly hcp. Our results suggest that the increases in strain to failure in the Nb/Mg nanolaminates with decreasing layer thicknesses can be corelated to the approximate volume fraction of the pseudomorphic bcc Mg present in the layers. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, we present a 3D microstructure-based, full-field crystal plasticity finite element (CPFE) model using a thermally activated dislocation-density based constitutive description and apply it to study the deformation of a two-phase hexagonal close packed (HCP)-body center cubic (BCC) Zr/Nb composite. The microstructure models were created using a synthetic grain structure builder (DREAM.3D) and a meshing toolset for the 3D network of grains, grain boundaries, and bimetal interfaces. The crystal orientations, grain shapes, and grain sizes for each phase were initialized based on the measured data. With this novel technique, we aspire to couple the evolution of microstructural heterogeneities with the evolution of spatially resolved mechanical fields during the deformation of complex composites. Here, we apply it to understand the role that microstructure plays in the development of the local concentrations in strain and strain rate that can trigger plastic instabilities, such as shear banding. Our chief findings are that 1) local areas of relatively high (and relatively very low) strain concentration occur at triple junctions or quadruple points and then connect via straining to create a banded configuration that extends across the polycrystalline layer, 2) this event starts in the Zr phase and not in the Nb phase, and 3) the triggering hot spots in strain occur at junctions that join grains with very dissimilar reorientation propensities and vice versa for cold spots. In order to determine how such influential localizations can be prevented during processing via application of intermediate annealing treatments, we used the model to also explore the effects of annealing-induced changes in accumulated dislocation density, crystallographic texture and grain shape on the development of strain localizations during subsequent deformation. We found that while it is difficult to avoid strain localizations at grain junctions, when provided a microstructure containing a few large grains spanning the thickness, elongated grain shapes, and reduced dislocation density, the linkage of hot spots in the form of a band can be postponed. At the end we show that when an additional softening mechanism is introduced, these localized strain concentration areas can lead to shear bands. [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]

We report phenomenal yield strengths—up to one-fourth of the theoretical strength of silver—recorded in microcompression testing of initially dislocation-free silver micro- and nanocubes synthesized from a multistep seed-growth process. These high strengths and the massive strain bursts that occur upon yield are results of the initially dislocation-free single-crystal structure of the pristine samples that yield through spontaneous nucleation of dislocations. When the pristine samples are exposed to a focused ion-beam to fabricate pillars and then compressed, the dramatic strain burst does not occur, and they yield at a quarter of the strength compared to the pristine counterparts. Regardless of the defect-state of the samples prior to testing, a size effect is apparent—where the yield strength increases as the sample size decreases. Since dislocation starvation and the single-arm-source mechanisms cannot explain a size effect on yield strength in dislocation-free samples, we investigate the dislocation nucleation mechanisms controlling the size effect through careful experimental observations and molecular statics simulations. We find that intrinsic or extrinsic symmetry breakers such as surface defects, edge roundness, external sample shape, or a high vacancy concentration can influence dislocation nucleation, and thus contribute to the size effect on yield strength in initially dislocation-free samples. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Nanolaminates have gained much attention due to exceptional mechanical, optical, electrical and biological properties. In this work, we explore the microstructure and mechanical properties of Al-SiC co-sputtered monolayers having different compositions. Co-sputtering enables tailoring the microstructure at an atomic level and hence is a promising route to develop new generation of materials. These co-sputtered samples were characterized through FIB/SEM, TEM and XPS. They had an amorphous microstructure, with the exception of nanocrystalline Al aggregates present in one of the compositions. The micromechanical properties were studied through nanoindentation. We observed that the modulus and hardness of the co-sputtered samples were much higher than traditional Al/SiC nanolaminate samples having the same composition. Graphical abstract Unlabelled Image Highlights • Novel co-sputtered monolayers of Al-SiC were synthesized by magnetron sputtering. • Thorough materials characterization showed a unique nanostructure that results in extremely high modulus and hardness compared to classical Al-SiC nanolaminates. • A unique nanostructure consisting of Al, SiC, Si, and C was obtained. [ABSTRACT FROM AUTHOR]