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Understanding the relationship between atomic-scale structure and properties is becoming increasingly critical as microstructures are now tailored at the nanometre length scale. Here we demonstrate 3-D mapping of grain orientations through atom probe tomography by utilizing Hough transforms to extract the orientation of crystallographic directions. The disorientation across boundaries is also determined. We are now able to combine the powerful capability of atom probe for measuring the 3-D distribution of atoms with the new ability to provide accurate crystallographic information. [ABSTRACT FROM AUTHOR]

The composition and site occupancy of Mg within ordered δ′ precipitates in a model Al–Mg–Li alloy have been characterized by atom probe microscopy and first-principles simulations. The concentration in the precipitates is found to be almost the same as that of the matrix; however, we show evidence that Mg partitions to the sites normally occupied by Li in the L12 structure. Density functional calculations demonstrate that this partitioning is energetically favorable, in agreement with experimental results. [ABSTRACT FROM AUTHOR]

We demonstrate that a Nb-microalloyed ultra-thin cast strip steel can be strengthened substantially without compromising ductility by performing a simple heat treatment at 700°C for 4min. The strengthening was attributed to a fine dispersion of Nb-rich solute atom clusters. These clusters had an average size of ∼60 atoms at peak hardness and resembled Guinier–Preston zones in Al–Cu alloys. The application of the Ashby–Orowan equation indicates that these clusters are potent strengthening agents when compared to conventional Nb(C,N) precipitation strengthening. [ABSTRACT FROM AUTHOR]

The dream of the microscopy and materials science communities is to see, identify, accurately locate, and determine the fundamental physical properties of every atom in a specimen. With this knowledge together with modern computer models and simulations, a full understanding of the properties of a material can be determined. This fundamental knowledge leads to the design and development of more advanced materials for solving the needs of society. The technique of atom probe tomography is the closest to fulfilling this dream but is still significantly short of the goal. The future of atom probe tomography, and the prospects for achieving this ultimate goal are outlined. [Copyright &y& Elsevier]

Abstract: Nitrided steels are widely used in the engineering field due to their superior hardness and other attractive properties. Atom probe tomography (APT) was employed to study two Nb-microalloyed CASTRIP steels with different N contents. A major challenge of using APT to study this group of materials is the presence of tails after Fe peaks in the mass spectra, which overestimates the composition for alloying elements such as Nb and Cu in the steels. One important factor that contributes to the tails is believed to be delayed field evaporation from Fe2+. This artefact of the mass spectrum was observed to be the most severe when voltage pulsing was used. The application of laser pulses with energy ranging from 0.2 to 1.2nJ successfully reduced the tails and lead to better compositional measurement accuracy. Spatial resolution in the z-direction (along the tip direction) was observed to be less affected by changing laser energy but deteriorates in x–y direction with increasing laser energy. This investigation suggests that pulsed-laser atom probe with ∼0.4nJ laser energy can be used to study this group of materials with improved mass resolution while still maintaining high spatial resolution. [Copyright &y& Elsevier]

In situ compression transmission electron microscopy was used to investigate the deformation behavior of alpha-Fe nanoblades. The results showed an inhomogeneous deformation process, composed of a series of short displacement bursts and single large displacement bursts. The short displacement bursts were associated with the collective motion of dislocations within the specimen, whilst the large displacement bursts occurred through dislocation-assisted slip band formation nucleated from the surface of the nanoblades. [ABSTRACT FROM AUTHOR]

Abstract: In situ bulk metallic glass (BMG) composites generally contain a crystalline phase(s) that forms throughout the amorphous matrix during cooling from the melt. The presence of the crystalline phase in these materials is known to improve both ductility and toughness. In this study the nucleation and growth behaviour of crystalline α-Mg flakes during casting of a series of Mg–Cu–Y–Zn glass forming alloys were investigated. It was demonstrated that the α-Mg phase nucleates preferentially on the surface of micron-sized yttria (Y2O3) particles that form in the melt during casting and subsequently grow in preferential crystallographic directions to generate an intimate distribution of interwoven flakes throughout the amorphous matrix. High resolution transmission electron microscopy revealed that a thin (∼5nm) intermediate Cu layer forms at the particle–flake interface resulting in full coherency with both the particle and flake, thereby resulting in well-defined orientation relationships. The formation of this intermediate layer is argued to be the necessary precursor for nucleation of Mg flakes at the Y2O3 particles in a manner similar to that found for the preferential nucleation at TiB2 particles in conventional Al alloys. The overall effect of this intermediate layer is a reduction in the interfacial energy between the particle and nucleus, thereby lowering the thermodynamic barrier for nucleation. In general terms, inoculation controlled formation of a crystalline phase throughout an amorphous matrix in selected glass forming compositions may be a viable means of generating the desired two phase structure for generating high strength BMG composites exhibiting suitable ductility. [Copyright &y& Elsevier]

Abstract: Progress in the reconstruction for atom probe tomography has been limited since the first implementation of the protocol proposed by Bas et al. in 1995. This approach and those subsequently developed assume that the geometric parameters used to build the three-dimensional atom map are constant over the course of an analysis. Here, we test this assumption within the analyses of low-alloyed materials. By building upon methods recently proposed to measure the tomographic reconstruction parameters, we demonstrate that this assumption can introduce significant limitations in the accuracy of the analysis. Moreover, we propose a strategy to alleviate this problem through the implementation of a new reconstruction algorithm that dynamically accommodates variations in the tomographic reconstruction parameters. [Copyright &y& Elsevier]

The mechanical properties of an electrodeposited nanocrystalline Ni–Fe alloy were studied as a function of the angle between the compression and columnar grain axes. Improved ductility was achieved as the applied load was along the grain column axis. After annealing at 250°C, the yield strength increased and the plastic strain dropped remarkably. However, the annealing embrittlement cannot be attributed to the impurity segregation. The roles of texture and grain boundary relaxation upon annealing on the strength and ductility of nanocrystalline alloys were discussed. [Copyright &y& Elsevier]

Abstract: Spatial Distribution Maps (SDM) in their various forms have previously been used to identify and characterize crystallographic structure within APT reconstructions. Importantly, it has been shown that such SDM analyses can also provide the crystallographic orientation of the specimen with respect to the direction of the detector in the original experiment. In this study, we investigate the application of SDMs to the analysis of APT reconstruction of a nanocrystalline Al film. We demonstrate that significant intra-granular crystallographic information is retained in the reconstruction, even in the x–y plane perpendicular to the direction of the detector. Further, the crystallographic orientation of the grains can be characterized highly accurately not only with respect to the bulk specimen but also their misorientation with respect to neighbouring grains. [Copyright &y& Elsevier]

Abstract: The solute segregation at grain boundaries (GBs) of an ultrafine grained (UFG) Al–Zn–Mg–Cu alloy processed by equal-channel angular pressing (ECAP) at 200°C was characterised using three-dimensional atom probe. Mg and Cu segregate strongly to the grain boundaries. In contrast, Zn does not always show clear segregation and may even show depletion near the grain boundaries. Trace element Si selectively segregates at some GBs. An increase in the number of ECAP passes leads to a decrease in the grain size but an increase in solute segregation at the boundaries. The significant segregation of alloying elements at the boundaries of ultrafine-grained alloys implies that less solutes will be available in the matrix for precipitation with a decrease in the average grain size. [Copyright &y& Elsevier]

Abstract: The compositional variation, morphology and microstructure of cold gas-dynamic spray are of great importance for its proper application. This study investigates titanium powder deposition on an Al 6063 substrate using light optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composition was examined using energy dispersive X-ray spectroscopy (EDX), X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF SIMS). Optical and electron microscopy revealed heavily deformed Ti powder particles penetrating 10 to 30μm into the Al substrate. Examination using TEM did not reveal any evidence of second phases at the interface suggesting a sharp transition between the two metals. The presence of nanocrystals and grain refinement of both the coating and the substrate suggest the formation of a partial hetero-epitaxy condition near the interface. EDX results from a dedicated high-resolution scanning transmission electron microscope showed a sharp compositional change with a maximum inter-diffusion region of about 5nm. Bonding of the coating to the substrate is therefore thought to be achieved by the particle/substrate interlocking and direct metal to metal bonding. However, it is most likely that the refine crystalline structure near the interface will be beneficial to the adhesion of the coating. XPS and ToF SIMS provided evidence of nitrogen pick-up during the spray process in the form of N and TiN even when utilizing Helium as the gas carrier. The presence of TiN suggests reaction of the Ti with the entrained air during spraying which explains the occurrence of flashing jet outside the nozzle. Investigation of the material properties using nanoindentation showed reasonably consistent hardness and elastic modulus values throughout the titanium coating and at the transition region. The hardness was slightly higher than typical commercially available bulk Ti. [Copyright &y& Elsevier]

Abstract: The implementation of fast pulsed laser has significantly improved the performance of the atom probe technique by enabling near-atomic-scale three-dimensional analysis of poorly conducting materials. This has broadened the range of applications for the atom probe, addressing a major limitation of the technique. Despite this, the implications of lasing on the tomographic reconstruction of atom probe data have yet to be fully characterised. Here, we demonstrate how changes in the shape of the specimen surface, induced by laser pulsing, affect the ion trajectories, and hence the projection parameters used to build the three-dimensional map. [ABSTRACT FROM AUTHOR]

Abstract: Poly(3,4-ethylenedioxythiophene) (PEDOT) films with a flower-like nanostructure have been electrochemically deposited on indium tin oxide (ITO) electrode simply by a one-step cyclic voltammetry (CV) method in an aqueous media in the absence of any surfactant. The PEDOT films deposited on the substrates were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The results indicate that the flower-like hierarchical structure of the PEDOT film is composed of nanosheets with a thickness of even less than 2nm at the edge. The resulted porous structure of the PEDOT coating leads to a two-order increase of magnitude in the electrochemical capacitance-current. The growth process of the electrodeposited PEDOT as well as the effect of polymerization potential on the properties of products was studied. [ABSTRACT FROM AUTHOR]

Abstract: α-Al2O3 nanotubes were synthesized in bulk quantity by using simple physical evaporation of pure aluminum powders at 1000°C. Field emission scanning electron microscopy and transmission electron microscopy observations show that the nanotubes have diameters smaller than 100nm and lengths up to several microns. Cathodoluminescence measurements revealed a strong luminescence band in the wavelength range of 280–380nm centered at 330nm, which could be attributed to the oxygen vacancies in the α-Al2O3 nanotubes. Sacrificial template model is regarded as the possible formation mechanism of the nanotubes. [Copyright &y& Elsevier]

Solute clustering is increasingly recognised as a significant characteristic within certain material systems that can be tailored to the optimization of bulk properties and performance. Atom probe tomography (APT) is emerging as a powerful tool for the detection of these nanoscale features; however, complementary to experiment, precise and efficient characterization algorithms are required to identify and characterise these nanoclusters within the potentially massive three-dimensional atomistic APT datasets. In this study, a new three-dimensional Markov field (3DMF) cluster identification algorithm is proposed. The algorithm is based upon an analysis of the direct atomic neighbourhood surrounding each atom, and the only input parameter required utilises known crystallographic properties of the system. Further, an array of statistical approaches has been developed and applied with respect to the results generated by the 3DMF algorithm including: an SN statistic, a two-tailed z-test, a difference measure, the χ2 test, and a direct evaluation of the Warren-Cowley parameter for short-range ordering. Finally, the methodologies have been applied to the characterization of the nanostructural evolution of an Al-1.1Cu-0.5Mg (at.%) alloy subjected to a variety of heat treatments. [ABSTRACT FROM AUTHOR]

Abstract: The microstructural evolution of a b.c.c.-based, spinodally formed alloy Fe35Ni15Mn25Al25 has been studied as a function of annealing time at 550°C using atom probe tomography and transmission electron microscopy, including energy-filtered imaging. The sizes, crystal structures, orientation relationships and compositions of the phases present were determined as a function of annealing time. The hardness showed complicated behavior as a function of annealing time, consisting of initial hardening, followed by softening and finally, by a rapid hardening behavior. The hardness is controlled both by the coarsening of the spinodally formed phases, and the precipitation and growth of β-Mn structured particles. [Copyright &y& Elsevier]

Abstract: Nanocomposite membranes are fabricated from sodalite nanocrystals (Sod-N) dispersed in BTDA-MDA polyimide matrices and then characterized structurally and for gas separation. No voids are found upon investigation of the interfacial contact between the inorganic and organic phases, even at a Sod-N loading of up to 35wt.%. This is due to the functionalization of the zeolite nanocrystals with amino groups (ph name="sbnd" />(CH3)(CH2)3NH2), which covalently link the particles to the polyimide chains in the matrices. The addition of Sod-N increases the hydrogen-gas permeability of the membranes, while nitrogen permeability decreases. Overall, these nanocomposite membranes display substantial selectivity improvements. The sodalite–polyimide membrane containing 35wt.% Sod-N has a hydrogen permeability of 8.0 Barrers and a H2/N2 ideal selectivity of 281 at 25°C whereas the plain polyimide membrane exhibits a hydrogen permeability of 7.0 Barrers and a H2/N2 ideal selectivity of 198 at the same testing temperature. [Copyright &y& Elsevier]

Abstract: New and improved spatial distribution map (SDM) methods are developed to identify and extract crystallographic information within atom probe tomography three-dimensional (3D) reconstructions. Detailed structural information is retrieved by combining z-SDM offset distribution analyses computed in multiple crystallographic directions, accurately determining inter-planar spacings and crystallographic angles. The advantages of this technique in comparison to applying the complete z-SDM and complementary xy-SDM analysis to a single crystallographic direction are investigated. Further, in determining these multidirectional z-SDM and xy-SDM profiles, background noise reduction and automatic peak identification algorithms are adapted to attain increased accuracy and is shown to be particularly effective in cases where crystal structure is present but poorly resolved. These techniques may be used to calibrate the reconstruction parameters and investigate their dependence on the design of individual atom probe experiments. [Copyright &y& Elsevier]

Abstract: The recent discovery of arsenic-based high temperature superconductors has reignited interest in the study of superconductor: biological interfaces. However, the new superconductor materials involve the chemistry of arsenic and their toxicity remains unclear [Hand, E., 2008. Nature 452 (24), 922]. In this study the possible adverse effects of this new family of superconductors on cells have been examined. Cell culture studies in conjunction with microscopy and viability assays were employed to examine the influence of arsenic-based superconductor PrO x FeAs (x =0.75) material in vitro. Imaging data revealed that cells were well adhered and spread on the surface of the superconductor. Furthermore, cytotoxicity studies showed that cells were unaffected during the time-course of the experiments, providing support for the biocompatibility aspects of PrO x FeAs-based superconductor material. [Copyright &y& Elsevier]

Abstract: For the purpose of controlling zeolite crystal size, crystallization of zeolite NaA and NaY in glutaraldehyde crosslinked chitosan (GA-CS) hydrogels was studied in this paper. The zeolite crystals were produced by penetration of Na2O–Al2O3–H2O alkaline solution into GA-CS hydrogels filled with colloidal silica, followed by hydrothermal treatment and removal of GA-CS hydrogels. We systematically investigated the effects of the synthesis parameters – including the amounts of silica, chitosan, and glutaraldehyde, and the aging and heating times – on the size, size distribution and crystallinity of the particles. A hydrogen peroxide treatment method was shown to be an effective way for removing GA-CS hydrogels, thereby avoiding the conventional calcination step. X-ray diffraction (XRD), light scattering, scanning electron microscopy (SEM), thermogravimetric analysis (TG), and N2 sorption were used to characterize the zeolite samples. This work showed that GA-CS is a promising space-confinement medium for the synthesis of zeolite nanocrystals with tunable crystal sizes and excellent dispersibility. [Copyright &y& Elsevier]

Single phase high-entropy alloys (HEAs) are often assumed to be random solid solutions with homogeneous elemental distributions. This may not always be true and atomic arrangements and chemical homogeneity depend on the processing history of the material. In this study, electron probe microanalysis (EPMA) and atom-probe tomography (APT) were performed on nominally equiatomic CrMnFeCoNi HEAs with different processing histories. Our EPMA analysis revealed that the different processing routes can produce both compositionally homogenous and compositionally heterogeneous materials. The homogenous material was used for an APT parameter optimization study that was conducted in both voltage and laser-pulsed mode. The data acquisition parameters, i.e., specimen base temperature, detection rate, pulse fraction/pulse energy and pulse rate were varied, and results such as detector hit events, mass-spectra, signal-to-noise ratio, and local chemical composition analyzed. A set of optimized parameters was then used to examine micro and nanoscale compositional heterogeneities in the second HEA. Results of the parameter study indicate that while the laser-mode APT data yielded marginally better data quality, a wide range of APT parameters in either mode can be used to produce a compositionally accurate analysis. The APT data of the heterogeneous HEA revealed that the material contains nanoscale compositional heterogeneities in addition to the microscale heterogeneities revealed by EPMA. The combination of both methods provides a complementary set of characterization techniques to reliably identify chemical heterogeneities across nanometer to micrometer length scales that may affect local deformation mechanisms. • WDXS-based EPMA and APT experiments reveal that nominally equiatomic, single-phase CrMnFeCoNi HEAs may contain chemical heterogeneities and a compositional meso-structure despite having a fully recrystallized microstructure. • Depending on ingot size, homogenizing for 48 h at 1200 °C prior to cold working and recrystallization may be insufficient to break down large compositional heterogeneities. • Due to the convolution of K α and K β X-ray emission energies of the species in CrMnFeCoNi HEAs conventional EXDS may not be able to resolve differences in chemical composition. • A wide range of APT parameters can be used to obtain a high level of compositional accuracy and reliably characterize CrMnFeCoNi HEAs. [ABSTRACT FROM AUTHOR]

The influence of solute drag effects on austenite grain growth in microalloyed steels has been overshadowed by the well-established phenomenon of Zener pinning associated with a dispersion of fine precipitates. Enhanced toughness in the weld heat-affected zone (HAZ) of high Nb steels suggests that microalloying effects are still operative at peak temperatures even beyond known precipitate stability. As the cornerstone for unveiling the solute drag effect, the solute concentration in the matrix should be accurately measured. In this work, we compared inductively coupled plasma mass spectroscopy (ICP-MS) and atom probe tomography (APT) in determining the extent of Nb dissolution as a function of increasing temperature in two commercial American Petroleum Institute steel grades with different levels of Nb and marked variations in weld HAZ toughness. Both techniques demonstrated that the majority of Nb exists in solid solution at the peak temperatures. APT provided a more consistent determination of soluble Nb, in a better agreement with thermodynamic calculations, whilst ICP-MS underestimated the concentration of Nb in the matrix. This work provides valuable insights in determining soluble Nb concentration in steels. [Display omitted] • Nb content in solid solution was analysed as a function of temperature using ICP-MS and APT techniques. • Experimental results were compared with thermodynamic simulations. • High Nb steel provides increased levels of soluble Nb following thermal cycles. • APT provided a more consistently reliable determination of soluble Nb. • ICP-MS qualitatively recorded Nb dissolution as a function of temperature but in general recorded lower values due to limitations in sample preparation. [ABSTRACT FROM AUTHOR]

The design of additively manufactured metallic alloys with tailored mechanical properties requires a detailed understanding of the microstructural evolution throughout the printing process. In Ti-6Al-4V, this involves a complex combination of phase transformations, leading to microstructural and property variations within a single as-fabricated build. The origin of such property variations and the sequence of phase changes occurring during the cyclic heating and cooling process remain uncertain. We have studied the phase transformation pathway by following how, in particular, the β phase growth varies within the build. Samples manufactured by electron beam powder bed fusion were analysed using electron microscopy and atom probe tomography techniques. We demonstrate that a significant β phase fraction variation occurs within a given build plane. We reveal that the high-temperature β phase can be separated into two categories, depending on whether it was retained from cooling from above the β transus temperature, or nucleated below it. This is the first direct evidence of the coexistence of both types of β transformation products in Ti-6Al-4V. The abrupt cyclic nature of the additive manufacturing process is what has facilitated this unusual transformation sequence. The work provides a complete and general description of the phase transformation pathway, informed by these observations. The implication of the phase transformation pathway on hardness is discussed in relation to chemical variation and oxygen pickup. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: An initial characterization was carried out on the heat affected zone between a 30CrMnSi steel and a Cu–4Zn (wt.%) alloy formed from a novel welding technique involving induction melting of a Cu alloy over a steel substrate at 1100 °C. A very thin (∼20 nm) reaction interface between the steel substrate and the Cu alloy is shown to play a key role in effecting these joints. This reaction interface is an Fe–Cu rich discrete phase with a FCC structure and substantial coherence to both the steel substrate and the Cu alloy layer. This reaction interface is expected to form under highly non-equilibrium conditions and provides a bridging effect for the join. This is proposed as the major reason for the strength and mechanical integrity of the weld. [Copyright &y& Elsevier]

Abstract: Four series of nanocomposites of layered clays and cadmium sulfide have been prepared from laponite, saponite, hectorite and montmorillonite. These nanocomposites have been characterized in terms of the sizes and morphologies of the sulfide species, their textural features, and light absorption properties. From this detailed study, the similarities and differences in structure and properties of the four types of composite have been determined. The composites consist of CdS pillars and CdS nanoparticles, which tend to increase in size as the amount of complex precursor increases. The sizes of the sulfide prepared from the same amount of complex differ across the four series of composites due to the effect of the different clays on precursor exchange, and on the subsequent nucleation and growth of CdS particles. The composites show the characteristic light absorbance of CdS, and absorbance increases with the sulfide content. The composites are generally mesoporous. Each series of composites maintains a similar structure to its parent clay, but the specific surface areas, total pore volumes and average pore sizes of the composites vary with the amount of complex precursor and type of clays used for the synthesis. [Copyright &y& Elsevier]

Abstract: The rare-earth element europium has been doped into the skeleton of BN nanotubes (BNNTs) up to 0.5at.%. The doing and synthesis processes have been systematically studied. The Eu-doping greatly increases the nanotube formation yield. The successful synthesis of Eu-doped BNNTs not only facilitates the exploration of the genuine structure but also presents a fascinating potential in creating new physical properties of BNNTs for various practical applications. [Copyright &y& Elsevier]

Abstract: Hydroxy-sodalite nanocrystals with organic functional groups (i.e., ;(CH3)(CH2)3NH2, denoted Sod-N, or ;CH3, denoted Sod-C) were synthesized by the direct transformation of organic-functionalized silicalite nanocrystals. The chemical structure of organic-functionalized sodalite nanocrystals was confirmed by 29Si MAS NMR spectroscopy. Gas sorption results showed that the sodalite nanocrystals contained uniform pore channels that were accessible to hydrogen, but inaccessible to nitrogen, as expected. The BET surface areas are calculated to be 22.8, 19.6 and 19.1m2/g for plain sodalite nanocrystals (Sod), Sod-N, and Sod-C, respectively; similarly, Sod-N and Sod-C exhibited slightly lower hydrogen adsorption than Sod. The dispersion of Sod-N and Sod-C in organic solvents was favored by the presence of organic functional groups. Therefore, the organic-functionalized sodalite nanocrystals prepared in this work may be very useful for fabricating zeolite nanostructures and sodalite-polymer nanocomposite membranes. [Copyright &y& Elsevier]

The microstructure of aluminum (Al) solution-doped soot layers in modified chemical vapor deposition fabrication of silica-based optical fibers has been studied. It is shown that such Al doping is predominantly determined by deposition temperature. Radial and longitudinal Al doping distributions have been investigated in soot layers, in fully sintered glass layers, and in collapsed preforms. Formation mechanisms are discussed. [ABSTRACT FROM AUTHOR]

Abstract: A variety of nanocomposites were synthesised by bulk polymerisation of methyl methacrylate (MMA), and also by extrusion of poly(methyl methacrylate) (PMMA). These were characterised by wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). We applied image analysis to the TEM images of these PMMA–clay nanocomposites to quantify their structures; an analysis was made of the resulting parameters to determine which were most useful for quantifying the microscale and nanoscale structures. Frequently, these quantitative results differed from those expected on the basis of WAXD, demonstrating the limitations of using diffraction data as the sole measure of nanocomposite structure. By combining the quantitative parameters from TEM with the WAXD data, we have explored the effects of processing conditions and organoclay properties on final nanocomposite structure. Factors examined included the effect of the reactivity of the surface modifiers, platelet size, the incorporation of excess modifier within the organoclay, and bulk polymerisation versus extrusion. [Copyright &y& Elsevier]

Abstract: We demonstrate control of the size and morphology of aluminum hydrate nanoparticles synthesized by a hydrothermal reaction through manipulating the pH value of the reaction mixture, hydrothermal temperature and the surfactant used. Porous laths were formed under acidic conditions, while the lath-width increased with temperature resulting in the formation of single-crystal porous laths. At neutral or high pH values, porous plates of several nanometers thick were obtained. The pore sizes on both laths and plates were ∼2–3nm. Stringy lath-shaped nanoparticles were obtained with polyethylene glycol surfactant. The control nanoparticle size and morphology using soft chemical methods is demonstrated. Furthermore, these nanoparticles transformed to γ-alumina nanocrystallites after heating to 673K, and retained the morphology of the parent boehmite. A detailed characterization of the nanoparticulates and discussion of the mechanism of their formation and subsequent transformation is provided. [Copyright &y& Elsevier]

The Al compositional profile across the AlAs/GaAs heterostructural interface before and after rapid thermal annealing was investigated by a thickness fringe-imaging technique. The diffusion of Al has been quantified by comparison between experimental thickness intensity profiles and the simulated intensity profiles. [Copyright &y& Elsevier]

• Combining the oxidation of the biomass-derived benzaldehyde with simultaneous proton reduction in a closed redox cycle. • Both benzaldehyde oxidation and H 2 production follows the order of single atom > nanocluster > nanoparticle. • Pt single atom catalyst demonstrates a nearly 100% efficiency per atom in producing benzoic acid and clean H 2 fuel. Sustainable development requires the use of renewable and clean energy resources to manufacture end-user products with high efficiency. Herein, we report an artificial photocatalysis system that combines the oxidation of the biomass-derived benzaldehyde with simultaneous proton reduction in a closed redox cycle driven by supported nanocatalysts in an aqueous solution. Our results demonstrate a nearly 100 % reactant efficiency for water splitting on a per-atom basis, and generates two targeted end-user products: benzoic acid and clean H 2 fuel. Nanocatalysts can be conveniently categorized into three groups according to their size: single atom, nanocluster, and nanoparticle. Nanocatalysts smaller in size are generally outstanding for oxidation, while larger particles are more efficient in proton reduction. To elucidate the size effects for the overall reaction in both half-reactions, we prepared Pt single atom (0.2 nm), nanocluster (1 nm), and nanoparticle (4 and 7 nm diameter) catalysts supported on polymeric carbon nitride (g-C 3 N 4) for the artificial photocatalytic oxidation of benzaldehyde and hydrogen production. The reaction rate for both benzaldehyde oxidation and H 2 production on the Pt nanocatalysts follows the order of single atom > nanocluster > nanoparticle. Photon-induced charge carriers are more likely to be trapped by single Pt atoms, which guarantees the efficiency of charge splitting and limits the recombination. In addition, the outstanding oxidation performance of the single atom and nanocluster catalysts consumes large amount of holes, which otherwise contribute more electrons for proton reduction and enhance H 2 production. On the other hand, the large nanoparticles potentially provide a stage to trap both photo-induced electrons and holes, with the potential to reduce the photocatalysis rate of hydrogen production from the proton reduction via the excess electrons and the benzaldehyde oxidation and the excess holes. [ABSTRACT FROM AUTHOR]

Solute clustering is a technologically important microstructural process in Al alloys. Exerting control over this process to enhance the alloy properties and reduce the energy costs of production is a major scientific and technological focus, with automotive sheet applications serving as a key driver. In this work, we detail changes in the state of clustering arising from the insertion of a thermomechanical pre-ageing process, via a coil-cooling step in a commercial production line, immediately after solution treatment. This pre-ageing step effectively mitigates the negative effects of the natural ageing on the mechanical properties that would otherwise occur after solution treatment and ahead of the final paint-bake step. Our work was focussed on a short duration/low temperature single-step pre-ageing process on a Cu-lean grade of AA6016. Using a combination of atom probe tomography and first principles density functional theory simulations, we are able to reveal and explain the atomic-scale microstructure arising from this thermomechanical process. Mg–Si co-clusters ≥ 20 solute atoms were found responsible for the excellent properties in the material exposed to the pre-ageing plus paint-baking process. Our simulations revealed that vacancies can effectively stabilise single-species Si clusters enabling them to attract further solute and serving as a pathway to formation of the larger Mg–Si co-clusters that are so beneficial to alloy properties. Our simulations also revealed that the nearest neighbour configurations are a critical aspect to the stability of the clusters. Image, graphical abstract [ABSTRACT FROM AUTHOR]

As-sintered multi-main-phase Nd-Ce-Fe-B permanent magnets typically exhibit a higher coercivity than as-sintered single-main-phase Nd-Ce-Fe-B magnets with identical content of Ce. To clarify the microstructural features that are relevant to the coercivity, as-sintered multi-main-phase Nd-Ce-Fe-B permanent magnets are characterised by high-resolution magnetic force microscopy and atom probe tomography down to the atomic scale. Though inhomogeneous distribution of rare earth elements (Nd, Pr, and Ce) is observed inside 2:14:1 matrix grains, Ce atoms unexpectedly show similar partitioning behaviour (∼14–27% of rare earth element) at the edge of these grains in the vicinity of rare earth-rich grain boundary compared with as-sintered single-main-phase Nd-Ce-Fe-B magnets with a 20% Ce substitute of Nd and Pr. By contrast, the observation of stripe-liked magnetic domains pinned at the grain boundaries and a thin (Nd,Pr,Ce)-rich grain boundary with a composition of Nd 9.9 Pr 2.6 Ce 19.0 Fe 65.3 Co 1.9 Balance 1.3 (at.%) jointly indicates the enrichment of Ce in grain boundaries benefit to the magnetic isolation of neighbouring matrix grains in the as-sintered state. Unusual Ce-rich clustering regions are also observed in the grain boundary, which also contribute to the coercivity enhancement. The segregation of Ce, Co, and Cu and rare-earth-Cu clusters are only observed at the interface between rare earth-Cu rich phase and matrix phase while no obvious elemental segregation and clusters are observed at the interface between the rare earth-Ga rich phase and matrix phase, suggesting the occurrence of rare earth-Cu rich phase may be one of the reasons for achieving high coercivity. These findings offer fresh insights into the as-sintered multi-main-phase Nd-Ce-Fe-B permanent magnets. Image 1 • High intrinsic coercivity is achieved in the as-sintered multi-main-phase Nd-Ce-Fe-B magnets. • The formation of thin (Nd,Pr,Ce)-rich grain boundary in the as-sintered state. • The formation of Ce-rich clustering regions at grain boundaries in the as-sintered state. • The segregation of Cu at the interfaces between the rare earth-Cu rich phase and matrix phases. • No Ga segregation at the interfaces between the rare earth-Ga rich phase and matrix phases. [ABSTRACT FROM AUTHOR]

The dry sliding wear behaviors of the face-centred cubic (f.c.c.) high entropy alloys carbon-doped Fe 40.4 Ni 11.3 Mn 34.8 Al 7.5 Cr 6 and equiatomic CoCrFeMnNi were determined under ambient conditions and compared with that of 316 stainless steel at two sliding velocities and in argon at a slow sliding velocity. Scanning electron microscopy, energy dispersive X-ray spectrometry, electron backscattered diffraction, X-ray photoelectron spectroscopy, and atom probe tomography analyses were employed to characterize the worn microstructures. It was found that in air at the slow sliding velocity of 0.1 m/s C-doped FeNiMnAlCr exhibited a much lower wear rate of 3.0 × 10−5 mm3/N/m compared to either 316 stainless steel (2.9 × 10−4 mm3/N/m) or CoCrFeMnNi (3.4 × 10−4 mm3/N/m). In contrast, both in argon at this slow sliding velocity and in air at the high sliding velocity of 1.0 m/s, all three material showed similar wear rates of ~ (2.4 ± 0.6) × 10−5 mm3/N/m and ~ (1.2 ± 0.3) × 10−5 mm3/N/m, respectively, indicating the strong effect of the environment and pin tip temperature on the wear rates. The oxide that formed on the C-doped FeNiMnAlCr alloy was found to be more stable and durable than that on either the CoCrFeMnNi or on the 316 stainless steel, and the wear debris from C-doped FeNiMnAlCr had the smallest diameter (3 μm) and the lowest oxygen content of 39 at. %. Greater Al 2 O 3 and less Fe 2 O 3 , MnO x or Cr 2 O 3 on the worn surface of C-doped FeNiMnAlCr contributed to a peeled-off or delaminated morphology with a higher oxygen content of 46 at. % compared to the worn surfaces of the 316 stainless steel and the CoCrFeMnNi, which both exhibited grooved worn surfaces with lateral cracks and lower oxygen contents of 7.5 at. % and 31 at. %, respectively. The harder Al 2 O 3 oxide film was stable and adherent during wear testing and helped protect the worn pin's tip, which was the reason for the increased wear resistance of the C-doped FeNiMnAlCr. The wear protection mechanism of 316 stainless steel was attributed to a hard mechanically deformed layer, while the CoCrFeMnNi lacked protection from either the oxide film or a hard deformed layer. Unlabelled Image • C-doped FeNiMnAlCr HEA has a lower wear rate than 316 stainless steel and CoCrFeMnNi HEA in air. • The worn surface of C-doped FeNiMnAlCr HEA was the flattest with the highest oxygen content. • XPS indicated that the C-doped FeNiMnAlCr HEA worn surface contained a large amount of Al 2 O 3. • The oxides formed on the C-doped FeNiMnAlCr HEA pin were more stable and adherent. • The wear mechanism of the C-doped FeNiMnAlCr HEA is predominantly oxidative wear. [ABSTRACT FROM AUTHOR]

The effects of milling time on the particle size distribution (PSD), densification, microstructure, hardness and fracture toughness of spark plasma sintered (SPS) TiN+graphite ceramic were studied. TiN with varying amount of graphite (1, 3, and 5 wt%) were milled at different milling time (8, 24 and 40 h), thereafter sintered at sintering temperature of 1800 °C, holding time of 10 min and pressure of 50 MPa. The relative density and hardness increased as milling time progressed from 24 to 40 h, however, the relative density, hardness, and particle size decreased after 8 h of milling. The microstructural analyses showed that a fully sintered TiN+graphite compact could be achieved at sintering temperature of 1800 °C, with no significant grain growth. Residual stress effect of TiN+5 wt% graphite composite was analyzed using XRD method and the result indicated that there is no significant residual stress on the sample. The relative density, Vickers hardness and fracture toughness of TiN+ 1 wt% Gr, milled for 40 h were 99.24%, 13.90 GPa and 4.0 MPa.m1/2 respectively. Unlabelled Image • Microstructures and mechanical behaviour of TiN-Graphite composites. • The sample preparation was carried out in order to highlight the impact of powder properties and performance. • Sub-micron sizes of each powder were determined using Microtrac particle size distribution, Raman spectroscopy and XRD analysis. • Both the rim and core phases in the structure show uniform phases with similar patterns of diffractions. • The inner and outer rims present distinctive direction of Fcc-phases with equiaxed grains using EBSD. [ABSTRACT FROM AUTHOR]

Abstract: Positron annihilation spectroscopy in two variants (coincidence Doppler-broadening CDB and lifetime spectroscopy LT) was used for the characterisation of severely deformed nanocrystalline 7075 Al alloy, with specific attention to the distribution of solute in the proximity of grain boundaries. The 7075 samples were deformed via the high pressure torsion (HPT) technique after solution treatment and quenching. The grain size at the end of the deformation was sub 100nm. The deformed samples have undergone 3 months of natural ageing post-processing. CDB and LT measurements consistently indicate that the fraction of trapped positrons in these samples is near to 90%. The analysis of CDB data shows that the environment of the positron traps is enriched with solute up to 50at.%, nearly evenly divided between Mg and transition metals (Zn and Cu). The CDB results indicate an enhancement of solute concentration at grain boundaries associated with HPT deformation. [Copyright &y& Elsevier]

Abstract: The thermodynamics of nanocrystalline TiO2 ceramics during the whole sintering process were analyzed using differential scanning calorimetry (DSC) for different heating rates (10, 20 and 30°C/min). The raw TiO2 powder was also studied comparably. The DSC and specific heat capacity (C p ) were also studied. The results show that there is no obvious endothermic or exothermic peak at the stage where the maximum densification rate occurred for TiO2 ceramics. The ordering process induced by the microstructural densification counteracts the disordering process induced by increasing the sintering temperature. The sintering process is a result of combination of the ordering process and the disordering one. The activation energy of nanometer TiO2 ceramics determined by Kissinger method is 103.8kJ/mol. [Copyright &y& Elsevier]

Carbon atoms are counted at near atomic-level precision using a scanning transmission electron microscope calibrated by carbon nanocluster mass standards. A linear calibration curve governs the working zone from a few carbon atoms up to 34 000 atoms. This linearity enables adequate averaging of the scattering cross sections, imparting the experiment with near atomic-level precision despite the use of a coarse mass reference. An example of this approach is provided for layer counting of stacked graphene sheets. Suspended graphene sheets with a size below 100 nm are visualized, providing quantitative measurement in a regime inaccessible to optical and scanning probe methods. [ABSTRACT FROM AUTHOR]

Atom-probe microscopy offers unprecedented insights on the subnanometer structure and chemistry of materials in three dimensions. The actual spatial resolution achievable is however still an uncertain parameter, as no comprehensive study has been undertaken to unveil the physics underpinning how key parameters impact the performance. Here, we present a comprehensive investigation of the in-depth and lateral resolution of the technique. We discuss methods to estimate the resolution and show a resolution better than 20 pm in-depth. Models to support our results were developed and are discussed in the present letter. [ABSTRACT FROM AUTHOR]

Vertically aligned CrO2nanorods with an areal density as high as 1.2 × 1010cm−2were obtained viaatmospheric pressure CVD assisted by AAO templates for the first time. [ABSTRACT FROM AUTHOR]

A new approach to the stimulation of atomic clustering reactions shows potential to address the 'strength-ductility trade-off' in Al–Cu–Mg alloys. The evolution of the alloy microstructure during this thermomechanical processing was followed carefully using electron microscopy, X-ray diffraction, and atom probe microscopy. The distributions of the Mg and Cu solute atoms, and the characteristic distributions of Mg–Cu co-clusters, were investigated in detail. The factors affecting the strength of the alloy were assessed semi-quantitatively and the results suggest that Mg–Cu atom co-clusters contribute significant strengthening in this Al–Cu–Mg alloy, when subjected to this thermomechanical processing. The novel introduction of asymmetric rolling into the thermomechanical process increases the overall strength and we propose that this is due to the synergistic effects of cluster strengthening, dislocation strengthening, and texture engineering. The significant improvement in plasticity is attributed to a combination of the shear texture, the relatively high ratio of low-angle grain boundaries, and the avoidance of microstructural stress and strain concentrations such as those often associated with precipitation and precipitate-free-zones. [ABSTRACT FROM AUTHOR]

Understanding the pathways and mechanisms of human tooth decay is central to the development of both prophylaxes and treatments, but only limited information is presently available about the initiation of caries at the nanoscale. By combining atom probe tomography and high-resolution electron microscopy, we have found three distinct initial sites for human dental enamel dissolution: a) along the central dark line (CDL) within carbonated apatite nanocrystals, b) at organic-rich precipitates and c) along high-angle grain boundaries. 3D maps of the atoms within hydroxyapatite nanocrystallites in sound and naturally-decayed human dental enamel reveal a higher concentration of Mg and Na in the CDL. The CDL is therefore thought to provide a pathway for the exchange of ions during demineralization and remineralization. Mg and Na enrichment of the CDL also suggests that it is associated with the ribbon-like organic-rich precursor in amelogenesis. Organic-rich precipitates and high-angle grain boundaries were also shown to be more vulnerable to corrosion while low-angle grain boundaries remained intact. This is attributed to the lower crystallinity in these regions. [ABSTRACT FROM AUTHOR]

• Intragranular rare earth (RE)-rich phase was characterized in strip-cast Nd-Fe-B flakes. • The intragranular RE-rich phase is made up of amorphous and crystalline regions. • Cu, Co, and Ga are enriched in the amorphous region. • The crystalline region is made up of hexagonal LRE-rich and cubic LRE/HRE/O-rich phases. • The formation of these intragranular glass/crystal phases was proposed. Intragranular rare earth-rich phases play a vital role in affecting the intrinsic coercivity of sintered Nd-Fe-B permanent magnets. To explore the origin of these intragranular rare-earth-rich phases, the starting material-strip cast Nd-Fe-B flakes were characterized by a variety of high-end microscopy techniques. It was surprisingly found that the intragranular rare-earth-rich phase is spherical in a diameter of ~150–300 nm and consists of amorphous regions rich in additive elements (e.g., Cu, Co, and Ga) and crystalline regions which are a combination of hexagonal light-rare-earth-rich phases and body centered cubic phases rich in light and heavy rare earth, and oxygen. Amorphous interfacial layers between the glass/crystal particles and the crystalline matrix were observed, probably due to insufficient time to reach a crystalline equilibrium state. Based on the microstructural observation, we proposed a formation mechanism of these intragranular glass/crystal conjugated particles in strip cast Nd-Fe-B flakes, which may facilitate to minimize the volume of these detrimental intragranular phases during the strip casting process. [ABSTRACT FROM AUTHOR]

Thermo-mechanical processing with warm-deformation in the ferrite is a promising pathway towards manufacturing of large volumes of steels with ultrafine grain sizes. We apply this processing to HSLA steels to invoke grain refinement coupled with strengthening arising from microalloying. The aim is to systematically unravel the strengthening via the addition of 'modern' microalloying elements Mo versus Cr besides Nb. These elements have been proposed to provide significant additional strengthening during such processing but the mechanisms yet remain unknown. Therefore, three model Fe-1.6Mn-0.04C-0.1Nb+0.5Mo/Cr steels were warm-rolled at ∼600 °C with an overall reduction of 50% followed by ageing. It was found that Mo leads to an increase in hardness of ∼20% compared to the base alloy, whereas Cr provides only a minor hardening increment. SEM, EBSD, TEM and atom probe were used to reveal the beneficial effect of Mo versus Cr. It was found that Mo is more effective delaying dislocation recovery. We also report that Mo partitions into nanoscale Nb–C solute clusters and precipitates of NbC and Fe 3 C during ageing, retarding the coarsening of these phases. However, Cr was found to partition into Fe 3 C only, and does not contribute to the nature of the dispersion of clusters and NbC. Image 1 • Systematic study of hardening through additions of Cr/Mo in a Nb-HSLA steel deformed in the ferrite. • Mo provides significant strengthening by precipitation, clustering, solute drag and interface segregation. • Mo partitions into NbC and cementite impeding their growth upon ageing at 600 °C. • Cr partitions into and impedes growth of cementite upon ageing at 600 °C only. • Nb–Mo is a more promising design approach than Nb–Cr for ultrafine-grained strong and tough HSLA steels. [ABSTRACT FROM AUTHOR]

Solute segregation of Zn, Mg and Cu in and around Al 3 (Sc,Zr) precipitates in an Al-Zn-Mg-Cu-Sc-Zr alloy was systematically studied using atom probe microscopy, aberration-corrected scanning transmission electron microscopy and first-principles simulations. Results show that the Al 3 (Sc,Zr) precipitates occur as a Sc-rich 'core' and Zr-rich 'shell' structure. Zn segregates to the Zr-rich shell of Al 3 (Sc,Zr) precipitates and substitute mainly for the Al atoms, and the Zn segregation intensifies with increasing ageing time. Mg and Cu atoms segregate to the Zr-rich shell during the early stages of ageing, while the Mg atoms prefer the Al-matrix with longer ageing time. Density functional theory calculations demonstrate that such segregation is energetically favored and highlight the diverse role of Al 3 (Sc,Zr) in influencing the distribution of the major alloying elements. Unlabelled Image • Segregation of Zn, Mg and Cu to Al 3 (Sc,Zr) in Al-Zn-Mg-Cu-Sc-Zr alloy was studied. • Al 3 (Sc,Zr) precipitates occur as a Sc-rich 'core' and Zr-rich 'shell' structure. • Zn segregates to the Zr-rich shell of Al 3 (Sc,Zr) and substitutes for the Al atoms. • Mg and Cu atoms segregate to the Zr-rich shell during the early stages of ageing. • Results using atomic-resolution microscopy are rationalized by DFT calculations. [ABSTRACT FROM AUTHOR]

Heterogeneous ferroelastic transition that produces hierarchical 90° tetragonal nanodomains via mechanical loading and its effect on facilitating ferroelectric domain switching in relaxor-based ferroelectrics were explored. Combining in situ electron microscopy characterization and phase-field modeling, we reveal the nature of the transition process and discover that the transition lowers by 40% the electrical loading threshold needed for ferroelectric domain switching. Our results advance the fundamental understanding of ferroelectric domain switching behavior. [ABSTRACT FROM AUTHOR]

Modulation of material physical and chemical properties through selective surface engineering is currently one of the most active research fields, aimed at optimizing functional performance for applications. The activity of exposed crystal planes determines the catalytic, sensory, photocatalytic, and electrochemical behavior of a material. In the research on nanomagnets, it opens up new perspectives in the fields of nanoelectronics, spintronics, and quantum computation. Herein, we demonstrate controllable magnetic modulation of α-MnO2 nanowires, which displayed surface ferromagnetism or antiferromagnetism, depending on the exposed plane. First-principles density functional theory calculations confirm that both Mn- and O-terminated α-MnO2 (1 1 0) surfaces exhibit ferromagnetic ordering. The investigation of surface-controlled magnetic particles will lead to significant progress in our fundamental understanding of functional aspects of magnetism on the nanoscale, facilitating rational design of nanomagnets. Moreover, we approved that the facet engineering pave the way on designing semiconductors possessing unique properties for novel energy applications, owing to that the bandgap and the electronic transport of the semiconductor can be tailored via exposed surface modulations. [ABSTRACT FROM AUTHOR]