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A survey of published literature reveals a difference in the density of amorphous and crystalline solids (organic and inorganic) on the order of 10%–15%, whereas for metallic alloys, it is found to be typically less than 5%. Standard geometric models of atomic packing can account for the polymeric and inorganic glasses without requiring changes in interatomic separations (bond lengths). By contrast, the relatively small difference in density between crystalline and glassy metals (and metallic alloys) implies variations in interatomic separations due to merging orbitals giving rise to reduced atomic volumes. To test this hypothesis, quantum density functional theory computations were carried out on ordered and irregular clusters of aluminum. The results point to decreasing interatomic distances with decreasing coordination, from which one can deduce that the geometrical method of random hard sphere packing significantly underestimates the densities of amorphous metallic alloys. [ABSTRACT FROM AUTHOR]

Abstract The capability of precisely determining the atomic identity and position, coupled with an understanding of the inter-atomic interactions is crucial to enabling microstructure-property relationships in modern materials science. Two approaches to the investigation of materials at the atomic-scale are atom probe microscopy (APM) and density functional theory (DFT). On the one hand, APM offers an ultimate in 3D elemental analysis by determining the chemical identity and atomic position in a material. On the other, first principles DFT simulations allow the prediction of atomic structure and, critically, the electronic structure which is the gateway to calculating the real-world properties of materials. Both approaches are undertaken at the atomic-scale, and so are intrinsically complementary. This paper provides a review of the opportunities and challenges in combining these approaches to do materials science. We first summarise the status of these approaches and set out a framework for the current main workflows by which APM experiments inform DFT simulations and vice-versa. We point out certain gaps between the approaches and ways that these may be bridged via a series of case-studies organised into the aforementioned workflow framework. [ABSTRACT FROM AUTHOR]

We have investigated the detailed microstructural mechanisms associated with the excellent crystal plasticity and ultra-fine grain refinement observed under high strain-rate deformation of Mg alloys, focusing on ZK60. Firstly, we have identified the clear formation of stacking faults in deformation-induced twinned crystal segments. Specifically, we have found that intrinsic I 1 and I 2 stacking faults bounded by 1 6 < 2 ¯ 023> and 1 3 <10 1 ¯ 0> partial dislocations, respectively, were found to occur in very high number densities within the twins. This was due to the high Schmid factor for stacking fault shearing in twins and the critical role that twin boundaries played in emitting partial dislocations. Secondly, we have clarified the interplay between twinning and stacking faults on the enhanced crystal plasticity. Apart from the strain accommodated by the extensive twinning itself, we propose that the improved plasticity during high strain-rate deformation is mainly due to the nucleation of 1 3 < 11 ¯ 23>{11 2 ¯ 2} dislocation within twins, which provides enough independent slip systems to achieve a homogeneous deformation in the material. Finally, we have demonstrated the interplay between twinning and stacking fault formation on the nucleation of new grains via dynamic recrystallisation. The twin boundaries and stacking faults, especially those of the I 1 type, facilitate the formation of low-angle grain boundaries that can subsequently transition into high-angle grain boundaries, and form ultra-fine dynamically recrystallised grains. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the strategy underpinning the formation and operation of the Australian Microscopy & Microanalysis Research Facility (AMMRF). The governance and funding of the organisation are described and the advantages and achievements of a nationally coordinated facility for microscopy and microanalysis are set out. Selected data are presented that benchmark the performance of the facility, describe the economic impact and demonstrate the impact on the quality of research outcomes as a result of operating national collaborative research infrastructure for microscopy and microanalysis. [Copyright &y& Elsevier]

Abstract: High-resolution TEM was used to study the Er distribution and the formation of Si nanocrystallites in Er-doped SiO2 films fabricated by laser ablation. Formation of Er nanoparticles up to 40nm in diameter were observed and characterised. [Copyright &y& Elsevier]

Additive manufacturing (AM) of alloys has attracted much attention in recent years for making geometrically complex engineering parts owing to its unique benefits, such as high flexibility and low waste. The in-service performance of AM parts is dependent on the microstructures and grain boundary networks formed during AM, which are often significantly different from their wrought counterparts. Characteristics such as grain size and morphology, texture, and the detailed grain boundary network are known to control various mechanical and corrosion properties. Advanced understanding on how AM parameters affect the formation of these microstructural characteristics is hence critical for optimising processing parameters to unlock superior properties. In this study, the difficult-to-weld nickel-based superalloy Inconel 738 was fabricated via electron-beam powder bed fusion (EPBF) following linear and random scanning strategies. Random scanning resulted in finer, less elongated, and crystallographically more random grains compared to the linear strategy. However, both scanning strategies achieve unique high grain structure stability up to 1250 ℃ due to the presence of carbides pinning the grain boundaries. Despite significant difference in texture and morphology, majority of grains terminated on {100} habit planes in both linear and random built samples. The results show potential for controlling grain boundary networks during EPBF by tuning scan strategies. • Electron powder bed fusion Inconel 738 builds possess thermally stable grain structures up to 1250 ℃. • Change of scanning strategy from linear to random results in texture randomization and grain refinement. • The unique thermal stability can be due to the pinning of grain boundaries by carbides. • Grain boundaries mostly terminate on {100} habit planes irrespective of the scanning strategy. [ABSTRACT FROM AUTHOR]

Pair distribution function (PDF) analysis is a powerful technique to understand atomic scale structure in materials science. Unlike X‐ray diffraction (XRD)‐based PDF analysis, the PDF calculated from electron diffraction patterns (EDPs) using transmission electron microscopy can provide structural information from specific locations with high spatial resolution. The present work describes a new software tool for both periodic and amorphous structures that addresses several practical challenges in calculating the PDF from EDPs. The key features of this program include accurate background subtraction using a nonlinear iterative peak‐clipping algorithm and automatic conversion of various types of diffraction intensity profiles into a PDF without requiring external software. The present study also evaluates the effect of background subtraction and the elliptical distortion of EDPs on PDF profiles. The EDP2PDF software is offered as a reliable tool to analyse the atomic structure of crystalline and non‐crystalline materials. [ABSTRACT FROM AUTHOR]

We report an unexpected yet significant precipitation-strengthening effect with remarkable thermal stability in an otherwise conventionally non-heat treatable AA3104 aluminium alloy. We reveal that a minor addition of Cu plays a critical role in the alloy's strength and thermal stability, and explain the underpinning mechanisms. The primary strengthening β′ phase can be engineered to exhibit distinctive structural characteristics, including regularly-spaced Cu atom columns at the coherent β′ /Al interfaces, stacking faults and resultant domains. Our atomistic simulations rationalise that these microscopic characteristics are directly promoted by the Cu addition. The Cu-decorated interfaces promote β′ phase nucleation and result in strong, directional covalent-like Cu-Si bonding at the β′ /Al interfaces. Specifically, the interfacial Cu columns increase the work of separation of the habit-plane interfaces and reduce the interface energy, resulting in significant strengthening and stabilising effects. The Cu columns also facilitate the stacking fault formation in the β′ phase. Collectively, these features enhance the strengthening effect and thermal stability of the precipitates. This study demonstrates the potential for exploring "new" features in "old" alloys to advance alloy science and technology. [Display omitted] [ABSTRACT FROM AUTHOR]

Additive manufacturing of bulk metallic glasses (BMGs) has opened this material class to an exciting new range of potential applications, as bulk-scale, net-shaped amorphous components can be fabricated in a single step. However, there exists a critical need to understand the structural details of additive manufactured BMGs and how the glassy structure is linked to the mechanical properties. Here, we present a study of structure and property variations along the build height for a laser powder bed fusion (LPBF) processed Zr-based BMG with composition Zr59.3Cu28.8Nb1.5Al10.4 commercially termed AMZ4, using hardness testing, calorimetry, positron annihilation spectroscopy, synchrotron X-ray diffraction, and transmission electron microscopy. A lower hardness, more rejuvenated glassy structure was found at the bottom of the build compared to the middle region of the build, with the structure and properties of the top region between the two. Such differences could not be attributed to variability in chemical composition or crystallisation; rather, the softer bottom region was found to have a larger medium range order cluster size, attributed to heat dissipation into the build plate during processing, which gave faster cooling rates and less reheating compared to the steady-state middle of the build. However, at the top of the build less reheating occurs compared to the middle, leading to a somewhat softer and less relaxed state. [ABSTRACT FROM AUTHOR]

A series of novel CoCrFeNi-based high-entropy alloys containing Sc and C were designed. These HEAs exhibited hardness, fracture toughness and wear resistance comparable or better than a range of selected benchmark systems. Microstructurally, we observed composite microstructures comprising variously a Sc-rich intermetallic phase, a sigma phase and an FCC solid solution phase within which precipitated M23C6 carbides. The Sc-rich intermetallic phase possessed a stoichiometry close to (Co, M)2(Sc, M), where M = Ni and Fe. As the carbon content increased, the hardness levels 'softened' from 799 VHN (C-free) to 674 VHN (C = 4 at.%), though the fracture toughness was increased ~ 112%. At the same time, the specific wear rate was enhanced from 0.33 × 10−3 to 0.14 × 10−3 mm3·(N m)−1. The effectiveness of these microstructures in balancing high hardness, crack deflection and a relatively low wear rate was attributed to the enhanced stability of the FCC solid phase as the C content was increased. [ABSTRACT FROM AUTHOR]

Cluster-strengthened Nb-microalloyed strip cast steels are of interest as clustering during aging leads to an enhancement in strength without compromising ductility, resulting in desirable mechanical properties. However, the precise strengthening mechanism is not well understood. Using in situ heating transmission electron microscopy, clustering was found to impede the movement of dislocations during aging. The attractive combination of ductility and strength was attributed to the effects of recovery and the restricted movement of dislocations through clustering. [Copyright &y& Elsevier]

Abstract: We electrostatically model a local electrode atom probe microscope using the commercial software IES LORENTZ 2D v9.0 to investigate factors affecting the reconstruction parameters. We find strong dependences on the specimen geometry and voltage, and moderate dependences on the tip-aperture separation, which confirm that the current approach to atom probe reconstruction overlooks too many factors. Based on our data, which are in excellent agreement with known trends and experimental results, we derive a set of empirical relations which predict the values of the reconstruction parameters. These may be used to advance current reconstruction protocols by enabling the parameters to be adjusted as the specimen geometry changes. [Copyright &y& Elsevier]

Additive manufacturing (AM) is well-known for its capability to produce and repair intricate parts e.g., Ni-based superalloy components used in aero-engine applications. However, a comprehensive understanding of the microstructure evolution and its link to properties remains elusive, with gaps in the through-process evolution of γ grains, γ', γ'', δ, and other phases in response to thermal cycling. The outstanding challenge here is to observe these transformations dynamically during the 3D printing process, as this usually requires complex in-situ measurements. Here we apply a different approach to systematically reveal the impact of thermal cycling on the solid-state microstructure evolution of IN718, via a combination of physical simulations and thermo-kinetic modelling. We replicate the thermal cycles IN718 experiences during laser directed energy deposition. Solid-state thermal cycles are shown to have minor effects on the grain morphology due to short holding times at critical temperatures, however, they do induce plastic strain accumulation. Significantly, we show how thermal cycling influences the evolution of γ', γ", and δ phases. While high initial peak temperatures inhibit the precipitation of γ', γ", and δ phases, prolonged thermal cycling to gradually decreasing peak temperatures promotes their precipitation. The δ phase forms along grain and twin boundaries, while both γ' and γ" predominantly precipitate in Nb-enriched regions, causing heterogeneities in hardness. Our results underpin the suitability of physical simulations for replicating superalloy AM, highlighting its potential as a tool to advance the current limited understanding of the microstructure and property evolution. [Display omitted] • Physical and thermo-kinetic simulation of solid-state thermal cycling in L-DED IN718. • Physical Gleeble experiments show excellent correlation with actual L-DED process. • Variation in γ′, γ′′, and δ precipitates correlates with hardness. • Solid-state thermal cycling affects γ′, γ′′, and δ morphology in individual layers. • Solid-state thermal cycling has negligible influence on grain morphology. [ABSTRACT FROM AUTHOR]

Additive manufacturing has made the fabrication of large-dimensioned bulk metallic glasses (BMGs) achievable; however, questions remain regarding how to control the processing parameters to obtain dense and fully amorphous BMGs with desirable mechanical properties. Here, laser powder bed fusion (LPBF) was used to produce dense and fully amorphous Zr 59.3 Cu 28.8 Nb 1.5 Al 10.4 BMG samples from two different starting powders within a large processing window of laser powers and scanning speeds. X-ray diffraction (XRD) revealed that fully amorphous XRD patterns were obtained for samples with high relative densities (>99 %) when the LPBF energy density ranged from ∼20 J/mm3 up to ∼33 J/mm3 for coarse powder with low oxygen and up to ∼30 J/mm3 for fine powder with higher oxygen. For the fully XRD amorphous samples, strength and hardness increased with increasing energy density while the relaxation enthalpy and ductility decreased. Transmission electron microscopy revealed that the softer samples contain larger medium range order clusters within the amorphous matrix. With higher LPBF energy density, high relative density was still achieved along with devitrification and embrittlement. While lower energy densities below ∼20 J/mm3 could retain a fully XRD amorphous structure, such samples had relative densities <99 %. When comparing the two powders, the coarse powder with four times lower oxygen content gave better glass forming ability, compression ductility up to 6 % plastic strain, and fracture toughness up to ∼38 MPa√m. These findings demonstrate that it is possible to tailor the structure and mechanical properties of BMGs by tuning the LPBF process parameters within a wide processing window. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: This paper outlines an inverse analysis approach aimed at the identification of the mechanical properties of metallic materials based on the experimental results obtained from indentation tests. Previous work has shown the ill-posed nature of the inverse problem based on the load-penetration curve when dealing with mystical materials, which exhibit identical indentation curves even if possessing different yield and strain-hardening properties. For this reason, an additional measurement is used in the present study as input for the inverse analysis which consists of the maximum pile-up height measured after the indentation test. This approach lends itself for practical applications as the load-penetration curve can be easily obtained from commonly available micro-indenters while the pile-up present at the end of the test can be measured by different instruments depending on the size of the indented area, for example by means of an atomic force microscope or a laser profilometer. The inverse analysis procedure consists of a batch deterministic approach, and conventional optimization algorithms are employed for the minimization of the discrepancy norm. The first part of the paper outlines how the inclusion of both the maximum height of the pile-up and the indentation curve in the input data of the inverse analysis leads to a well-defined inverse problem using parameters of mystical materials. The approach is then applied to real experimental data obtained from three sets of 2024 Al alloy samples prepared using different age-hardening treatments. The accuracy of the identification process is validated against the mechanical properties obtained independently from standard tensile coupon tests. The reported results highlight the advantages of the proposed methodology in identifying the elastic modulus, yield stress and strain-hardening coefficient while minimizing the amount of information required to be collected from the experimental indentation tests. [Copyright &y& Elsevier]

Pseudo-binary solute clustering in crystals was modelled analytically using expressions for the site-occupation probabilities that depend on solute concentration, crystallography and nearest-neighbour short-range order. Up to a cluster-size of 10 solute atoms, theoretical random and non-random cluster-size distributions were calculated for diamond (Si), simple (Mn), body centred (Fe) and face centred (Al) cubic lattices and the hexagonal close-packed (Mg) lattice. These calculations were then used to generate simulations of atom probe data, by stochastically removing atoms to simulate the effect of detector efficiency. These simulations may be used to determine self-consistent clustering algorithm parameters, measure short range order parameters and recover the effect of detector efficiency on the observed frequency distributions. [ABSTRACT FROM AUTHOR]

Abstract: In this report we investigate the onset and evolution of precipitation in the early stages of ageing in the alloy WE 91, a variant of the Ni–Fe–Cr superalloy Inconel 718 (IN718). Transmission electron microscopy and atom probe tomography were used to study the size and volume fraction of γ′ and γ″ precipitates and the extent of pre-precipitate clustering of Al/Ti and Nb. Co-located γ′ and γ″ precipitates were observed from the shortest ageing times that precipitates could be visualised using atom probe. At shorter times, prior to the observation of precipitates, clustering of Al/Ti and Nb was shown to occur. The respective volume fraction of the γ′ and γ″ precipitates and the clustering of Al/Ti and Nb suggest that γ″ nucleates prior to γ′ during ageing at 706°C for this alloy. [ABSTRACT FROM AUTHOR]

The microstructures of nanostructured Ti–Si–N hard coatings were investigated by transmission electron microscopy and pulsed laser atom probe. C and O impurities were detected. No evidence of increased Si levels at the grain boundaries was found, suggesting that Si is either in the form of a layer too thin to be detected using the techniques employed or in the form of a solid solution of SiN clusters. [Copyright &y& Elsevier]

Abstract: Laser-assisted atom probe tomography was used to investigate the nanostructure and composition of high-performance, ultra-hard Ti–Si–N nanocomposite films. However, the quality of data is heavily dependent on analysis conditions. In order to obtain reliable data from these, and other ‘less conducting’ specimens, the analysis parameter space was thoroughly investigated to optimize the mass resolution and hit multiplicity obtained in atom probe tomography. Geometric factors including tip radius and shank angle were found to play a significant role in mass resolution but had no apparent effect on the number of multiple hits observed. Increased laser energy led to a gradual increase in the number of single hits, but a modest improvement in mass resolution. The influence of other instrumental factors including detection rate and base temperature was investigated separately. Preliminary PLAP results are presented, and correlated with TEM analysis of the microstructure of the film. [Copyright &y& Elsevier]

Atomically thin sheets of carbon known as "graphene" have captured the imagination of much of the scientific world during the past few years. Although these single sheets of graphite were under our noses for years—within technologies ranging from the humble pencil, which has been around since at least 1565 (Petroski, H. The Pencil: A History of Design and Circumstance; Alfred A. Knopf: New York, 1993), to modern nuclear reactors—graphene was merely considered as part of graphite's crystal structure until 2004, when Novoselov, Geim, and colleagues (Science 2004, 306, 666-669) first presented some of the surprising electrical properties of graphene layers they had isolated by mechanically peeling sheets off graphite crystals. Today, graphene's unique electronic structures and properties, bolstered by other intriguing properties discovered in the intervening years, threaten the dominance of carbon nanotubes, a more mature allotrope of carbon, in potential applications from electronics to sensors. In this review, we will consider the promise of graphene for producing small-scale gas sensors for environmental monitoring. [ABSTRACT FROM AUTHOR]

Abstract: In situ bulk polymerization of polymethylmethacrylate (PMMA)–clay nanocomposites was initiated with a benzoyl peroxide/amine redox couple at room temperature. This was accomplished with a newly synthesized cationic molecule—containing an aliphatic chain and an aromatic tertiary amine—that was ion exchanged onto the clay surface in order to control the rate of intragallery polymerization relative to that of extragallery polymerization. The rate and location of initiation significantly affected the degree of dispersion of the silicate layers. Accelerating intragallery polymerization of clay with low cation exchange capacity was found to produce the maximum interlayer distance as evident from transmission electron microscope images. [Copyright &y& Elsevier]

Abstract: Cross-linked polyacrylamide (C-PAM) hydrogels were employed to reduce the crystal size of SAPO-34 molecular sieves in a vapor-phase transport process. A wide size distribution of SAPO-34 crystals, ranging from a few nanometers to 3–5μm, was produced when the synthesis precursor gels contained the appropriate amount of C-polyacrylamide (C-PAM) hydrogels. Specifically, these dispersions of SAPO-34 crystallites were formed when the molar ratio of polyacrylamide to Al2O3 was between 0.29 and 043. These crystals exhibited a BET surface area of 342–325m2/g, micropore volume of 0.15–0.12cm3/g, and TEA entrapment of 9.3–8.0%. Microanalysis using EDXS revealed the presence of residual precursor materials, such as phosphorus, supporting the fact that our samples possessed a lower BET surface area and micropore volume as compared with the SAPO-34 prepared by hydrothermal method in the literature. [Copyright &y& Elsevier]

Objective. The present study, divided into two parts, aimed to compare the strength, fracture toughness and microstructure of a range of all-ceramic materials. In part I, three hot-pressed glass–ceramics (IPS-Empress, Empress 2 and a new experimental ceramic) and alumina glass-infiltrated ceramics (In-Ceram Alumina), processed by both slip casting and dry pressing, were compared.Methods. Tensile strength was appraised on 10 bar-shaped specimens (20×4×1.2 mm3) for each material with the three-point bending method; the fracture toughness was measured from 20 specimens (20×4×2 mm3), by using the indentation strength technique. Data were compared with ANOVA and the Sheffe´ post hoc test (p=0.05). The volume fraction of each phase, the dimensions and shapes of the grains, porosity and the crack patterns were investigated using SEM.Results. The average and standard deviation in strength (MPa) and fracture toughness (MPa m1/2) were: IPS-Empress 106(17)1, 1.2(0.14)1; Empress 2 306(29)2, 2.9(0.51)2, new experimental ceramic 303(49)2, 3.0(0.65)2, In-Ceram Alumina dry-pressed 440(50)2, 3.6(0.26)2, In-Ceram Alumina slip 594(52)3, 4.4(0.48)3. Values with the same superscript number showed no significant statistical difference. Microscopy revealed the relationship between the glass matrix and the crystalline phase and the characteristics of the latter were correlated to the strengthening and toughening mechanisms of these glass–ceramics.Significance. The mechanical properties and microstructure of core materials have been advocated as crucial to the clinical long-term performance of all-ceramic dental restorations. This investigation provides the clinician with data regarding strength, fracture toughness and microstructure of a broad range of current materials. [Copyright &y& Elsevier]

Objective: The present study is the second part of an investigation of strength, fracture toughness and microstructure of nine all-ceramic materials. In the present study, DC Zirkon, an experimental yttria partially stabilized zirconia, In-Ceram Zirconia slip and In-Ceram Zirconia dry-pressed were compared.Methods: Strength was appraised on ten bar-shaped specimens for each material (20×4×1.2 mm) with the three-point bending method. The fracture toughness (Indentation Strength) was measured on twenty specimens (20×4×2 mm) for each ceramic. The volume fraction of each phase, the dimensions and shapes of the grains and the crack pattern were investigated with SEM. Phase transformation was investigated with X-ray diffraction. Data were compared with an ANOVA and Sheffe´ post hoc test (p=0.05).Results: Means of strength (MPa) and fracture toughness (MPa m1/2) values and their standard deviation were: In-Ceram Zirconia dry-pressed 476 (50)1, 4.9 (0.36)1; In-Ceram Zirconia slip 630 (58)2, 4.8 (0.50)1; the experimental yttria partially stabilized zirconia 680 (130)2, 5.5 (0.34)2; DC-Zirkon 840 (140)3, 7.4 (0.62)3. Values with the same superscript number showed no significant statistical difference. Microscope investigation and X-ray diffraction revealed the important role played by the tetragonal to monoclinic phase transformation and by the relationship between the glassy matrix and the crystalline phase in the strengthening and toughening mechanisms of these ceramics.Significance: the zirconia-based dental ceramics are stronger and tougher materials than the conventional glass-ceramics. Better properties can have positive influence on the clinical performance of all-ceramic restorations. [Copyright &y& Elsevier]

Ti-6Al-4 V is a popular alloy in additive manufacturing (AM) due to its applications in the biomedical implants and aerospace industries where the complex part geometries allowed by AM provide cost and performance benefits. Ti-6Al-4 V goes through a β → α' transformation after solidification which is known to experience variant selection, e.g., through the formation of clusters of variants which, when situated together, partially accommodate the strain of the phase transformation. During electron beam powder bed fusion AM, an in situ decomposition of α' martensite occurs during the cyclic reheating caused by melting successive layers, resulting in α + β microstructures. How variant selection influences the evolution beyond the initial rapid cooling remains an open question. Using 3D electron backscatter diffraction, we provide a clearer understanding without ambiguity from sectioning effects of how α' decomposes into microstructures with distinct morphologies and variant/intervariant distributions. We extract quantitative 3D information on the various intervariant boundaries networks formed in samples printed using three different electron beam scanning strategies. This shows that differing mechanisms during the decomposition result in a shift from self-accommodating clusters in an acicular microstructure, to either the preferred growth of six variants in a basketweave microstructure, or to a colony microstructure where variant selection is determined by prior-β grain boundaries. We propose a new representation of the misorientations arising from the Burgers orientation relationship, which we refer to as intervariant network diagram, to reveal how variant selection during the martensitic transformation and subsequent decomposition leads to the intervariant boundary networks observed. This holistic understanding of the microstructural evolution has the potential to allow tailoring of microstructures and properties for specific applications. [ABSTRACT FROM AUTHOR]

• Reconstruction method for APT requiring information from only a single crystallographic pole • Accounts for dynamic variations in reconstruction parameters • Single pole crystallography mediated reconstruction protocol is largely automated Spatially accurate atom probe tomography reconstructions are vitally important when quantitative spatial measurements such as distances, volumes and morphologies etc. of nanostructural features are required information for the researcher. It is well known that the crystallographic information contained within the atom probe data of crystalline materials can be used to calibrate the tomographic reconstruction. Specifically, the crystallographic information projected into the field evaporation images is used. This offers a powerful and accurate enhancement of the atom probe technique. However, this is often difficult to do in practice. In previously reported approaches, it was necessary to index at least two poles to compute the image compression factor ' ξ' and observe crystallographic planes in at least one of the pole regions to obtain a measure of the field factor ' k f ' while also manually accounting for a change in reconstruction parameters throughout the dataset. Not only is this error-prone and time consuming, it does not work for materials that exhibit limited crystallographic information in their field evaporation image. Here, we extend the applicability of the crystallographic calibration of atom probe data by proposing a reconstruction methodology where only one pole with observable lattice planes is required in the projected detector image. Our proposal also accounts for dynamic variations in the reconstruction parameters throughout the 3D dataset. The method is simpler and significantly faster to implement and is applicable to more atom probe situations than previously approaches. Our single-pole crystallography mediated reconstruction (SP-CMR) utilizes the Hawkes-Kasper projection model (equivalent to the equidistant-azimuthal projection model) and the direct fourier (DF) fit algorithm to determine the precise reconstruction parameters required to produce flat atomic planes. It is applied to experimental Al and highly Sb-doped Si data. The discrepancies between the spatial dimensions of the SP-CMR reconstructions compared to uncalibrated reconstructions are visually apparent. Consistent plane spacings and angles between crystallographic directions matching the theoretically known values for each crystal structure are demonstrated. [ABSTRACT FROM AUTHOR]

[Display omitted] Bulk metallic glasses (BMGs) are materials with outstanding strength and elastic properties that make them tantalizing for engineering applications, yet our poor understanding of how their amorphous atomic arrangements control their broader mechanical properties (hardness, wear, fracture, etc.) impedes our ability to apply materials science principles in their design. In this work, we uncover the hierarchical structure that exists in BMGs across the nano- to microscale by using nanobeam electron diffraction experiments. Our findings reveal that local hardness of microscale domains decreases with increasing size and volume fraction of atomic clusters with higher local medium range order (MRO). Furthermore, we propose a model of ductile phase softening that will enable the future design of BMGs by tuning the MRO size and distribution in the nanostructure. [ABSTRACT FROM AUTHOR]

Hydroxyapatite nanoparticles (HAP NPs) are important for medicine, bioengineering, catalysis, and water treatment. However, current understanding of the nanoscale phenomena that confer HAP NPs their many useful properties is limited by a lack of information about the distribution of the atoms within the particles. Atom probe tomography (APT) has the spatial resolution and chemical sensitivity for HAP NP characterization, but difficulties in preparing the required needle‐shaped samples make the design of these experiments challenging. Herein, two techniques are developed to encapsulate HAP NPs and prepare them into APT tips. By sputter‐coating gold or the atomic layer deposition of alumina for encapsulation, partially fluoridated HAP NPs are successfully characterized by voltage‐ or laser‐pulsing APT, respectively. Analyses reveal that significant tradeoffs exist between encapsulant methods/materials for HAP characterization and that selection of a more robust approach will require additional technique development. This work serves as an essential starting point for advancing knowledge about the nanoscale spatiochemistry of HAP NPs. [ABSTRACT FROM AUTHOR]

The development of high-performance Nd–Dy–Fe–B magnets that minimise the consumption of the scarce rare earth (RE) element Dy remains a major global scientific and technological quest. Here, we designed an alloy microstructure comprising of a uniform Dy-lean core–Dy-rich shell in a series of multi-main-phase (MMP) Nd–Dy–Fe–B magnets. The resulting MMP Dy1 and Dy3 magnets with an overall Dy level of 1 and 3 wt.% possessed values of 0.48 and 0.29 T/wt.% of coercivity increment per unit weight percentage of the Dy addition, respectively. Most importantly, the resulting MMP Dy3 magnet exhibited a high coercivity (2.38 T), an excellent thermal stability of the coercivity (| β | = 0.531%/°C), a high squareness factor (> 95%), all with little diminishment in the remanent magnetisation (1.35 T) and maximum energy product (43.6 MGOe). These properties are superior to the currently available sintered Nd–Dy–Fe–B magnets which utilise higher levels of Dy of 5 wt.%. Via magnetic and multi-scale microstructural characterisation experiments and micromagnetic simulations, the formation of the Dy-lean core–Dy-rich shell microstructure is rationalised via solid-state-diffusion and solution reprecipitation during liquid-phase sintering. The Dy-lean core–Dy-rich shell microstructure and the non-ferromagnetic low-Fe RE-rich grain boundary phase led to the synergistic magnetic performance. This is significant in the context of the MMP Nd–Dy–Fe–B magnets being applied to large-scale production. The present work establishes a pathway for the more sustainable utilisation of Dy in permanent magnets via formation of a uniform core–shell microstructure. [Display omitted] [ABSTRACT FROM AUTHOR]

• Al, Ni and Zr alloys used to compare Cameca Invizo 6000 atom probe to LEAPs. • Field-of-view, mass resolving power, sample yield are greater on Invizo 6000. • Routine analysis of metal-oxide interfaces demonstrated. The CAMECA Invizo 6000 atom probe microscope uses ion optics that differ significantly from the local electrode atom probe (LEAP). It uses dual antiparallel deep ultraviolet lasers, a flat counter electrode, and a series of accelerating and decelerating lenses to increase the field-of-view of the specimen without reducing the mass resolving power. In this work we characterise the performance of the Invizo 6000 using three material case studies: a model Al-Mg-Si alloy, a commercially-available Ni-based superalloy, and a Zr alloy, using a combination of air and vacuum-transfer between instruments. The ion optics of the Invizo 6000 significantly increase the field-of-view compared to the same specimen on a LEAP 4000 X Si. We also observe a significant increase in specimen yield, especially for the Zr alloy. These results combine to make the Invizo 6000 well-suited to research projects requiring large analysis volumes, particularly so for traditionally difficult samples such as oxides. [ABSTRACT FROM AUTHOR]

The article discusses the study of the giant tuning of ferroelectricity in single crystals by thickness engineering. Topics discusses include thickness effect and mechanical tuning behavior such as strain engineering in thin-film ferroelectrics have been extensively studied and widely used to tailor the ferroelectric properties; and the results provide important insights in tuning polarization/domain of single-crystal ferroelectric via sample thickness engineering.

Additive manufacturing is a promising alternative method for fabricating components of Ni-based superalloys which are difficult to cast, form and join. However, typical thermal cycles associated with laser powder bed-fusion techniques suppress the formation of desirable microstructures containing γ′ particles, necessitating long-time post-process heat treatments. Here we report in-situ precipitation of γ′ (L12-ordered) particles and carbides during electron-beam powder bed-fusion of Inconel-738. The γ′ particles are homogenously distributed across the build and exhibit a multimodal size distribution. Based on atom-probe microscopy, we propose a eutectic reaction and multiple nucleation, growth, coarsening and dissolution bursts during thermal cycling as formation mechanism. [ABSTRACT FROM AUTHOR]

The microstructure of WC-(Co+Ru) cemented carbides was studied using transmission Kikuchi diffraction (TKD). We report that the Co FCC grains contain Σ3-annealing twins which undergo an incomplete martensitic transformation to form Co HCP laths on cooling below T Ms. The parent Co FCC and product Co HCP phases are related via the Shoji-Nishiyama orientation relationship. Four variants of the Co HCP plates exhibit a special misorientation of 70.5 ± 0.2° 〈 11 2 ¯ 0 〉. A higher transformed fraction was observed in the sample possessing the lower binder content and finer WC grains. We suggest that this is due to the availability of more WC-binder interfaces, which facilitate Co HCP plate nucleation. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Boron (B) and phosphorous (P) co-doped colloidal silicon nanocrystals (Si NCs) have unique size-dependent optical properties, which lead to potential applications in optoelectronic and biomedical applications. However, the microstructure of the B and P co-doped colloidal Si NCs – in particular, the exact location of the dopant atoms in real space, has not been studied. A lack of understanding of this underlying question limits our ability to better control sample fabrication, as well as our ability to further develop the optical properties. To study the microstructure, a process enabling atom probe tomography (APT) of colloidal Si NCs was developed. A dispersion of colloidal Si NCs in a SiO 2 sol-gel solution and a low temperature curing are demonstrated as the key sample preparation steps. Our APT results demonstrate that a B-rich region exists at the surface of the Si NCs, while P atoms are distributed within the Si NCs. First principles density functional theory calculations of a Si NC embedded in SiO 2 matrix reveal that P atoms, which always prefer to reside inside a Si NC, significantly influence the distribution of B atoms. Specifically, P atoms lower the B diffusion barrier at Si/SiO 2 interface and stabilize B atoms to reside within individual Si NCs. We propose that the B-modified surface changes the chemical properties of the Si NCs by (i) offering chemical resistance to attack by HF and (ii) enabling dispersibility in solution without aggregation. Image 1 [ABSTRACT FROM AUTHOR]

Modern wide field-of-view atom probes permit observation of a wide range of crystallographic features that can be used to calibrate the tomographic reconstruction of the analyzed volume. In this study, methodologies to determine values of the geometric parameters involved in the tomographic reconstruction of atom probe data sets are presented and discussed. The influence of the tip to electrode distance and specimen temperature on these parameters is explored. Significantly, their influence is demonstrated to be very limited, indicating a relatively wide regime of experimental parameters space for sound atom probe tomography (APT) experiments. These methods have been used on several specimens and material types, and the results indicate that the reconstruction parameters are specific to each specimen. Finally, it is shown how an accurate calibration of the reconstruction enables improvements to the quality and reliability of the microscopy and microanalysis capabilities of the atom probe. [ABSTRACT FROM AUTHOR]

Abstract Traditional approaches for increasing the intrinsic coercivity of magnets typically come at the expense of remanence, a dilemma known as intrinsic coercivity-remanence trade-off, leading to a substantial reduction of maximum energy product. New metallurgical processing might offer the possibility of overcoming this trade-off. Here, we achieve a combination of an intrinsic coercivity of 26.9 kOe, a remanence of 11.2 kG, and a maximum energy product up to 26.6 MGOe, which surpasses most of conventional Sm-Co based permanent magnets, by manipulating the gradient of domain wall energy landscape of constituent phases to realize the attractive domain wall pinning in Sm(Co,Fe,Cu,Zr) z permanent magnets. Using powerful atomic-scale analysis technique known as atom probe tomography and micromagnetic simulations, we reveal that an enlarged attractive domain wall pinning strength results in the substantial coercivity enhancement with little sacrifice of remanence and maximum energy product in the Cu-particle-alloyed magnet. These results provide atomic-level insights into the coercivity mechanism of rare earth permanent magnets, with the methodology offering exciting possibilities for quantitative analyses and prediction between compositions and magnetic properties of other magnetic materials. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract Combining transmission Kikuchi diffraction, high resolution transmission electron microscopy and atom probe tomography, we investigated an Al-Zn-Mg-Cu alloy (AA7075) processed by high-pressure torsion (HPT) at room temperature and 200 °C, with an objective to reveal the deformation-induced precipitation and segregation of elements at grain boundaries, and to study their appearance at different processing regimes. Although HPT processing at the two temperatures both induced the formation of ŋ phase, ŋ precipitates formed at the two temperatures have different chemical compositions. The increase of the HPT processing temperature increased significantly segregation of Mg and Cu at grain boundaries. The HPT–induced segregation and decomposition of the alloy have a significant effect on its mechanical strength. Our results open a way for achieving advanced mechanical properties in nanostructured metals and alloys by designing their precipitation and segregation through the control of SPD processing regimes. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

A novel thermomechanical processing that significantly augments the tensile mechanical strength of an Al-Mg-Si alloy while maintaining excellent tensile ductility is reported. Our thermomechanical processing involved solution treatment followed by low-temperature hold and asymmetric rolling with thickness reduction of 5–10%, and speed ratios between 1.1 and 1.5. The resultant strength and ductility is striking: the tensile strength levels were similar to or higher than the T6 and T8 tempers, while the tensile ductility was similar to that of the T3 temper. The mechanism of the novel thermomechanical processing is thought to be the result of solute clusters, dislocation substructures, and textural microstructural influences. [ABSTRACT FROM AUTHOR]

Atom probe microscopy (APM) is a relatively new in situ tool for measuring isotope fractions from nanoscale volumes (< 0.01 μm3). We calculate the theoretical detectable difference of an isotope ratio measurement result from APM using counting statistics of a hypothetical data set to be ± 4δ or 0.4% (2s). However, challenges associated with APM measurements (e.g., peak ranging, hydride formation and isobaric interferences), result in larger uncertainties if not properly accounted for. We evaluate these factors for Re‐Os isotope ratio measurements by comparing APM and negative thermal ionisation mass spectrometry (N‐TIMS) measurement results of pure Os, pure Re, and two synthetic Re‐Os‐bearing alloys from Schwander et al. (2015, Meteoritics and Planetary Science, 50, 893) [the original metal alloy (HSE) and alloys produced by heating HSE within silicate liquid (SYN)]. From this, we propose a current best practice for APM Re‐Os isotope ratio measurements. Using this refined approach, mean APM and N‐TIMS 187Os/189Os measurement results agree within 0.05% and 2s (pure Os), 0.6–2% and 2s (SYN) and 5–10% (HSE). The good agreement of N‐TIMS and APM 187Os/189Os measurements confirms that APM can extract robust isotope ratios. Therefore, this approach permits nanoscale isotope measurements of Os‐bearing alloys using the Re‐Os geochronometer that could not be measured by conventional measurement principles. [ABSTRACT FROM AUTHOR]

Electric fields are regarded as a promising means of graphene oxide reduction, but previous studies have only focused on pristine graphene. Here, based on first principles density functional theory calculations, we report on electric field mediated reduction of neutral and charged O and hydroxyl groups from both pristine and defective graphene sheets. The critical electric field strengths for different species are determined in facilitating a progressive and selective graphene oxide reduction. Our results demonstrate that the presence of vacancy defects significantly inhibits the effectiveness of electric fields as a means of reduction of O and OH functionals, due to the complexities that arise between the functional group and vacancy edge atoms in the presence of an applied electric field. [ABSTRACT FROM AUTHOR]

The phenomenological interplay in the segregation of phosphorus (P) and transition metal (TM) elements at grain boundaries (GBs) in steels has long been suspected to be the main contributor to temper embrittlement. However, many of the details remain unclear. Here, we investigate the segregation, co-segregation and cohesion effects of TMs (Co, Cr, Cu, Mn, Mo, Ni, Nb, Ti, V, W) along with P in various ferritic iron (α -Fe) GBs utilising density functional theory and simulations of kinetics. Our findings demonstrate that P is unlikely to cause intergranular fracture via weakened interfacial bonding when segregated by itself. Nevertheless, the stronger segregation binding of P compared to TMs can explain the ubiquitous presence of P segregated at GBs. We find that most P-TM interactions at ferritic GBs are repulsive and differ significantly from the corresponding interactions in the bulk. Due to the repulsive interactions and strong segregation binding of P, the enrichment of P over time at GBs leads to the depletion of prior-segregated cohesion-enhancing solutes at general GBs. Additionally, certain P-TM co-segregation combinations that are cohesion-lowering are energetically favoured at such GBs. We posit these mechanisms act in tandem as critical causalities of P-induced temper embrittlement in alloyed steels. Finally, we reveal a contradiction in the predicted cohesion effects of segregated P calculated in the Rice–Thomson–Wang theory of interfacial embrittlement compared to that as assessed by chemical bonding strength, calculated in the DDEC6 bond-order framework. These findings have important implications for GB engineering for interfacial cohesion. [Display omitted] [ABSTRACT FROM AUTHOR]

Understanding the band structure evolution of (AlxGa1−x)2O3 alloys is of fundamental importance for developing Ga2O3-based power electronic devices and vacuum ultraviolet super-radiation hard detectors. Here, we report on the bandgap engineering of β-(AlxGa1−x)2O3 thin films and the identification of compositionally dependent electronic band structures by a combination of absorption spectra analyses and density functional theory calculations. Single-monoclinic β-phase (AlxGa1−x)2O3 (0 ≤ x ≤ 0.54) films with a preferred (−201) orientation were grown by laser molecular beam epitaxy with tunable bandgap ranging from 4.5 to 5.5 eV. The excellent fitting of absorption spectra by the relation of (αhν)1/2∝ (hν-E) unambiguously identifies that β-(AlxGa1−x)2O3 alloys are indirect bandgap semiconductors. Theoretical calculations predict that the indirect nature of β-(AlxGa1−x)2O3 becomes more pronounced with increased Al composition due to the increased eigenvalue energy gap between M and Г points in the valence band. The experimentally determined indirect bandgap exhibits almost a linear relationship with Al composition, which is consistent with the theoretical calculation and indicates a small bowing effect and a good miscibility. The identification and modulation of (AlxGa1−x)2O3 band structures allows rational design of ultra-wide bandgap oxide heterostructures for the applications in power electronics and solar-blind or X-ray detection. [ABSTRACT FROM AUTHOR]

Atom probe tomography is a powerful microscopy technique capable of reconstructing the 3D position and chemical identity of millions of atoms within engineering materials, at the atomic level. Crystallographic information contained within the data is particularly valuable for the purposes of reconstruction calibration and grain boundary analysis. Typically, analysing this data is a manual, time-consuming and error prone process. In many cases, the crystallographic signal is so weak that it is difficult to detect at all. In this study, a new automated signal processing methodology is demonstrated. We use the affine properties of the detector coordinate space, or the ‘detector stack’, as the basis for our calculations. The methodological framework and the visualisation tools are shown to be superior to the standard method of crystallographic pole visualisation directly from field evaporation images and there is no requirement for iterations between a full real-space initial tomographic reconstruction and the detector stack. The mapping approaches are demonstrated for aluminium, tungsten, magnesium and molybdenum. Implications for reconstruction calibration, accuracy of crystallographic measurements, reliability and repeatability are discussed. [ABSTRACT FROM AUTHOR]

Ferroelectric materials have been extensively explored for applications in electronic devices because of their ferroelectric/ferroelastic domain switching behaviour under electric bias or mechanical stress. Recent findings on applying mechanical loading to manipulate reversible logical signals in non-volatile ferroelectric memory devices make ferroelectric materials more attractive to scientists and engineers. However, the dynamical microscopic structural behaviour of ferroelectric domains under stress is not well understood, which limits the applications of ferroelectric/ferroelastic switching in memory devices. Here, the kinetics of reversible and irreversible ferroelectric domain switching induced by mechanical stress in relaxor-based ferroelectrics was explored. In-situ transmission electron microscopy investigation revealed that 90° ferroelastic and 180° ferroelectric domain switching can be induced by low and high mechanical stresses. The nucleation and growth of nanoscale domains overwhelm the defect-induced pinning effect on the stable micro-domain walls. This study provides deep insights for exploring the mechanical kinetics for ferroelectric/ferroelastic domains and a clear pathway to overcome the domain pinning effect of defects in ferroelectrics. [ABSTRACT FROM AUTHOR]

In this work, the microstructure and texture evolution of the strip cast Nd-Fe-B flake has been systematically investigated by correlating multiple state-of-the-art characterization techniques. We found that (i) besides the existence of random ultrafine equiaxed grains at the wheel side of the flake, elongated (001) textured grains were formed into a V-shape zone between neighboring nucleation sites, which possibly resulted from the in-plane growth of the low energy preferred growth direction of grains (a axis). Both ultrafine random equiaxed grains and elongated (001) textured grains are detrimental to achieving a high-performance Nd-Fe-B magnet, due to the inhomogeneous grain shape and nonuniform distribution of rare earth-rich phase within these grains or along the grain boundaries, which deteriorate the alignment of the Nd-Fe-B powders in the subsequent hydrogen decrepitation process and jet milling procedure. To overcome the issues mentioned above, two potential approaches are proposed, which are increasing the nucleation rate on the wheel side and homogenization of rare earth-rich phase within grains or along grain boundaries; (ii) columnar grains containing (Nd,Pr)2Fe14B lamellae with an average spacing of ~5 μm and discontinuous rare-earth rich phase were formed in the remaining part of the flake. Accordingly, a model in terms of the microstructure and texture evolution was proposed. [ABSTRACT FROM AUTHOR]

Micrometre to sub-micrometre-scale alloys of platinum group elements (PGEs) known as Refractory Metal Nuggets (RMNs) have been observed in primitive meteorites. The Australian Synchrotron X-ray Fluorescence (XRF) beamline, in tandem with the Maia detector, allows rapid detection of PGEs in concentrations as low as 50–100 ppm at 2 μm resolution. Corroborating these analyses with traditional electron microscopy techniques, RMNs can be rapidly identified in situ within carbonaceous chondrites. These results dispute the assumption of most previous studies: that RMNs are unique to Ca–Al-rich inclusions (CAIs). We find that RMNs are, in fact, observed within all components of carbonaceous chondrites, such as the matrix, chondrules (consistent with observations from Schwander et al. (2015b) and Wang et al. (2007)), and sulphides; though the majority of RMNs are still found in CAIs. The chemistry of RMNs reveals a complex diversity of compositions, which nevertheless averages to CI chondrite abundance ratios. This implies that RMNs are the dominant, if not sole host phase for PGEs. One hundred and thirteen RMNs from this study are combined with reported compositions in the literature, and compared to condensation model compositions similar to Berg et al. (2009), RMNs derived experimentally by precipitation (Schwander et al., 2015a), host phase and host meteorite. Comparisons reveal only weak correlations between parent body processes (sulphidation) and nebular processes (condensation and precipitation) with RMN compositions. It appears that none of these processes acting in isolation or in tandem can explain the diversity observed in the RMN population. Our interpretation is that the Solar Nebula inherited an initially compositionally diverse population of RMNs from the Giant Molecular Cloud; that a variety of Solar System processes have acted on that population; but none have completely homogenised it. Most RMNs have experienced disk and asteroidal processing, but some may have retained a primordial composition. RMNs have been identified in pre-solar graphite grains (Croat et al., 2013). We anticipate that pre-solar RMNs will be present elsewhere in primitive meteorites. [ABSTRACT FROM AUTHOR]

Transmission Kikuchi diffraction (TKD) is a relatively new technique that is currently being developed for geological sample analysis. This technique utilises the transmission capabilities of a scanning electron microscope (SEM) to rapidly and accurately map the crystallographic and geochemical features of an electron transparent sample. TKD uses a similar methodology to traditional electron backscatter diffraction (EBSD), but is capable of achieving a much higher spatial resolution (5–10 nm) (Trimby, 2012; Trimby et al., 2014). Here we apply TKD to refractory metal nuggets (RMNs) which are micrometre to sub-micrometre metal alloys composed of highly siderophile elements (HSEs) found in primitive carbonaceous chondrite meteorites. TKD allows us to analyse RMNs in situ , enabling the characterisation of nanometre-scale variations in chemistry and crystallography, whilst preserving their spatial and crystallographic context. This provides a complete representation of each RMN, permitting detailed interpretation of their formation history. We present TKD analysis of five transmission electron microscopy (TEM) lamellae containing RMNs coupled with EBSD and TEM analyses. These analyses revealed textures and relationships not previously observed in RMNs. These textures indicate some RMNs experienced annealing, forming twins. Some RMNs also acted as nucleation centres, and formed immiscible metal-silicate fluids. In fact, each RMN analysed in this study had different crystallographic textures. These RMNs also had heterogeneous compositions, even between RMNs contained within the same inclusion, host phase and even separated by only a few nanometres. Some RMNs are also affected by secondary processes at low temperature causing exsolution of molybdenite. However, most RMNs had crystallographic textures indicating that the RMN formed prior to their host inclusion. TKD analyses reveal most RMNs have been affected by processing in the protoplanetary disk. Despite this alteration, RMNs still preserve primary crystallographic textures and heterogeneous chemical signatures. This heterogeneity in crystallographic relationships, which mostly suggest that RMNs pre-date their host, is consistent with the idea that there is not a dominant RMN forming process. Each RMN has experienced a complex history, supporting the suggestion of Daly et al. (2017) , that RMNs may preserve a diverse pre-solar chemical signature inherited from the Giant Molecular Cloud. [ABSTRACT FROM AUTHOR]

Quantification of microstructure, especially grain size, in polycrystalline materials is a vital aspect to understand the structure-property relationships in these materials. In this paper, representative characterization techniques for determining the grain size, including optical microscopy (OM), electron backscatter diffraction (EBSD) in the scanning electron microscopy (SEM), and atomic force microscopy/magnetic force microscopy (AFM/MFM), are thoroughly evaluated in comparison, illustrated by rare-earth sintered Nd-Fe-B permanent magnets. Potential applications and additional information achieved by using aforementioned characterization techniques have been discussed and summarized. [ABSTRACT FROM AUTHOR]

Superplastic deformation of polycrystalline materials is usually accommodated by diffusion-assisted grain boundary (GB) sliding at high temperatures. Lowering the temperature requirement for commercial superplastic forming enables green and cost-effective manufacturing. Recently, room-temperature (RT) superplasticity was realized in ultrafine-grained Al–Zn based alloys, but the underlying mechanism remains unclear. Here, we conducted in-situ tensile straining and post-mortem electron microscopy characterization, and atomistic density functional theory simulation to understand the RT superplasticity of an Al–15 Zn (at%) alloy. Results showed that the superplasticity is achieved by GB sliding and grain rotation, assisted by the continuous diffusion of Zn. In-situ observations showed Zn atoms diffusing from within grains to GBs, resulting in a Zn nanolayer at the GBs that acts as a solid lubricant to decrease the energy barrier of GB sliding. This research advances our understanding of diffusion-assisted deformation mechanism that is a prerequisite for the rational design of new materials with RT superplasticity. [Display omitted] [ABSTRACT FROM AUTHOR]

The solid solubility of Si in a quaternary Al–4Mg–1Cu–0.5Si (wt%) alloy has been found to be only about 0.061 at% at 520 °C, and 0.093 at% at 560 °C, less than 1/10 of that in the ternary Al–Mg–Si system. The excess Si in the alloy remains as coarse Mg 2 Si dispersoids which produce no significant age-hardening effect. Interestingly, a small change of Si content (from 0.061 at.% to 0.093 at.%) in the solid solution of the alloy has been found to be effective in modifying precipitation microstructure by promoting the formation of fine Guinier–Preston–Bagaryasky (GPB) zones and postponing the formation of the S phase during ageing at 200 °C. Consequently, the quaternary alloy exhibits an enhanced age-hardening response during earlier-stage ageing. [ABSTRACT FROM AUTHOR]