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Designing novel Multicomponent Metallic Glasses (MMGs) based on empirical parameters such as enthalpy of mixing ( Δ H m i x ) and configurational entropy ( Δ S m i x ) is a time-consuming exercise that requires various assumptions, limiting the capability to predict new MMG compositions. The current study involves constructing a modified Mendeleev Number ( M N P ) element scale based on many important elemental properties that impact the glass forming phenomena. Machine learning (ML) was used to assess the competence of the proposed M N P to predict MMGs. The ML findings demonstrate that proposed M N P can be utilised as a salient attribute to predict MMGs with 87.8% cross-validation accuracy. Further, the mean square variation in the M N P of the alloy constituents ( Δ M N P ) provides a delineated zone of glass forming multicomponent alloys. In summary, the research work presents a novel phenomenological coordinate system that can effectively predict new MMGs while avoiding the limitations of empirical parameters based design strategies. [ABSTRACT FROM AUTHOR]

Ferritic/martensitic (F/M) Fe--Cr-based steels are candidates for applications in nuclear fission and fusion. Previous experimental results for neutron-irradiated binary Fe--Cr alloys and high-dose neutron-irradiated F/M steels contributed greatly to the understanding of the irradiation behaviour of these groups of materials. However, some details still need to be addressed. Such gaps are related to the effect of secondary alloying and impurity elements, such as Ni and Si, as well as the dose dependence at lower neutron doses [e.g. in the range 0.1--1 displacements per atom (dpa)]. This input is essential, for example, for multiscale modelling of irradiation effects or the evaluation of nuclear fission or fusion components at the first stages of operation. Using small-angle neutron scattering, three issues are addressed: (1) the effect of Cr undersaturation (5% Cr) and supersaturation (14% Cr) on the formation of irradiation-induced solute atom clusters/precipitates in low-dose neutron-irradiated Fe--Cr alloys in the presence of intentionally added levels of Ni, Si and P; (2) the effect of irradiation temperature (290 °C versus 450 °C); and (3) the effect of neutron dose in the range 0.06--0.6 dpa on the irradiation response of the reduced-activation F/M 9%Cr steel Eurofer97. The irradiation-enhanced formation of Cr-rich α'-phase particles was found to be the dominant effect for supersaturated Fe-- 14Cr--NiSiP at both irradiation temperatures. In contrast, α' formation is impossible in Fe--5Cr--NiSiP, for which the pronounced irradiation effects observed at 0.1 dpa are mainly attributed to added Ni, Si and P. Finally, Eurofer97 exhibits an exceptionally weak irradiation effect at low neutron doses, the reasons for which are also considered. [ABSTRACT FROM AUTHOR]

Deformation behaviour of multicomponent metallic glasses are determined by the evolution/reconfiguration of the short- and medium-range order (SRO and MRO) atomic structures. A precise understanding of how different atom species rearrange themselves in different stress states is still a great challenge in materials science and engineering. Here, we report a systematic and synergetic research of using electron microscopy imaging, synchrotron X-ray total scattering plus empirical potential structure refinement (EPSR) modelling to study in situ the deformation of a Zr-based multicomponent metallic glassy alloy with 5 elements. Systematic and comprehensive analyses on the characteristics of the SRO and MRO structures in 3D and the decoupled 15 partial PDFs at each stress level reveal quantitatively how the SRO and MRO structures evolve or reconfigure in 3D space in the tensile and compressive stress states. The results show that the Zr-centred atom clusters have low degree of icosahedra and are the preferred atom clusters to rearrange themselves under the tensile and compressive stresses. The Zr-Zr is the dominant atom pair in controlling the shear band's initiation and propagation. The evolution and reconfiguration of the MRO clusters under different stress states are realised by changing the connection modes between the Zr-centred atom clusters. The coordinated changes of both bond angles and bond lengths of the Zr-centred clusters are the dominant factors in accommodating the tensile or compressive strains. While other solute-centred MRO clusters only play minor roles in the atomic structure reconfiguration/evolution. The research has demonstrated a synergetic and multimodal materials operando characterization methodology that has great application potential in design and development of high performance multiple-component engineering alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

Metastable precipitates of solute atoms, known as Guinier–Preston (GP) zones, play a significant role in the age hardening of Al–Cu alloys. In this study, we utilized the classical nucleation theory (CNT) to obtain time-temperature-transformation (TTT) diagrams for steady-state nucleation over a wide temperature range. The CNT model, which is based on atomistic simulations using artificial neural network potentials, was constructed to predict the nucleation kinetics of GP zones in the Al–Cu system with solute concentrations ranging from 1.3 to 2.5 at% (3.0 to 5.7 wt%). The nose temperature at which the steady-state nucleation time for GP zone formation is the shortest was calculated. The nose temperature increased and the minimum nucleation time decreased as the solute concentration increased. These predictions are comparable to previous theoretical results and are in good qualitative agreement with experimental observations. Furthermore, two formation scenarios of double-layer GP (GP2) zones, considering synchronous and asynchronous attachments of solute atoms to clusters, were compared in terms of nucleation efficiency. This provides new insights into the nucleation pathways of the GP2 zone in Al–Cu alloys. [Display omitted] • Classical nucleation theory was applied to predict nucleation times of the GP zone. • This method is based on atomistically informed parameterization. • Time-temperature-transformation diagrams over a wide temperature range were obtained. • The predicted nose temperatures agreed well with the experimental results. • Two formation scenarios of the GP2 zone were compared regarding nucleation efficiency. [ABSTRACT FROM AUTHOR]

The structures of atomic clusters and GP-zones preceding precipitation in an Al-0.70Mg-0.85Si-0.15Fe-0.25Mn (wt. %) alloy have been investigated by annular dark field scanning transmission electron microscopy imaging and density functional theory calculations. One analysed condition consisted of one-month natural aging, and another was in a pre-baked state after 24 h aging at 90 °C. To quantify the effect of clusters and GP-zones on microstructure development during a subsequent isothermal artificial aging at 185 °C, hardness evolution was measured, and precipitate statistics was performed at the peak hardness corresponding to 5 h aging. Several types of clusters and GP-zones have been observed and based on structure and visual appearance named 'Disordered Frank-Kasper', 'Square', 'Binocular', and 1β", 2β", 3β", 4β". The first four are most common in the natural aged condition and are associated with a well-known influence on the initial hardness evolution. The last three are fractions of the hardening β" phase and refer to the number of structural units they contain. These GP-zones have an increased density in the pre-baked condition, leading to a rapid increase in hardness during artificial aging and to a finer microstructure of high-density small needle precipitates at peak hardness. [Display omitted] [ABSTRACT FROM AUTHOR]

• Primary phase is mainly combined by stable FCC atoms with few metastable BCC atoms under slow cooling rate. • Primary phase is mainly combined by stable FCC atoms and metastable BCC phase under fast cooling rate. • Metastable BCC phases gradually transform into stable FCC phases during the growth process under fast cooling rate. • Much more ICO-like atomic clusters in undercooled liquids is favorable to the formation of metastable BCC phase in primary nuclei. The formation and evolution of metastable BCC phase during the solidification of CoCrFeNi HEA is studied by molecular dynamics (MD) method. It is found that the primary phase is mainly combined by stable FCC atoms under the cooling rate of 0.5 K/ps, while few metastable BCC atoms are observed during the nucleation and growth process. Under the cooling rate of 0.5 K/ps, the metastable FCC nuclei inside with bulk BCC structures and HCP twinning planes are formed during the primary nucleation and the metastable BCC phases gradually transform into stable FCC phase during the growth of nuclei, and few BCC phases is retained in the solidified solids. It is also found that the volume fraction of metastable BCC phases decreases with the reduction of cooling rate, and the formation and evolution of metastable BCC phases in CoCrFeNi HEA are different from that in some conventional metals and alloys. [ABSTRACT FROM AUTHOR]

The rates of atomic clustering and precipitation hardening are closely related to the diffusivity of solutes and the concentration of vacancies during the natural aging of aluminum alloys. The measurement of the diffusivity of solutes at room temperature, especially in systems with an equilibrium vacancy concentration, is beneficial to the design of the aging process. However, this measurement has long been challenging because of the extremely low diffusion rates of solutes in aluminum at room temperature and the presence of supersaturated vacancies. In this work, we propose a method to quantify the diffusivity of solutes based on the kinetic evaluation of the spinodal decomposition process. This evaluation involves conducting atom probe tomography experiments, analyzing the radial distribution function, and modeling the phase separation process using the Cahn–Hilliard theory. The aging experiments were conducted on nanoscale samples, where excess vacancies can be eliminated at free surfaces due to a high surface-to-volume ratio. The results yielded a diffusivity of Zn in the Al-12.5 at.% Zn alloy of (1. 32 ± 0. 46) × 1 0 − 25 m 2 /s at 295 K. This work introduces a novel approach to assess the solute diffusivity under conditions of equilibrium vacancy concentration at room temperature and expands the temperature range for measuring the diffusivity in systems with spinodal decomposition, particularly in cases where kinetic data at low temperatures are scarce. [Display omitted] [ABSTRACT FROM AUTHOR]

The atomic structures of Cu-Zr alloys have been extensively studied due to the unusually high glass forming ability of this system. In this work, we investigate the nearest-neighbor atomic structures of several simulated disordered Cu-Zr compositions at three temperatures: 1450 K (liquid), 700 K (undercooled liquid), and 350 K (disordered solid). The results show that over 90 % of the local structures in these systems can be described by one of 12 "building-block" atomic cluster geometries, regardless of composition or temperature, and that these structures all exhibit icosahedral or quasi-icosahedral geometries. Most of the building-blocks are unique in their combination of representative Voronoi polyhedron geometry, predominant central atom type, and occupation probability for each site in the cluster. In addition to the 12 common building-blocks, 35 "outlier" structures unique to their simulated compositions and temperatures were observed. The outliers were primarily non-icosahedral. While the populations of the common building-blocks do not exhibit clear trends with temperature or composition, the overall population of outliers increased with decreasing temperature, suggestive of their role in accommodating the lack of translational order in the disordered solid. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of atomic imperfections within oxide films from high-temperature oxidation of heat-resistant alloys significantly limits the self-protectiveness of the surface oxide, contributing to the failure of energy generating system components such as turbines, engines, and heat exchanges. Directly probing the dynamics of such atomic defects is challenging because of the extreme thermochemical conditions of high-temperature oxidation. Using environmental transmission electron microscopy observations, here we directly capture atomic-scale dynamics of vacancies in growing Cr 2 O 3 film during high-temperature oxidation of NiCr alloy in CO 2. Coordinated with theory modeling, we delineate the atomistic mechanisms associated with the effect of interstitial carbon derived from CO 2 on promoting the formation, migration and clustering of atomic vacancies to result in the enhanced alloy oxidation. The identified oxidation mechanism can find broader applicability in utilizing the atmosphere to tune the formation and evolution of atomic-scale defects, thereby affecting the mass transport properties of the growing oxide film. [Display omitted] In-situ ETEM combined with first-principles calculations revealed the atomistic origin of CO 2 -promoted oxidation of chromia-forming alloys [ABSTRACT FROM AUTHOR]

Modulating the electronic properties of single-atomic metal sites with metal clusters is a promising strategy for boosting their intrinsic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity. Herein, we report an effective isolation-confinement strategy for synthesis of well-dispersed Fe-Co atom clusters and N 4 Fe-CoN 4 atomic pair sites on carbon nanofibers (marked as β-FeCo-PCNF), in which the addition of β-cyclodextrin is crucial in avoiding the agglomeration of metal species. The Fe-Co atomic clusters induce a downward shift in the d -band center of Fe-Co atomic sites, and this shift effectively reduces the adsorption energy of OOH* on Fe-Co atomic sites, resulting in lower energy barriers for ORR and OER. Remarkably, the β-FeCo-PCNF-based Zn-air battery exhibits excellent power density and cycling stability. This work paves the way for a universal strategy to regulate the electronic localization of atomic pair sites by alloy clusters and provides essential guidance for designing multifunctional electrocatalysts. [Display omitted] • β-cyclodextrin prevents metal agglomeration. • Fe-Co atomic pair sites and Fe-Co alloy clusters anchored to carbon nanofibers. • Fe-Co alloy clusters modulate the d -band center of Fe-Co atomic sites. • The assembled Zn-air battery exhibits excellent power density and cycling stability. [ABSTRACT FROM AUTHOR]

Accurate, repeatable and quantitative analysis of nanoscale solute clustering in atom probe tomography (APT) datasets is a complex challenge which is made more difficult by the positional uncertainty and lack of absolute resolution inherent to the technique. In this work a new method, the point excess solute, is introduced for quantifying solute segregation in datasets with limited spatial resolution. This new method is based on measuring the matrix concentration using a dataset sampling method. We show the new method can accurately reproduce the values expected from synthetic datasets a priori and when the dataset spatial resolution and or phase contrast is too low for accurate quantification this is observable. The method is then applied to naturally aged solute clusters in the Al-Mg-Si-Cu system. Datasets were collected with a range of natural ageing times from 8 min to 76 weeks. The formation of the solute clusters is shown to be unaffected by the Cu content of the alloy. • New method developed for determining matrix solute concentration in APT data. • Method verified against synthetic APT data with a range of cluster characteristics. • Quantification of solute clusters with low solute density contrast achieved. • Naturally aged solute clusters in Al-Mg-Si-Cu quantified over range of ageing times. • Cu does not influence rate of naturally aged solute clustering in Al-Mg-Si-Cu. [ABSTRACT FROM AUTHOR]

We report on the crystal morphology and Raman scattering features of high structural quality GaSb1−xBix alloys grown by molecular beam epitaxy with a high Bi content (x up to ∼0.10). The Raman spectra were measured at room temperature with different laser excitation wavelengths of 532 nm, 633 nm, and 785 nm. We observed well-defined Bi-induced Raman peaks associated with atomic Bin clusters and GaBi vibrational modes. Remarkably, some Bi-induced Raman modes were strongly enhanced when the laser energy was selected near an optical transition for the 5.8%Bi sample. This effect was attributed to a Raman resonant effect near an excited optical transition of the GaSbBi layer and has been used to identify the nature of the observed Raman peaks. [ABSTRACT FROM AUTHOR]

Metal superatomic nanoclusters, with electronic structures similar to those of one certain atom, are an important type of metal clusters. Interestingly, metal clusters with metal cores composed of either icosahedral M13 or icosahedral assemblies always have a greater potential to become superatomic clusters. Furthermore, superatomic clusters with similar electronic compositions could possess various geometric structures, owing to differences in the shells; this provides a deeper understanding of the metal superatomic cluster and the assembly for nanomaterials. Therefore, this review focuses on the geometric and electronic structures of gold/silver superatomic clusters based on icosahedron M13 units and their alloys, which will facilitate the development of various applications of superatomic clusters. [ABSTRACT FROM AUTHOR]

Palladium (Pd) has been widely regarded as a high-performance catalyst for various oxidative reactions, however, the actual structure of active site remains controversial due to structural evolution under operation conditions. Herein, we prepared a series of bismuth (Bi)-doped silica-supported Pd catalysts and found a hydrogen-controlled structural reconstruction mechanism of palladium-bismuth oxide cluster to single atom alloy to efficiently catalyze low-temperature CO oxidation. The formation of Pd x Bi y O z clusters with unique Pd−O−Bi coordination structure could enhance the sinter-resistance ability of Pd species. This structural evolution of active site is clearly uncovered by in-situ XAFS results, in which metallic Bi−Pd shell gradually generates as the increase of reduction temperature without any metallic Bi−Bi bond. More importantly, PdBi 1 single atom alloy exhibits a good CO oxidation activity with a CO 2 production rate of 413 μmol CO2 ·g Pd −1·s−1 at 100 °C and excellent catalytic stability. Density function calculation (DFT) results indicate that there are geometric and electronic effects between Bi and Pd atoms, which favor total linear-CO adsorption, activate CO and O 2 molecules, and reduce the barrier for the formation of OO-CO intermediates in PdBi 1 single atom alloy. [Display omitted] • Pd x Bi y O z oxide cluster significantly enhance anti-sintering ability of palladium species via Pd O Bi structure. • A structural reconstruction of palladium-bismuth cluster to single atom alloy is observed by in-situ XAFS. • There are geometric and electronic effects between Bi and Pd in PdBi 1 single atom alloy, favoring linear-CO adsorption. [ABSTRACT FROM AUTHOR]

In this study we demonstrate the complementarity of transmission electron microscopy (TEM) and atom probe tomography (APT) in studying the early stages of phase decomposition in the age-hardening Al–Mg–Si alloy AA 6016. Samples are subjected to natural ageing at ambient temperature or artificial pre-ageing at elevated temperature in order to produce different types of atomic clusters and early stages of precipitation before age hardening commences. APT is utilized to detect clusters and identify their number density, size and compositions, whereas TEM is applied to analyse and quantify number density, sizes and types of the hardening precipitates during artificial ageing. Finally, the particle statistics derived by APT and/or TEM were utilized to predict the mechanical properties of the various samples and conditions analysed. [ABSTRACT FROM AUTHOR]

Herein we report a crystal structure of [Au0.5Ag0.5@Ag20{S2P(OiPr)2}12](PF6) [Cl@Ag8{S2P(OiPr)2}6](PF6) (1), which compositions were supported by positive-mode electrospray ionization mass spectrometry. The structural elucidation indicates that the encapsulated atom of an Ag13 the entered icosahedron can be replaced by a gold atom. Surprisingly, the capping Ag atoms on the surface of an icosahedron in 1 reveal a different arrangement from the previously reported [Ag21{S2P(OiPr)2}12](PF6) of C3 symmetry. Besides, the preference for the central silver atom being oxidized by Au(I) is rationalized by the DFT calculations on three different computed [AuAg20{S2PH2}12]+ models having C1, C3, and T symmetry, respectively. [ABSTRACT FROM AUTHOR]

Tungsten-based complex concentrated alloy (CCA) W-Ta-Cr-V films with bcc single-phase have been investigated for its exceptional radiation tolerance. This work aims to investigate the formation of helium (He) bubble and He retention behavior in the CCA film under 100 eV He plasma at a fluence of 2.02 × 1025 He/m2. The results show that the size of He bubbles in the CCA film is smaller than that in the pure W film, and the depth distribution is shallower, which indicates that the evolution of He bubbles is inhibited. As for the underlying mechanism of resistance to the formation of He bubbles in CCAs, it is believed that the characteristic of low He mobility reduces the diffusion depth of He, and the sluggish diffusion of He inhibits the aggregation of He atoms or He clusters to a certain extent. In other words, the unique energy and microstructure characteristics also inhibit the diffusion of He in the CCA film, which affects the nucleation and growth of He bubbles. Furthermore, the release of He is mainly from He adsorption of the near surface, and the desorption peaks shift to lower temperatures in the CCA film within the desorption temperature of 1273 K. [ABSTRACT FROM AUTHOR]

The effect of overheating on the morphological evolution of primary silicon in undercooled Al–70%Si-0.5%RE alloys was investigated by observing and recording their growth processes and then analyzing the as-solidified microstructure. Investigations revealed that an increase in the overheating and undercooling temperatures, transforms the primary silicon's growth morphology from dendrite with several long and thin branches to a blocky shape and then to equiaxed grains as the silicon atom clusters disappear. In addition, we observed that, in contrast to previously reported and theoretically predicted critical undercooling promoting morphology transition, the critical undercooling actually deceased the transformation from dendrite to blocky shape and then to equiaxed grains. • Highly undercooled Al–70%Si-0.5%RE alloys were studied under various overheating and undercooling temperatures. • Study the morphological evolution of primary silicon. • Study the morphological evolution of solid/liquid and recalescence interfaces. • Study the relationship of overheating and undercooling. • Study the critical undercooling for morphology transition. [ABSTRACT FROM AUTHOR]

This study examines the precipitation of AlCu solute clusters by re-aging at high temperatures for a long time. It provides evidence for their long-term stable existence in the range of 25–450 °C. In this study, T6 heat-treated Al–4Cu alloys were aged at 350 and 420 °C for 100 h, respectively. The microstructure characteristics of the alloys, corresponding to three kinds of treatments were examined using scanning electron microscopy, high-resolution transmission electron microscopy, and high-resolution scanning transmission electron microscopy. Two types of AlCu solute atomic clusters precipitate during the two re-aging processes. One is disordered clusters precipitated by aging at 350 °C for 100 h, and the other is L1 2 ordered clusters precipitated by aging at 420 °C for 100 h. Face centered cubic (Al)+L1 2 (AlCu cluster) microstructure was successfully prepared by re-aging at 420 °C for 100 h. Owing to this microstructure, the tensile strength and yield strength of the re-aged alloy at 420 °C was higher than that of the re-aged alloy at 350 °C. The structure and composition of the L1 2 AlCu solute clusters were studied using transmission electron microscopy and its energy-dispersive X-ray spectrometry. The atoms belonging to the cluster mostly adapt to the Al lattice positions, and few atoms are located in the interstitial position of FCC Al. In this study, utilizing AlCu solute clusters is proposed as a novel and promising approach for designing heat-resistant Al–Cu system alloys. [ABSTRACT FROM AUTHOR]

Needle-shaped precipitates and atomic clusters were evaluated in two model Al-Mg-Si alloys with different Mg/Si ratios by transmission electron microscopy (TEM) and atom probe tomography (APT). Following a solution heat treatment with rapid quenching, specimens were naturally aged for about 3 month and then artificially aged for various times at 170 °C. In the peak-aged condition (aged for 86.4 ks) the Si-rich alloy (6M9S) produced a higher fraction of perfect β" phase with a narrower size distribution than the Mg-rich alloy (8M7S). This resulted in a Mg-depleted matrix in the 6M9S alloy. Clusters with a mean radius of about 1 nm were observed in-between the needle precipitates in both alloys. Their number density was clearly higher in the 8M7S alloy than in the 6M9S alloy in the peak-aged condition. The number fraction of Mg-rich clusters is increasing in the Mg-rich alloy with prolonged aging time, indicating a higher stability of these clusters. Finally, the mechanical properties of the two alloys were predicted using precipitate and cluster statistics measured by APT and TEM. These simulations indicate that clusters present in-between the needle precipitates contribute significantly to strength. [ABSTRACT FROM AUTHOR]

Multi-material design concept is growing rapidly in association with the advancement of dissimilar alloy joining technology implementing FSW technique. In this paradigm, the major concern in joining Al alloys to steel by FSW technique, is to manage the intermetallic layer formation. In this context, knowing the types of Al-Fe series IMCs and their distribution is an important aspect for determining the joint performance. The present research thoroughly examined the interface region of the dissimilar welded joint between AA5083 and HSLA steel fabricated by FSW technique in butt configuration. The joint interface was deeply investigated by XRD, EBSD, TEM and APT studies to explore the distribution pattern of the various type of Al-Fe intermetallic compounds across the joint thickness. The study identified from the inverse pole figure (IPF) maps the presence of Al rich IMCs Al 6 Fe and Al 13 Fe 4 , in Al side and Fe rich phases AlFe and AlFe 4 in steel side. A massively recrystallized microstructure with ultrafine grains of order ∼1 μm in diameter and a misorientation of 0.82 high angle grain boundary (HAGB) fraction were observed at the interface along with the aforesaid IMCs. Overall, the EBSD along with TEM study depicted that the distribution of Al 13 Fe 4 , Al 5 Fe 2 , Al 9 Fe 2 and AlFe intermetallic in the microstructure of the interface mainly due to the typical CDRX and DDRX process occurs during FSW. The dominance of HAGBs are found to be the potential factor for diffusion of Fe in Al and vice-versa and which in turn influenced the type and distribution of IMCs across the interface. Moreover, the APT data analysis was successful to explain the atomic mixing pattern by the FSW process and typically Fe rich fragments of AlFe IMC phase was discovered from the reconstruction image and the proximity histogram. • FSW joint interface of AA 5083 and HSLA steel is characterized. • Presence of multiple Al/Fe IMCs are analyzed from XRD2 patterns. • The EBSD IPF maps are examined to study the microstructure and the distribution of IMCs across the interface.. • The proximity histograms from APT data are analysed to discover the atomic cluster and IMCs , if any. [ABSTRACT FROM AUTHOR]

[Display omitted] • There are multi-structural changes from disordered to ordered packing for the Ih clusters having different compositions. • The clusters containing a small number of the Cu atoms can form the perfect core–shell icosahedral geometry in which the Ag atoms segregate on the surface at room temperature. • The substitution of the Cu atoms for the Ag atoms is beneficial to the stability of the alloying Cu@Ag cluster. • The freezing process of the clusters is the result of the interaction between the kinetic trapping effect and the entropic effect. Molecular dynamics simulations were performed to investigate the freezing process of Cu n Ag 55-n (n = 0–55) alloying cluster at the atomic scale. Potential energy and shape factors indicate the structural transformation accompanying with the atom motion. Pair-distribution function gives different atomic packing characteristics of some typical structures. Entropy combined with BP neural network is used to analyze the disorder degree of atomic packing in the binary alloying clusters as well as the influence of the number of Cu atoms on the entropy values. The simulation results show that the clusters having fewer or quantity Cu atoms prefer the perfect core–shell icosahedral structures at room temperature. Significant composition effects can be observed during cooling the small size alloying clusters. With changing compositions and decreasing the temperature, the packing structures change from disorder to order accompanying with the changes of atomic energy, shape factor, pair distribution functions, and entropy. In the restricted composition space having 55 atoms, the structure of the melt has an effect on the structural transformation during cooling and the room temperature structure. [ABSTRACT FROM AUTHOR]

In the present study, the effect of C micro-alloying on microstructure evolution and properties of metastable immiscible Cu-20Fe alloy was comprehensively investigated. Experimental results indicate that the microstructure of Cu-Fe alloy is extremely sensitive to the C content. It was found that obvious liquid-liquid phase separation (LLPS) behavior is observed in Cu-20Fe alloy after C micro-alloying, and the tendency of LLPS is enhanced with increasing C content. The calculation of ΔScc(0) suggests that C atoms preferentially pair with free Fe atoms to form new Fe (C) atomic clusters, thus resulting in the enhancement of bonding of the like-atom pairs. In addition, the quasi-binary phase diagram calculation further reveals the existence of a stable miscibility gap for C-containing alloys, and the temperature interval of miscibility gap is significantly enlarged with increasing C content. Meanwhile, the interface energy between two liquids formed by LLPS also slightly increases as C content increasing. These above reasons should be responsible for the microstructure evolution of Cu-20Fe-xC alloys. In addition, the C micro-alloying deteriorates the soft magnetic properties of Cu-Fe alloys to a certain extent, whereas improves its corresponding wear-resistance. • The microstructure evolution and solidification behavior of Cu-20Fe-xC alloys were clearly elucidated. • The calculation of ΔScc(0) indicates that C atoms preferentially pair with free Fe atoms to form new Fe(C) atomic cluster. • Phase calculation indicates that the metastable miscibility gap of Cu-20Fe alloy is stabilized by the introduction of C. • The addition of appropriate amount C enhances the wear-resistance of Cu-20Fe alloy. [ABSTRACT FROM AUTHOR]

The precipitation behavior of a typical Si-rich low Cu Al-Mg-Si-Cu alloy (AA6022 alloy) was thoroughly investigated by atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), atom probe tomography (APT) and first-principles calculations. It was revealed that the slight Cu addition significantly alters the precipitate sequence of the Al-Mg-Si alloy, resulting in a distinct sequence compared with the Cu-free and high Cu alloys. Low amounts of Cu are incorporated in the clusters and the β″ phase in the under- and peak-aged stages. During over-aging, fragmentation and hybridization of different unit cells or substructures linked to the intermediate stage of the β″ → B′/Q′ transformation is observed. The B′/Q′ composite precipitate is shown to be the dominant precipitate in the over-aged condition, while other precipitates, i.e., β', U1 and U2, commonly displayed in the Si-rich Cu-free alloys, are suppressed. During subsequent aging, a B′/Q composite precipitate with a core-shell structure is formed due to the segregation of Cu atoms at the precipitate/matrix interface. The Cu segregation is shown to be beneficial for stabilizing the precipitate interface structure. The proposed altered precipitation reaction of the Si-rich low Cu Al-Mg-Si-Cu alloy is: SSSS → atomic clusters → GP zones → β″ → B′/Q′ → B′/Q + Si. [Display omitted] • The β', U1 and U2 phases are suppressed after slight addition of Cu. • The B′/Q′ composite precipitate is the dominant precipitate formed in over-aged stage. • An altered precipitation reaction of the Si-rich low Cu Al-Mg-Si-Cu alloy is proposed. [ABSTRACT FROM AUTHOR]

Metallic glasses are metallic alloys that exhibit exotic material properties. They may have fractal structures at the atomic level, but a physical mechanism for their organization without ordering has not been identified. We demonstrated a crossover between fractal short-range (<2 atomic diameters) and homogeneous long-range structures using in situ x-ray diffraction, tomography, and molecular dynamics simulations. A specific class of fractal, the percolation cluster, explains the structural details for several metallic-glass compositions. We postulate that atoms percolate in the liquid phase and that the percolating cluster becomes rigid at the glass transition temperature. [ABSTRACT FROM AUTHOR]

The effects of Bi modification and ultrasonic treatment (UST) on the microstructure and mechanical properties of AlMg5Si2Mn alloy were investigated. Compared to the alloy without any treatment, the eutectic Mg 2 Si phases are refined effectively by Bi addition, and its morphology is changed from the mazelike thick lamellars for the base alloy to thin coralline fibers for the containing Bi alloy. The modification of eutectic Mg 2 Si phase is attributed to the Bi segregation and composition supercooling in front of the growing Mg 2 Si phase. UST can assist modification of Bi on the eutectic Mg 2 Si phase and change the morphology of the primary α-Al phase in the AlMg5Si2Mn alloy from coarse dendrites to small near-spherical equiaxed crystals, meanwhile, which can also promote the homogenization of the treated melt and uniform distribution of Bi atoms or clusters in the melt. Moreover, the yield strength, ultimate tensile strength and elongation of the alloy modified by 0.3% Bi addition combined with UST at 660 °C are obviously enhanced, and the fracture modes of the alloys are changed from brittleness to toughness. • For the first time we combine the effect of bismuth modification and ultrasonic treatment to investigate the microstructure evolution and tensile properties of as-cast AlMg5Si2Mn alloy. • Both the Mg 2 Si and α-Al phases were significantly modified and refined simultaneously. • The tensile properties were significantly enhanced by changing fracture mode from brittleness to ductility. [ABSTRACT FROM AUTHOR]

[Display omitted] • For face and body centered cubic metal element A, clusters based on cluster-plus-glue-atom model are [ A C e n t r a l - A 12 N e a r e s t n e i g h b o r ] A 3 G l u e and [ A C e n t r a l - A 14 N e a r e s t n e i g h b o r ] A G l u e . • For face centered cubic solid solution alloys, unit cluster with cluster-plus-glue-atom model is C l u s t e r C e n t r a l - C l u s t e r N e a r e s t n e i g h b o r 14 C l u s t e r G l u e . • For body centered cubic solid solution alloys, unit cluster with cluster-plus-glue-atom model is C l u s t e r C e n t r a l - C l u s t e r N e a r e s t n e i g h b o r 12 C l u s t e r G l u e 3. • The composition origin of all solid solution alloys used in thermocouple are analyzed by unit cluster with cluster-plus-glue-atom model. The chemical composition proportion of solid solution alloys in thermocouples (TCs) field is preliminarily explored by the cluster-plus-glue-atom (CPGA) model. CPGA clusters for face-centered cubic (fcc) and body-centered cubic (bcc) structure elemental metal are established, which are the cubic octahedron and rhombic dodecahedron respectively. With introducing the solute A element into solvent B matrix, the solute A atoms will prefer to the certain sites of solvent B atoms in CPGA cluster. Setting a CPGA cluster consisted of solute A and solvent B atoms as the central cluster, Friedel oscillation perturbation of central cluster on surrounding CPGA clusters will be totally shielded along radial at the position of 3 times of size of central cluster. Then, CPGA unit clusters for fcc and bcc structure solid solution alloys are established, which consist of the central, nearest neighbor, and glue clusters. Take K type TCs as an example. The nominal and theoretical stable composition proportion for Ni-Cr/Ni-Si solid solution alloys are Ni 90 Cr 10 /Ni 97 Si 3 (wt. %) and Ni 96.9 Si 3.1 /Ni 89.5 Cr 10.5 (wt. %), which correspond well with each other. Finally, CPGA unit clusters for most solid solution alloys in TCs field are analyzed, which display the better correspondence to the nominal composition proportion of them. [ABSTRACT FROM AUTHOR]

● Short range order in CrMnFeCoNi high-entropy alloy surveyed from the resistivity. ● Electric pulse current (electropulsing) applied to reveal hidden properties. ● No large resistivity changes indicated absence of unstable local atom clusters. ● Slight resistivity changes suggested Cr-Ni pair formation tendency in CrMnFeCoNi. High-entropy alloys (HEAs) are equimolar solid solution alloys composed of more than five elements, and their atomic arrangement is chemically disordered. Some ordering in HEAs, however, is suspected from the characteristic properties, such as high strength with good ductility at low temperatures or sluggish diffusion. Herein, we report that quasi-stable states inherent in nonequilibrium systems can be extracted by applying an electric pulse current to the system (electropulsing). In this study, changes in the electrical resistivity of the rapid-quenched CrMnFeCoNi HEA were investigated after electropulsing. No step-like large decreases reflecting nanocrystallization in amorphous alloys were observed for rapid-quenched CrMnFeCoNi by electropulsing. This indicates that quasi-stable ordered atom clusters do not exist in the CrMnFeCoNi HEA. However, the resistivity showed a slight decrease and increased with increasing electropulsing current density. A tendency to form short-range order, as Cr is preferentially surrounded by Ni, is suggested by comparison with the results of NiCr alloys. [ABSTRACT FROM AUTHOR]

• In addition can suppress the negative effect of NA and improve precipitation during AA for Al-Mg-Si alloys. • In atoms incorporate into clusters and facilitate their transformation to β′′ phase at the early AA. • In atoms segregate at the β′′/α-Al and β′/α-Al interfaces by replacing the Si atoms or Al atoms. • In-rich particles are formed at the edge of the β′ phase or in the α-Al matrix. [Display omitted] The impact of In addition on the precipitation behavior and properties for Al-Mg-Si alloys under different aging treatments was systematically studied by hardness measurements, atom probe tomography (APT), high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and density functional theory (DFT) calculations. We found that the In addition effectively suppresses the harmful effect of natural aging (NA), and improves the age hardening for the Al-Mg-Si alloy. Mg-Si-In clusters are formed in the early stage of aging caused by the incorporation of In atoms, which can facilitate the nucleation of the β" phase. During peak aging, In atoms distort the well-ordered structure of the β" and occupy the positions in the interface of the β", facilitating the transition of β" to post-β" (i.e., U2 and β′). During the following aging, In atoms are presented in two different configurations: forming In-rich particles and aggregation at the interfaces of β′. Most of the In-rich particles are formed at the edge of the β′ particles. The segregation of In atoms at the precipitate/matrix interface and the formation of In-rich particles can probably be attributed to the reduced strain energy of the β′ phase it brings about. [ABSTRACT FROM AUTHOR]

• Quench-hardening depth of a novel Al-Zn-Mg-Cu-Sc-Zr alloy exceeds 150 mm. • Quenching rate is reduced to 1.5 °C/s, the hardness loss value of the aged alloy is < 8%. • The Al 6 Mn and E phase promote heterogeneous precipitation of η phase. • The coherent Al 3 (Sc, Zr) and fine G.P zones effectively strengthen the studied alloy. This paper studies a novel Al-Zn-Mg-Cu-Mn-Sc-Zr alloy that exhibits outstanding quenching sensitivity with a quench-hardening depth of more than 150 mm. Jominy end quenching allows the alloy to obtain different quenching rates. The Brinell hardness of the aged alloy with a quenching rate of 27 °C/s is 154 HB; when the quenching rate drops to 1.5 °C/s, its hardness value loses about 8%, which is 142 HB. The quenching-induced equilibrium precipitates heterogeneously precipitated at the grain boundary and the incoherent phase interfaces (E phase, Al 6 (Mn, Fe) phase), but no heterogeneous precipitates are observed along the coherent L1 2 -Al 3 (Sc, Zr) particles. After artificial aging, densely distributed nano-scaled atomic clusters and G.P zones, as well as grain boundary precipitation free zones (PFZs) were observed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two kinds of hexagonal structures are identified in the β precipitates of a Cu-40Zn alloy to be formed through a two-stepped atomic displacement. • The concomitant formation of the two hexagonal structures minimize the lattice distortion of each single formation. • The new information on the formation mechanism of the two hexagonal structures in a Body Centre Cubic matrix are provided, which is a common feature of many alloys systems. Two nano-scaled hexagonal distortions in high temperature BCC phase during cooling is commonly observed in many alloys systems. Although efforts have been made on studying the lattice softening of the BCC structure during cooling, the distortion mechanisms are less addressed. Thus, the formation of two hexagonal structures in the β precipitates in a Cu-40Zn alloy treated by ECP was thoroughly investigated. Results show that the β precipitates contain two kinds of nano-sized and diffuse atomic clusters one with a η structure obeying the Burgers OR and the other a ω structure obeying the Blackburn OR. They were each formed through a two-stepped atomic displacement. For the η structure, the first step is the atomic shuffle of each second 110 β plane in the < 1 1 ¯ 0 > β direction and the second is a structure change mainly by a {1 1 ¯ 2} < 1 ¯ 11> β shear. For the ω structure, the first is an atomic shuffle on each second and third { 11 2 ¯ } β plane in the ± [1 1 1] β directions and then normal strains in three mutually perpendicular directions. The concomitant formation of the two structures minimizes the lattice distortion of single formation. The present results provide new information on the formation mechanism of the two hexagonal structures in a BCC matrix. [ABSTRACT FROM AUTHOR]

The precipitation phenomena and the related hardening in an --- alloy were studied by calorimetry, X-ray diffraction analysis and microhardness measurements. The main calorimetric peaks were identified to be due to β′′, θ′ and Q′ phases precipitation. The hardening during aging at room temperature and 160°C, was respectively, explained by atomic clusters and GP zones formation and by GP zones and β′′/θ′ phases coprecipitation. Although the mechanical properties variation during aging at 200°C is simple, the corresponding microstructural evolution is complex: on the basis of the DSC results, the increasing of microhardness values, is mainly due to the coprecipitation of GP zones and β′′/θ′ phases, however, the maximum hardening is explained by the coexistence of β′′/θ′ and θ′′ phases. Another important conclusion is that during aging at 160°C and 200°C, the θ′ phase is essentially developed from GP zones. [ABSTRACT FROM AUTHOR]

Due to the high solubility limit of oxygen in Zr, dissolution of oxygen in the Zr-based alloys is unavoidable. However, as an alloying element, the effect of oxygen on the microstructure and mechanical properties of monolithic Zr-based bulk metallic glasses (BMGs) is rarely reported. Here, we systematically investigated the evolution of microstructure and mechanical properties of monolithic Zr 61 Cu 25 Al 12 Ti 2 BMGs with alloying oxygen content ranging from 650 at. ppm to 5600 at. ppm. With increasing oxygen content from 650 at. ppm to 3500 at. ppm, the compressive plasticity only decreased slightly, from 2.00±0.85% to 1.60±0.91%; however, it plunged to 0.77±0.33% when the oxygen content was further increased to 5600 at. ppm. The threshold oxygen content level for the ductile-brittle transition was revealed at 3500 at. ppm, and the embrittlement at high oxygen content is closely related with a number of changes in microstructure: sharply increases in the size of shear transformation zone (STZ) and in the degree of local ordering, including the imperfect ordered packing (IOP) atomic clusters and large medium-range ordering (MRO) domains. The above findings not only advance the understanding of the effect of alloying oxygen on the microstructure and mechanical properties, but also help to design Zr-based BMGs with excellent performance, promoting their wider commercial application. [Display omitted] [ABSTRACT FROM AUTHOR]

Co-deposited, immiscible alloy systems form hierarchical microstructures under specific deposition conditions that accentuate the difference in constituent element mobility. The mechanism leading to the formation of these unique hierarchical morphologies during the deposition process is difficult to identify, since the characterization of these microstructures is typically carried out post-deposition. We employ phase-field modeling to study the evolution of microstructures during deposition combined with microscopy characterization of experimentally deposited thin films to reveal the origin of the formation mechanism of hierarchical morphologies in co-deposited, immiscible alloy thin films. Our results trace this back to the significant influence of a local compositional driving force that occurs near the surface of the growing thin film. We show that local variations in the concentration of the vapor phase near the surface, resulting in nuclei (i.e., a cluster of atoms) on the film's surface with an inhomogeneous composition, can trigger the simultaneous evolution of multiple concentration modulations across multiple length scales, leading to hierarchical morphologies. We show that locally, the concentration must be above a certain threshold value in order to generate distinct hierarchical morphologies in a single domain. [ABSTRACT FROM AUTHOR]

Complex metallic alloys (CMAs) are materials composed of structurally complex intermetallic phases (SCIPs). The SCIPs consist of large unit cells containing hundreds or even thousands of atoms. Well-defined atomic clusters are found in their structure, typically of icosahedral point group symmetry. In SCIPs, a long-range order is observed. Aluminum-based CMAs contain approximately 70 at.% Al. In this paper, the corrosion behavior of bulk Al-based CMAs is reviewed. The Al–TM alloys (TM = transition metal) have been sorted according to their chemical composition. The alloys tend to passivate because of high Al concentration. The Al–Cr alloys, for example, can form protective passive layers of considerable thickness in different electrolytes. In halide-containing solutions, however, the alloys are prone to pitting corrosion. The electrochemical activity of aluminum-transition metal SCIPs is primarily determined by electrode potential of the alloying element(s). Galvanic microcells form between different SCIPs which may further accelerate the localized corrosion attack. The electrochemical nobility of individual SCIPs increases with increasing concentration of noble elements. The SCIPs with electrochemically active elements tend to dissolve in contact with nobler particles. The SCIPs with noble metals are prone to selective de-alloying (de–aluminification) and their electrochemical activity may change over time as a result of de-alloying. The metal composition of the SCIPs has a primary influence on their corrosion properties. The structural complexity is secondary and becomes important when phases with similar chemical composition, but different crystal structure, come into close physical contact. [ABSTRACT FROM AUTHOR]

• High Mg-content AlSiMg1.4 alloy was fabricated by selective laser melting. • YS and UTS of SLMed AlSiMg1.4 alloy reached 341 ± 14 MPa and 518 ± 6 MPa, respectively. • The strength of alloy are much higher than most known SLM fabricated Al-Si-Mg alloys. • The new strengthening mechanism was mentioned in the paper. A high Mg-content AlSiMg1.4 alloy was designed for selective laser melting (SLM) processing. The SLMed AlSiMg1.4 alloy exhibits a high yield strength of 341±14 MPa and a high ultimate tensile strength of 518±6 MPa, along with a total elongation of 7.1±0.4%. The composition profile in the α -Al matrix of the alloy manifests in-phase concentration fluctuations of Mg and Si. The presence of high density Mg-Si atomic clusters as strong obstacles to dislocation gliding is suggested to provide an additional strengthening mechanism for the SLMed Al-Si-Mg alloy. [ABSTRACT FROM AUTHOR]

The short-range order of liquid Al Sn alloys (0, 3, 8, 13, 20, 35, 50, 75, 100 at. % Sn) at 973 and 1273 K has been studied by X-ray diffraction and Reverse Monte Carlo simulation. The analysis of the experimental and simulation data points out the presence of atomic clusters with a local structure similar to liquid Sn even at low tin content (8 at. %). An impact of these clusters on the formation of short-range order of Al Sn melts becomes dominant at 35 at. % Sn, resulting in the similarity between experimental structure factors and pair correlation functions of binary melts and liquid tin. On the other hand, the short-range order of liquid binary alloy with high Al content (97 at. %) is structurally homogeneous and based on the local atomic structure of liquid aluminium. The comparison between the short-range order of the liquid Al Sn, Al Ge, and Al Si alloys has been discussed. • X-ray diffraction study and RMC simulation of liquid Al Sn alloys. • An impact of atomic clusters with local structure similar to liquid Sn on short-range order of Al Sn melts. • Comparison between the short-range order of the liquid Al Sn, Al Ge, and Al Si alloys. [ABSTRACT FROM AUTHOR]

The effect of step-quenching (SQ) on two/multi-step aging and the bake-hardening response in Al-0.9Mg-1.0Si (in wt.%) alloy was investigated in terms of nanocluster formation and vacancy behavior using advanced methods, including atom probe tomography (APT) and positron annihilation lifetime spectroscopy (PALS) analysis. The SQ treatment was found to be highly effective at suppressing the negative effects of natural aging during two/multi-step aging, compared with pre-aging (PA) treatment. The characteristic behaviors of nanoclusters formed by PA and SQ treatments were completely different. SQ is likely to preferentially form Si–V complexes, which are different than Cluster (1), and Si-rich clusters, as detected by the distribution of cluster compositions using APT analysis. Si–V complexes pre-formed during SQ treatment result in the formation of Mg–Si clusters with higher atomic density, inducing favorable transformation to the pre-β" phase because there are fewer vacancies inside the Mg–Si cluster. Also, the Si–V complexes reduce the fraction of Si-rich clusters commonly formed during natural aging (NA). The step-quenched Al–Mg–Si alloy with great bake-hardening response has promising potential for automotive outer panel applications. [ABSTRACT FROM AUTHOR]

Al-4.5Si-1Cu-0.3Mg(-1Fe) (wt%) alloys fabricated by a deformation-semisolid extrusion (D-SSE) process have been investigated by transmission electron microscopy, down to the atomic level. T5 and T6 heat treatments were conducted to understand the age-hardening behavior of the alloys. Disordered Mg-Si(-Cu) precipitates with strong Cu enrichments at their interfaces with the Al matrix have been observed in the overaged conditions of both heat treatments and in the peak hardness of the T6 condition, but only Cu-containing atomic clusters were detected in the peak hardness of the T5 heat treatment. Despite having a lower bulk precipitate number density at comparable precipitate size and volume fraction, hardness in the T6 condition was higher in the alloy with highest Fe content due to the extra contribution from the precipitates nucleated on fragmented β-Al 5 FeSi particles and grain boundaries. Many of these precipitates were Q'-phase, and two new coherent interfaces with the Al matrix are reported for this phase. • Fragmented β-Al 5 FeSi particles and grain boundaries act as nucleation sites for the Q' phase. • Two new types of interfaces along the coherent <510>Al direction of the Q' phases have been found. • Cu-containing atomic clusters have been found in the peak hardness of an artificially aged T5 condition. [ABSTRACT FROM AUTHOR]

In this work, precipitation behavior and mechanical performances of A356.2 alloy (treated by Al–6Sr–7La composite refinement-modification agent) were studied for the first time. Artificial aging treatment (T6) and long-time natural aging treatment (>10,000 h, T4) were applied to clarify the precipitation and growth behavior of Mg 5 Si 6 phase. The results show that vacancies and dislocations formed during solution treatment promote the nucleation and growth of Mg 5 Si 6 phase in the eutectic area during the subsequent aging process. During the T6 treatment, the growth of Mg 5 Si 6 phase is promoted due to the interaction of atomic diffusion channel caused by higher Si concentration gradients and dislocations, leading to a large number of uniform distributed spherical Mg 5 Si 6 phase in eutectic area. While, for the T4 treated alloy, atomic clusters with short rod-like Mg 5 Si 6 phase exists inside the alloy. In addition, T6 treatment resulted in significant improvement of tensile strength (UTS), yield strength (YS) and vickers hardness (HV) compared with the T4 treated alloy and the reasons were discussed. • Precipitation behavior of A356.2 alloy (treated by Al–Sr–La) in eutectic area was clarified. • Precipitation mechanism of Mg 5 Si 6 both under T6 and T4 were found. • Mechanical performances of Al–Sr–La treated A356.2 alloy (treated by Al–Sr–La) were investigated. [ABSTRACT FROM AUTHOR]