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Ultrastable metallic glasses (SMGs) exhibit enhanced stability comparable to those of conventional glasses aged for thousands of years. The ability to understand why certain alloy compositions and processing conditions generate an SMG is an emerging challenge. Herein, amplitude-modulation dynamic atomic force microscopy was utilized for tracking the structure of Zr50Cu50, Zr50Cu44.5Al5.5 and Zr50Cu41.5Al5.5Mo3 thin film metallic glasses (TFMGs) that were produced by direct current magnetron sputtering at room temperature with the rate of deposition being the only variable. The transition in stability from bulk- to SMG-like behavior resides in the change of relaxation mechanism as the deposition rate is decreased. The formation of SMGs is directly linked with the degree of structural heterogeneity, whereby MGs with greater heterogeneity have a higher potential to form SMGs with more significant enhancement in stability. Slower deposition rates, however, are required to yield the more homogenous structure and lower energy state underlying the ultrastability. Ultrastability is closely linked with the geometric shape and distribution of loosely packed phases, whereby SMGs containing more slender loosely packed phases with a more skewed distribution achieve more significant improvements in stability. This work not only provides direct evidence of the structure of SMGs, but also opens new horizons for the design of SMGs.

Multi-principal element alloys (MPEAs) have attracted rapidly growing attention from both research institutions and industry due to their unique microstructures and outstanding physical and chemical properties. However, the fabrication of MPEAs with desired microstructures and properties using conventional manufacturing techniques (e.g., casting) is still challenging. With the recent emergence of additive manufacturing (AM) techniques, the fabrication of MPEAs with locally tailorable microstructures and excellent mechanical properties has become possible. Therefore, it is of paramount importance to understand the key aspects of the AM processes that influence the microstructural features of AM fabricated MPEAs including porosity, anisotropy, and heterogeneity, as well as the corresponding impact on the properties. As such, this review will first present the state-of-the-art in existing AM techniques to process MPEAs. This is followed by a discussion of the microstructural features, mechanisms of microstructural evolution, and the mechanical properties of the AM fabricated MPEAs. Finally, the current challenges and future research directions are summarized with the aim to promote the further development and implementation of AM for processing MPEAs for future industrial applications.

Binder-free Ni modified-MoS2 electrocatalysts with superior hydrogen evolution reaction (HER) catalytic performance were fabricated by a facile electrodeposition method.

Crystallization among amorphous alloy is a crucial study since it generally affects it properties, which may detrimental or beneficial, depending in the intended application of the materials. Controlling crystallization is crucial for obtaining the desired properties. The crystallization study was performed using differential scanning calorimeter (DSC). Samples were heated at heating rate between 20 and 40 K·min-1. Structural evolution during crystallization was studied under X-ray diffraction (XRD). Apparent activation energy for each temperature characteristics was determined using Kissinger’s equation. Local Avrami exponent was investigated using modified Johnson-Mehl-Avrami-Kolgomorov equation. Liquid fragility, which indicates the strength of the glass formation, was predicted using temperature characteristics instead of its viscosity. It was found that upon crystallization both as-cast samples crystallize to cubic-Al, Al2CuMg and Al2Cu and Al3Ni. Alloy with composition of (Al75Cu17Mg8)95Ni5 shows superior activation energy at every temperature characteristics than alloy with composition of Al75Cu10Mg8Ni7. Local Avrami exponent and local activation energy for (Al75Cu17Mg8)95Ni5 show high values at the beginning and at the end of crystallization process. From liquid fragility, it was predicted that the samples are stronger glass former than previous studied Al-amorphous alloys.

Genome-scale technologies have enabled mapping of the complex molecular networks that govern cellular behavior. An emerging theme in the analyses of these networks is that cells use many layers of regulatory feedback to constantly assess and precisely react to their environment. The importance of complex feedback in controlling the real-time response to external stimuli has led to a need for the next generation of cell-based technologies that enable both the collection and analysis of high-throughput temporal data. Toward this end, we have developed a microfluidic platform capable of monitoring temporal gene expression from over 2,000 promoters. By coupling the “Dynomics” platform with deep neural network (DNN) and associated explainable artificial intelligence (XAI) algorithms, we show how machine learning can be harnessed to assess patterns in transcriptional data on a genome scale and identify which genes contribute to these patterns. Furthermore, we demonstrate the utility of the Dynomics platform as a field-deployable real-time biosensor through prediction of the presence of heavy metals in urban water and mine spill samples, based on the the dynamic transcription profiles of 1,807 unique Escherichia coli promoters.

Sandwiched between two fused silica blocks, thin-gauge samples of Ag-39.9 at.%Cu eutectic alloy were solidified over a range of undercoolings. Subsequently, the samples that consisted consistently of fully lamellar eutectic were rapidly heated to a target temperature below the eutectic temperature. Increasing the initial undercooling prior to solidification or the target temperature of heating led to more anomalous eutectic and worse orientation of phases in the final microstructure. It is conclusively indicated that the formation of anomalous eutectic in bulk samples results from remelting of the primary lamellar eutectic.

Grain boundary migration in magnesium alloys has been studied using quantum mechanical calculations implementing the nudged elastic band method. Four crystallographically different boundaries were examined: two twin boundaries and two general grain boundaries that showed no crystallographic symmetry across the boundary plane. The activation energies for boundary migration were determined from the minimum energy pathways, and these energies were consistent with experimental values. It was found that the activation energy is linearly related to the coordination number of the boundaries. This indicates that boundaries with lower coordination numbers showed smaller activation energies and thus higher mobilities than the more orderly boundaries with larger coordination number and larger activation energies. The effect of solutes at the boundary was also studied, and it was found that most solutes with low co-ordination number decreased the activation energy for boundary migration, but the effect of solutes on boundaries with high coordination number was strongly dependent on the solute chemistry Refereed/Peer-reviewed

The surface film formed on an ultra-lightweight Mg-Li(-Al-Y-Zr) alloy was investigated. Previous research reported that this body-centered cubic (bcc) Mg-Li(-Al-Y-Zr) alloy demonstrated high corros...

The effect chemical composition on the shock response of two bulk metallic glass (BMG) alloys with slightly different elemental compositions (Zr55Cu10Ni5Al30 and Zr46Cu38Ag8Al8) has been investigated. Plate-impact experiments were conducted at a peak compressive stress of ∼10GPa, above the expected elastic limit of these alloys (∼7GPa). Velocity interferometry was used to measure the particle (up) and free surface velocity (FSV) histories. These measurements allowed calculation of the Hugoniot elastic limits and onset stresses of fracture (i.e. spall strength) for each alloy. The soft recovered specimens were characterized by means of optical and electron microscopy. It was found that the Zr55Cu10Ni5Al30 exhibited a higher HEL and spall strength and a smooth fracture surface morphology consisting of dimple-like features. Conversely, the lower spall strength of the Zr46Cu38Ag8Al38 alloy seems to correlate with rougher fracture surface that shows cup-cone features associated with a predominantly brittle dynamic fracture.

This paper examines the potential of thermodynamic modelling as a simple and inexpensive means for assessing phase stability in a series of non-equiatomic high entropy alloys and compares with CALPHAD calculations to demonstrate an appropriate level of simplifying assumptions. The modelling was motivated by alloys from the Al–Ti–Co–Ni–Fe–Cr system, which were produced by iteratively following the natural compositional segregation of the two-phase BCC + B2 microstructure present in a Al2TiCoNiFeCr alloy after casting and heat treatment. This produced a range of multicomponent B2-type alloys with different volume fractions of a BCC secondary phase. The solubility limits and traditional empirical thermodynamic driving forces for phase stability were investigated to explain the formation of the two phases. Limitations of prior semi-empirical models are highlighted, with advancements demonstrated by accounting for contributions from the effect of ordering on configurational entropy, the difference in enthalpy from intermetallic compounds, and thermal influences on both entropy and enthalpy. The new models are compared against the current leading thermodynamic modelling approach, CALPHAD, with excellent correlation. This work outlines a methodology to predict and design phase constitution in future high-performance BCC + B2 alloys and, more generally, it demonstrates the value of models with temperature-dependent thermodynamic quantities for exploring new, complex compositional regions.

Atomic structures of Cu100−xZrx (x = 41.18–66.67) metallic glasses were investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy and molecular dynamics (MD) simulations. It is demonstrated that both the fraction and average volume of the typical atomic clusters, characterized by Voronoi cells, are of compositional dependence. With the increasing of Zr content, the fraction of Cu and Zr centered Voronoi clusters with coordination number lower than 11 and 14 respectively increases, while that of clusters with larger coordination numbers reduces. Among the major Voronoi clusters, the Cu-centered icosahedra are distinctive. Their average volume is far smaller than that of the other Cu-centered Voronoi cells with the same coordination number. More importantly, they prefer to interlink into pentagon-rich icosahedral super-clusters. However, compared with their neighbors, the glasses with x = 44 and x = 50 exhibit no other particularity in Cu-centered icosahedra than a slightly enhanced interlink at x = 50 although glass forming ability (GFA) reaches a local maximum at these two compositions, indicating that there are other factors dominating the GFA change with composition. A significant reduction in free volume for the loosely packed regions takes place at x = 44 and x = 50, due to which the corresponding Cu-Zr metallic glasses have the maximum microhardness.

A high strength Al-5024 alloy containing Sc and Zr with a bi-modal microstructure consisting of fine equiaxed and coarse columnar grains was successfully fabricated by laser powder bed fusion (LPBF) additive manufacturing. The formation of the bi-modal microstructure was mainly due to both the formation of primary Al3Sc precipitates that act as nucleation sites and the steep temperature gradient during LPBF. By simulating the thermal field of a single melt pool, the formation mechanism of the bi-modal microstructure was explained. It was found by simulation that a solidification interface velocity less than 110 mm/s was beneficial to the nucleation of Al3Sc precipitates and, hence, facilitated the formation of a fine grain microstructure. Applying different heat treatments revealed a trade-off trend between yield strength and ductility as a function of the heat treatment time, and a correlation in fatigue life and yield strength was observed, both of which were closely related to the status of the secondary Al3Sc precipitates. The highest ultimate tensile strength of 450 MPa and corresponding 107 cycle fatigue strength of 105 MPa were achieved after hot isostatic pressing for 4 h at 325 °C with 100 MPa pressure. Dynamic strain aging was found to occur in both as-built and some heat treated samples, which was related to magnesium (Mg) solute atom clustering attributed to: (i) the formation of a diffuse “Mg wall” due to the repetitive melting and rapid cooling in LPBF, and (ii) the growth of intragranular (Al3Sc) and intergranular precipitates (Fe-, Mn-rich) during subsequent heat treatment, thereby leading to an increasing number of misfit dislocations that promote the formation of Mg atom clusters.

Ternary Mg-Zn-Ca metallic glasses show promise as a bioresorbable implant material. Their susceptibility to relatively rapid corrosion rates, however, requires new ways to reduce their initial rate of corrosion post-implantation. To this end, the application of a simple phosphate conversion coating was studied on Mg 66 Zn 30 Ca 4 to determine the metallic glasses impact on coating development. A model for coating growth is proposed. The results demonstrate corrosion resistance can be improved by an order of magnitude in simulated body fluid, with a significant reduction in anodic kinetics. Furthermore, the mechanical reliability under a compressive load is improved two-fold, despite substrate relaxation due to coating.

An understanding of nanocrystallization is an important precondition for controlling the microstructure and properties of nanocrystal-reinforced amorphous alloys. In the present work, the microstructures of Al86Ni9La5 and (Al86Ni9La5)98Si2 amorphous alloys and their annealed products were investigated systematically to reveal why the nanocrystallization behavior of primary α-Al was considerably changed with Si addition. Upon heating, α-Al nucleates in the Al-rich regions of two amorphous alloys. The addition of Si significantly shrinks the size of single Al-rich region in the as-quenched amorphous sample, but raises the local maximum Al concentration and slows down the rate of diffusion of solute atoms. As a result, the primary crystallization of α-Al first takes place at a higher nucleation rate in the Al-rich regions at lower temperatures. However, the residual amorphous phase enriched with solute elements does not crystallize until the alloy is heated to a high enough temperature for massive atomic diffusion to occur, with further crystallization of α-Al occurring through epitaxial growth of the existing α-Al crystals. The high bonding strength between Si with Ni, and especially La, is responsible for the splitting of α-Al nanocrystallization into two stages.

The composition-dependent oxidation film formation behaviour in Mg-Li-Al alloys was investigated via diffusion couple experiments. The concentration gradients of alloying elements across the bonded interface resulted in both microstructural and oxidation behaviour changes. The interdiffusion of alloying elements led to four different matrix zones. Different oxidation behaviours in single-phase zones were caused mainly by Li concentration variations among them, specifically, higher Li contents bring about thicker oxide films. A thicker oxidation film induced by accelerated oxidation in the duplex diffusion zone was observed compared to those in the single-phase zones, which was a result of galvanic degradation.

Ultrastable metallic glasses (SMGs) formed by physical vapor deposition are an interesting new class of material, exhibiting enhanced stability argued to be equivalent to conventionally quenched metallic glasses that have been aged for thousands of years. The factors controlling the formation and structural development of SMGs are still not well understood. For the first time, the impact of film thickness toward the development of SMGs was explored. By controlling the thickness, we can tune the thermophysical and mechanical properties of SMGs. Geometrical and statistical analyses indicate that the films initially contain loose-packing phases that tend to elongate and present with a larger average size and less dispersive distribution as a result of induced geometric confinement. As the film is built up, structural heterogeneity develops, leading to variations in properties as the glass undergoes rejuvenation. This study provides direct evidence for the structural changes underlying the unique properties of SMGs and challenges the empirical rules for SMGs design.

It is well-known that the stability of Pd-Si amorphous alloys can be improved substantially by minor additions of alloying elements such as Cu and Ag. Such improvement in stability is explained herein, whereby microscopic models based on efficient atomic packing and electronic structure were applied to the results of first principles simulations of Pd82Si18, Pd77.5Si16.5Cu8and Pd75Si15Cu7Ag3metallic glasses. It was revealed that while the atomic packing model fails to unequivocally explain the stabilizing effect of the binary Pd-Si alloy due to minor additions of Cu and/or Ag, the contribution of electronic states with lower energies to the stability of the amorphous structure is increased markedly. Further, the observed enhancement in the compressive ductility as a result of the addition of Ag to the Pd77.5Si16.5Cu8alloy can be correlated to the combined effects of an increased heterogeneity in the local topology, weakened covalency and, hence, reduced directionality of Pd-Pd bonds as well as enhanced metallicity in the Pd75Si15Cu7Ag3amorphous alloy. The analysis was further expanded to amorphous alloys where their characteristic binary prototypes are synthesised from late transition metals and non-metals as well as those comprising early transition metals and late transition metals. The findings shed light on the effects of minor alloying on the cooperative and competitive relationship between the topological and electronic structure of amorphous alloys. Refereed/Peer-reviewed

We present details of a blended quantum molecular dynamics scheme, utilizing both the canonical and isobaric-isothermal ensembles, in order to not only circumvent the need for any experimental input data ordinarily required for simulations involving the strictly canonical ensemble, but also minimize the relatively high extra computational cost imposed by the increased cutoff energy necessary to avoid the so called Pulay stress error while performing isobaric-isothermal ab initio molecular dynamics simulations using plane-wave basis set. We compare the results of the blended and canonical schemes via the simulated quench of the damage-tolerant Zr 61 Ti 2 Cu 25 Al 12 (ZT1) alloy to below its glass transition temperature. There were subtle differences in structural evolution between the two schemes. Notably, the blended scheme generates a more efficiently packed structure, which is feasibly permitted due to the volume changes that transpire as a result of incorporating a parallel NPT component. Further, while the blended scheme obviates the need for any experimental input data, it is shown that the starting volume is not particularly critical and the computed final density of the alloy is within ∼1% of the reported experimental value of 6.43–6.50 g/cm3. Furthermore, the blended scheme demonstrated a greater degree of transformation in the coordination number compared with the canonical, which remains relatively static. The final value of 12.97 obtained from the blended scheme is closer to the ideal of 13.33 as per close-packing theory, a feature that appears to be related to the evolution of a more complex family of Voronoi polyhedra relative to the icosahedral dominant motifs present in the canonical scheme. Furthermore, in both schemes, the partial coordination number in the Zr species, being the primary constituent, demonstrates a plateau in its evolution, but which commences in the blended scheme at a temperature approximately 300 K closer to the reported glass transition temperature. The findings suggest a more reliable and an optimally efficient method for implementing ab initio molecular dynamics in the simulation of complex alloys.

A series Co-(18.5–20.7) at.% B melts encompassing the eutectic composition (Co81.5B18.5) were solidified at different degrees of undercooling. It is found that the metastable Co23B6 phase solidifies as a substitute for the stable Co3B phase in the alloy melts undercooled above a critical undercooling value of ~60 K. The Co23B6 and α-Co phases make up a metastable eutectic. The corresponding eutectic composition and temperature are Co80.4B19.6 and 1343 K, respectively. On exposure of the metastable Co23B6 phase at a given temperature above 1208 K, it does not decompose even after several hours. But it transforms by a eutectoid reaction to α-Co + Co3B at lower temperature.

(Co 76 Sn 24 ) 100- x Nb x ( x = 0, 0.5, 0.8, 1.0) eutectic alloy melts were solidified at small undercooling for investigating the effect of Nb addition on microstructural development. With increasing Nb content, the solidification interface transits from eutectic seaweed ( x = 0) to eutectic dendrite ( x = 0.5) as a response to the change in the anisotropy of interfacial energy. Coupled eutectic growth can no longer be maintained within the main stems at x = 0.8 because the enrichment of Nb in the liquid ahead of the interface causes a significant difference in growth velocity between the α-Co and β-Co 3 Sn 2 phases and, as such, Co 3 Sn 2 doublons form. For x = 1.0, the difference in growth kinetics between the two eutectic phases is so large that divorced eutectic growth takes place on a large scale. Letting the undercooling prior to solidification increase, the eutectic interface morphology of (Co 76 Sn 24 ) 99.5 Nb 0.5 eutectic alloys returns from dendritic pattern back to factual seaweed pattern at more than 38 K undercooling and then transits to compact seaweed pattern at more than 181 K undercooling. The eutectic growth velocity slightly increases at low and intermediate undercooling but obviously decreases at large undercooling due with Nb addition.

The high strain deformation and recrystallization behaviour of a Fe/Ni multilayered composite sheet fabricated by accumulative roll bonding has been investigated. The comparable initial hardness and subsequent strain hardening behaviour of the Ni and Fe layers reduces the flow compatibility related challenges at the bonding interfaces, thereby generating parallel layers of uniform thickness during rolling to true strains up to 4.18. Typical body centred cubic ( α- and γ- fibres) and face centred cubic ( β- fibre) rolling textures were generated in the Fe and Ni layers, respectively. During annealing at 700 °C, recrystallization takes place homogenously in the Ni layers but commences initially by particle stimulated nucleation at oxide debris present at the interface of adjacent Fe layers. After recrystallization, the texture of the Ni layers is similar to the starting material prior to ARB, but considerable texture modification occurs in the Fe layers. For both metals, oriented growth of nucleated grains has the greatest influence on the final annealing textures, which generates the classic Cube texture in Ni and a {511} texture in Fe. While these final textures of the individual Fe and Ni layers are not conducive to good formability, texture-based Schmidt factor calculations of the combined layers show an overall balance in texture components that points to a reduction in planar anisotropy. The ability to fabricate multilayered textured sheets by this route is a promising way of controlling the anisotropy of both strength and ductility.

Microstructure and texture evolution of commercially pure Ni processed by accumulative roll-bonding (ARB) up to eight cycles were studied using electron back scattered diffraction (EBSD). During ARB processing, the original coarse equiaxed grains were gradually transformed into refined lamellar grains along the rolling direction (RD). Shear bands started forming after three cycles. The fraction of low angle grain boundaries (LAGBs) increased after the first and second cycle because of orientation spreading within the original grains. However, their fraction decreased with the evolution of high angle grain boundaries (HAGBs) during subsequent deformations, until saturation was reached after six cycles. Overall, the typical deformation texture components (S, Copper and Brass) were enhanced up to six ARB cycles and then only Copper was further strengthened. At higher cycles a higher Copper concentration was found near sample surface than the interiors due to a high frictional shear of ARB processing.

Body-centred cubic magnesium-lithium-aluminium-base alloys are the lightest of all the structural alloys, with recently developed alloy compositions showing a unique multi-dimensional property profile. By hitherto unrecognised mechanisms, such alloys also exhibit exceptional immediate strengthening after solution treatment and water quenching, but strength eventually decreases during prolonged low temperature ageing. We show that such phenomena are due to the precipitation of semi-coherent D03-Mg3Al nanoparticles during rapid cooling followed by gradual coarsening and subsequent loss of coherency. Physical explanation of these phenomena allowed the creation of an exceptionally low-density alloy that is also structurally stable by controlling the lattice mismatch and volume fraction of the Mg3Al nanoparticles. The outcome is one of highest specific-strength engineering alloys ever developed., Solution treatment and quenching can strengthen magnesium-lithium-aluminium alloys, but this strength decreases with ageing. Here, the authors show this is due to semi-coherent nanoparticle precipitation followed by coarsening, and control the lattice mismatch to stabilise the microstructure.

Organometallic iridium(III) complexes have seen widespread use over the past two decades, particularly as phosphorescent dopants in organic light emitting diodes (OLEDs) due to their large spin-orbit coupling and metal-toligand charge transfer (MLCT) excited states. Interest in the non-linear optical (NLO) applications of these materials has increased recently with reports of both two-photon absorption (2PA) and reverse saturable absorption (RSA). A family of materials of the form [IrIII(NO2piq)2(acac)] were synthesized and characterized, where acac is acetylacetonate and NO2piq is a nitrophenylisoquinoline ligand. In order to assess structure-property relationships for the photophysics of these complexes, the placement of the nitro group was altered on the phenyl ring. Systematic control over the maxima of the absorption and photoluminescence bands attributed to the MLCT excited states was achieved through the ligand variation. The photophysical properties of this family of materials are discussed in detail and include their linear absorption spectra, photoluminescence measurements at 298 and 77K, excited state lifetimes, and CIE color chromaticity coordinates.

In this work, we use molecular dynamics simulations to study the stress overshoots of metallic glass Cu50Zr50 in three scenarios (unloading-reloading, slide-stop-slide, and stress serrations) that are associated with shear band relaxation. We found that, after the elastic recovery effect is factored out, atomic volume in the shear band barely changes during compressive relaxation but decreases during tensile relaxation, while local fivefold symmetry increases consistently for both cases. We propose that the atomistic mechanism for the related stress overshoots is due to the relaxation of structural symmetry, instead of free volume, in the shear band. Upon unloading, a propagating shear band continues for some time before arrested, which results in a stress undershoot and could contribute to material fatigue under cyclic elastic loads. We did not directly observe stress serrations via molecular dynamics simulations due to the very high simulated strain rates. While athermal quasistatic simulations produce serrated flow stress, we note that such serrations result from global avalanches of shear events rather than the relaxation of the shear band. Our studies provide atomistic insights on shear-banding dynamics and deepen the understanding of inhomogeneous mechanical response of metallic glasses.

Temperature rise ($\mathrm{\ensuremath{\Delta}}T$) associated with shear banding of metallic glasses is of great importance for their performance. However, experimental measurement of $\mathrm{\ensuremath{\Delta}}T$ is difficult due to temporal and spatial localization of shear bands and, as a result, our understanding of the mechanism of $\mathrm{\ensuremath{\Delta}}T$ is limited. Here, based on molecular dynamics simulations, we observe a spectrum of $\mathrm{\ensuremath{\Delta}}T$, which depends on both sample size and strain rate, in the shear bands of CuZr metallic glass under tension. More importantly, we find that the maximum sliding velocity of the shear bands correlates linearly with the corresponding $\mathrm{\ensuremath{\Delta}}T$, ranging from $\ensuremath{\sim}25$ K up to near the melting point for the samples studied. Taking heat diffusion into account, we expect $\mathrm{\ensuremath{\Delta}}T$ to be lower than 25 K for the lower end of sliding velocity. At high temperature, shear band bifurcation and/or multiplication can occur as a negative feedback mechanism that prevents temperature rising well above the melting point.

This short communication presents 2–4 μm sized TiCN reinforced AlSi10Mg composites (TiCN/AlSi10Mg) fabricated by laser powder bed fusion (LPBF) with refined Al-Si eutectic microstructure consisting of equiaxed bi-modal α-Al grains and enhanced elevated temperature tensile strength. The formation mechanism of reported bi-modal structure is related to the modified temperature gradients and induced heterogeneous nucleation in LPBF. The enhancement in elevated temperature tensile strength is mainly attributed to refined bi-modal Al-Si microstructure and thermal stability of TiCN particles.

Ultrastable metallic glasses (SMGs) are of exceptional interest as they are promising candidates to solve the stability issues of conventional metallic glasses. The annealing-driven structural evolution of a Zr50Cu44.5Al5.5 SMG fabricated by direct current magnetron sputtering, alongside its thermophysical and mechanical properties, were systematically investigated over the temperature range 0.74 to 1.03 T g , where T g is the glass transition temperature. A temperature limit for further improvements in key properties due to annealing was found at 0.8 T g , as a relaxation-to-rejuvenation transition was observed beyond this temperature. This transition temperature agrees well with the optimal temperature range for an SMG formation. The origin of this transformation resides in the local structure deviation from short range order- to medium range order- and the resultant disorder-dominated state upon annealing. Rejuvenation occurs upon the activation of α relaxation, as structural units revert to bulk-like behavior due to a liquid–liquid transition. The abnormal three-stage sub- T g relaxation pattern observed in SMG was caused by a non-monotonic change in structural heterogeneity as annealing temperature increased from 0.74 to 0.93 T g . This work firstly provides direct evidence for an annealing-induced structural evolution in SMG fabricated at room temperature and imparts a better understanding of the optimal temperature range for SMG formation.

The underlying structural changes that provide the perceived unique properties of ultrastable metallic glasses (SMGs) are presently not well understood. Herein, Zr50Cu44.5Al5.5 and Zr50Cu41.5Al5.5Mo3 thin film metallic glasses (TFMGs) fabricated by direct current magnetron sputtering deposition at room temperature were investigated systematically. By tuning the deposition rate from ~250 nm/min to ~5 nm/min, the thermophysical and mechanical properties, as well as the corresponding structural evolution of TFMGs was examined. A clear transition from bulk-like to ultrastable-like behaviour was observed, whereby reducing the deposition rate results in a gradual enhancement in thermal stability and mechanical properties. A distinct structural difference was observed between conventional metallic glasses (MGs) and SMGs, with the latter yielding a more homogeneous and looser-packed structure under greater induced geometric frustration. SMGs show a greater resistance to crystallization as seen by a change in crystallization pathway. The results also show that MGs with more pronounced slow β relaxation have a greater potential to form SMGs with more significant variations in key properties. This work provides new insights into the structural evolution of SMGs with varying deposition rate and has implications in the design and fabrication of SMGs by considering their relaxation dynamics.

Two Al-Sc alloys were examined to establish the relative influence of grain boundary segregation and precipitation of Sc on the microstructural evolution during equal channel angular pressing (ECAP). Due to the ultra-low Sc content in the low-Sc alloy additional measures were taken to ensure a homogenous distribution of the Sc. After casting, this alloy was swaged and homogenised. One ECAP pass and a solution treatment were undertaken before carrying out 10 ECAP passes. For the analysis with transmission electron microscopy (TEM) and transmission Kikuchi diffraction (TKD), electron transparent thin foils were cut parallel to the ECAP extrusion axis and then thinned by using a Struers TenuPol5, at a voltage of 12 V in 30% nitric acid and 70% methanol at -30°C. To assess the grain size stability, the samples were heated to 550°C. Analysis of grain orientation maps obtained by TKD revealed that the grain size, defined by the HAGBs, is three times larger than expected. The distribution of Al3Sc precipitates after heat treatment indicated that recovery occurs.

The growth behavior of the primary β-Co3Sn2 phase in (Co67Sn33)100−x Nb x (x = 0, 0.5, 0.8, 1.0) hypereutectic alloys at different melt undercoolings was investigated systematically. The growth pattern of the β-Co3Sn2 phase at low undercooling changes with the Nb content from fractal seaweed (x = 0, 0.5) into dendrite (x = 0.8) and then returns to fractal seaweed (x = 1.0) as a response to the changes in interface energy anisotropy and interface kinetic anisotropy. As undercooling increases, the dendritic growth of the β-Co3Sn2 phase in (Co67Sn33)99.2Nb0.8 alloy gives way to fractal seaweed growth at an undercooling of 32 K (−241 °C). At larger undercooling, the fractal seaweed growth is further replaced by compact seaweed growth, which occurred in the other three alloys investigated. The growth velocity of the β-Co3Sn2 phase slightly increases at low and intermediate undercooling but clearly decreases at larger undercooling due to the Nb addition. The growth velocity sharply increases as the growth pattern of the Co3Sn2 phase transits from fractal seaweed into compact seaweed.

M23X6 (M-transition metal, X-nonmetal) phases widely exist in alloy steels and some other multicomponent alloys, but were seldom solidified from binary alloys. In the present work, the alloy melt with the nominal composition of Co23B6 phase, Co79.3B20.7, was undercooled to different degrees, and metastable Co23B6 phase was solidified at undercooling beyond 60 K owing to its lower energy barrier to nucleation than the equilibrium Co3B phase. The Co23B6 phase formed at high temperature can be retained to room temperature if the cooling rate is larger than 25 K min−1. This phase was confirmed to be the classic Cr23C6-type structure (space group \( {\text{Fm}}\bar{3}{{\rm m}} \)) with a lattice parameter, measured by Rietveld refinement method, of a = 10.4912(1) A.

Subgrain structures formed during plastic deformation of metals can be observed by electron backscatter diffraction (EBSD) but are challenging to identify automatically. We have adapted a 2D image segmentation technique, fast multiscale clustering (FMC), to 3D EBSD data using a novel variance function to accommodate quaternion data. This adaptation, which has been incorporated into the free open source texture analysis software package MTEX, is capable of segmenting based on subtle and gradual variation as well as on sharp boundaries within the data. FMC has been further modified to group the resulting closed 3D segment boundaries into distinct coherent surfaces based on local normals of a triangulated surface. We demonstrate the excellent capabilities of this technique with application to 3D EBSD data sets generated from cold rolled aluminum containing well-defined microbands, cold rolled and partly recrystallized extra low carbon steel microstructure containing three magnitudes of boundary misorientations, and channel-die plane strain compressed Goss-oriented nickel crystal containing microbands with very subtle changes in orientation.

Bulk metallic glasses (BMGs) are multicomponent metal alloys that form a glassy structure with relative ease upon cooling from the melt. Unique to glassy materials is a glass-transition (temperature), whereby the vitreous solid relaxes into a supercooled liquid state, leading to a dramatic decrease in viscosity. This softening behaviour allows novel thermoplastic forming and bonding processes to be carried out that are simply unachievable among conventional metal processing methods. The work presented herein utilises this supercooled liquid state by infiltrating carbon fibres within a Mg-based BMG to manufacture fully-dense carbon fibre reinforced BMGs which also exhibit unique secondary forming capabilities.

The corrosion and dissolution of a new magnesium-lithium (Mg-Li) alloy was studied using an electrochemical flow cell coupled with inductively coupled plasma-mass spectroscopy (ICP-MS) allowing real-time spectroelectrochemical analysis. The alloy studied is a corrosion resistant Mg-33at. % Li alloy, which possesses a body centered cubic matrix and a homogenous nanostructure. A detailed investigation of the dissolution kinetics of this alloy is important for understanding the origins of its apparently high corrosion resistance. Whilst the alloy composition ratio of Mg: Li is similar to 2, it was revealed that the dissolution ratio of metallic Mg: Li in 0.01 M NaCl was similar to 3.4 via downstream detection of ions. The deficiency of Li detected in the downstream electrolyte via ICP-MS was attributed to the development of a persistent Li-rich surface film that forms dynamically in the open circuit condition and for applied potentials below similar to-1050 mV(Ag/AgCl). For potentials positive to similar to-1050 mV(Ag/AgCl), significant Li ion detection in solution was observed, commensurate with the alloy compositional ratio.

The limit in structural refinement of lamellar bands (LBs) generated during accumulative roll bonding (ARB) of commercially pure nickel was investigated by transmission electron microscopy and transmission Kikuchi diffraction. A typical LB consists of an internal cellular substructure of low angle boundaries (LABs) bounded by two high angle boundaries (HABs) that are aligned parallel to the rolling plane. At low true strains (e 4.8; 6 to 10 ARB cycles), a homogenous distribution of well-defined, highly elongated LBs of average thickness 75 nm was generated throughout the entire thickness of the material. The thickness of these LBs decreased with increasing number of ARB cycles and reached a saturation thickness of ~75 nm after 6 to 8 cycles. A theoretical framework for the limit to LB refinement during ARB is presented based on the refinement rate due to the stored energy of deformation balanced by the growth rate caused by adiabatic heating. The analysis takes into account the unique features of LB structures and processing parameters.

The effect of substrate temperature on the structure and properties of magnetron sputtered Zr–Cu–Ni–Al–Hf–Ti thin films were systematically investigated. With increasing deposition temperature from 293 K to 493 K, the films remain amorphous but their thermal stability decreases. Crystallization occurs as the substrate temperature reaches 563 K. It was demonstrated that the hardness and Young's modulus of glassy films were enhanced and fracture toughness was worsen by increasing the substrate temperature, along with generating a denser structure. Through the scaling analysis, it was revealed that all glassy films grow in an anomalous mode. These metallic glass films prepared herein exhibit extremely low roughness, less than 1 nm, high thermal stability and excellent mechanical properties, which are useful properties for their potential use for MEMS and other industry applications.

As a promising remedy for overcoming the limited ductility and work softening of bulk metallic glasses (BMGs), BMG composites incorporating a B2 crystalline phase have attracted considerable attention. Here, we explore the formation of Zr-Co-Al BMG composites by quenching alloys Zr55Co31Al14, Zr54.5Co33.5Al12, Zr53.5Co36.5Al10, Zr52.5Co37.5Al10, and Zr43Co43Al14. We found the first alloy fully amorphous whereas the fifth was fully crystallized upon quenching. The other three were quenched to generate composite structures, with a higher fraction of B2 ZrCo phase with increasing Co/Zr ratio and decreasing Al content. For comparison, the formation of B2 ZrCo in annealed Zr55Co31Al14 was also studied. For both approaches the influence of crystalline phases on hardness was examined.

Experimental observations of grain boundary fracture behavior have been used as exemplars, and boundaries with the same crystallography as the experiments were developed. These boundaries were non-symmetrical, and this necessitated the first ever study of non-symmetrical boundaries in magnesium using density functional theory. The broad agreement of the calculated boundary cohesion values with the experimental observations of fracture behavior showed the simulations to be good approximations of real behavior, and from this point the simulations were further interrogated to understand the differences between the boundary types and solute species. Solutes with both larger and smaller radii than magnesium had a preference for segregation to the grain boundary. The boundary cohesion was examined by the parameter known as embrittlement potency, and it was found that solutes smaller than magnesium had a toughening effect, while those solutes larger than magnesium had more tendency to embrittle. The two boundaries studied in most detail, the { 10 1 ‾ 2 } twin boundary, and a general grain boundary observed experimentally, showed different cohesive behaviors. Although the symmetrical twin boundary behaved in a similar manner to previous reports, the non-symmetrical boundary showed more complex cohesive behavior, highlighting the importance of studying the non-symmetrical boundaries that predominate real materials.

The temperature rise in shear bands is of significant importance for the mechanical behaviour of metallic glasses since it changes their atomic structure and viscosity. However, experimental measurement of any temperature rise of a shear band is difficult, due to their temporal and spatial localization within the bulk. Molecular dynamics simulations were carried out on a CuZr metallic glass under tensile loading. It is shown that the observed temperature rise in a shear band, ranging from ~25 K up to the melting point of the alloy, correlates linearly with the maximum sliding velocity of the shear band, which is a function of both sample size and loading rate. In response to the high energy flux into the shear band, shear band bifurcation occurs and hinders further temperature rise well above the melting point. This negative feedback mechanism imposes an upper limit of temperature rise in a shear band before the theoretical limit of shear velocity is reached.

Al71.25Cu16.15Mg7.6Ni5 amorphous alloy ribbons were prepared using melt-spinning technique. The structure related to the phase transformation of the amorphous alloy ribbon was studied by X-ray diffraction and differential scanning calorimetry (DSC). It was found that the ribbon exhibits two separate diffuse shoulders with peak positions. Formation of cubic-Al was observed when the ribbon was heated beyond the primary crystallization peak. Upon secondary crystallization peak, cubic-Al, Al3Ni and Al2CuMg were observed. The evolution of the lattice constant, a, for the cubic-Al and Al2CuMg, were determined by the Rietveld procedure. The lattice constant for cubic-Al remains almost constant between the primary and fully crystallization temperature after sudden change at secondary crystallization temperature. The lattice constant for Al2CuMg increases when the temperature increases. Both crystallite size of cubic-Al and Al2CuMg were increased as temperature increases.

Quantum mechanical calculations have been performed to establish general trends in propensity for the segregation of solutes across the periodic table at or in the neighborhood of an extended set of commonly observed special grain boundaries in face centered cubic aluminium. To this end, Al has been considered as the matrix and elements from 3d and 4d transition metals as well as those from group II, III and IV have been selected as solute atoms. For transition metal solutes, we find a concave-up parabolic-like dependency of segregation energy as a function of atomic number that is argued to be caused by the competition between chemical bonding and atomic size effects. The analysis is corroborated quantitatively by the computation of crystal orbital Hamiltonian population for solute-Al and Al-Al pairs as well as the Voronoi polyhedral surrounding solutes at a sample GB. The parabolic-like (concave-down trend) dependency of the cohesiveness of grain boundaries is explained by an equivalent trend in the bonding strength of Al-Al pairs at the segregated GBs. We extend this investigation to examine the stability of the solid solution polycrystalline state by comparing the calculated segregation energy against the combined energetic cost of grain boundary and intermetallic precipitate formation. The results may serve as a design tool for tailoring polycrystalline alloys with desired properties Refereed/Peer-reviewed