Multiscale structures and phase transitions in metallic glasses：A scattering perspective

Amorphous materials are ubiquitous and widely used in human society, yet their structures are far from being fully understood. Metallic glasses, a new class of amorphous materials, have attracted a great deal of interests due to their exceptional properties. In recent years, our understanding of metallic glasses increases dramatically, thanks to the development of advanced instrumentation, such as in situ x-ray and neutron scattering. In this article, we provide a brief review of recent progress in study of the structure of metallic glasses. In particular, we will emphasize, from the scattering perspective, the multiscale structures of metallic glasses, i.e., short-to-medium range atomic packing, and phase transitions in the supercooled liquid region, e.g., crystallization and liquid-to-liquid phase transition. We will also discuss, based on the understanding of their structures and phase stability, the mechanical and magnetic properties of metallic glasses.

Evolution of medium-range order and its correlation with magnetic nanodomains in Fe-Dy-B-Nb bulk metallic glasses

Fe-based metallic glasses are promising functional materials for advanced magnetism and sensor fields.Tailoring magnetic performance in amorphous materials requires a thorough knowledge of the correlation between structural disorder and magnetic order,which remains ambiguous.Two practical difficulties remain:the first is directly observing subtle magnetic structural changes on multiple scales,and the second is precisely regulating the various amorphous states.Here we propose a novel approach to tailor the amorphous structure through the liquid-liquid phase transition.In-situ synchrotron diffraction has unraveled a medium-range ordering process dominated by edge-sharing cluster connectivity during the liquid-liquid phase transition.Moreover,nanodomains with topological order have been found to exist in composition with liquid-liquid phase transition,manifesting as hexagonal patterns in small-angle neutron scattering profiles.The liquid-liquid phase transition can induce the nanodomains to be more locally ordered,generating stronger exchange interactions due to the reduced Fe–Fe bond length and the enhanced structural order,leading to the increment of saturation magnetization.Furthermore,the increased local heterogeneity at the medium-range scale enhances the magnetic anisotropy,promoting the permeability response under applied stress and leading to a better stress-impedance effect.These experimental results pave the way to tailor the magnetic structure and performance through the liquid-liquid phase transition.

Frontiers in high entropy alloys and high entropy functional materials

Owing to their exceptional properties,high-entropy alloys(HEAs)and high-entropy materials have emerged as promising research areas and shown diverse applications.Here,the recent advances in the field are comprehensively reviewed,organized into five sections.The first section introduces the background of HEAs,covering their definition,significance,application prospects,basic properties,design principles,and microstructure.The subsequent section focuses on cutting-edge high-entropy structural materials,highlighting developments such as nanostructured alloys,grain boundary engineering,eutectic systems,cryogenic alloys,thin films,micro-nano-lattice structures,additive manufacturing,high entropy metallic glasses,nano-precipitate strengthened alloys,composition modulation,alloy fibers,and refractory systems.In the following section,the emphasis shifts to functional materials,exploring HEAs as catalysts,magneto-caloric materials,corrosion-resistant alloys,radiation-resistant alloys,hydrogen storage systems,and materials for biomedicine.Additionally,the review encompasses functional high-entropy materials outside the realm of alloys,including thermoelectric,quantum dots,nanooxide catalysts,energy storage materials,negative thermal expansion ceramics,and high-entropy wave absorption materials.The paper concludes with an outlook,discussing future directions and potential growth areas in the field.Through this comprehensive review,researchers,engineers,and scientists may gain valuable insights into the recent progress and opportunities for further exploration in the exciting domains of high-entropy alloys and functional materials.

In situ scattering study of multiscale structural evolution during liquid–liquid phase transition in Mg-based metallic glasses

The glass-forming ability of Mg-Cu-Gd alloys could be significantly promoted with the addition of Ag.A calorimetric anomaly could be observed in the supercooled liquid region of the Mg-Cu-Ag-Gd metallic glass,indicating the occurrence of a liquid-state phase transition driven by entropy.However,the underlying mechanism of the polyamorphous phase transition remains unsettled.In the paper,in situ scattering techniques were employed to reveal multiscale structure evidence in a Mg65Cu15Ag10Gd10metallic glass with an anomalous exothermic peak upon heating.Resistivity measurements indicate a reentrant behavior for the Mg-Cu-Ag-Gd metallic glass in the anomalous exothermic peak temperature region during heating.In situ synchrotron diffraction results revealed that the local atomic structure tends to be ordered and loosely packed first,followed by reentering into the initial state upon heating.Moreover,time-resolved small-angle synchrotron X-ray scattering(SAXS) results show an increase in nanoscale heterogeneity first followed by a reentrant supercooled liquid behavior.A core-shell structure model has been used to fit the SAXS profiles when polyamorphous phase transition occurs.In contrast,there is no structure anomaly for the reference Mg-Cu-Gd alloy system.The detailed multiscale structural evidence suggests the occurrence of a liquid-liquid phase transition followed by a reentrant behavior in the MgCu-Ag-Gd metallic glass.Our results deepen the understanding of the structural origin of the glass-forming ability and shed light on the possibility of tuning the physical and mechanical properties by heat-treatment in the supercooled liquid region of Mg-based metallic glasses.

Phase selection rule of high-entropy metallic glasses with different short-to-medium-range orders

When an equiatomic multi-component alloy is quenched from its molten state down to room temperature,either a solid solution crystalline alloy or a metallic glass is formed.The former is called a high-entropy alloy,whereas the latter is referred as a high-entropy metallic glass(HE-MG).In such multicomponent alloys,thermodynamic parame-ters,e.g.,the mixing entropy,the mixing enthalpy and other parameters such as atomic size mismatch,determine the resulting phases.

Ultrahard BCC-AlCoCrFeNi bulk nanocrystalline high-entropy alloy formed by nanoscale diffusion-induced phase transition

In the current work,the BCC-AlCoCrFeNi bulk nanocrystalline high-entropy alloy(nc-HEA)with ultrahigh hardness was formed by nanoscale diffusion-induced phase transition in a nanocomposite.First,a dual-phase Al/CoCrFeNi nanocrystalline high-entropy alloy composite(nc-HEAC)was prepared by a laser source inert gas condensation equipment(laser-IGC).The as-prepared nc-HEAC is composed of well-mixed FCC-Al and FCC-CoCrFeNi nanocrystals.Then,the heat treatment was used to trigger the interdiffusion between Al and CoCrFeNi nanocrystals and form an FCC-AlCoCrFeNi phase.With the increase of the annealing temperature,element diffusion intensifies,and the Al Co Cr Fe Ni phase undergoes a phase transition from FCC to BCC structure.Finally,the BCC-AlCoCrFe Ni bulk nc-HEA with high Al content(up to 50 at.%)was obtained for the first time.Excitingly,the nc-HEAC(Al-40%)sample exhibits an unprecedented ultra-high hardness of 1124 HV after annealing at 500℃ for 1 h.We present a systematic investigation of the relationship between the microstructure evolution and mechanical properties during annealing,and the corresponding micro-mechanisms in different annealing stages are revealed.The enhanced nanoscale thermal diffusion-induced phase transition process dominates the mechanical performance evolution of the nc-HEACs,which opens a new pathway for the design of high-performance nanocrystalline alloy materials.

Phase transformation behavior of a dual-phase nanostructured Fe-Ni-B-Si-P-Nb metallic glass and its correlation with stress-impedance properties

A study of the phase transformation process of a Fe-Ni-B-Si-P-Nb metallic glass using a suite of advanced characterization tools is reported.Transmission electron microscopy(TEM)and small angle neutron scattering(SANS)experiments show that the as-spun metallic glass ribbon has a dual-phase structure with bcc nanoclusters of a size of 2-3 nm.In situ high-energy X-ray diffraction(XRD)reveals a three-stage crystallization process when heating the metallic glass into supercooled liquid states.The isothermal annealing experiment shows the nanoclusters grow instantly without incubation.The easy formation and phase stability of the nanoclusters are due to the low interfacial energy between the amorphous matrix and clusters,as real space analysis shows that the nanoclusters and the amorphous matrix share similar short-to-mediumrange orders.We further find that the dual-phase structure reduces local magneto-anisotropy and enhances effective magnetic permeability,resulting in an excellent stressimpedance effect without sacrificing coercivity.Our work sheds light on the structure-property engineering of soft magnetic metallic glasses and provides a foundation for developing novel magnetic functional materials with nanostructured dual-phases.

Continuous chemical redistribution following amorphous-to-crystalline structural ordering in a Zr-Cu-Al bulk metallic glass

Bulk metallic glasses(BMGs)are thermodynamically metastable.As such,crystallization occurs when a BMG is thermally annealed at a temperature above the glass transition temperature.While extensive studies have been performed on the crystallization kinetics of BMGs,most of them have focused on the amorphous-to-crystalline structural ordering,and little attention has been paid to chemical distribution and its relationship with the structural ordering during the crystallization process.In this paper,a new approach,with simultaneous differential scanning calorimetry(DSC)and small angle neutron scatter-ing(SANS)measurements,was applied to study in situ the crystallization of a Zr_(45.5)Cu_(45.5)Al_(9)BMG upon isothermal annealing at a temperature in the supercooled liquid region.Quantitative analysis of the DSC and SANS data showed that the structural evolution during isothermal annealing could be classified into three stages:(Ⅰ)incubation;(Ⅱ)amorphous-to-crystalline structural ordering;(Ⅲ)continuous chemical redistribution.This finding was validated by composition analysis with atom probe tomography(APT),which further identified a transition region formed by expelling Al into the matrix.The transition re-gion,with a composition of(Cu,Al)_(50)Zr_(50),served as an intermediate step facilitating the formation of a thermodynamically stable crystalline phase with a composition of(Cu,Al)_(10)Zr_(7).

In situ study on medium-range order evolution during the polyamorphous phase transition in a Pd-Ni-P nanostructured glass

Engineering multiscale structural hierarchies in glassy alloys enable a broad spectrum of potential applications.Metallic glasses were born in hierarchical structures from atomic-to-nanometer scales.However,the frozen-in structures in traditional metallic glasses prepared by rapid quenching techniques are challenging to tailor.Here,we show that a PdNiPbulk nanostructured glass of polyamorphous interfacial structures was prepared by inert-gas condensation with a laser evaporation source,and its multiscale structures could be engineered.In-situ scattering experiment results reveal polyamorphous phase transitions occurred in the interfacial regions,which are accompanied by the evolution of medium-range order and the nanoscale heterogeneous structures during the condensation process of glassy nanoparticles under high pressure and the following heating process.Moreover,changes in the cluster connectivity resulting from repacking of the local ordering induced by pressure and temperature could be observed.The thermophysical and mechanical properties,including boson peaks,hardness,and elasticity modulus,could be changed as a function of heat-treatment parameters.Our findings would shed light on the synthesis of bulk nanostructured glassy alloys with tailorable thermodynamic and dynamical behavior as well as mechanical properties based on the understanding of metastability for polyamorphous interfacial phases.

Effects of casting current on structure and properties of a nanostructured Zr-Cu-Fe-Al bulk metallic glass

The effects of casting currents on the thermophysical behaviors, atomic and nanoscale structure, and mechanical properties of two Zr-based-bulk metallic glasses, i.e., Zr59Cu33A18 and Zr59（Cuo.55Feo.45）33A18, were studied by using differential scanning calorimetry, wide-angle X-ray diffraction, and small-angle X-ray scattering, as well as compression tests. The casting currents can be tuned to change the casting initiative temperature. Results revealed that there is no anomalous structural change for the Zr59Cu33A18 molten liquid before crystallization during cooling with different casting currents. In contrast, liquid-state phase separation was suggested to occur in the Zr59（Cuo.55Feo.45）33A18 molten liquid prepared using lower casting current before crystallization during cooling. The position shift of the first sharp diffraction peak for the diffraction pattern of Zr59（Cuo.55Feo.45）33A18 shows that the density of the molten liquid may decrease upon cooling at different casting currents. The small-angle X-ray scattering results indicate that the heterogeneity of the Zr59（Cuo.55- Feo.gs）33A18 metallic glasses increases with decreasing the casting temperature. As a result, the metallic glasses with a liquid-state phase separation possess better mechanical properties, including higher-yielding stress and more significant compressive ductility. The increase in degree of heterogeneity formed by nanoscale liquid-state phase separation and their interactions with the shear bands for the Zr-Cu-Fe-Al bulk metallic glasses were suggested to be responsible for the enhanced mechanical properties.

Medium-range order endows a bulk metallic glass with enhanced tensile ductility

Developing ductile bulk metallic glasses(BMGs)can benefit from an in-depth understanding of the structure-property relation during plastic deformation.However,endowing BMGs with tensile ductility in BMGs needs to reveal the response of critical structure units during deformation.Here,we report the experimental results of an in-situ synchrotron high-energy X-ray study of a Zr-based BMG under uniaxial tension after preprocessing by canning compression of the three-dimensional compressive stress state.It is revealed that the canning-compressed BMG(CC-BMG)sample has better tensile ductility and higher ultimate strength than the as-cast sample,which possesses heterogeneous and loosely packed local struc-tures on medium-range scales.The experimental results revealed two stages of plastic deformation in the CC-BMGs compared with one stage of plastic deformation in the as-cast BMG.Moreover,the shift in the first sharp diffraction peak along the tension direction for the canning-compressed sample is substan-tially more pronounced than that of the as-cast sample.Furthermore,the real-space analysis illustrates a competition mechanism between the 2-atom and 3-atom connection modes on medium-range order during the plastic deformation of the CC-BMG.Additionally,the ordering on the medium-range scale de-creases in the first plastic deformation stage but increases in the second plastic deformation stage.There-fore,a structural crossover phenomenon occurs in the CC-BMG during plastic deformation.Our results demonstrate a structure-property correlation for the CC-BMGs of heterogeneous medium-range ordered structures,which may be beneficial for endowing BMGs with ductility based on medium-range order engineering techniques.

In Situ Scattering Studies of Crystallization Kinetics in a Phase-Separated Zr-Cu-Fe-Al Bulk Metallic Glass

Thermal stability and the crystallization kinetics of a phase-separated Zr-Cu-Fe-Al bulk metallic glass were investigated using in situ high-energy synchrotron X-ray and neutron diffraction,as well as small-angle synchrotron X-ray scattering.It was revealed that this glass with excellent glass-forming ability possesses a two-step crystallization behavior.The crystalline products and their evolution sequence are more complicated than a homogeneous Zr-Cu-Al glass with average glass-forming ability.The experimental results indicate that a finely distributed nanometer-sized cubic Zr_(2)Cu phase forms first and then transforms to a tetragonal Zr_(2)Cu phase,while the matrix transforms to an orthorhombic Zr_(3)Fe phase.The strength of the Zr-Cu-Fe-Al composite containing cubic Zr_(2)Cu phase and glass matrix increases,and the plasticity also improves compared to the as-cast Zr-Cu-Fe-Al bulk metallic glass.Our results suggest that the formation of multiple and complex crystalline products would be the characteristics of the Zr-Cu-Fe-Al glass with better glass-forming ability.Our study may shed light on the synthesis of bulk-sized glass-nanocrystals composites of high strength and good plasticity.

Inheritance factor on the physical properties in metallic glasses

Material genetic engineering can significantly accelerate the development of new materials.As an important topic in material science and condensed matter physics,the development of metallic glasses(MGs)with specific properties has largely been the result of trial and error since their discovery in 1960.Yet,property design based on the physical parameters of constituent elements of MGs remains a huge challenge owing to the lack of an understanding of the property inheritance from constitute elements to the resultant alloys.In this work,we report the inherent relationships of the yield strengthσ_(y),Young’s modulus E,and shear Modulus G with the valence electron density.More importantly,we reveal that the electronic density of states(EDOSs)at the Fermi surface(E_(F))is an inheritance factor for the physical properties of MGs.The physical properties of MGs are inherited from the specific element with the largest coefficient of electronic specific heat(γ_(i)),which dominates the value of the EDOS at E_(F).This work not only contributes to the understanding of property inheritances but also guides the design of novel MGs with specific properties based on material genetic engineering.