Design and implementation of the monochromator shielding for the cold neutron spectrometers XINGZHI and BOYA

An innovative monochromator shielding is designed and implemented for the cold neutron spectrometers XINGZHI and BOYA operated by Renmin University of China at China Advanced Research Reactor.Via Monte Carlo simulations and careful mechanical designs,a shielding configuration has been successfully developed to satisfy safety requirements of below 3μSv/h dose rate at its exterior,meanwhile fulfilling space,floor load and nonmagnetic requirements.Composite materials are utilized to form the sandwich-type shielding walls:the inner layer of boron carbide rubber,the middle layer of steel-encased lead and the outer layer of borated polyethylene.Special-shaped liftable shielding blocks are incorporated to facilitate a continuous adjustment of the neutron energy while preventing radiation leakage.Our work has demonstrated that by utilizing composite shielding materials,along with the sandwich structure and liftable shielding blocks,a compact and lightweight shielding solution can be achieved.This enables the realization of advanced neutron scattering instruments that provide expanded space of measurement,larger energy and momentum coverage,and higher flux on the sample.This shielding represents the first of its kind in neutron scattering instruments in China.Following its successful operation,it has been subsequently employed by other neutron instruments across the country.

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.

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.

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.

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.

Direct Ethylene Purification from Cracking Gas via a Metal–Organic Framework Through Pore Geometry Fitting

The direct one-step separation of polymer-grade C_(2)H_(4) from complex light hydrocarbon mixtures has high industrial significance but is very challenging.Herein,an ethylene-adsorption-weakening strategy is applied for precise regulation of the pore geometry of four tailor-made metal–organic frameworks(MOFs)with pillar-layered structures,dubbed TYUT-10/11/12/13.Based on its pore geometry design and functional group regulation,TYUT-12 exhibits exceptional selective adsorption selectivity toward C_(3)H_(8),C_(3)H_(6),C_(2)H_(6),C_(2)H_(2),and CO_(2) over C_(2)H_(4);its C_(2)H_(6)/C_(2)H_(4) adsorption selectivity reaches 4.56,surpassing the record value of 4.4 by Fe_(2)(O_(2))(dobdc)(dobdc^(4-)=2,5-dioxido-1,4-benzenedicarboxylate).The weak p–p stacking binding affinity toward C_(2)H_(4) in TYUT-12 is clearly demonstrated through a combination of neutron powder diffraction measurements and theoretical calculations.Breakthrough experiments demonstrate that C_(2)H_(4) can be directly obtained from binary,ternary,quaternary,and six-component light hydrocarbon mixtures with over 99.95%purity.

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.

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).

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.