Microstructures and micromechanical behaviors of high -entropy alloys investigated by synchrotron X-ray and neutron diffraction techniques: A review

High-entropy alloys(HEAs)possess outstanding features such as corrosion resistance,irradiation resistance,and good mechan-ical properties.A few HEAs have found applications in the fields of aerospace and defense.Extensive studies on the deformation mech-anisms of HEAs can guide microstructure control and toughness design,which is vital for understanding and studying state-of-the-art structural materials.Synchrotron X-ray and neutron diffraction are necessary techniques for materials science research,especially for in situ coupling of physical/chemical fields and for resolving macro/microcrystallographic information on materials.Recently,several re-searchers have applied synchrotron X-ray and neutron diffraction methods to study the deformation mechanisms,phase transformations,stress behaviors,and in situ processes of HEAs,such as variable-temperature,high-pressure,and hydrogenation processes.In this review,the principles and development of synchrotron X-ray and neutron diffraction are presented,and their applications in the deformation mechanisms of HEAs are discussed.The factors that influence the deformation mechanisms of HEAs are also outlined.This review fo-cuses on the microstructures and micromechanical behaviors during tension/compression or creep/fatigue deformation and the application of synchrotron X-ray and neutron diffraction methods to the characterization of dislocations,stacking faults,twins,phases,and intergrain/interphase stress changes.Perspectives on future developments of synchrotron X-ray and neutron diffraction and on research directions on the deformation mechanisms of novel metals are discussed.

Intensity correlation properties of x-ray beams split with Laue diffraction

Beam splitting is one of the main approaches to achieving x-ray ghost imaging, and the intensity correlation between diffraction beam and transmission beam will directly affect the imaging quality. In this paper, we investigate the intensity correlation between the split x-ray beams by Laue diffraction of stress-free crystal. The analysis based on the dynamical theory of x-ray diffraction indicates that the spatial resolution of diffraction image and transmission image are reduced due to the position shift of the exit beam. In the experimental setup, a stress-free crystal with a thickness of hundredmicrometers-level is used for beam splitting. The crystal is in a non-dispersive configuration equipped with a double-crystal monochromator to ensure that the dimension of the diffraction beam and transmission beam are consistent. A correlation coefficient of 0.92 is achieved experimentally and the high signal-to-noise ratio of the x-ray ghost imaging is anticipated.Results of this paper demonstrate that the developed beam splitter of Laue crystal has the potential in the efficient data acquisition of x-ray ghost imaging.

Tracking the phase transformation and microstructural evolution of Sn anode using operando synchrotron X-ray energy-dispersive diffraction and X-ray tomography

Tin(Sn)holds great promise as an anode material for next-generation lithium(Li)ion batteries but suffers from massive volume change and poor cycling performance.To clarify the dynamic chemical and microstructural evolution of Sn anode during lithiation and delithiation,synchrotron X-ray energydispersive diffraction and X-ray tomography are simultaneously employed during Li/Sn cell operation.The intermediate Li-Sn alloy phases during de/lithiation are identified,and their dynamic phase transformation is unraveled which is further correlated with the volume variation of the Sn at particle-and electrode-level.Moreover,we find that the Sn particle expansion/shrinkage induced particle displacement is anisotropic:the displacement perpendicular to the electrode surface(z-axis)is more pronounced compared to the directions(x-and y-axis)along the electrode surface.This anisotropic particle displacement leads to an anisotropic volume variation at the electrode level and eventually generates a net electrode expansion towards the separator after cycling,which could be one of the root causes of mechanical detachment and delamination of electrodes during long-term operation.The unraveled chemical evolution of Li-Sn and deep insights into the microstructural evolution of Sn anode provided here could guide future design and engineering of Sn and other alloy anodes for high energy density Li-and Na-ion batteries.

Thermal expansivity of geikielite and ilmenite utilizing in-situ synchrotron X-ray diffraction at high temperature

The unit-cell parameters and volumes of geikielite(MgTiO_(3))and ilmenite(FeTiO_(3))were investigated at high temperatures up to 700 K and ambient pressure,using in-situ angle-dispersive synchrotron X-ray diffraction.No phase transition was detected over the experimental temperature range.Using(Berman in J Petrol29:445-522,1988.10.1093/petrology/29.2.445)equations to fit the temperature-volume data,the volumetric thermal expansion coefficients at ambient conditions(α_(V0))of MgTiO_(3) and FeTiO_(3) were obtained as follows:2.55(6)×10^(-5)K^(-1)and 2.82(10)×10^(-5)K^(-1),respectively.We infer that the larger effective ionic radius of Fe^(2+)(Ⅵ)(0.78 A)than that of Mg^(2+)(Ⅵ)(0.72?)renders FeTiO_(3)has a larger volumetric thermal expansivity than MgTiO_(3).Simultaneously,the refined axial thermal expansion coefficients under ambient conditions areα_(a0)=0.74(3)×10^(-5)K^(-1)andα_(c0)=1.08(5)×10^(-5)K^(-1)for the aaxis and c-axis of MgTiO_(3),respectively,andα_(a0)=0.95(5)×10^(-5)K^(-1)andα_(c0)=0.92(12)×10^(-5)K^(-1)for the aaxis and c-axis of FeTiO_(3),respectively.The axial thermal expansivity of MgTiO_(3) is anisotropic,but that of FeTiO_(3) is nearly isotropic.We infer that the main reason for the different axial thermal expansivity between MgTiO_(3) and FeTiO_(3) is that the thermal expansion mode of the Mg-O bond in MgTiO_(3) is different from that of the Fe-O bonds in FeTiO_(3).

Thermal expansion of kyanite at ambient pressure:An X-ray powder diffraction study up to 1000℃

The thermal expansion coefficients of kyanite at ambient pressure have been investigated by an X-ray powder diffraction technique with temperatures up to 1000 ℃. No phase transition was observed in the experimental temperature range. Data for the unit-cell parameters and temperatures were fitted empirically resulting in the following thermal expansion coefficients： αa = 5.8（3） × 10^-5, αb = 5.8 （1）× 10^-5, αc = 5.2（1）× 10^-5, and αv = 7.4（1） × 10^-3 ℃ 1 in good agreement with a recent neutron powder diffraction study. On the other hand, the variation of the unit-cell angles α, β and γ of kyanite with increase in temperature is very complicated, and the agreement among all studies is poor. The thermal expansion data at ambient pressure reported here and the compression data at ambient temperature from the literature suggest that, for the kyanite lattice, the most and least thermally expandable directions correspond to the most and least compressible directions, respectively.

X-ray Diffraction of Dust Particles in Spring Beijing

X-ray diffractometry was utilized to study the mineralogical characteristics of the inhalable particles （PM10） sampled during two dust storms in Beijing city on March 18th and May 21st, 2008. We confirm, for the first time, that there stably exists ammonium chloride in the atmosphere when temperature is low. The total sulfates particles were affected by relative humidity. Both species and concentration of sulfates decreased first and then grew back by the end of each dust storm. Koninckite, a phosphate mineral never reported as particulate aerosol before, was identified. Meanwhile, our result shows that a chemical modification on dust minerals occurs during long range transportation. PM10 samples collected during the period of dust storms were dominated by crustal minerals such as quartz, illite/smectite, illite, chlorite, feldspar and calcite, and were notably higher in concentration than that in normal periods of time. The amounts of total sulfates, calcite and feldspar altered in each dust storm. It is derived from 24-hour isentropic backward trajectories that two dust events in spring 2008 originated in different sources.

MULTI-PEAK MATCH INTENSITY RATIO METHOD OF QUANTI-TATIVE X-RAY DIFFRACTION PHASE ANALYSIS

A new method for quantitative phase analysis is proposed by using X-ray diffraction multi-peak match intensity ratio. This method can obtain the multi-peak match intensity ratio among each phase in the mixture sample by using all diffraction peak data in the mixture sample X-ray diffraction spectrum and combining the relative intensity distribution data of each phase standard peak in JCPDS card to carry on the least square method regression analysis. It is benefit to improve the precision of quantitative phase analysis that the given single line ratio which is usually adopted is taken the place of the multi-peak match intensity ratio and is used in X-ray diffraction quantitative phase analysis of the mixture sample. By analyzing four-group mixture sample, adopting multi-peak match intensity ratio and X-ray diffraction quantitative phase analysis principle of combining the adiabatic and matrix flushing method, it is tested that the experimental results are identical with theory.

Investigation of Peak Separation for X-ray Diffraction Profiles of Spinodal Decomposition by a Kind of Optimized Voigt Function

The intensity and position of sidebands (satellites) on both sides of main diffraction peak in a great number of X-ray diffraction profiles of alloys always change with progress of aging. The sidebands position is determined by a newly optimized Voigt function in present investigation. Furthermore, for Cu-4 wt pet Ti alloy aged at 400℃ for 720 min and 1080 min, after introducing the weight factor of above two satellites intensity, the relative error between the fitting curves and X-ray diffraction profiles is less than 0.185%, which is more precise than the previously calculating result.

Operando X-ray diffraction analysis of the degradation mechanisms of a spinel LiMn2O4 cathode in different voltage windows

The understanding of reaction mechanisms of electrode materials is of significant importance for the development of advanced batteries.The LiMn2O4 cathode has a voltage plateau around 2.8 V(vs.Li^+/Li),which can provide an additional capacity for Li storage,but it suffers from a severe capacity degradation.In this study,operando X-ray diffraction is carried out to investigate the structural evolutions and degradation mechanisms of LiMn2O4 in different voltage ranges.In the range of 3.0-4.3 V(vs.Li^+/Li),the LiMn2O4 cathode exhibits a low capacity but good cycling stability with cycles up to 100 cycles and the charge/discharge processes are associated with the reversible extraction/insertion of Li^+from/into LixMn2O4(0≤x≤1).In the range of 1.4-4.4 V(vs.Li^+/Li),a capacity higher than 200 mAh/g is achieved,but it rapidly decays during the cycling.The voltage plateau around 2.8 V(vs.Li^+/Li)is related to the transformation of the cubic LiMn2O4 phase to the tetragonal Li2Mn2O4 phase,which leads to the formation of cracks as well as the performance degradation.

Structure of MgSO_4 in Concentrated Aqueous Solutions by X-Ray Diffraction

Detailed time-and-space-averaged structure of MgSO4 in the concentrated aqueous solutions was investigated via X-ray diffraction with an X’pert Pro θ-θ diffractometer at 298 K, yielding structural function and radial distribution function（RDF）. The developed KURVLR program was employed for the theoretical investigation in consideration of the ionic hydration and ion association. Multi-peaks Gaussian fitting method was applied to deconvolving the overlapping bands of Differential radial distribution function（DRDF）. The calculation of the geometric model shows that octahedrally six-coordinated Mg（H2O）62＋, with an Mg2＋…OW bond length of 0.201 nm dominates in the solutions. There exists contact ion-pair（CIP） in the more concentrated solution（1：18, H2O/salt molar ratio） with a coordination number of 0.8 and a characteristic Mg…S distance of 0.340 nm. The result indicates the hydrated SO42– ion happens in the solution. The S…OW bond distance was determined to be 0.382 nm with a coordination number of 13. The fraction of CIP increases significantly with the increasing concentration. The symmetry of the hydration structure of sulfate ion is lowered by forming complex with magnesium ion.

X-ray Multiple Diffraction Topographic Imaging Technique For Growth History Study of Habit Modifying Impurity Doped Crystals

A novel crystal characterization instrument has been built up in which a combination of X-ray multiple diffraction and X-ray topography is applied to enabling the cross-correlation between micro-crystallographic symmetry and its spatial dependence in relation to lattice defects. This facility is used to examine, in a self-consistent manner, growth sector-dependant changes to both the crystallographic structure and the lattice defects associated with the action of habit-modifying additives in a number of representative crystal growth systems. In addition, the new instrument can be used to probe micro-crystallographic aspects(such as distortion to crystal symmetry) and relate these in a spatially resolved manner to the crystal defect structure in crystals doped with known habit modifiers.

Ultrafast structural dynamics using time-resolved x-ray diffraction driven by relativistic laser pulses

Based on a femtosecond laser plasma-induced hard x-ray source with a high laser pulse energy(>100 mJ)at 10 Hz repetition rate,we present a time-resolved x-ray diffraction system on an ultrafast time scale.The laser intensity is at relativistic regime(2×10^(19)W/cm^(2)),which is essential for effectively generating K_(α)source in high-Z metal material.The produced copper K_(α)radiation yield reaches to 2.5×10^(8)photons/sr/shot.The multilayer mirrors are optimized for monochromatizating and two-dimensional beam shaping of Kαemission.Our experiment exhibits its ability of monitoring the transient structural changes in a thin film SrCoO_(2.5)crystal.It is demonstrated that this facility is a powerful tool to perform dynamic studies on samples and adaptable to the specific needs for different particular applications with high flexibility.

High pressure x-ray diffraction techniques with synchrotron radiation

This article summarizes the developments of experimental techniques for high pressure x-ray diffraction（XRD） in diamond anvil cells（DACs） using synchrotron radiation. Basic principles and experimental methods for various diffraction geometry are described, including powder diffraction, single crystal diffraction, radial diffraction, as well as coupling with laser heating system. Resolution in d-spacing of different diffraction modes is discussed. More recent progress, such as extended application of single crystal diffraction for measurements of multigrain and electron density distribution, timeresolved diffraction with dynamic DAC and development of modulated heating techniques are briefly introduced. The current status of the high pressure beamline at BSRF（Beijing Synchrotron Radiation Facility） and some results are also presented.

Evaluation of zirconia–porcelain interface using X-ray diffraction

The aim of this study was to determine if accelerated aging of porcelain veneering had an effect on the surface properties specific to a tetragonal-to-monoclinic transformation（TMT） of zirconia restorations. Thirty-six zirconia samples were milled and sintered to simulate core fabrication followed by exposure to various combinations of surface treatments including as-received（control）,hydrofluoric acid（HF）, application of liner plus firings, application of porcelain by manual layering and pressing with firing, plus accelerated aging. The quantity of transformed tetragonal to monoclinic phases was analyzed utilized an X-ray diffractometer and one-way analysis of variance was used to analyze data. The control samples as provided from the dental laboratory after milling and sintering process had no TMT（X m5 0）. There was an effect on zirconia samples of HF application with TMT（X m5 0.8%） and liner plus HF application with TMT（X m5 8.7%）. There was an effect of aging on zirconia samples（no veneering） with significant TMT（X m5 70.25%）. Both manual and pressing techniques of porcelain applications reduced the TMT（manual, X m5 4.41%, pressing,X m5 11.57%）, although there was no statistical difference between them. It can be concluded that simulated applications of porcelain demonstrated the ability to protect zirconia from TMT after aging with no effect of a liner between different porcelain applications.The HF treatment also caused TMT.

In situ X-ray diffraction and thermal analysis of LiNi0.8Co0.15Al0.05O2 synthesized via co-precipitation method

LiNi0.9Co0.15Al0.05O2 （NCA） material is successfully synthesized with a modified co-precipitation method,in which NH3,H2O and EDTA are used as two chelating agents. The obtained LiNi0.9Co0.15Al0.05O2 materialhas well-defined layered structure and uniform element distribution, which reveals an enhanced electro-chemical performance with a capacity retention of 97.9% after 100 cycles at 0.2 C, and reduced thermalrunaway from the isothermal calorimetry test. In situ X-ray diffraction （XRD） was employed to capturethe structural changes during the charge-discharge process. The reversible evolutions of lattice parame-ters （a, b, c, and V） further verify the structural stability.

Influence of Replacement Level of Coal-series Kaolin on Hydration of Ordinary Portland Cement by X-ray Diffraction/Rietveld Method

The influence of replacement level of calcined coal-series kaolin (CCK) on hydration of ordinary Portland cement (OPC) was studied by X-ray diffraction(XRD)/Rietveld method. X-ray diffraction/ Rietveld method was used to quantify the crystalline phase composition of the hydrated samples. Additionally, the morphology of hydrated samples was observed by scanning electron microscopy (SEM). The results showed that, calcium hydroxide (CH), ettringite (AFt) and amorphous phase content in hydrated samples decreased as the replacement level of CCK increased, while AFm and stratiingite increased, which was caused by the combination of dilute, physical and pozzolanic effects. The hydration of anhydrous cement phases was accelerated by physical effect but hindered by the retardation effect of CCK. The role of each effects was discussed in detail to analyze the mechanism of OPC hydration with CCK addition. The SEM images showed that the shortening of AFt at 1 day and the denser texture at 28 days was observed with CCK addition, which was caused by the physical and pozzolanic effects, respectively.

In-situ high pressure X-ray diffraction studies of orthoferrite SmFeO_3

The high-pressure behaviors of SmFeO3 are investigated by angle-dispersive synchrotron X-ray powder diffraction under a pressure of up to 40.3 GPa at room temperature. The crystal structure of SmFeO3 remains stable at up to the highest pressure. The different pressure coefficients of the normalized axial compressibility are obtained to be βa = 0.60 × 10-3 GPa-1,βb = 0.79 × 10-3 GPa-1, βc = 1.28 × 10-3 GPa- 1, and the bulk modulus （B0） is determined to be 293（3） GPa by fitting the pressure-volume data using the Birch-Murnaghan equation of state. Furthermore, the larger compressibility of the FeO6 octahedra suggests the evolution of the orthorhombic structure towards higher symmetry configuration at high pressures.

Elastic modulus of TiN film investigated with Kroner model and X-ray diffraction

The four point bending method was applied to measure X ray elastic constants(XEC) of (422) and (331) planes of TiN coating. Elastic Modulus and XECs of all the crystal planes were calculated by Kroner method. The results from the calculation and the experiment were compared. It is concluded that the XECs values of same film prepared by different techniques scatter a little because of the effects of stoichiometric proportion and microstructure of films. [

An in situ high-pressure X-ray diffraction experiment on hydroxyapophyllite

The compression behavior of a natural hydroxyapophyllite is investigated up to about 10.01 GPa at 300 K using in situ angle-dispersive X-ray diffraction and a diamond anvil cell at the High Pressure Experiment Station, Beijing Synchrotron Radiation Facility （BSRF）. Over this pressure range, no phase change or disproportionation is observed. The isothermal equation of state is determined for the first time. The values of zero-pressure volume V0, isothermal bulk modulus K0, and K0＇ refined with a third-order Birch-Mumaghan equation of state are V0 = 1276.3 ± 0.9 A3, K0 = 71± 3 GPa, and K0＇ = 8 ±1. Furthermore, we confirm that the values of linear compressibility β along the a and c directions of hydroxyapophyllite are elastically anisotropic.

Thermal Behavior and Determination of the Heated Structure of 11ÅAnomalous Tobermorite by in situ X-ray Diffraction

This article presents the thermal transitions of a tobermorite-bearing sample when heated from 30℃ up to 1200℃,both in vacuum and in static air,including tobermorite transforming to wollastonite,aragonite to calcite and calcite to lime.Characteristics obtained by in situ high temperature X-ray diffraction,field emission scanning electron microscopy and scanning transmission electron microscopy analyses jointly indicate that the investigated tobermorite is anomalous.The variations along the a,b,c axes and the volume changes of tobermorite with increasing temperature are described,and its thermal shrinkage coefficients therefore determined.The comparison between the refined structures at 30℃ and 800℃ demonstrates that the shrinkage degree(Δa/a0)along the a axis is higher than those(Δb/b0,Δc/c0)along the b and c axes.The wollastonite is formed in two ways:Tobermorite converting to wollastonite and lime reacting with quartz to form wollastonite.