High-energy X-ray Diffraction Experiments Research Articles

Manipulation of magnetostructural transition and realization of prominent multifunctional magnetoresponsive properties in NiCoMnIn alloys

Promising multifunctional magnetoresponsive effects such as magnetoresistance, magnetostrain, and the magnetocaloric effect have recently been extensively studied in Ni-Mn-based metamagnetic shape memory alloys, but large reversible magnetoresponsive effects are usually obtained under high magnetic fields, which is an obstacle for practical applications. Here, through manipulating magnetostructural transition, we achieved large reversible magnetoresponsive effects under a relatively low magnetic field of 3 T in a Ni-Co-Mn-In alloy. By systematically tuning the Mn/In ratio and Co substitution, an optimum composition ${\mathrm{Ni}}_{49}{\mathrm{Co}}_{3}{\mathrm{Mn}}_{34}{\mathrm{In}}_{14}$ with a low thermal hysteresis (8 K), a narrow transformation interval (7 K) and a high sensitivity of transformation temperature to field change ($6\phantom{\rule{0.16em}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{K}\phantom{\rule{0.16em}{0ex}}{\mathrm{T}}^{\ensuremath{-}1}$), was obtained. Good geometric compatibility between austenite and martensite was revealed by in situ synchrotron high-energy x-ray diffraction experiment, which accounts for the low hysteresis and narrow transformation interval. A reversible transformation between pure austenite and pure martensite is induced by a relatively low field of 3 T, which was directly evidenced by in situ neutron diffraction experiments. As a result, a large reversible magnetocaloric effect with entropy change of $16.5\phantom{\rule{0.16em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}\mathrm{k}{\mathrm{g}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$, a large reversible magnetostrain of 0.26%, and a large reversible magnetoresistance of 60%, under a relatively low field of 3 T, were simultaneously achieved. These reversible magnetoresponsive effects are comparable to the maximum reversible values obtained under high fields in other Ni-Mn-based alloys, but the magnetic field we applied is much lower. This study may guide the design of metamagnetic shape memory alloys with low-field-induced magnetoresponsive properties for magnetic refrigeration, magnetic sensing, and magnetic recording applications.

Development and Characterisation of New Biocompatible Sn-Mg Lead-Free Solder

This work is focused on a development and research of a new lead-free Sn-Mg solder, alloy compatible with the human body. Tin and magnesium are biocompatible elements which do not cause an inflammation or allergic reactions with living tissues. We have prepared the Sn97Mg3 solder (wt. %) by a rapid solidification of its melt on a copper wheel (melt-spinning technique). This solder may find applications in electronic devices for intracorporeal utilisation. The microstructure of the prepared solder exhibits a heterogeneous distribution of the SnMg2 intermetallic particles within the β-Sn matrix. Structure of the solder was studied by an in-situ high energy X-ray diffraction experiment (energy of an X-ray photon: 60 keV) where 2D XRD patterns were collected from the sample in the temperature range from 298 K to 566 K. The experiment was performed at a high brilliance 3rd generation synchrotron source of radiation (PETRA III storage ring, DESY, Hamburg, Germany) at the P02 undulator beamline. From the measured X-ray diffraction data by applying the Rietveld refinement technique we have obtained thermal volume expansion data, mean positions of atoms as well as isotropic atomic displacement parameters of the constituent SnMg2 and the β-Sn crystalline phases. Thermal behaviour was studied by differential scanning calorimetry at heating rates of 5, 15, 30 and 60 K.min-1 and compared with the measured X-ray data. Our main goal lies in a preparation of a lead-free solder with fine grain structure made exclusively of biocompatible elements. We demonstrated that the rapid melt solidification technique leads to in an improvement and better thermal stability of this alloy.

Alloying-element interactions with austenite/martensite interface during quenching and partitioning of a model Fe-C-Mn-Si alloy

The alloying elements partitioning from martensite to austenite during quenching and partitioning was analysed by coupling in situ High Energy X-Ray Diffraction experiments and 3D atom probe tomography. A rapid and significant carbon partitioning from martensite to austenite without any partitioning of both Mn and Si was highlighted while the interface was immobile. After a relatively short time at 400 °C, a clear Mn partitioning occurs at the vicinity of the α′/γ interface. The analysis conducted indicates that manganese equilibrates its chemical potential during partitioning and raises the issue of the Constrained Carbon Equilibrium model applicability throughout the partitioning process.

Giant tensile superelasticity originating from two-step phase transformation in a Ni-Mn-Sn-Fe magnetic microwire

Large recoverable strain of more than several percent arising from superelasticity in shape memory alloys is important for actuators, sensors, and solid-state refrigeration. Here, we report a Ni50.0Mn31.4Sn9.6Fe9.0 magnetic microwire showing a giant tensile recoverable strain of about 20.0% along the ⟨001⟩ direction of austenite at 263 K. The recoverable strain represents the largest value reported heretofore in Ni-Mn-based shape memory alloys and is also larger than that of the Ni-Ti wire available for practical applications at present. This giant tensile superelasticity is associated with the stress-induced two-step transformation, and the transformation sequence could be L21 (austenite) → 6M (six-layered modulated martensite) → NM (non-modulated martensite), as suggested by the temperature-dependent in-situ synchrotron high-energy X-ray diffraction experiments and the transformation strain calculation based on the crystallographic theory of martensitic transformation. In addition, this Ni50.0Mn31.4Sn9.6Fe9.0 microwire shows a transformation entropy change ΔStr of 22.9 J kg−1 K−1 and has the advantages of easy fabrication and low cost, promising for miniature sensor, actuator, and solid-state refrigeration applications.

Application of differential resonant high-energy X-ray diffraction to three-dimensional structure studies of nanosized materials: A case study of Pt–Pd nanoalloy catalysts

Atoms in many of the increasingly complex nanosized materials of interest to science and technology do not necessarily occupy the vertices of Bravais lattices. The atomic scale structure of such materials is difficult to determine by traditional X-ray diffraction and so their functional properties remain difficult to optimize by rational design. Here, the three-dimensional structure of PtxPd100-x nanoalloy particles is determined, where x = 0, 14, 36, 47, 64 and 100, by a non-traditional technique involving differential resonant high-energy X-ray diffraction experiments conducted at the K edge of Pt and Pd. The technique is coupled with three-dimensional modeling guided by the experimental total and element-specific atomic pair distribution functions. Furthermore, using DFT (density functional theory) calculation based on the positions of atoms in the obtained three-dimensional structure models, the catalytic performance of Pt-Pd particles is explained. Thus, differential resonant high-energy X-ray diffraction is shown to be an excellent tool for three-dimensional structure studies of nanosized materials. The experimental and modeling procedures are described in good detail, to facilitate their wider usage.

Characterization of crystallographic texture of Zirconium alloy components by neutron diffraction

The reproducibility of the determination of crystallographic texture of Zr-based components by neutron diffraction has been studied through a small round-robin exercise, with the participation of texture and residual stress diffractometers from five international laboratories. Both constant-wavelength and polychromatic neutron beams have been used to define the texture of specimens from a warm-rolled and annealed Zircaloy-4 plate, and from a Zr-2.5%Nb pressure tube. Measurements were also compared to synchrotron high energy X-ray diffraction experiments, as a complementary volumetric technique with much shorter data collection times compared to neutrons. Results are qualitatively consistent and reproducible in terms of pole figures and orientation distribution function, underlining the suitability of neutrons for bulk texture measurements. Expected uncertainty of measurements has been quantified by global parameters such as texture indexes and Kearns factors, and local parameters associated to the main texture components (volume fraction, centroids, and widths of fiber components). The typical uncertainties found for these parameters are compared to spatial differences found in a small batch of cold-rolled Zr-2.5%Nb pressure tubes.

Mechanism of Li3PS4 Liquid Phase Synthesis By Total X-Ray Scattering Measurement Coupled to Pair Distribution Function Analysis

Introduction All-solid-state batteries are one of the most promising candidates for next generation batteries because of their safety property and high power density1. The sulfur solid electrolyte is prepared conventionally by hand-mixing in the all-solid-state batteries. The ball-milling method is not suitable for large-scale preparation. Therefore it is important to develop the large-scale synthesis method of solid electrolyte. Recently, some research groups have reported on the synthesis of Li3PS4 electrolyte via liquid phase by dissolving the starting sulfide materials such as Li2S and P2S5 in organic solvents2. However, the formation mechanism has not been clearly understood. In this study, we evaluate a local structure change of Li3PS4 (LPS) in the liquid phase synthesis process by total X-ray scattering measurement coupled with pair distribution function (PDF) analysis to clarify the formation mechanism. Experimental Li3PS4 was prepared by liquid-phase shaking method as previously reported2. Li2S (Sigma-Aldrich), P2S5(Sigma-Aldrich), dehydrated ethyl propionate (Sigma-Aldrich) and zirconia balls were added in centrifugation tube and shaken under Ar atmosphere from 0 min to 360 min at 1500 rpm. The tube was centrifuged at 10000 rpm for 5 min. The supernatant was decanted and the residual solvent was evacuated at room temperature. Then the precursor was annealed at 170 ºC in low pressure for 2 h. The high-energy X-ray diffraction experiments were carried out at the beamline BL08W using a two-dimensional detector in SPring-8, Japan. The incident X-ray energy was 115 keV. The diffraction patterns of the samples and an empty tube were measured in the transmission geometry. The obtained data of each sample was corrected for background, absorption correction, multiple scattering and inelastic scattering. Results and discussion Figure 1 shows that reduced pair distribution functions, G(r), obtained from a Fourier transformation of total structure factors for each liquid phase sample. In the initial stage of the synthesis process, peaks were attributed to the starting materials of P2S5 and Li2S. In the middle stage of the synthesis process, although the intensity of the peak from Li2S decrease, intensity of the first peak from P-S bond of PS4 tetrahedral anion increased. In the end stage of the synthesis process, two peaks, which were observed in Li3PS4 obtained by subsequent annealing treatment, appeared around 3.3 Å, 4.0 Å. These results indicate that the locally ordered structure of Li2S is broken while the locally ordered structure at short range is grown in the middle stage of the synthesis process. In the end stage of the synthesis process, locally ordered structure at middle range of Li3PS4 forms with keeping locally ordered structure at the short range. Acknowledgement This research was financially supported by the Japan Science and Technology Agency (JST), Advanced Low Carbon Technology Research and Development Program (ALCA), Specially Promoted Research for Innovative Next Generation Batteries (SPRING) Project. Figure 1

Prediction of tensile stiffness and strength of Ti-6Al-4V using instantiated volume elements and crystal plasticity

Based on simulations of tensile tests, the macroscopic stiffness and strength of the α phase of Ti-6Al-4V are estimated. Sets of virtual samples are instantiated using characterization data from three-dimensional electron back-scattered diffraction (EBSD) scans collected with the TriBeam microscope and local properties extracted from in situ loading high-energy x-ray diffraction (HEXD) experiments. The simulations use a crystal-scale finite element framework to compute the mechanical response of the virtual samples under tensile loading. From the simulation data, mechanical properties are extracted from volume elements ranging in size from a fraction of the gage section to its entire length. To detect macroscopic yield, a flood-fill algorithm is used to identify a zone of plastically deformed finite elements extending through a volume element. Trends in the estimated properties as functions of the volume element size are examined. The lower bound of volume element size necessary to replicate experimentally measured macroscale properties is indicated. The technique and results provide a guideline for estimating macroscale property values in components designed with size smaller than the lower bound due to constraint.

Crystal plasticity based constitutive modeling of ZEK100 magnesium alloy combined with in-situ HEXRD experiments

In the current works, both micro- and macro-mechanical properties of a hexagonal close-packed (HCP) polycrystalline ZEK100 magnesium alloy were investigated. In the experimental perspective, in-situ high energy X-ray diffraction (HEXRD) from a synchrotron source was conducted during the uniaxial tension along the rolling direction (RD) and the transverse direction (TD) to measure the lattice strain evolutions and stress-strain behaviors. In the modeling perspective, crystal plasticity finite element (CPFE) model was developed incorporating the deformation twinning for the HCP-structured metals. The HEXRD experiments and crystal plasticity models were then coupled to characterize the constitutive behaviors of the ZEK100 alloy. The lattice strain data representing the microscopic behavior of the material and the macroscopic stress-strain behavior were then tied together as objective values to estimate the critical resolved shear stress (CRSS) and hardening parameters of available slip and twin systems of the ZEK100 alloy using the developed CPFE model. The stress-strain behavior as well as the lattice strain variation during the uniaxial tension tests are presented using the CPFE model and compared with the actual HEXRD data.

In Situ Investigation of the Iron Carbide Precipitation Process in a Fe-C-Mn-Si Q&P Steel

Quenching and Partitioning (Q&P) steels are promising candidates for automotive applications because of their lightweight potential. Their properties depend on carbon enrichment in austenite which, in turn, is strongly influenced by carbide precipitation in martensite during quenching and partitioning treatment. In this paper, by coupling in situ High Energy X-Ray Diffraction (HEXRD) experiments and Transmission Electron Microscopy (TEM), we give some clarification regarding the precipitation process of iron carbides in martensite throughout the Q&P process. For the first time, precipitation kinetics was followed in real time. It was shown that precipitation starts during the reheating sequence for the steel studied. Surprisingly, the precipitated fraction remains stable all along the partitioning step at 400 °C. Furthermore, the analyses enable the conclusion that the iron carbides are most probably eta carbides. The presence of cementite was ruled out, while the presence of several epsilon carbides cannot be strictly excluded.

In situ synchrotron X-ray diffraction investigations of the physical mechanism of ultra-low strain hardening in Ti-30Zr-10Nb alloy

A warm-rolled, metastable β-type Ti-30Zr-10Nb alloy exhibited a peculiar two-stage yielding behavior under uniaxial tensile loading, showing a first plastic stage with obvious strain hardening at 0.4%–10.4% strain and a second plastic stage with ultra-low strain hardening at 10.4%–23.5% strain. In situ high-energy X-ray diffraction (HE-XRD) was used to reveal the stress-induced martensitic transformation scenarios and physical mechanism of the different strain hardening rates. It was found that the deformation-induced phase transformation dominated the onset of the first plastic stage corresponding to the selection of favorable martensitic variants, and their elastic interaction contributed to the obvious strain hardening. HE-XRD experiments further verified that the ultra-low strain hardening rate in the second plastic stage was related to an interesting superelasticity of the martensite, which was characterized by the reversible, stress-induced reorientation of the martensite variants. This reorientation of the martensite variants was primarily due to the rigid lattice rotation of ∼23° about the [110]α″ axis toward the tensile direction. Our investigations provide in-depth understanding of the mechanism of the excellent plasticity with ultra-low strain hardening in β-type titanium alloys.

Corium lavas: structure and properties of molten UO2-ZrO2 under meltdown conditions

In the exceedingly rare event of nuclear reactor core meltdown, uranium dioxide fuel reacts with Zircaloy cladding to produce eutectic melts which can subsequently be oxidized by coolant/moderator water. Oxidized corium liquids in the xUO2·(100 − x)ZrO2 system were produced via laser melting of UO2-ZrO2 mixtures to temperatures in excess of 3000 K. Contamination was avoided by floating the droplets on a gas stream within an aerodynamic levitator and in-situ high-energy x-ray diffraction experiments allowed structural details to be elucidated. Molecular dynamics simulations well reproduced diffraction and density data, and show less compositional variation in thermal expansion and viscosity than suggested by existing measurements. As such, corium liquids maintain their highly penetrating nature irrespective of the amount of oxidized cladding dissolved in the molten fuel. Metal-oxygen coordination numbers vary with both composition and temperature. The former is due to mismatch in native values, nUO(x = 100) ≈ 7 and nZrO(x = 0) ≈ 6, and the requirement for oxygen site stabilization. The latter provides a thermal expansion mechanism.

Temperature dependent structural evolution in liquid Ag50Ga50 alloy

The temperature dependence of atomic structural evolution in liquid Ag50Ga50 alloy has been studied using an in situ high energy x-ray diffraction (XRD) experiment combined with first-principles molecular dynamics (FPMD) simulations. The experimental data show a reversible structural crossover at the temperature of about 1050 K. Changes in both electrical resistivity and absolute thermoelectric power at about 1100 K strongly support the XRD results. Additionally, FPMD simulations reveal the abnormal temperature dependent behavior of partial coordination number and atomic diffusivity at about 1200 K, elucidating that the partition experimentally observed changes in structure and properties could be linked with the repartition between Ag and Ga atoms in the liquid at around 1050–1200 K. This finding will trigger more studies on the structural evolution of noble-polyvalent metals in particular and metallic liquids in general.

Internal stresses and carbon enrichment in austenite of Quenching and Partitioning steels from high energy X-ray diffraction experiments

Quenching and Partitioning (Q&P) process permits to produce innovative microstructures containing large fraction of carbon enriched retained austenite. The present study highlights that austenite undergoes significant internal stresses generated during such thermal cycle. Both mechanical and chemical contributions are likely to affect its stability at room temperature and thus the resulting mechanical properties of the steel. The experiments carried out by High Energy X-Ray Diffraction (HEXRD) show unambiguously that internal stresses in austenite originate from martensitic transformation strain and from additional hydrostatic stresses induced during both reheating to partitioning temperature and final cooling. These eigenstrains are attributed to the difference in Coefficients of Thermal Expansion (CTE) between martensite and austenite and are predicted successfully with a purely elastic mean field approach. In the present study, retained austenite is shown to be in compression at room temperature. As a consequence, this state of stress contributes to stabilize retained austenite against a possible strain induced transformation at room temperature and affects the way to determine the carbon content in austenite.

Determining the strengths of HCP slip systems using harmonic analyses of lattice strain distributions

A robust methodology is presented to extract slip system strengths from lattice strain distributions for polycrystalline samples obtained from high-energy x-ray diffraction (HEXD) experiments with in situ loading. The methodology consists of matching the evolution of coefficients of a harmonic expansion of the distributions from simulation to the coefficients derived from measurements. Simulation results are generated via finite element simulations of virtual polycrystals that are subjected to the loading history applied in the HEXD experiments. Advantages of the methodology include: (1) its ability to utilize extensive data sets generated by HEXD experiments; (2) its ability to capture trends in distributions that may be noisy (both measured and simulated); and (3) its sensitivity to the ratios of the family strengths. The approach is used to evaluate the slip system strengths of Ti-6Al-4V using samples having relatively equiaxed grains. These strength estimates are compared to values in the literature.

Study of residual stresses in Ti-7Al using theory and experiments

Finite element simulations are carried out to follow the evolution of residual stresses in Ti-7Al (α-hcp) alloy, as developed under an applied stress gradient. A model built upon phenomenological mesoscopic field dislocation mechanics is employed to simulate the deformation behavior. Model predictions are validated with results generated from high energy X-ray diffraction experiments using synchrotron radiation. These experiments provide for important simulation input, viz. grain positions and orientations, and strain rate sensitivities of the prismatic and basal slip systems of Ti-7Al. X-ray diffraction data obtained from individual grains enabled calculation of strain rate sensitivities of the prismatic and basal slip systems and the values are estimated as ∼ 0.04 and ∼ 0.02 respectively. Residual stresses at the length scale of individual grains and subgrains are successfully predicted and validated against experimental data. A key achievement of the present work is the measurement and simulation of residual stress gradients within individual grains. Conclusions from this work are that grains deform mainly via prismatic slip, and accurate characterization of rate-sensitivity is needed to model the development of grain-level residual stresses.

Investigations of deformation-induced δ → ζ phase transformation in zirconium hydride by in situ high-energy X-ray diffraction

In situ high-energy X-ray diffraction (HE-XRD) was used to study the micromechanical behavior of Zircaloy-4 during tensile loading, revealing for the first time a deformation-induced phase transformation from δ-hydride to ζ-Zr2H in the hydride at a critical stress of approximately 370 MPa. Detailed investigations using transmission electron microscopy confirmed that the ζ-Zr2H phase had a “hexagon-on-hexagon” orientation relationship with the α-Zr matrix, i.e., (0002)ζ//(0002)α and [21¯1¯0]ζ//[21¯1¯0]α. The ζ phase has almost the same lattice parameters for a and b and twice the c parameter as those of α-Zr. The affinity in crystal structure and lattice parameters between ζ-hydride and α-Zr suggests that ζ-Zr2H as an intermediate phase could be important to the dissolution and reprecipitation of δ-hydride during plastic deformation. The HE-XRD experiments provide evidence that the fracture of ζ-hydride plates aligned perpendicular to the loading direction (LD) causes the premature failure of the grains oriented with [0001]//LD in the matrix. The new finding regarding the deformation-induced phase transformation in the hydride is important to deepen the understanding of delayed hydride cracking in Zr alloys.

Composition–Structure–Activity Correlation of Platinum–Ruthenium Nanoalloy Catalysts for Ethanol Oxidation Reaction

Understanding the evolution of the composition and atomic structure of nanoalloy catalysts in the ethanol oxidation reaction (EOR) is essential for the design of active and robust catalysts for direct ethanol fuel cells. This article describes a study of carbon-supported platinum–ruthenium electrocatalysts (PtRu/C) with different bimetallic compositions and their activities in the EOR, an important anode reaction in direct ethanol fuel cells (DEFCs). The study focused on establishing the relationship between the catalyst’s composition, atomic structure, and catalytic activity for the EOR. Ex situ and in situ synchrotron high-energy X-ray diffraction (HE-XRD) experiments coupled with atomic pair distribution function (PDF) analysis and in situ energy-dispersive X-ray (EDX) analysis were employed to probe the composition and structural evolution of the catalysts during the in situ EOR inside a membrane electrode assembly (MEA) in the fuel cell. The results revealed an intriguing composition–structure–activi...

Anomalous temperature dependence in the structural organization of charge alternation in imidazolium-based ionic liquids of various alkyl chain lengths

We report on trends observed in the X-ray static structure factor obtained for four homologous imidazolium-based ionic liquids. In a series of low-energy (laboratory) and high-energy synchrotron X-ray diffraction experiments, the temperature dependent structure was investigated in 1-alkyl-3-methylimidazolium cations, with chain lengths of n=4, 6, 8, and 10, paired with the trifluoromethylsulfonate (TF) anion. Interestingly, the charge alternation peak in the liquids displays an anomalous temperature evolution, increasing in amplitude as the temperature is raised. Analysis of the pair distribution function (PDF) evolution with temperature for all compositions attributes the observed anomalous behavior to a specific distance in the liquid. Extensive peak modelling of the structure factors confirms the anomaly for all compositions, which combined with the analysis of the temperature of the PDFs, suggests that the entropic tendency to decohere strict charge alternation overcomes enthalpic tendencies in these liquids.

Effects of Q&P Processing Conditions on Austenite Carbon Enrichment Studied by In Situ High-Energy X-ray Diffraction Experiments

We report the first ultra-fast time-resolved quantitative information on the quenching and partitioning process of conventional high-strength steel by an in situ high-energy X-ray diffraction (HEXRD) experiment. The time and temperature evolutions of phase fractions, their carbon content, and internal stresses were determined and discussed for different process parameters. It is shown that the austenite-to-martensite transformation below the martensite start temperature Ms is followed by a stage of fast carbon enrichment in austenite during isothermal holding at both 400 and 450 °C. The analysis proposed supports the concurrent bainite transformation and carbon diffusion from martensite to austenite as the main mechanisms of this enrichment. Furthermore, we give evidence that high hydrostatic tensile stresses in austenite are produced during the final quenching, and must be taken into account for the estimation of the carbon content in austenite. Finally, a large amount of carbon is shown to be trapped in the microstructure.