High-energy X-ray Diffraction Measurements Research Articles

Microstructural and Chemical Changes of a Ti-Stabilized Austenitic Stainless Steel After Exposure to Liquid Sodium at Temperatures Between 500 °C and 650 °C

Ti-stabilized austenitic stainless steel was carburized in sodium containing a high carbon activity at three different temperatures, 500 °C, 600 °C, and 650 °C during 1000 hours and 5000 hours. The carbon profile, the carbide volume fraction, and the lattice parameter evolution as function of depth were determined using high-energy X-ray diffraction and electron probe microanalysis. At 650 °C and 600 °C, the carbon precipitated as M23C6 and M7C3 carbides in the sample. The volume fraction of M7C3 carbides was lower than predicted by thermodynamic equilibrium using Thermo-Calc software®. At 500 °C, carbides almost did not form in the steel. Instead, high carbon supersaturation of the austenitic matrix occurred. Both results demonstrate that the carburization profile was strongly influenced by the kinetics of carbide formation at temperatures lower than 650 °C. High-energy X-ray diffraction measurements demonstrated that the austenite and carbide lattice parameters evolved along the carbon profile. Both measured lattice parameter profiles of austenite and M23C6 carbide were compared to the ones predicted from chemical changes of austenite and carbides.

High-energy x-ray diffraction study on phase transition asymmetry of plastic crystal neopentylglycol

As a prototype material of colossal barocaloric effects, neopentylglycol is investigated by combining high-precision differential scanning calorimetric measurement and high-energy x-ray diffraction measurement. The diffraction data at constant temperatures indicate a first-order phase transition with thermal hysteresis as well as the phase transition asymmetry, specifically, the phase transition is completed faster at cooling than at heating. The analysis of resulting pair distribution function confirms the intermolecular disorder in the high-temperature phase. The phase transition asymmetry is quantitatively characterized by time-resolved x-ray diffraction, which is in agreement with the thermal measurement. Also, such an asymmetry is observed to be suppressed at high pressures.

Insight into the capacity decay mechanism of cycled LiNi0.5Co0.2Mn0.3O2 cathodes via in situ x-ray diffraction

Layered LiNi x Co y Mn1-x-y O2 (NCM) is expected to dominate the future cathode technology of the automotive industry, due to its high energy density and low cost. Despite its excellent prospects, however, the severe capacity decay of NCM cathodes has prevented this promising material from achieving further success. The mechanism underlying this phenomenon is controversial and has been generally understood as arising from the complex structural changes that take place upon Li-(de)intercalation. However, deeper insight has not been available due to unclear structural kinetics, in particular, in cycled NCM cathodes. For this study, we conducted in situ high-energy synchrotron x-ray diffraction (XRD) measurements on a typical LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode that had been operated for 90 cycles, then compared the results with those collected from a fresh NCM532 electrode. It was revealed that the H1–H2 phase transition that only occurs at the first cycle is irreversible. Remarkably, the c-contraction triggered by the H2-H3 transition, which is expected to be the major cause of intergranular cracks in electrodes, became even more profound after cycling. Combining the above results with electrochemical testing and microscopic imaging, we discuss the interplay between structural dynamics and performance degradation in NCM532 in detail. This study provides key evidence for a mechanically induced capacity decay mechanism, which is expected to be extended to NCM materials with various compositions.

Temperature-Induced Structural Changes in the Liquid GaInSn Eutectic Alloy

The temperature-dependent structure and properties of a liquid GaInSn eutectic alloy have been investigated by using in situ high-energy X-ray diffraction, thermal expansion, and heat capacity measurements together with ab initio molecular dynamics simulations. It is found that below and above 550 K, the liquid exhibits differences in heat capacity, density, the first two peak positions of the structure factor and pair distribution function, partial coordination numbers, polyhedron connection, as well as Bader charge and Bader volume of In atoms. Both experimental and theoretical results obtained here clearly reveal a liquid-to-liquid crossover in the liquid GaInSn eutectic alloy at around 550 K, which mainly originates from the aggregation of In atoms upon cooling together with Sn atoms tending closer to In. The finding here deepens the understanding of the disorder-to-disorder transition in disordered materials.

Screening for O phase in advanced γ–TiAl alloys

This is a screening study using high-energy X-ray diffraction measurements to determine whether an orthorhombic phase forms in γ-based TiAl alloys of different compositions. The 13 alloy compositions investigated were chosen to be either close to commercial alloys or to identify the effects of different single alloying elements on the formation of orthorhombic phase. The orthorhombic O phase with Cmcm structure was found in several of those γ-TiAl alloys after an aging heat treatment at 550 °C for 20 h. The presence of different β-stabilising elements such as niobium, tantalum, molybdenum or vanadium did promote the formation of orthorhombic phase, while micro alloying elements such as carbon or boron were neutral in this respect. Furthermore, a limit for aluminium was also found, below which the orthorhombic O phase is formed in the alloys investigated. This limit lies between 46 at.% and 47 at.%.

Improvement of lithium ionic conductivity of Li3PS4 through suppression of crystallization using low-boiling-point solvent in liquid-phase synthesis

Liquid-phase synthesis for solid electrolytes has received considerable attention owing to its shape control, with the potential to produce particles easily on a large scale, and its low cost and energy consumption. However, solid electrolytes prepared through liquid-phase synthesis have been shown to have lower ionic conductivity than solid electrolytes prepared through the mechanical milling method. Recently, following various efforts, our group found that the crystallinity and remaining intermediate are the reasons for the low ionic conductivity of these materials. By using tetrahydrofuran (THF), we successfully improved the ionic conductivity of Li3PS4 to 1.85 × 10−4 S cm−1 at 25 °C, higher than that afforded by ethyl propionate, which was reported to produce the highest ionic conductivity among the solvents used for liquid-phase synthesis. High-energy X-ray diffraction (XRD) measurements coupled with pair distribution function (PDF) analysis were employed to analyze the synthesized materials in order to determine why the ionic conductivity was higher than that of a sample prepared using ethyl propionate. The PDF analysis revealed that the crystallization of Li3PS4 can be suppressed using THF, which has a lower boiling point than ethyl propionate. Moreover, it was revealed that the solvent could not be removed completely when the material has an amorphous structure, and thus, the ionic conductivity was lower than that of a material prepared using the solid-phase synthesis method.

Synthesis of Sulfide Solid Electrolytes through the Liquid Phase: Optimization of the Preparation Conditions.

All-solid-state lithium batteries using inorganic sulfide solid electrolytes have good safety properties and high rate capabilities as expected for a next-generation battery. Presently, conventional preparation methods such as mechanical milling and/or solid-phase synthesis need a long time to provide a small amount of the product, and they have difficult in supplying a sufficient amount to meet the demand. Hence, liquid-phase synthesis methods have been developed for large-scale synthesis. However, the ionic conductivity of sulfide solid electrolytes prepared via liquid-phase synthesis is typically lower than that prepared via solid-phase synthesis. In this study, we have controlled three factors: (1) shaking time, (2) annealing temperature, and (3) annealing time. The factors influencing lithium ionic conductivity of Li3PS4 prepared via liquid-phase synthesis were quantitatively evaluated using high-energy X-ray diffraction (XRD) measurement coupled with pair distribution function (PDF) analysis. It was revealed from PDF analysis that the amount of Li2S that cannot be detected by Raman spectroscopy or XRD decreased the ionic conductivity. Furthermore, it was revealed that the ionic conductivity of Li3PS4 is dominated by other parameters, such as remaining solvent in the sample and high crystallinity of the sample.

Combined synchrotron X-ray diffraction, dilatometry and electrical resistivity in situ study of phase transformations in a Ti2AlNb alloy

Phase transformations in near Ti2AlNb alloy occurring on cooling of 10 °C min−1 from 1020 °C were studied in situ using high energy X-ray diffraction and electrical resistivity measurements coupled with simultaneous dilatometric analysis. From Rietveld refinement of X-ray data, it was established that high temperature range from about 870 to 1020 °C contained partially ordered β phase. The degree of long-range order was of 0.6 at 1020 °C and decreased slowly with temperature decrease and fast when O-phase was formed. The formation of O-Ti2AlNb phase started from about 870 °C and consisted of two stages: (i) fast transformation of partially ordered β into O phase at higher temperatures followed by (ii) slow transformation of fully disordered β into O-phase at lower temperatures. The appearance of O-phase was accompanied by important volume decrease of the alloy as recorded using dilatometry as well as by a decrease of electrical resistivity. The transformations temperatures revealed by high energy X-ray diffraction, dilatometry and electrical resistivity were in good agreement. The obtained results were discussed using thermodynamic simulations carried out with Thermo-Calc software and TCTI2 database.

Structural Origin of Additional Infrared Transparency and Enhanced Glass-Forming Ability in Rare-Earth-Rich Borate Glasses without B–O Networks

R2O3-B2O3 binary glasses (R denotes rare-earth elements or Y) were fabricated in a very wide composition region using a levitation technique. The maximum R2O3 content of light rare-earth compounds reached 63 mol % and decreased with a decrease in the ionic radius of R3+. The thermal, optical, vibrational, and structural properties were investigated, particularly for 50R2O3-50B2O3 glasses. The glass transition temperature increased with a decrease in the ionic radius of R3+, while the thermal stability was not affected by the glass composition. The packing density increased with a decrease in the ionic radius of R3+ due to lanthanoid contraction. Raman scattering and Fourier transform infrared spectra revealed that, in the rare-earth-rich glasses, no conventional three-dimensional networks consisting of corner-sharing BOn (n = 3 or 4) units existed because all B atoms were formed as isolated BO3 units. The simple environment around B atoms in the glasses led to additional IR transmittance regions, irrespective of the kinds of R. The total correlation functions obtained from high-energy X-ray diffraction measurements were analyzed using the pair-function method and compared with those of various RBO3 crystalline phases. It was suggested that the local structure around R resembles the ν-NdBO3-type crystal structure, and the O coordination number of R ranged from 6.5 to 7.7, smaller than that of the crystalline phase. The glass-forming ability depending on R was discussed based on the structural similarities between the melt, glass, and crystalline phases.

Operando time- and space-resolved high-energy X-ray diffraction measurement to understand hydrogen-microstructure interactions in duplex stainless steel

Local strain development in the microstructure of a commercial 25Cr-7Ni super duplex stainless steel was mapped using high-energy x-ray diffraction during cathodic hydrogen charging under constant uniaxial load. The infusion of hydrogen resulted in tensile strains in austenite grains, one order of magnitude larger than those in the ferrite. Most strain evolution occurred at the near-surface, with compensating compressive forces developed in underlying regions, with up to two-times more compression occurring in the ferrite than the austenite. The strains along the loading axis were more pronounced than in the transverse direction, in which mostly compressive strains developed in the ferrite.

Macro and micro mechanical in-situ characterization using synchrotron diffraction of architectured micro-composite duplex stainless steels

The mechanical behavior of micro-composites Duplex Stainless steels (DSS) produced by Accumulative re-Bundling and Drawing (ABD) has been investigated. We evidenced a systematic increase in the yield strength, as a function of the manufacturing step, independently from the phases' volume fraction. A simple rule of mixture (ROM) successfully predicted the first generation of composites presenting a simple microstructure. However, a modified ROM taking into account the contribution of each component and its grain size could not predict the mechanical response of the composites of higher generation. An in-depth analysis is conducted to investigate the microstructure-mechanical behavior relationship and to rationalize the resultant mechanical behavior from that of each constitutive phase. For this purpose, in-situ synchrotron High Energy X-ray Diffraction measurements during uniaxial tensile experiments have been carried out to calculate the stress partitioning within each phase of the composites.

Large elastic strains and ductile necking of W nanowires embedded in TiNi matrix

The deformation behaviors of W nanowires embedded in a TiNi matrix were investigated by means of in-situ synchrotron high energy X-ray diffraction (HEXRD) and in-situ transmission electron microscopy (TEM) analysis during tensile deformation. The HEXRD measurement indicated that the W nanowires exhibited an average lattice strain of about 1.50 %, whereas the TEM examination revealed a local elastic strain of about 4.59 % in areas adjacent to the TiNi matrix where stress-induced martensitic transformation occurred. This strain corresponds to a stress of ∼15 GPa for the W nanowires. In addition, in areas adjacent to the TiNi matrix where plastic deformation and cracking were generated, the W nanowire showed significant ductile necking with ∼80 % reduction in cross-section area. The ductile necking of W nanowire is attributed to the lack of protection from the stress-induced martensitic transformation of the TiNi matrix.

Comparing CALPHAD predictions with high energy synchrotron radiation X-ray diffraction measurements during in situ annealing of Al0.3CoCrFeNi high entropy alloy

High-entropy alloys (HEAs) offer the unique ability to tailor microstructures through thermal processing techniques. One family of alloys of interest is AlxCoCrFeNi, where x varies from 0.0 to 2.0 molar fraction which allows for a transition from face-centered cubic (FCC) to body-centered cubic (BCC) crystal structure, as well as the formation of various secondary phases, such as B2, sigma, and L12. In this study, we focus on the Al0.3CoCrFeNi HEA. Based on CALPHAD simulations, the Al0.3CoCrFeNi HEA consists of the following phases from highest to lowest temperature: a) FCC at high temperature, followed by b) B2 precipitation in an FCC matrix, c) then B2 and σ phase co-precipitation in an FCC matrix, d) then B2, σ phase, and L12 phase in an FCC matrix, and finally e) B2, σ phase, and L12 phase in a BCC matrix at low temperature. The purpose of our study is to compare phases observed using high-energy synchrotron radiation X-ray diffraction measurements during in situ annealing with the equilibrium phases predicted using CALPHAD. Phase evolution and dissolution are discussed and compared with the CALPHAD simulation predictions. Our experimental results matched well with the CALPHAD predictions of the phase evolution for the B2 phase, however, the phase dissolution of L12 and σ phases was incomplete, which is likely only observable using high resolution synchrotron radiation X-ray diffraction. Better CALPHAD models are needed as well as longer annealing times due to the complexity of achieving phase equilibrium in multi-phase HEAs.

In situ high-energy X-ray diffraction study of thermally-activated martensitic transformation far below room temperature in CuZr-based bulk metallic glass composites

Abstract The martensitic transformation within B2 phase plays a critical role for the ductility of CuZr-based bulk metallic glass (BMG) composites, yet the underlying mechanism for the martensitic transformation process needs further investigations. Here, we found that the onset temperature of the thermally-activated martensitic transformation for CuZr-based BMG composites was reduced to 162.7 ± 2.5 K, which is far lower than those of polycrystalline samples, due to the stabilization of the austenitic phase induced by crystalline-amorphous interfaces. In situ high-energy X-ray diffraction measurements (HEXRD) further demonstrate that the thermally-activated martensitic transformation is governed by an extremely incomplete martensitic transformation from B2 to B19’ and B33 phases without the decomposition of B2 phase which generally appears in polycrystalline samples. Due to unconfined stress states during the thermally-activated martensitic transformation, B33 phase forms more early during thermal process than deformation process. The present study provides a further understanding on the martensitic transformation behaviors of shape memory type CuZr-based BMG composites.

Probing the Atomic-Scale Structure of Amorphous Aluminum Oxide Grown by Atomic Layer Deposition.

Atomic layer deposition (ALD) is a well-established technique for depositing nanoscale coatings with pristine control of film thickness and composition. The trimethylaluminum (TMA) and water (H2O) ALD chemistry is inarguably the most widely used and yet to date, we have little information about the atomic-scale structure of the amorphous aluminum oxide (AlOx) formed by this chemistry. This lack of understanding hinders our ability to establish process-structure-property relationships and ultimately limits technological advancements employing AlOx made via ALD. In this work, we employ synchrotron high-energy X-ray diffraction (HE-XRD) coupled with pair distribution function (PDF) analysis to characterize the atomic structure of amorphous AlOx ALD coatings. We combine ex situ and in operando HE-XRD measurements on ALD AlOx and fit these experimental data using stochastic structural modeling to reveal variations in the Al-O bond length, Al and O coordination environment, and extent of Al vacancies as a function of growth conditions. In particular, the local atomic structure of ALD AlOx is found to change with the substrate and number of ALD cycles. The observed trends are consistent with the formation of bulk Al2O3 surrounded by an O-rich surface layer. We deconvolute these data to reveal atomic-scale structural information for both the bulk and surface phases. Overall, this work demonstrates the usefulness of HE-XRD and PDF analysis in improving our understanding of the structure of amorphous ALD thin films and provides a pathway to evaluate how process changes impact the structure and properties of ALD films.

Possible quantum fluctuations in the vicinity of the quantum critical point of (Sr,Ca)3Ir4Sn13 revealed by high-energy x-ray diffraction

We explore the evolution of the structural phase transition of $\rm{(Sr, Ca)_3Ir_4Sn_{13}}$, a model system to study the interplay between structural quantum criticality and superconductivity, by means of high-energy x-ray diffraction measurements at high pressures and low temperatures. Our results confirm a rapid suppression of the superlattice transition temperature $T^*$ against pressure, which extrapolates to zero at a critical pressure of $\approx 1.79(4)$ GPa. The temperature evolution of the superlattice Bragg peak in $\rm{Ca_3Ir_4Sn_{13}}$ reveals a drastic decrease of the intensity and an increase of the linewidth when $T \rightarrow 0$ K and $p \rightarrow p_c$. Such anomaly is likely associated to the emergence of quantum fluctuations that disrupt the formation of long-range superlattice modulation. The revisited temperature-pressure phase diagram of $\rm{(Sr, Ca)_3Ir_4Sn_{13}}$ thus highlights the intertwined nature of the distinct order parameters present in this system and demonstrates some similarities between this family and the unconventional superconductors.

Thermally-Activated Martensitic Transformation Behaviour Below Room Temperature in CuZr-Based Bulk Metallic Glass Composites

During the thermally-activated martensitic transformation (MT) of CuZr-based bulk metallic glass (BMG) composites containing B2 CuZr crystals, the MT temperatures were reduced to 162.7 ± 2.5 K due to the constraint effect from glassy matrix, which is far lower than those of crystalline counterparts. In situ high-energy X-ray diffraction measurements demonstrate that the thermally-activated MT is governed by an extremely incomplete MT from B2 to B19' and B33 phases without the decomposition of B2 phase which appears in crystalline counterparts. Due to free stress states during the thermally-activated MT, B33 phase forms more easily during thermal process than deformation process.

In situ high energy X-ray diffraction measurement of strain and dislocation density ahead of crack tips grown in hydrogen

The deformation fields near fatigue crack tips grown in hydrogen and in air were measured using high-energy x-ray diffraction. A larger magnitude of elastic strain was observed in the hydrogen case compared to the air case. The magnitude of elastic strain was quantified through an effective crack tip stress intensity factor. The dislocation profile ahead of the crack was probed via x-ray line broadening and electron back-scatter diffraction was used to assess the crack path (intergranular vs. transgranular). Ahead of the crack tip grown in hydrogen, an order of magnitude lower dislocation density, compared to a baseline density far from the crack, was observed. This decrease in dislocation density was not observed in the air case. These differences are discussed in terms of two leading hydrogen embrittlement mechanisms, Hydrogen Enhanced Localized Plasticity (HELP) and Hydrogen Enhanced Decohesion (HEDE). We have observed a decrease in transgranular cohesion (transgranular HEDE), as well as an increase in intergranular fracture. The measurements of dislocation activity support a model of a decrease in intergranular cohesion (intergranular HEDE) which is likely facilitated by the HELP mechanism. This suggests that the increase in fatigue crack growth rate is due to a sum of the two effects of hydrogen, in which the crack grows faster in the transgranular fracture mode and faster due to an increase in a new mode of intergranular fracture.

Evidence for a short-range chemical order of Ge atoms and its critical role in inducing a giant magnetocaloric effect in Gd5Si1.5Ge2.5

Crystal structure and magnetic properties of Gd5Si1.5Ge2.5 and Gd4.9Zr0·1Si1.5Ge2.5 were investigated using high-energy X-ray diffraction and magnetic measurements. Results showed that a Zr substitution for 2% Gd reduces unit cell volumes of a room-temperature monoclinic and a low-temperature orthorhombic lattice and a difference between them at a magnetostructural transition. At a microscopic level, the Zr substitution increases length of disconnected interlayer T–T bonds of the monoclinic lattice at the expense of length of connected interlayer T–T bonds (T = Si, Ge). These opposing changes of the interlayer T–T bonds provided evidence for existence of a short-range chemical order of Ge atoms in lattices of Gd5Si1.5Ge2.5 and its weakening by the Zr substitution. Magnetic measurements revealed that the Zr substitution brings about a change of the magnetic structure and a reduction of a giant magnetocaloric effect of Gd5Si1.5Ge2.5. Based on such structural and magnetic changes due to the Zr substitution, we propose a relation between the short-range chemical order and the total entropy change at the magnetostructural transition. Using this relation, a giant magnetocaloric effect and an annealing effect observed over a wide range of Gd5(Si,Ge)4 composition can be explained quantitatively.

Determination of local residual stress in an air plasma spray thermal barrier coating (APS-TBC) by microscale ring coring using a picosecond laser

A picosecond laser for incremental annular trench cutting is combined with digital image correlation (DIC) to extend the incremental ring-core method to the profiling of residual stress in thick (>100 μm) coatings. In this case the local residual stress in a TBC is depth profiled after exposure to 1150 °C for 190 h. The topcoat was found to be in compression with an average compressive stress of −94 ± 8 MPa which is representative of the stresses that would be generated elastically on cooling from a stress-free temperature of ~970 °C. The stress profile measurements have been validated by high-energy synchrotron X-ray diffraction measurements.