Situ Synchrotron X-ray Diffraction Research Articles

Thermally activated damage recovery in ion‐irradiated Gd2Ti2‐yZryO7 pyrochlore

AbstractIonizing events having a wide variety of radiation‐induced effects can radically affect the kinetics of defect production or structural transformation in the pyrochlore structured oxides (A2B2O7). Therefore, a thorough understanding of the kinetics associated with cation ordering and disordering is required for various technological applications. The structural responses of Gd2Ti2‐yZryO7 (y = 0.4, 1.2, 1.6) pyrochlore series irradiated by 120 MeV Au9+ ions were investigated using in situ synchrotron x‐ray diffraction (SR‐XRD), micro‐Raman spectroscopy, and scanning electron microscopy (SEM). Each pyrochlore composition irradiated at the highest fluence, where structural modifications occur, was subsequently isochronally annealed from room temperature to 1000°C. The SR‐XRD results indicate that Ti‐rich composition (y = 0.4) retains its pre‐irradiated pyrochlore structure (Fdm) at 1000°C. In contrast, Zr‐rich compositions exhibit recrystallization to an intermediate defect‐fluorite phase (Fmm) above 500°C, and the pre‐irradiated pyrochlore superstructure does not recover even on annealing at 1000°C. These results reveal that recrystallization temperature strongly depends on the accumulated radiation damage, generally described with the cationic radius ratio (rA/rB). Thus, investigation of the thermal annealing behavior of irradiated pyrochlores helps better understanding the general mechanisms of radiation damage and recovery of pyrochlores, which is important for their use in nuclear applications.

Reaction pathways for the formation of complex fluorides revealed by in situ synchrotron X-ray diffraction

This study investigated the reaction between LiF, Mo metal, and CuF2 as a solid-state fluorine source to form a complex fluoride, tetragonal trirutile (TR)-type Li2MoF6, in an Ni metal tube by in situ synchrotron X-ray diffraction (SXRD) experiments. As a result, two formation pathways of TR-type Li2MoF6 were identified: one involving a reaction among intermediate phases, i.e., MoF3, and an unknown Mo-containing fluoride, and the starting materials, i.e., LiF, Mo, and CuF2, the other involving a direct reaction between LiF, Mo, and CuF2. The combination of in situ SXRD with differential scanning calorimetry (DSC) revealed that the direct reaction was facilitated by the presence of the liquid phase of LiF-CuF2. Further, the first-order phase transition of Li2MoF6 with a great volume change of 21% was found to occur in the vicinity of 520 °C–550 °C reversibly. Finally, this study demonstrated that an in situ SXRD experiment supported by DSC measurement is a powerful tool for revealing the reaction routes and identifying new phases occurring in sample-loaded metal tubes.

High-pressure X-ray study of NbON oxynitride: direct transition from baddeleyite to cotunnite structure

Abstract The structural properties of NbON oxynitride under high pressure were investigated through in situ synchrotron X-ray diffraction (SXRD) up to 43 GPa. It was found that the bulk modulus of baddeleyite NbON (290 GPa) is larger than that of ZrO2 (150 GPa), indicating that the introduction of highly covalent nitrogen imparts greater stiffness. Furthermore, SXRD patterns reveal the emergence of a peak signaling a new crystalline phase above around 20 GPa. This is in contrast to TaON, where diffraction patterns only show an increase in background beyond 33 GPa. First-principle calculations suggest that the high-pressure phase adopts an orthorhombic cotunnite-type structure, distinguishing it from the oxide counterparts, wherein the ambient pressure phase transforms to a cotunnite structure via an orthorhombic-I structure.

In situ synchrotron X-ray diffraction analysis of ultrasonically assisted microstructure refinement during laser melting process

This work investigates the effect of ultrasonic treatment (UST) on the microstructure of AA4043 alloy during laser melting process. The study utilizes in situ synchrotron X-ray diffraction (SXRD) and postmortem electron backscatter diffraction (EBSD) techniques to examine the ultrasonic grain refinement mechanism. The SXRD diffraction patterns exhibit higher continuity of major diffraction rings in the UST-test pattern, indicating a more refined grain structure. The presence of new diffraction spots in the post-test diffraction pattern with UST suggests the breakdown of epitaxial growth of columnar dendrites during solidification. Thermal profiles determined by analyzing the lattice parameter evolution show a faster cooling rate with UST. The inverse pole figures and aspect ratio distribution from EBSD reveal that the UST samples exhibit a refined, more equiaxed grain structure along the weld centerline. UST sample also develops more fine-sized low angle grain boundaries (LAGBs). These features offer better hot-cracking resistance in aluminum alloys.

Bimetallic NiFe Nanoparticles Supported on CeO2 as Catalysts for Methane Steam Reforming.

Ni-Fe nanocatalysts supported on CeO2 have been prepared for the catalysis of methane steam reforming (MSR) aiming for coke-resistant noble metal-free catalysts. The catalysts have been synthesized by traditional incipient wetness impregnation as well as dry ball milling, a green and more sustainable preparation method. The impact of the synthesis method on the catalytic performance and the catalysts' nanostructure has been investigated. The influence of Fe addition has been addressed as well. The reducibility and the electronic and crystalline structure of Ni and Ni-Fe mono- and bimetallic catalysts have been characterized by temperature programmed reduction (H2-TPR), in situ synchrotron X-ray diffraction (SXRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Their catalytic activity was tested between 700 and 950 °C at 108 L gcat-1 h-1 and with the reactant flow varying between 54 and 415 L gcat-1 h-1 at 700 °C. Hydrogen production rates of 67 mol gmet-1 h-1 have been achieved. The performance of the ball-milled Fe0.1Ni0.9/CeO2 catalyst was similar to that of Ni/CeO2 at high temperatures, but Raman spectroscopy revealed a higher amount of highly defective carbon on the surface of Ni-Fe nanocatalysts. The reorganization of the surface under MSR of the ball-milled NiFe/CeO2 has been monitored by in situ near-ambient pressure XPS experiments, where a strong reorganization of the Ni-Fe nanoparticles with segregation of Fe toward the surface has been observed. Despite the catalytic activity being lower in the low-temperature regime, Fe addition for the milled nanocatalyst increased the coke resistance and could be an efficient alternative to industrial Ni/Al2O3 catalysts.

Stabilization of Ti5Al11 at room temperature in ternary Ti-Al-Me (Me = Au, Pd, Mn, Pt) systems

Ti5Al11 is known as a high-temperature phase in binary Ti-Al alloys. However, its existence at low temperatures was previously observed in ternary Ti-Al-based systems alloyed with some transition metals. In this study, we systematically evaluated Ti-Al-Me ternary systems (Me = Au, Pd, Mn, or Pt) to determine the influence of transition elements on low-temperature stabilization of Ti5Al11 phase. The temperature ranges in which Ti5Al11 existed in Ti-Al-Me systems were experimentally found using in situ synchrotron X-ray diffraction (SXRD). It was established that addition of Mn and Pt retains Ti5Al11 at room temperature. The obtained data were compared with predictions of density functional theory (DFT). The total energy, volume, and bond length are especially significantly reduced by addition of Mn and Pt. Ti5Al11 compound containing both of these elements is less prone to saturation with Ti upon preserving the lattice tetragonality and suppressing Ti5Al11 → TiAl transformation. These factors finally contribute to the retention of this phase at room temperature.

Triggering Mixed Cationic‐Anionic Redox in Cu2‐xSe Cathodes via Tailored Charge‐Carrier for High Energy Density Aqueous Zn Batteries

AbstractThe further application of promising transition‐metal chalcogenides (TMCs) cathodes in dilute neutral aqueous Zn batteries (AZBs) is mainly plagued by unsatisfactory working voltages (usually <1 V vs Zn2+/Zn) and their conventional cationic redox centers reaching theoretical capacity limit. Hence, to break the confinement, a novel Zn‐Cu2‐xSe battery is developed in dilute neutral‐aqueous electrolyte by introducing a tailored charge‐carrier, which not only alters the intercalation potential of ions embedded into Cu2‐xSe (vs Zn2+/Zn, working voltage from ≈0.4 to ≈1.2 V) but also activates the anionic redox centers of Cu2‐xSe (capacity release from 143.4 to 323.2 mAh g−1 at 0.4 A g−1). In situ synchrotron X‐ray diffraction (SXRD) and substantial ex situ characterizations reveal the multi‐step phase conversion undergone by cathode and triggered additional Se‐based anionic (Sen2−/Se2−) reversible redox reaction. A multi‐electron synergistic transfer process established on the cationic‐anionic redox centers circumvents the slow relaxation of single‐ion charge compensation achieving high‐capacity and enhanced ion diffusion kinetics. As a result, an extraordinary energy density of up to 406.2 Wh kg−1 at 240 W kg−1 is implemented (calculated based on the mass of Cu2‐xSe cathode), which is ≈8.4 times higher than that of conventional Zn‐Cu2‐xSe batteries, representing an advanced development toward energetic AZBs.

An in situ study of microstructural strain localization and damage evolution in an (α+β) Ti-Al-V-Fe-Si-O alloy

Multi-phase titanium (Ti) alloys exhibit highly heterogeneous plastic deformation patterns. Understanding the micro-mechanisms of plastic deformation causing strain heterogeneity is thus of fundamental importance for enhanced manufacturability and in-service performance of Ti alloys. In this study, the critical microstructural factors responsible for microscopic strain localization are systematically investigated in an (α+β) Ti-Al-V-Fe-Si-O alloy by integrating the microstructural insights obtained from in situ microstructure-based digital image correlation (μ-DIC), in situ synchrotron X-ray diffraction (SXRD), and statistical analyses of strain localization incidents. The uniaxial tensile tests along the transverse direction reveal strain localization (i) across favorably oriented adjacent α grains (multi-grain strain localization) and (ii) along grain/phase boundaries (boundary strain localization), both of which suggest the strong influence of local crystallographic orientation on strain heterogeneity. The boundaries shared by soft and hard α grains are observed to be highly susceptible to strain localization, although ductile damage mechanisms are mostly delayed until the later stages of necking. While the majority of the (α+β) microstructure can co-deform to high strain levels without significant ductile damage evolution, micro-void nucleation and growth eventually initiate at the α/β phase interfaces, with work-hardening of the β phase. The insights provided through these in situ experiments highlight the importance of local texture in the strain localization and damage in (α+β) Ti alloys.

Complex multi-step martensitic twinning process during plastic deformation of the superelastic Ti-20Zr-3Mo-3Sn alloy

The Ti-20Zr-3Mo-3Sn (at.%) alloy is investigated before and after deformation by conventional and cyclic tensile tests, electron back-scattered diffraction (EBSD), in situ synchrotron X-ray diffraction (SXRD) and transmission electron microscopy (TEM). On one hand, the maximum recovery strain of 3.3% is obtained, which is attributed to the favorable {111}<101>β texture of β phase after short solution treatment. On the other hand, plastic deformation mechanisms are studied from specimens strained to 5% and 8%. The reversible stress-induced martensitic (SIM) α" transformation is preliminary detected by SXRD during loading and after unloading in both specimens. Then, the deformation microstructures are further investigated in details by TEM. At 5% of strain, primary α" deformation bands are observed with an abnormal orientation relationship (OR) with β phase. From crystallographic reconstruction, this OR is shown to be due to {130}<310>α" twinning followed by {111}α″ type Ⅰ reorientation twinning during loading. At 8% of strain, a complex hierarchical microstructure composed of primary and secondary α" bands is observed, which corresponds to residual primary {130}<310>α" twins with secondary {130}<310>α" twins occurring after {111}α″ reorientation twinning of primary {130}<310>α" twins. The sequence of plastic deformation is then composed of primary {130}<310>α" twinning, followed by {111}α″ reorientation twinning and finally secondary {130}<310>α" twinning. A thin layer of ω phase is also observed at the β/α" inter-phase boundary. Occurrence of this unprecedented complex multi-step martensitic twinning process is rationalized by means of Schmid factor analysis and transformation strain calculations.

Mechanisms of near-linear elastic deformation behavior in a binary metastable β-type Ti-Nb alloy with large recoverable strain

A binary metastable β-type Ti-Nb alloy possessing large near-linear recoverable strain was designed to clarify the physical mechanisms responsible for high near-linear elastic deformability in near‑oxygen-free Ti-based alloys. The in situ synchrotron X-ray diffraction (SXRD) investigation reveals that in addition to the inherent elastic deformation, a reversible β↔α'' stress-induced martensitic transformation (SIMT) occurs during the near-linear elastic deformation. During the SIMT, the α'' martensitic variant 5 (V5) forms preferentially due to its maximum phase transformation strains among all 6 equivalent α'' variants. The orientation dependence of phase transformation strains of the preferential V5 leads to the appearance of different α'' diffraction peaks in the loading and Poisson’s directions during the SIMT, which is beneficial for accommodating the external macroscopic deformation to the great extent. Our experimental results show that the high near-linear elastic deformability of present Ti-Nb alloy is attributed to a combined effect of the large inherent elastic deformation arising from low Young's modulus as well as a reversible SIMT that covers a wide stress range and exhibits small phase transformation strains limited by the lattice constants of β and α'' phases. These results could provide a comprehensive understanding of the mechanisms responsible for huge near-linear elastic deformability of β-type titanium alloys.

Synthesis and characterization of a new TiZrHfNbTaSn high-entropy alloy exhibiting superelastic behavior

In this study, a new single-phase bcc Ti35Zr35Hf15Nb5Ta5Sn5 high-entropy alloy (HEA) was developed and investigated by means of cyclic tensile tests, transmission electron microscopy (TEM), electron back-scattered diffraction (EBSD) and in situ synchrotron X-ray diffraction (SXRD). The alloy reveals a superelastic behavior due to the reversible stress-induced martensitic transformation that occurs between the β phase and the α'' phase. A high strain recovery of 3.8% is obtained by tensile test, which is attributed to the <110>β{447}β recrystallization texture observed.

In Situ Synchrotron X-ray Diffraction Investigations of the Nonlinear Deformation Behavior of a Low Modulus β-Type Ti36Nb5Zr Alloy

The low modulus β-type Ti alloys usually have peculiar deformation behaviors due to their low phase stability. However, the study of the underlying mechanisms is challenging since some physical mechanisms are fully reversible after the release of the load. In this paper, the deformation behavior of a low modulus β-type Ti36Nb5Zr alloy was investigated with the aid of in situ synchrotron X-ray diffraction (SXRD) during tensile loading. The evolution of lattice strains and relative integrated diffraction peak intensities of both the β and α” phases were analyzed to determine the characteristics of the potential deformation mechanisms. Upon loading, the α” diffraction spots appeared at specific azimuth angles of the two-dimensional SXRD patterns due to the &lt;110&gt; fiber texture of original β grains and the selection of favorable martensitic variants. The nonlinear deformation behavior originated from a reversible stress-induced martensitic transformation (SIMT). However, the SIMT contributed a little to the large recoverable strain of over 2.0%, which was dominated by the elastic deformation of the β phase. Various deformation mechanisms were activated successively at different applied strains, including elastic deformation, SIMT and plastic deformation. Our investigations provide in-depth understandings of the deformation mechanisms in β-type Ti alloys with low elastic modulus.

In situ synchrotron X-ray diffraction analysis of deformation behavior of a Nb/NiTi composite for biomedical applications

The deformation behavior involved in Nb/NiTi composite for biomedical applications within a large macroscopic strain range was investigated by tensile loading–unloading test and in situ synchrotron X-ray diffraction (SXRD). Experimental results show that during loading, the Nb/NiTi composite experiences the elastic elongation of B2-NiTi austenitic, B19′-NiTi martensitic and β-Nb phases, B2 → B19′ stress-induced martensitic (SIM) transformation and tensile plastic deformation of β-Nb phase. During unloading, the deformation behavior involved in Nb/NiTi composite includes the elastic recovery of B2-NiTi austenitic, B19′-NiTi martensitic and β-Nb phases, reverse phase transformation B19′ → B2 and compressive deformation of β-Nb phase. The martensitic transformation in this composite is almost reversible and occurs in a localized manner. These results might contribute to a comprehensive understanding of the deformation mechanism involved in Nb/NiTi composite and shed some light on design and development of novel composites with a combination of good biocompatibility and excellent superelasticity for biomedical applications.

Effect of grain size on the recovery strain in a new Ti–20Zr–12Nb–2Sn superelastic alloy

In this study, the superelastic performance of a new β-type Ti–20Zr–12Nb–2Sn alloy has been investigated by means of cyclic tensile tests, electron back-scattered diffraction (EBSD) and in situ synchrotron X-ray diffraction (SXRD). It is shown that the β-grain size has an important influence on the superelastic property and for the same crystallographic texture, the smaller the grain size, the greater the recovery strain.

In situ observations of continuous cooling transformations in low alloy steels

A typical heat treatment for a low alloy steel will often involve a quenching heat treatment step, in which the steel is cooled from high temperatures to trigger austenite decomposition. The particular cooling rate during the quenching step can have a marked influence on the phase transformations taking place, and the resulting steel microstructure and mechanical properties. Although methods such as dilatometry have been available for many decades to characterise continuous-cooling transformation (CCT) behaviour in steels, the use of in situ synchrotron X-ray diffraction (SXRD) to elucidate CCT behaviour in a systematic way has not been reported.In this work, we measure the CCT behaviours of two pressure vessel steels in situ using simultaneous dilatometry and SXRD. Both steels are subject to austenitisation followed by quenching at a range of cooling rates. On comparing results from SXRD and dilatometry, it is found that recorded starts of transformations appear to be in good agreement. However, calculations of phase fractions derived from dilatometry data significantly overestimate the fraction of ferrite that forms in comparison to SXRD when the formation involves the partitioning of carbon. This happens for two reasons: first, because the method to extract ferrite volume fractions from dilatometry data generally ignores the presence of any retained austenite at low temperatures, and second, because analyses of dilatometry data do not account for the expansion of the austenite during transformation due to enrichment in carbon. This enrichment leads to an increase in strain, and the standard analysis method falsely attributes this increase to ferrite formation, thereby overestimating it. The results highlight that caution must be exercised when interpreting the results of dilatometry, since levels of ferrite (especially diffusively-formed) and retained austenite are important quantities for the prediction of mechanical behaviour, and they are not readily quantified by the analysis of dilatometry data alone.

Influence of texture and transformation strain on the superelastic performance of a new Ti–20Zr–3Mo–3Sn alloy

In this work, the superelastic behavior of a new metastable β Ti–20Zr–3Mo–3Sn (at.%) biomedical alloy displaying stress-induced α" martensitic transformation (SIM) was investigated by cyclic tensile tests, electron back-scattered diffraction (EBSD) and in situ synchrotron X-ray diffraction (SXRD) for 3 different solution treatment temperatures: 700 °C, 800 °C and 900 °C. The EBSD observations revealed that the Ti–20Zr–3Mo–3Sn alloy showed a strong dependence of the solution treatment temperatures on crystallographic texture. SXRD diffraction profiles acquired under cyclic loading/unloading tensile tests clearly illustrated the reversible SIM α" transformation. In addition, the lattice parameters of β and SIM α" phases were measured for each cycle in order to establish the evolution of lattice parameters during the deformation and to calculate the maximum transformation strain for any crystallographic direction. A high recovery strain of 3.5% was obtained by tensile test after a solution treatment at 700 °C for 30 min. This high recovery strain is due to the fact that the maximum transformation strain is obtained along the tensile direction displaying the favorable <011>β{100}β recrystallization texture. The performance of the Ti–20Zr–3Mo–3Sn alloy is discussed and compared with other superelastic alloys such as NiTi and (Ti–Nb)-based alloys.

Evidence of a Pseudo‐Capacitive Behavior Combined with an Insertion/Extraction Reaction Upon Cycling of the Positive Electrode Material P2‐NaxCo0.9Ti0.1O2 for Sodium‐ion Batteries

AbstractLayered oxides are promising materials due to their easy diffusion path for alkali metals. Specifically, NaxCoO2 can be regarded as an appealing candidate for next‐generation sodium‐ion batteries (SIBs), but the multiple steps revealed in the potential vs capacity curve have restricted its use. Herein, we report NaxCo0.9Ti0.1O2, synthesized by a high‐temperature solid‐state method, where 10 % of cobalt was substituted with titanium. Obviously, the number of potential steps found in the galvanostatic curves of NaxCoO2 has been reduced. The electrode material exhibits an initial charge capacity of 108 mAh/g within the potential window 2–4.2 V (vs. Na+/Na). The intercalation/deintercalation of NaxCo0.9Ti0.1O2 was investigated by in situ synchrotron X‐ray diffraction (SXRD), and the results demonstrated a combined solid solution and pseudocapacitive mechanism, where the pseudocapacitive behavior is predominant in the region from 3.73 V (charge) to 3.79 V (discharge). Finally, in situ electrochemical impedance spectroscopy has revealed an increasing impedance, specifically when inserting sodium into the structure.

Defects-dictated tensile properties of selective laser melted Ti-6Al-4V

As-processed metals and alloys by selective laser melting (SLM), or laser powder bed fusion (L-PBF), are often full of defects and flaws such as dislocations, twins, elemental segregations, impurities and porosities, which can positively or negatively impact mechanical properties. Here, we systematically characterize the tensile behavior of L-PBF Ti-6Al-4V at quasi-static strain rate and room temperature, including state-of-the-art in situ synchrotron X-ray diffraction (SXRD) and computed tomography (SXCT). These studies reveal that the tensile yield strength and uniform elongation are mainly dictated by the as-built microstructure, while the strain-to-failure is sensitive to the porosity, even in very high-density samples (>99.5%). in situ SXRD reveals that the micro-plasticity in as-built Ti64 initiates at a stress level well below its macroscopic yield strength, signified by the early lattice strain deviation behavior of {0002} and {112¯0} reflections. SXCT reveals pore growth mechanisms when the tensile axis is perpendicular to the build direction, whereas no such behavior is observed as the tensile axis is along the build direction. These anisotropic pore growth mechanisms result in vast differences in the strain-to-failure of L-PBF materials. Our melt-pool dynamics modeling with similar laser conditions to the experiments identifies a previously unknown pore source; i.e., edge-of-track pores. We present a normalized energy diagram to identify the optimized processing window for high quality samples.

In situ XRD investigation of the evolution of surface layers on Pb-alloy anodes

The electrochemical behaviour of a number of Pb-based anode alloys, under simulated electrowinning conditions, in a 1.6 M H2SO4 electrolyte at 45 °C was studied. Namely, the evolution of PbO2 and PbSO4 surface layers was investigated by quantitative in situ synchrotron X-ray diffraction (S-XRD) and subsequent Rietveld-based quantitative phase analysis (QPA). In the context of seeking new anode alloys, this research shows that the industry standard Pb-0.08Ca-1.52Sn (wt%) anode, when exposed to a galvanostatic current and intermittent power interruptions, exhibited poor electrochemical performance relative to select custom Pb-based binary alloys; Pb–0.73Mg, Pb–5.05Ag, Pb–0.07Rh, and Pb–1.4Zn (wt%). The in situ S-XRD measurements and subsequent QPA indicated that this was linked to a lower proportion of β-PbO2, relative to PbSO4, on the Pb-0.08Ca-1.52Sn alloy at all stages of the electrochemical cycling. The best performing alloy, in terms of minimisation of overpotential during normal electrowinning operation and minimising the deleterious effects of repeated power interruptions – both of which are significant factors in energy consumption – was determined to be Pb–0.07Rh.

In situ synchrotron X-ray diffraction study of deformation behaviour of a metastable β-type Ti-33Nb-4Sn alloy

In this study, the deformation behaviour of metastable β-type Ti-33Nb-4Sn alloys in different thermo-mechanical treatment states is investigated by tensile tests and in situ synchrotron X-ray diffraction (SXRD). In the case of solution-treated alloy, stress-induced martensitic (SIM) transformation takes place over a wide strain range of 0.5–14%. During this SIM transformation, the parameter of bα′′ ([020]α′′) increases with macroscopic strain within strain range of 1.5–4.7%, giving rise to that the α′′ variants, with bα′′-axis ([020]α′′) parallel to tensile direction, are formed preferentially to accommodate the macroscopic strain during loading. Similar SIM transformation behaviour also occurs in cold-rolled alloy with the exception that the extent of SIM transformation and pre-existing α′′ variants reorientation is much slighter than that in solution-treated specimen. This slighter SIM transformation gives rise to nonlinear deformation, instead of “stress plateau”, in the cold-rolled alloy. Upon annealing, the β phase survives against SIM transformation due to the suppression effects of dislocations and grain boundaries, resulting in a huge elastic deformability. Based on the results of tensile tests and SXRD, the activation sequence of different deformation mechanisms and the regions of different deformation mechanisms of Ti-33Nb-4Sn alloys, in solution-treated, cold-rolled and annealed states, are clarified unambiguously.