Synchrotron X-ray Diffraction Study Research Articles

In Situ Synchrotron X-ray Diffraction and Microstructural Studies on Cold and Hot Stamping Combined with Quenching & Partitioning Processing for Development of Third-Generation Advanced High Strength Steels

A novel combined process of Cold Stamping (CS) and Hot Stamping (HS) with Quenching and Partitioning (Q&P) treatment applied to advanced TRIP-assisted steel has been conducted by thermomechanical simulation to evaluate the influence of CS or HS in the Q&P processing. With this purpose, Q&P, CSQ&P, and HSQ&P cycles were designed to obtain multiphase microstructures containing ferrite, martensite, bainitic-ferrite, and the maximum retained austenite (RA) fraction after the processes. The objective was to investigate the effects of the variables involving the heat treatments, such as the intercritical austenitization temperature, the isothermal and non-isothermal deformation, the amount of deformation, and the temperature and partitioning times, and to analyze their influence on the microstructural and mechanical responses. Time-resolved X-ray diffraction using synchrotron radiation was undertaken in a thermomechanical simulator coupled to the synchrotron light source to understand the influence of time, temperature, and strain on the level of carbon enrichment in austenite. In addition, the in situ austenite transformation kinetics and lattice parameter evolution were tracked, making it possible to optimize the RA fraction at room temperature after Q&P processing. The newly developed combined process is promising as the transformation-induced plasticity phenomenon during deformation can contribute to the formability and energy absorption. The results also indicate that the deformation of austenite promotes the ferrite transformation while suppressing the bainite transformation. It was possible to plot the results in an elongation-mechanical strength diagram, coupled to material property charts, also known as, ‘banana curve’, allowing us to identify and correlate the thermal or thermomechanical treatment conditions that led to an increase in ductility or strength according to the volume fractions of the resulting phases. Comparing the results for the HSQ&P treatments, it was observed that isothermal strains at higher temperatures (≥800 °C) are more advantageous to increase mechanical strength, while non-isothermal strains (starting at 750 °C) are suggested if the objective is the increase in ductility, with mechanical strength being slightly sacrificed.

In-Situ Synchrotron X-Ray Diffraction Study on Stress-Induced Martensite Transformation in Maraging Steel with High Strength and Good Ductility

In-Situ Synchrotron X-Ray Diffraction Study on Stress-Induced Martensite Transformation in Maraging Steel with High Strength and Good Ductility

In-Situ Synchrotron X-Ray Diffraction Study on Stress-Induced Martensite Transformation in Maraging Steel with High Strength and Good Ductility

In-Situ Synchrotron X-Ray Diffraction Study on Stress-Induced Martensite Transformation in Maraging Steel with High Strength and Good Ductility

Pressure-induced superconductivity and structural transitions in topological insulator SnBi2Te4

The materials with topological phases have been a flexible platform for the realization of novel types of quantum matter due to their unique topology protected electron states. Herein, we report a comprehensive structural and electrical transport investigations on a topological insulator, SnBi2Te4, under high pressures by using diamond anvil cell techniques. Through in situ high pressure synchrotron x-ray diffraction studies, two structural phase transformations have been revealed. The powdered samples of SnBi2Te4 transform from the initial layered quasi-two-dimensional structure (phase I) to a monoclinic C2/m structure (phase II) at about 7.14 GPa, and eventually develop into a site-disordered body centered cubic structure (phase III) at pressures above 18.9 GPa. Modifications of the electronic band structure have been discovered by the in situ high-pressure electrical measurements at low temperatures. It is noteworthy that three distinct pressure induced superconducting states have been observed, one in phase II and two in phase III. In each of the pressure induced superconducting states, the critical temperature Tc decreases with pressure. The maximum value of Tc is obtained in the third superconducting state emerging at the highest pressure range, which is 8.9 K at 22.3 GPa. A deep understanding of the relationship between the pressure induced structure-dependent superconducting states and the ambient-pressure topologically insulating state of SnBi2Te4 may shed light on the universal physical nature that creates topologically insulating or superconducting states.

γ-phase evolution in aged Co–Ni–Ga shape memory alloy

A synchrotron X-ray diffraction study of high-temperature (HT) shape memory alloy 49Co–21Ni–30Ga (in at. pct.) was performed. The volume fraction, cell parameter and temperature evolution of the different secondary phases were analyzed. This study reports reliable experimental data on these parameters to be used as a future reference to adjust the composition of the material.

Phase transition of Mg3(PO4)2 polymorphs at high-temperature: In-situ synchrotron X-ray diffraction and Raman spectroscopic study

In-situ synchrotron X-ray diffraction and Raman spectroscopy were used to study the stabilities, thermal expansion and vibrational modes of synthetic Mg3(PO4)2. The polymorphs (Mg3(PO4)2-I, II, III) were investigated in the temperature range of 299 ∼ 1173 K at ambient pressure. An irreversible phase transition was observed for both Mg3(PO4)2-II and Mg3(PO4)2-III, whereas Mg3(PO4)2-I is stable in the present study. Based on the in-situ synchrotron X-ray diffraction and Raman spectroscopic measurements, Mg3(PO4)2-II and Mg3(PO4)2-III transform to Mg3(PO4)2-I at 1073 K and 1023 K, respectively. The volumetric thermal expansion coefficients of Mg3(PO4)2-I, II and III were determined as 3.31(4) × 10-5 K−1, 3.91(4) × 10-5 K−1, and 3.25(5) × 10-5 K−1, respectively. All three Mg3(PO4)2 polymorphs show axial thermal expansive anisotropy since the thermal expansion coefficients along different axes are inconsistent. The effect of temperature on the Raman vibrations of the three Mg3(PO4)2 polymorphs was quantitatively analyzed. And the isobaric mode Grüneisen parameters of three Mg3(PO4)2 polymorphs are calculated, which are in the range of 0.07 ∼ 3.54.

Iridate Li8IrO6: An Antiferromagnetic Insulator.

A polycrystalline iridate Li8IrO6 material was prepared via heating Li2O and IrO2 starting materials in a sealed quartz tube at 650 °C for 48 h. The structure was determined from Rietveld refinement of room-temperature powder neutron diffraction data. Li8IrO6 adopts the nonpolar space group R3̅ with Li atoms occupying the tetrahedral and octahedral sites, which is supported by the electron diffraction and solid-state 7Li NMR. This results in a crystal structure consisting of LiO4 tetrahedral layers alternating with mixed IrO6 and LiO6 octahedral layers along the crystallographic c-axis. The +4 oxidation state of Ir4+ was confirmed by near-edge X-ray absorption spectroscopy. An in situ synchrotron X-ray diffraction study of Li8IrO6 indicates that the sample is stable up to 1000 °C and exhibits no structural transitions. Magnetic measurements suggest long-range antiferromagnetic ordering with a Néel temperature (TN) of 4 K, which is corroborated by heat capacity measurements. The localized effective moment μeff (Ir) = 1.73 μB and insulating character indicate that Li8IrO6 is a correlated insulator. First-principles calculations support the nonpolar crystal structure and reveal the insulating behavior both in paramagnetic and antiferromagnetic states.

High-pressure single-crystal synchrotron X-ray diffraction study of lillianite

Abstract In this paper, high-pressure data from a synchrotron X-ray diffraction study on a lillianite (Pb3Bi2S6) single crystal up to ~21 GPa are presented. A phase transition from lillianite (space group Bbmm, LP lillianite) to the high-pressure form β-Pb3Bi2S6 (space group Pbnm, HP lillianite) was confirmed and bracketed between 4.90 and 4.92 GPa. The transition is reversible but of first-order with a hysteresis of ~2.8 GPa. It showed weak effects of pseudo-merohedral twinning that disappeared upon decompression, testifying to a full recovery of the single crystal of lillianite. This makes lillianite an interesting shape-memory material. With a bulk modulus K4.9 = 78(3) GPa and K′ = 5.1(4), β-Pb3Bi2S6 is markedly less compressible than lillianite [K0 = 44(2) GPa, K′ = 7(1)]. Compressional anisotropy increases markedly in β-Pb3Bi2S6 with compressibility along the b axis [M0b = 130(6) GPa and Mb′ = 19(3) in lillianite, M4.9b = 145(4) GPa and Mb′ = 16.0(7) in β-Pb3Bi2S6] significantly larger than that along the other two axes [M0a = 118(5) GPa, Ma′ = 21(3), M0c = 139(12) GPa, and Mc′ = 31(10) in lillianite, M4.9a = 242(12) GPa, Ma′ = 8(1), M4.9c = 242(5) GPa, and Mc′ = 29(1) in β-Pb3Bi2S6]. The behavior of lillianite at high pressure is an interesting case study in relation to non-quenchable ultrahigh-pressure phases likely occurring in the inner Earth, like post-perovskite MgSiO3, the oxide homologue N = 1 of the lillianite series. The β-Pb3Bi2S6 structure, on the other hand, is the N = 3 homologue of the meneghinite series to which the higher-pressure modification of the post-perovskite structure also belongs (homologue N = 1). This makes the two forms of Pb3Bi2S6 potential equivalents of high- and ultrahigh-pressure Mg silicates that could occur both in the deep earth and in other rocky extrasolar planetary bodies.

In situ synchrotron x-ray diffraction studies monitoring mechanochemical reactions of hard materials: Challenges and limitations.

In situ monitoring of mechanochemical reactions of soft matter is feasible by synchrotron diffraction experiments. However, so far, reactions of hard materials in existing polymer milling vessels failed due to insufficient energy input. In this study, we present the development of a suitable setup for in situ diffraction experiments at a synchrotron facility. The mechanochemical transformation of boehmite, γ-AlOOH, to corundum, α-Al2O3, was chosen as a model system. The modifications of the mill's clamping system and the vessels themselves were investigated separately. Starting from a commercially available Retsch MM 400 shakermill, the influence of the geometrical adaptation of the setup on the milling process was investigated. Simply extending the specimen holder proved to be not sufficient because changes in mechanical forces need to be accounted for in the construction of optimized extensions. Milling vessels that are suitable for diffraction experiments and also guarantee the required energy input as well as mechanical stability were developed. The vessels consist of a steel body and modular polymer/steel rings as x-ray transparent windows. In addition, the vessels are equipped with a gas inlet and outlet system that is connectable to a gas analytics setup. Based on the respective modifications, the transformation of boehmite to corundum could be observed in an optimized setup.

The effect of additives on the hydration of CaSO4·0.5H2O: A synchrotron X-ray diffraction study

To modulate the rate of hydration of calcium sulfate hemihydrate (HH) to calcium sulfate dihydrate for industrial applications, additives (both accelerants and retardants) are added to the HH. Here we explore in detail the kinetics and mechanism of HH hydration in the presence of the accelerators K2SO4 or ZnSO4, and also when a retardant (citric acid or tartaric acid) is added. Retardants tend to lower the maximum temperature of the reaction and increase the time needed to reach 50% hydration, yet the total conversion percentage is similar to that when an accelerant is added. The reaction process is found to involve heterogenous nucleation regardless of the nature of the additive. More soluble accelerants act mainly though increasing the rate of crystal growth, while less soluble species have a more significant effect on the rate of nucleation.

Confined Li metal storage in porous carbon frameworks promoted by strong Li–substrate interaction

Li metal suffers from uncontrollable dendrite formation and huge volume changes during cycling, resulting in shortened cycle lifetimes. Porous carbon frameworks have been explored as host materials to store Li metal; however, the low pore utilization and uneven Li plating remain crucial issues. Herein, we demonstrate that a strong interaction between Li and substrate plays a critical role in enhancing pore utilization in the carbon framework electrodes, thus improving their cycle lifetimes. As a model architecture, we examine a Li storage process in a framework electrode consisting of porous carbon derived from metal–organic frameworks (MOFs) and a galvanically displaced Ag layer on a Cu substrate. The MOF-derived carbon framework electrode on the Ag-deposited Cu substrate exhibits significantly better cycling stability (>250 cycles) than the electrode on bare Cu (140 cycles). In-operando synchrotron X-ray diffraction studies combined with microstructural characterizations reveal that the lithiophilic Ag on the substrate preferentially reacts with Li+ to form LixAg during the initial stage of Li plating and promotes confined Li storage in the carbon framework electrode while suppressing top plating. However, the Ag layer is found to lose its effectiveness when the thickness of the electrode exceeds a critical value. Based on simulation studies, the efficacy of lithiophilic layers toward improving pore utilization is discussed in terms of the kinetic competition between Li+ transport through porous channels and the interfacial reaction of Li+ with the substrate, which can provide a guideline for designing porous carbon frameworks with high capacity and long cycle lifetimes.

High-Pressure and High-Temperature Synthesis and In Situ High-Pressure Synchrotron X-ray Diffraction Study of HfSi2.

High-quality hafnium disilicide (HfSi2) has been successfully synthesized using a high-pressure and high-temperature (HPHT) method at 3 GPa and 1573 K in a DS6 × 10 MN cubic press. The modest synthesis temperature is aided by significant decreases in both liquidus and solidus temperatures at high pressure for the Si-rich portion of the Hf-Si binary system. The in situ high-pressure X-ray diffraction study yielded a bulk modulus of B0 = 124.4 ± 0.8 GPa with a fixed B0' = 4.0 for HfSi2, which exhibits a dramatically anisotropic compressibility, with a and c axes nearly twice as incompressible as the b axis. The bulk HfSi2 as synthesized has a Vickers hardness of 6.9 ± 0.1 GPa and high thermal stability of 1163 K in air, indicating its hard and refractory ceramic properties. The core-level XPS data of Hf 4f and Si 2p have been collected on the bulk samples of HfSi2, HfSi, and Hf, as well as Si powder to examine the Hf-Si bonding in hafnium silicides. The Hf 4f7/2 binding energies are 15.0 and 14.8 eV for bulk HfSi2 and HfSi, respectively.

In-situ quantification and density functional theory elucidation of phase transformation in carbon steel during quenching and partitioning

Phase transformation in low alloyed Fe-C steels during quenching and partitioning (Q&P), though authentically attributed to carbon diffusion, is scarcely quantified experimentally in terms of microstructural evolution and lack of fundamental backing at a quantum mechanics level. Herein, we report on a combined in-situ high energy synchrotron X-ray diffraction and density functional theory (DFT) study to unveil the physical mechanism of phase transformation in a Q&P processed advanced Fe-C steel. Beside a small fraction of bainite, a low air-quenching rate of ∼6 °C/s in the Ms to quenching temperature range leads to carbon enrichment into the untransformed austenite, which simultaneously turns up with the later stage of martensitic transformation at the existing austenite/martensite interfaces. The resulting transformations are ascertained by DFT results and attributed to a second energy barrier in ferrite/martensite facilitation to carbon diffusion to austenite at elevated temperatures, along with the well-known carbon solubility difference/equilibrium in austenite and martensite. The development of cubic martensite in the carbon steel is theoretically elucidated and attributed to more probable hopping sites and diffusion paths of carbon in the ferrite/martensite than in the austenite.

Effect of NiTi matrix grain size on the ultra-large elastic deformation of V nanowires in a V/NiTi composite

A vanadium nanowires/NiTi composite was fabricated by forging and drawing a Ni38Ti37V25 alloy and effect of NiTi matrix grain size on the elastic deformation of V nanowires in composite was investigated. The results revealed that NiTi grain size increased with the increasing annealing temperature, however, morphology of V nanowires was independent of annealing temperature. The in situ synchrotron X-ray diffraction studies revealed that V nanowires in the composite exhibited ultrahigh lattice strain during tension loading and the maximum lattice strain decreased with the increasing NiTi matrix grain size. This grain size effect is mainly attributed to the lattice strain mismatch at V/NiTi interface and inhomogeneity of stress distribution in NiTi matrix. The findings of this work provide a theoretical basis for the design of novel nanowire composites.

Important Roles of Water Clusters Confined in a Nanospace as Revealed by a Synchrotron X-ray Diffraction Study

States of water molecules confined in a nanospace designed by montmorillonite (negatively charged silicate layer) and charge compensating benzylammonium were investigated. Caffeine was used as a probe because of its compatibility for the fine structure of the interlayer water. Powder synchrotron radiation X-ray diffraction (SXRD) and adsorption isotherms of the water vapor revealed a metastable structure of bimolecular water layers (2WLs) in the interlayer space. Water molecules readily penetrated to expand the interlayer space to 0.56 nm. The interlayer space did not increase further even in the presence of excess water. According to the isosteric heat of water, the expansion was limited because of moderate hydration as forming 2WLs. Caffeine molecules replaced a part of the water molecules in the 2WLs to expand the interlayer space to 0.65 nm. Time-resolved SXRD with an accumulation time of 500 ms revealed that the interlayer expansion reached a steady state within a few minutes. The caffeine intercalation proceeded, involving a change in the molecular orientation that increased the contact area of the caffeine molecules. The interlayer expansion was limited in all the solvents examined (mixtures of water with methanol, ethanol, acetone, and tetrahydrofuran), while the packing density of the incorporated caffeine was maximized in the absence of an organic solvent. The water molecules confined in the interlayer space acted as an actuator to accommodate a large quantity of amphiphilic molecules by adapting the nanostructure, which was achieved by releasing the confined water molecules.

Pressure-Driven Symmetry-Preserving Phase Transitions in Co(IO3)2

High-pressure synchrotron X-ray diffraction studies of cobalt iodate, Co(IO3)2, reveal a counterintuitive pressure-induced expansion along certain crystallographic directions. High-pressure Raman and infrared spectroscopy, combined with density-functional theory calculations, reveal that with increasing pressure, it becomes energetically favorable for certain I–O bonds to increase in length over the full range of pressure studied up to 28 GPa. This phenomenon is driven by the high-pressure behavior of iodate ion lone electron pairs. Two pressure-induced isosymmetric monoclinic–monoclinic phase transitions are observed at around 3.0 and 9.0 GPa, which are characterized by increasing oxygen coordination of the iodine atoms and the probable formation of pressure-induced metavalent bonds. Pressure–volume equations of state are presented, as well as a detailed discussion of the pressure dependences of the observed Raman- and infrared-active modes, which clarifies previous inconsistencies in the literature.

Synchrotron x-ray diffraction and crystal plasticity modeling study of martensitic transformation, texture development, and stress partitioning in deep-drawn TRIP steels

The micromechanics of the formability of a lean duplex TRIP steel was investigated using Synchrotron X-Ray Diffraction (S-XRD) measurements and Crystal Plasticity Finite Element Modeling (CPFEM). Specifically, the effect of the ferrite phase on the reduction of stress concentrations in the martensite phase and the influence of the austenite texture on the distribution of the martensite phase in the deep-drawn duplex TRIP steel were studied in comparison to a TRIP steel case. A series of deep-drawing processes were carried out to examine the sheet formability at ambient temperature, followed by S-XRD evaluations of the phase fraction, texture, and the residual-stress distributions in the deep-drawn cups. The macroscopic residual stress and its partitioning among constituent phases were studied using both S-XRD and CPFEM. In the deep-drawn TRIP steel, large tensile hoop residual stresses concentrated in the strain-induced α’ martensite phase, correlating well with the cracking phenomenon observed. Furthermore, the initial austenite texture influenced the martensite transformation kinetics during the deep-drawing process, resulting in a heterogeneous distribution of the martensite phase fractions around the circumference of the deep-drawn cups, which, in turn, caused an orientation-dependent cracking behavior. In the deep-drawn duplex TRIP steel, the tensile hoop residual stresses in the α’ martensite phase were significantly reduced due to a favorable load partitioning to the ferrite phase, resulting in a better formability.

Crystallization Properties of Al-Sb Alloys for Phase Change Memory Applications

Material properties of Al-Sb binary alloy thin films deposited under ultra-high vacuum conditions were studied for multi-level phase change memory applications. Crystallization of this alloy was shown to occur in the temperature range of 180 °C–280 °C, with activation energy >2 eV. X-ray diffraction (XRD) from annealed alloy films indicates the formation of two crystalline phases, (i) an Al-doped A7 antimony phase, and (ii) a stable cubic AlSb phase. In-situ XRD analysis of these films show the AlSb phase crystalizes at a much higher temperature as compared to the A7 phase after annealing of the film to 650 °C. Mushroom cell structures formed with Al-Sb alloys on 120 nm TiN heater show a phase change material resistance switching behavior with reset/set resistance ratio >1000 under pulse measurements. TEM and in situ synchrotron XRD studies indicate fine nucleation grain sizes of ∼8–10 nm, and low elemental redistribution that is useful for improving reliability of the devices. These results indicate that Te-free Al-Sb binary alloys are possible candidates for analog PCM applications.

Magneto-structural correlation across the spin reorientation transition temperature in pure and Sm substituted TmFeO3: A temperature dependent Raman and synchrotron X-ray diffraction study

This paper presents the magneto-structural study on orthoferrite TmFeO3 and Sm substituted TmFeO3 across spin reorientation transition (SRT) temperature. A strong change in magnetic anisotropy due to the substitution of the Sm3+was observed, which is reflected as a change in spin reorientation transition (SRT) temperature. The SRT temperature of Tm0.5Sm0.5FeO3is found to be around 200–230 K, which is relatively high in comparison to TmFeO3. A sudden decrease in the value of coercivity has been observed in the SRT region for both the sample. The lattice dynamics of TmFeO3 and Tm0.5Sm0.5FeO3were investigated by temperature-dependent x-ray diffraction and Raman spectroscopy. We observed unusual contractions in the lattice parameter at low temperatures due to complex exchange interaction between RE3+ and Fe3+ ions sub-lattice. Anomalous behavior in lattice parameters was observed in the vicinity of SRT, which confirms the system’s spontaneous magnetostriction.The strong anomaly was observed in line width and phonon frequency of Raman modes of around SRT, which established the spin-lattice coupling in TmFeO3 and Tm0.5Sm0.5FeO3 nanoparticles. Observation of spin-lattice coupling utilizing Raman scattering substantiates our magnetic and structural correlation and supports its candidature for magneto-elastic applications.

Synchrotron X-ray diffraction studies of the phase-specific deformation in additively manufactured Ni–CrC composites

Cold spray is a promising solid-state additive manufacturing process for the fabrication of metal matrix composites in the forms of coatings, and more recently, bulk materials, particularly when deposition of two phases is needed with minimal alterations of the chemistry and phase composition. While prior studies have reported improved mechanical performance in cold sprayed composites, a fundamental understanding of the response and contribution of individual constituent phases to the collective mechanical properties of the composite is yet to be developed. In this work, we use in-situ synchrotron X-ray diffraction to study the strain partitioning between the soft and hard phases in cold sprayed Ni–CrC bulk composites. We conduct stepwise uniaxial tensile loading experiments and use high energy X-ray diffraction at multiple load steps to measure phase-specific strains and stresses upon loading. We find neither plasticity in the Ni phase nor a significant load transfer or redistribution between Ni and CrC phases during the loading process and attribute them to a premature failure governed by the presence of defects.