High-energy X-ray Diffraction Technique Research Articles

In-situ high-energy synchrotron X-ray diffraction study of micromechanical behavior of multiple phases in Ni47Ti44Nb9 shape memory alloy

High-energy synchrotron X-ray diffraction technique was used to in-situ characterize microstructure, lattice strain, and phase transition behavior of a Ni47Ti44Nb9 shape memory alloy. Phase transformation kinetics and deformation mechanisms were studied under a uniaxial tension at three testing temperatures, i.e., −70°C, 25°C, and 150°C. At a testing temperature of −70°C, a complicated phase transformation with four stages of micromechanical deformation was identified which is associated with changes of martensite substructures. At room temperature of 25°C, there was no stress-induced selection process of variants of B19′ phases observed. Whereas at a testing temperature of 150°C, there was no any phase transformation observed. It is verified that β-Nb phase, an effective stabilizer for the austenite, delays the process of martensitic transformation and relaxes the strain energy without strengthening the matrix. This new finding is important to understand the relationship between the micromechanical deformation behavior and phase transformations in the Ni47Ti44Nb9 SMA.

Structure of Disordered Materials Studied by High-Energy X-Ray Diffraction Technique

With the arrival of the third generation of synchrotron sources and/or the introduction of advanced insertion devices (wigglers and undulators), the high energy (E > 50 keV) x-ray diffraction technique has become feasible, leading to new approaches in the quantitative study of the structure of disordered materials than was hither to available. Since we built the SPring-8 bending magnet beamline BL04B2 and two-axis diffractometer for disordered materials in 1999, we have studied on disordered materials from ambient to extreme condition. In this article, the high-energy x-ray diffraction beamline BL04B2 of SPring-8 and recent developments of ancillary equipment (automatic sample changer, conventional high-temperature furnace, aerodynamic levitation furnace) are introduced. Furthermore the structural analysis on the basis of diffraction data with the aid of computer simulations, which we performed in the last 10 years is reviewed.

Large internal stress-assisted twin-boundary motion in Ni2MnGa ferromagnetic shape memory alloy

The twin boundary motion driven by thermo-magnetic coupling was in-situ studied in a NiMnGa single crystal using high-energy x-ray diffraction technique. An unstable martensite with an internal stress of ∼8 MPa was obtained through a thermo-magnetic training. The triple martensite variants assisted by internal stress are distinct from the self-accommodated martensite twin variants with a stress-free state, and a single martensite-variant can be actuated only by a magnetic field of ∼0.34 T, equivalent to an actuator stress of about 1.3 MPa. The generation of so large internal stress among variants is attributed to the altered martensite nucleation sites triggered by external fields during thermo-magnetic training.

Liquid Structure of and Li+ Ion Solvation in Bis(trifluoromethanesulfonyl)amide Based Ionic Liquids Composed of 1-Ethyl-3-methylimidazolium and N-Methyl-N-propylpyrrolidinium Cations

Liquid structures of the bis(trifluoromethanesulfonyl)amide based ionic liquids composed of 1-ethyl-3-methylimidazolium and N-methyl-N-propylpyrrolidinium ([C(2)mIm(+)][TFSA(-)] and [C(3)mPyrro(+)][TFSA(-)], respectively) and Li(+) ion solvation structure in their lithium salt solutions were studied by means of high-energy X-ray diffraction (HEXRD) technique with the aid of MD simulations. With regard to neat ionic liquids, a small but significant difference was found at around 3.5 Å in the intermolecular radial distribution functions G(inter)(r)s for these two ionic liquids; i.e., G(inter)(r) for [C(2)mIm(+)][TFSA(-)] was positioned at a slightly shorter region relative to that for [C(3)mPyrro(+)][TFSA(-)], which suggests that the nearest neighboring cation-anion interaction in the imidazolium ionic liquid is slightly greater than that in the other. With regard to Li(+) ion solvation structure, G(inter)(r)s for [C(2)mIm(+)][TFSA(-)] dissolving Li(+) ion exhibited additional small peak of about 1.9 Å attributable to the Li(+)-O (TFSA(-)) atom-atom correlation, though the corresponding peak was unclear in [C(3)mPyrro(+)][TFSA(-)] due to overlapping with the intramolecular atom-atom correlations in [C(3)mPyrro(+)]. In addition, the long-range density fluctuation observed in the neat ionic liquids diminished with the increase of Li(+) ion concentration for both ionic liquid solutions. These observations indicate that the large scale Li(+) ion solvated clusters are formed in the TFSA based ionic liquids, and well support the formation of [Li(TFSA)(2)](+) cluster clarified by previous Raman spectroscopic studies. MD simulations qualitatively agree with the experimental facts, by which the decrease in the long-range oscillation amplitude of r(2){G(r) - 1} for the Li(+) containing ionic liquids can be ascribed to the variation in the long-range anion-anion correlations caused by the formation of the Li(+) ion solvated clusters.

Analysis of 3D structures of platinum nanoparticles by high energy X-ray diffraction and reverse Monte Carlo simulations

In this paper, the atomic-scale three-dimensional structure of Pt nanoparticles were determined using high energy X-ray diffraction techniques and reverse Monte Carlo simulations. It was found that dendrimer encapsulated Pt nanoparticles are more ordered than those stabilized by long-chain alkanes. Furthermore, Pt nanoparticles measured in ambient dry conditions exhibit higher local atomic order compared to Pt nanoparticles measured in aqueous solutions. The atomic-scale structural information presented here can offer a more comprehensive understanding of the structure–property relationship for Pt nanoparticles and can be further used in the design of nanoparticles with improved properties.

Predicting Fracture Toughness of TRIP 800 Using Phase Properties Characterized by In-Situ High-Energy X-Ray Diffraction

Transformation-induced plasticity (TRIP) steel is a typical representative of first generation advanced high-strength steel, which exhibits a combination of high strength and excellent ductility due to its multiphase microstructure. In this article, we study the crack propagation behavior and fracture resistance of a TRIP 800 steel using a microstructure-based finite element method with the various phase properties characterized by in-situ high-energy X-ray diffraction (HEXRD) technique. Uniaxial tensile tests on the notched TRIP 800 sheet specimens were also conducted, and the experimentally measured tensile properties and R curves (resistance curves) were used to calibrate the modeling parameters and to validate the overall modeling results. The comparison between the simulated and experimentally measured results suggests that the micromechanics based modeling procedure can well capture the overall complex crack propagation behaviors and the fracture resistance of TRIP steels. The methodology adopted here may be used to estimate the fracture resistance of various multiphase materials.

In-situ studies of stress- and magnetic-field-induced phase transformation in a polymer-bonded Ni–Co–Mn–In composite

A polymer-bonded Ni 45Co 5Mn 36.6In 13.4 ferromagnetic shape–memory composite was fabricated, having magnetic-field-driven shape recovery properties. The thermo-magnetization curves of the composite suggested that the magnetic-field-induced reverse martensitic transformation occurs in the composite. The effects of temperature, stress, and magnetic-field on the phase transformation properties were systematically investigated using an in-situ high-energy X-ray diffraction technique. A temperature-induced reversible martensitic phase transformation was confirmed within the composite, showing a broad phase transformation interval. Stress-induced highly textured martensite was observed in the composite during uniaxial compressive loading, with a residual strain after unloading. The origin of the textured martensite can be explained by the grain-orientation-dependent Bain distortion energy. A recovery strain of ∼1.76% along the compression direction was evidenced in the pre-strained composite with an applied magnetic-field of 5 T. This recovery was caused by the magnetic-field-induced reverse martensitic phase transformation. The phase transformation properties of the ferromagnetic shape–memory composite, different from its bulk alloys, can be well explained by the Clausius–Clapeyron relation. The large magnetic-field-induced strain, together with good ductility and low cost, make the polymer-bonded Ni–Co–Mn–In composites potential candidates for magnetic-field-driven actuators.

An assessment of the contributing factors to the superior properties of a nanostructured steel using in situ high-energy X-ray diffraction

In contrast to most nanostructured materials, outstanding mechanical property has been demonstrated in a nanostructured metastable austenitic steel, owing to the new characteristics of deformation-induced martensitic transformation. In this paper, by employing an in situ high-energy X-ray diffraction technique, we explore these characteristics by examining factors from the load partitioning, Lüders banding, to texture development. It was found that the martensitic transformation was mainly driven through Lüders band propagation. Marked load transfer takes place from austenite to martensite as Lüders band propagates, and continues into the homogeneous deformation regime. The texture development is mostly contributed by martensitic transformation, but dislocation-based plasticity also plays a role. The effective load partitioning along with the deformability of martensite promotes sample ductility.

Structural characterization of Mn doped SiC magnetic thin films

Mn-doped SiC magnetic thin films prepared by co-deposited molecular beam epitaxy (MBE) method on Si (111) substrates at 950 ℃ have been investigated by reflection high energy diffraction (RHEED), X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) techniques. RHEED results reveal that the SiC thin films doped with Mn are of the cubic structure. XRD and XANES results show that in the thin films with Mn doping concentrations of 0.5％ and 18％ , almost all the Mn atoms react with Si atoms, forming Mn4Si7 compound embedded in the SiC matrix, and no substitutional or interstitial Mn atoms exist in the SiC lattice. Furthermore, we hold that the ferromagnetism of the Mn doped SiC thin films originates mainly from the Mn4Si7 secondary phase.

Neutron and X-Ray Studies of Advanced Materials

The selection of articles in the special topic 'Neutron and X-Ray Studies of Advanced Materials' is based on the materials presented during the TMS 2009 annual meeting in San Francisco, CA, February 15-19, 2009. The development of ultrabrilliant third-generation synchrotron X-ray sources, together with advances in X-ray optics, has created intense X-ray microbeams, which provide the best opportunities for in-depth understanding of mechanical behavior in a broad spectrum of materials. Important applications include ultrasensitive elemental detection by X-ray fluorescence/absorption and microdiffraction to identify phase and strain with submicrometer spatial resolution. X-ray microdiffraction is a particularly exciting application compared with alternative probes of crystalline structure, orientation, and strain. X-ray microdiffraction is nondestructive with good strain resolution, competitive or superior spatial resolution in thick samples, and with the ability to probe below the sample surface. Moreover, the high-energy X-ray diffraction technique provides an effective tool for characterizing the mechanical and functional behavior in various environments (temperature, stress, and magnetic field). At the same time, some neutron diffraction instruments constructed mainly for the purpose of engineering applications can be found at nearly all neutron facilities. The first generation-dedicated instruments designed for studying in-situ mechanical behavior have been commissioned and used, and industrial standardsmore » for reliable and repeatable measurements have been developed. Furthermore, higher penetration of neutron beams into most engineering materials provides direct measurements on the distribution of various stresses (i.e., types I, II, and III) beneath the surface up to several millimeters, even tens of millimeters for important industrial components. With X-ray and neutron measurements, it is possible to characterize material behavior at different length scales. It is predicted that the application of these techniques, in combination with theoretical simulations and numerical modeling, will lead to major breakthroughs in materials science in the foreseeable future, which will contribute to the development of materials technology and industrial innovation. Specifically, the use of these techniques provides bulk material properties that further augment new characterization tools including the increased use of atom probe tomography and high-resolution transmission electron microscopy systems. The combination of these techniques greatly assists the material property models that address multi-length-scale mechanisms. Different applications of diffuse scattering for understanding the fundamental materials properties are illustrated in the articles of Welberry et al., Goossens and Welberry, Campbell, Abe et al., Gilles et al., and Zhang et al. Analysis of thin films and two-dimensional structures is described in the articles of Gramlich et al., Brock et al., Vigliante et al., Kuzel et al., and Davydok et al. Recent advances in the line profile analysis are represented by the the articles of Scardi et al., Ungar et al., and Woo et al. Characterization of modern alloys is presented by the articles of Wollmershauser et al., Eidenberger et al., Garlea et al., Jia et al., Soulami et al., Wilson et al., and Wang et al. The collected articles are written by different scientific X-ray and neutron research groups. They represent a general trend in the development and application of diffraction techniques all over the world.« less

An in situ high-energy X-ray diffraction study of micromechanical behavior of multiple phases in advanced high-strength steels

The micromechanical behavior of high-strength steels with multiple phases was characterized using the in situ high-energy X-ray diffraction technique. For the materials investigated, the {2 0 0} lattice strains of the constituent phases (ferrite, bainite and martensite) with similar crystal structures were determined by separating their overlapped diffraction peaks and then examining the respective changes in peak positions during deformation. Based on those experimental data, the anisotropic elastic and plastic properties of the steels were simulated using a self-consistent model for predicting the grain-to-grain and phase-to-phase interactions. The constitutive laws for describing the elastic and plastic behavior of each constituent phase were directly obtained by comparing the predicted lattice strain distributions with the measured ones. The transmission electron microscopy observations of the microstructure development verified the partitioning of plastic strains among different phases. The present investigations provide a fundamental understanding of the stress partitioning of soft and hard phases, and the different work-hardening rates of the multiphase steels.

A study on the surface severe plastic deformation behavior of a Zr-based bulk metallic glass (BMG)

A surface treatment process, which can generate the severe plastic deformation in the near-surface layer of crystalline materials, is successfully applied on the Zr 50Cu 40Al 10 bulk metallic glass (BMG). The experiment is implemented using 20 WC/Co balls with a velocity of about 5 m/s to bombard the surface of the samples in a purified argon atmosphere. The plastic-flow deformation in the unconstrained sample edge was observed, which exhibits the good intrinsic ductility of this material under the experimental condition. In the sub-surface layer, the bombardment-induced shear-band operations generate the extrusion and intrusion marks on the side face. Differential scanning calorimetry (DSC) shows that the free volumes of the deformed BMG have increased, and possible crystallization may occur during the process. X-ray diffraction (XRD) and synchrotron high-energy X-ray diffraction techniques were used to inspect the possible crystal phase. A nanoindentation test shows that on the side surface, the hardness increases and, then, decreases with the distance from the processed surface. Four-point-bending-fatigue behavior has been studied and related to the modified surface structure and the compressive residual stress introduced by the surface treatment.

Stress and Strain Partitioning of Ferrite and Martensite during Deformation

The direct measurement of the stress or strain partitioning during deformation in the materials, consisting of two phases with the same crystallographic structure and different microstructures, is still difficult so far. This is due to the fact that no effective characterization tool is available with the ability to distinguish the local strain and stress at microscale level. In this article, we studied the micromechanical behavior of ferrite/martensite dual-phase (DP) alloys using the in-situ high-energy X-ray diffraction (HEXRD) technique. We established a new method to separate the stress and strain in the ferrite and martensite during loading. Although the ferrite and martensite exhibit the same crystal structure with similar lattice parameters, the dependence of (200) lattice strains on the applied stress is obviously different for each phase. A visco-plastic self-consistent (VPSC) model, which can simulate the micromechanical behavior of two-phase materials, was used to construct the respective constitutive laws for both phases from the experimental lattice strains and to fit the macro-stress-strain curve. The material parameters for each phase extracted from our experiments and simulations could be used for designing other DP alloys and optimizing some complex industrial processes.

Changes in the medium-range order during crystallization of aluminosilicate zeolites characterized by high-energy X-ray diffraction technique

ZSM-5 and faujasite, which are aluminosilicate zeolites with different compositions, were synthesized without using organic structure-directing agents, and the changes in the medium-range order during the crystallization of ZSM-5 and faujasite were characterized by high-energy X-ray diffraction (HEXRD) technique. It is found that that the amorphous aluminosilicates have larger fraction of 4 membered ring (4R), compared to 6 membered ring (6R) that is the most dominant in amorphous silica. Furthermore, HEXRD measurements reveal that changes in the medium-range order are characteristic for each zeolite although crystallizations of both zeolites proceeded via a similar way: that is, the dissolution of amorphous precursors to solution followed by the nucleation and crystal growth of zeolite from the soluble species. In ZSM-5 crystallization, no major changes in the medium-range order are observed although slight decrease of the fraction of 4R is confirmed. On the other hand, clear changes in the medium-range order, especially on the ordering of 4R and 6R are confirmed in faujasite crystallization.

Predicting failure modes and ductility of dual phase steels using plastic strain localization

Ductile failure of metals is often treated as the result of void nucleation, growth and coalescence. Various criteria have been proposed to capture this failure mechanism for various materials. In this study, ductile failure of dual phase steels is predicted in the form of plastic strain localization resulting from the incompatible deformation between the harder martensite phase and the softer ferrite matrix. Microstructure-level inhomogeneity serves as the initial imperfection triggering the instability in the form of plastic strain localization during the deformation process. Failure modes and ultimate ductility of two dual phase steels are analyzed using finite element analyses based on the actual steel microstructures. The plastic work hardening properties for the constituent phases are determined by the in-situ synchrotron-based high-energy X-ray diffraction technique. Under different loading conditions, different failure modes and ultimate ductility are predicted in the form of plastic strain localization. It is found that the local failure mode and ultimate ductility of dual phase steels are closely related to the stress state in the material. Under plane stress condition with free lateral boundary, one dominant shear band develops and leads to final failure of the material. However, if the lateral boundary is constrained, splitting failure perpendicular to the loading direction is predicted with much reduced ductility. On the other hand, under plane strain loading condition, commonly observed necking phenomenon is predicted which leads to the final failure of the material. These predictions are in reasonably good agreement with experimental observations.

Direct evidence of detwinning in polycrystalline Ni–Mn–Ga ferromagnetic shape memory alloys during deformation

In situ time-of-flight neutron diffraction and high-energy x-ray diffraction techniques were used to reveal the preferred reselection of martensite variants through a detwinning process in polycrystalline Ni–Mn–Ga ferromagnetic shape memory alloys under uniaxial compressive stress. The variant reorientation via detwinning during loading can be explained by considering the influence of external stress on the grain/variant orientation-dependent distortion energy. These direct observations of detwinning provide a good understanding of the deformation mechanisms in shape memory alloys.

Advanced Micromechanical Model for Transformation-Induced Plasticity Steels with Application of In-Situ High-Energy X-Ray Diffraction Method

Compared to other advanced high-strength steels, transformation-induced plasticity (TRIP) steels exhibit better ductility at a given strength level and can be used to produce complicated automotive parts. This enhanced formability comes from the transformation of retained austenite to martensite during plastic deformation. In this study, as a first step in predicting optimum processing parameters in TRIP steel productions, a micromechanical finite element model is developed based on the actual microstructure of a TRIP 800 steel. The method uses a microstructure-based representative volume element (RVE) to capture the complex deformation behavior of TRIP steels. The mechanical properties of the constituent phases of the TRIP 800 steel and the fitting parameters describing the martensite transformation kinetics are determined using the synchrotron-based in-situ high-energy X-ray diffraction (HEXRD) experiments performed under a uniaxial tensile deformation. The experimental results suggest that the HEXRD technique provides a powerful tool for characterizing the phase transformation behavior and the microstress developed due to the phase-to-phase interaction of TRIP steels during deformation. The computational results suggest that the response of the RVE well represents the overall macroscopic behavior of the TRIP 800 steel under deformation. The methodology described in this study may be extended for studying the effects of the various processing parameters on the macroscopic behaviors of TRIP steels.

Radiation-modified structure of Ge25Sb15S60 and Ge35Sb5S60 glasses

Atomic structures of Ge(25)Sb(15)S(60) and Ge(35)Sb(5)S(60) glasses are investigated in the gamma-irradiated and annealed after gamma-irradiation states by means of high-energy synchrotron x-ray diffraction technique. The first sharp diffraction peak (FSDP) is detected at around 1.1 A(-1) in the structure factors of both alloys studied. The FSDP position is found to be stable for radiation/annealing treatment of the samples, while the FSDP intensity shows some changes between gamma-irradiated and annealed states. The peaks in the pair distribution functions observed between 2 and 4 A are related to the Ge-S, Ge-Sb, and Sb-Sb first neighbor correlations and Ge-Ge second neighbor correlations in the edge-shared GeS(42) tetrahedra, and S-S and/or Ge-Ge second neighbor correlations in the corner-shared GeS(42) tetrahedra. Three mechanisms of the radiation-/annealing-induced changes are discussed in the framework of coordination topological defect formation and bond-free solid angle concepts.

Fullerene-like structure of activated carbons

The structure of the commercial activated carbons AX21 and BP71 has been studied using the high-energy X-ray diffraction and molecular dynamics techniques. The diffraction measurements were carried up to a maximum value of the scattering vector K max = 24 Å − 1 . The obtained diffraction data have been converted to a real space representation in the form of the radial distribution function. Structural models containing 2 and 4 graphene layers, approximately 16–20 Å in size, were computer generated and then relaxed using the reactive empirical bond order potential for carbon–carbon interactions and the Lennard–Jones potential with parameters for inter-layer interactions. The molecular dynamics simulations were performed at 300 K to account for the thermal oscillations. For such models the intensity and radial distribution functions were computed. The correctness of the models was verified by comparison of the simulations with the experimental data both in real and reciprocal space. The effects of hydrogen, saturating dangling bonds of edge atoms, the presence of non-six membered rings and the sp 3 defects on the resulting structure were investigated.

Intermediate-range Order in Mesoporous Silicas Investigated by a High-energy X-ray Diffraction Technique

Abstract We perform a high-energy X-ray diffraction study comparing bulk amorphous silica with MCM-41 and SBA-15 that are representative mesoporous silicas prepared in basic and acidic conditions, respectively. It is revealed that mesoporous silicas, especially SBA-15, have less ordered structures and contain larger fractions of three- and four-membered rings than does bulk amorphous silica.