Sven Vogel

Gallium oxide (Ga2O3) is a promising ultrawide bandgap semiconductor for radiation detection with the potential of integrating electronic and scintillation functions within a single crystal device. This study establishes the scintillation response of β-Ga2O3 gamma irradiation from yttrium-88 (88Y). Then, californium-252 (252Cf) is used as a spontaneous fission source of mixed neutron and gamma radiation field to measure scintillation signals. Pulse shape discrimination and constant fraction discrimination techniques were used to separate neutron and gamma interaction events. Further investigation indicates that the prompt temporal responses of β-Ga2O3 for gammas and neutrons may enable discrimination of the two by prompt pulse fitting methods, focused around the initial peak. For gamma irradiation, we observed a rise time (τr) of 2.1 ns, decay time (τd) of 9.5 ns, and a full width at half maximum (FWHM) of 6.2 ns. For neutrons, it showed a τr of 2.3 ns, a τd of 12.1 ns, 9.4 ns FWHM, and reduced peak intensity. A diamond detector exhibited a more symmetrical τr and τd for both gamma and neutron signals and therefore is less effective at discriminating between the two by this method. This draws attention to β-Ga2O3’s ability to distinguish neutron and gamma particles. These findings showcase Ga2O3’s potential as a next-generation semiconductor for applications in nuclear safety and medical imaging, where precise discrimination between neutron and gamma interactions is essential.

Molten fluoride salts such as Li₂BeF₄ (FLiBe) are used in molten salt reactors, fluoride-salt-cooled high-temperature reactors and fusion reactors as a fuel solvent, coolant and/or tritium breeding medium. In engineered systems that use molten salt, solid-state material will be present during melting and freezing scenarios, and therefore the temperature-dependent properties of the solid and solid/liquid phase transition merit investigation. To observe the behavior of the solid state of Li₂BeF₄ from room temperature to melting, this work used neutron and X-ray diffraction to measure the changes in the lattice parameters and volume of the crystalline unit cell and compared the results with prior low-temperature data for solid Li₂BeF₄. From neutron diffraction data it is also possible to identify anisotropy: centimetre-scaled crystals align preferentially with the a axes parallel to the direction of freezing front propagation, and the c axes expand 54% more than the a axes. This work provides the lattice constants as a function of temperature, quantifies the thermal expansion, and determines the equation describing the change in density for solid Li₂BeF₄ from room temperature to 459°C to be ρ_solid (kg m⁻³) = 2182 (3) − 0.115 (2) T (°C) and the volume expansion upon melting to be less than 5%. This density changes depending on molecular weight and enrichment.

Containerless solidification of Al–20wt%Ce is investigated experimentally using the electromagnetic levitation (EML) and impulse atomization (IA) techniques. In the processed EML samples, small primary undercooling and minimal eutectic undercooling are shown. The microstructure consists of large primary Al₁₁Ce₃ dendrites surrounded by an α‐Al–Al₁₁Ce₃ eutectic. Phase fractions determined by neutron diffraction are similar to the values obtained from a Scheil–Gulliver solidification simulation. Larger IA powders (between 425 and 1000 μm) show a microstructure qualitatively similar to that of EML samples, implying that they follow a similar solidification path. Quantitatively, microstructural features are finer due to the higher cooling rates involved in the solidification process. Atomized particles with a size lower than 425 μm show a strikingly different microstructure, with a very fine eutectic giving way to large intermetallic plates surround by a regular eutectic. Microhardness testing of the structures shows a significant increase in hardness as the sample size decreases, going from 45.8 ± 3.6 HV for the EML sample (lowest cooling rate) to 142.2 ± 12.0 HV for particles in the 106–150 μm range (highest cooling rate).

As the issue of climate change becomes more prevalent, engineers have focused on developing lightweight Al alloys capable of increasing the power density of powertrains. The characterization of these alloys has been focused on mechanical properties and less on the fundamental response of microstructures to achieve these properties. Therefore, this study assesses the quality of the microstructure of two high-temperature Al alloys (A356 + 3.5RE and Al-8Ce-10Mg), comparing them to T6 A356. These alloys underwent thermal conditioning at 250 and 300 °C for 200 h. Time-of-flight neutron diffraction experiments were performed before and after conditioning. The phase evolution was quantified using Rietveld refinement. It was found that the Si phase grows significantly (13–24%) in T6 A356, A356 + 3.5RE, and T6 A356 + 3.5RE alloys, which is typically correlated with a reduction in mechanical properties. Subjecting the A356 3.5RE alloy to a T6 heat treatment stabilizes the orthorhombic Al4Ce3Si6 and monoclinic β-Al5FeSi phases, making them resistant to thermal conditioning. These two phases are known for enhancing mechanical properties. Additionally, the T6 treatment reduced the vol.% of the cubic Al20CeTi2 and hexagonal ᴨ-Al9FeSi3Mg5 phases by 13% and 23%, respectively. These phases have detrimental mechanical properties. The Al-8Ce-10Mg alloy cubic β-Al3Mg2 phase showed significant growth (82–101%) in response to conditioning, while the orthorhombic Al11Ce3 phase remained stable. The growth of the beta phase is known to decrease the mechanical properties of this alloy. These efforts give valuable insight into how these alloys will perform and evolve in demanding high-temperature environments.

Gallium oxide is a newly emerged ultrawide bandgap (4.9 eV) semiconductor that is suitable as a combined electronics and radiation detection platform. We have experimentally demonstrated fast neutron and gamma-ray scintillation from Czochralski-grown β-Ga2O3 in a recent series (October 2023) of experiments at the unmoderated pulsed neutron spallation source located at the Los Alamos Neutron Science Center. Using the neutron time-of-flight (TOF) technique and a fast-gated intensified CCD camera, we observed energy-dependent neutron scintillation for neutron energies ranging from 1 to 400 MeV, including the 14.1 MeV neutron energy relevant to D–T fusion. Neutron flux is quantified and calibrated by cascading the scintillator after the fission chamber, enabling a detailed analysis of temporal and energy-dependent characteristics of the scintillation events. A pronounced scintillation signal from the spallation gamma flash with a temporal full width of half maximum of ∼4 ns is indicative of the material’s rapid response. Neutron energy dependent scintillation is observed using the TOF method at a 22.6-m distance from the neutron source. These results highlight the possibility of developing a Ga2O3 based fusion neutron diagnostic platform integrated with both scintillation and electronics functions on the integrated chip scale.

Comprehensive information on in situ microstructural and crystallographic changes during the preparation/manufacturing processes of various materials is highly necessary to precisely control the microstructural morphology and the preferred orientation (or texture) characteristics for achieving an excellent strength–ductility–toughness balance in advanced engineering materials. In this study, in situ isothermal annealing experiments with cold-rolled 17Ni-0.2C (mass%) martensitic steel sheets were carried out by using the TAKUMI and ENGIN-X time-of-flight neutron diffractometers. The inverse pole figures based on full-profile refinement were extracted to roughly evaluate the preferred orientation features along three principal sample directions of the investigated steel sheets, using the General Structure Analysis System (GSAS) software with built-in generalized spherical harmonic functions. The consistent rolling direction (RD) inverse pole figures from TAKUMI and ENGIN-X confirmed that the time-of-flight neutron diffraction has high repeatability and statistical reliability, revealing that the principal preferred orientation evaluation of steel materials can be realized through 90° TD ➜ ND (transverse direction ➜ normal direction) rotation of the investigated specimen on the sample stage during two neutron diffraction experiments. Moreover, these RD, TD, and ND inverse pole figures before and after the in situ experiments were compared with the corresponding inverse pole figures recalculated from the MUSASI-L complete pole figure measurement and the HIPPO in situ microstructure evaluation, respectively. The similar orientation distribution characteristics suggested that the principal preferred orientation evaluation method can be applied to the in situ microstructural evolution of bulk orthorhombic materials and spatially resolved principal preferred orientation mappings of large engineering structure parts.

In crystallographic texture analysis, ensuring that sample directions are preserved from experiment to the resulting orientation distribution is crucial to obtain physical meaning from diffraction data. This work details a procedure to ensure instrument and sample coordinates are consistent when analyzing diffraction data with a Rietveld refinement using the texture analysis softwareMAUD. A quartz crystal is measured on the HIPPO diffractometer at Los Alamos National Laboratory for this purpose. The methods described here can be applied to any diffraction instrument measuring orientation distributions in polycrystalline materials.

Space levitation processing allows researchers to conduct benchmark tests in an effort to understand the physical phenomena involved in rapid solidification processing, including alloy thermodynamics, nucleation and growth, heat and mass transfer, solid/liquid interface dynamics, macro- and microstructural evolution, and defect formation. Supported by ground-based investigations, a major thrust is to develop and refine robust computational tools based on theoretical and applied approaches. This work is accomplished in conjunction with experiments designed for precise model validation with application to a broad range of industrial processes.

Modern diffraction experiments (e.g. in situ parametric studies) present scientists with many diffraction patterns to analyze. Interactive analyses via graphical user interfaces tend to slow down obtaining quantitative results such as lattice parameters and phase fractions. Furthermore, Rietveld refinement strategies (i.e. the parameter turn-on-off sequences) tend to be instrument specific or even specific to a given dataset, such that selection of strategies can become a bottleneck for efficient data analysis. Managing multi-histogram datasets such as from multi-bank neutron diffractometers or caked 2D synchrotron data presents additional challenges due to the large number of histogram-specific parameters. To overcome these challenges in the Rietveld software Material Analysis Using Diffraction (MAUD), the MAUD Interface Language Kit (MILK) is developed along with an updated text batch interface for MAUD. The open-source software MILK is computer-platform independent and is packaged as a Python library that interfaces with MAUD. Using MILK, model selection (e.g. various texture or peak-broadening models), Rietveld parameter manipulation and distributed parallel batch computing can be performed through a high-level Python interface. A high-level interface enables analysis workflows to be easily programmed, shared and applied to large datasets, and external tools to be integrated with MAUD. Through modification to the MAUD batch interface, plot and data exports have been improved. The resulting hierarchical folders from Rietveld refinements with MILK are compatible with Cinema: Debye–Scherrer, a tool for visualizing and inspecting the results of multi-parameter analyses of large quantities of diffraction data. In this manuscript, the combined Python scripting and visualization capability of MILK is demonstrated with a quantitative texture and phase analysis of data collected at the HIPPO neutron diffractometer.

Cosmic ray muons are massive, charged particles created from high energy cosmic rays colliding with atomic nuclei in Earth’s atmosphere. Because of their high momenta and weak interaction, these muons can penetrate through large thicknesses of dense material before being absorbed, making them ideal for nondestructive imaging of objects composed of high-Z elements. A Giant Muon Tracker with two horizontal 8 × 6 ft.2 and two vertical 6 × 6 ft.2 modules of drift tubes was used to measure muon tracks passing through samples placed inside the detector volume. The experimental results were used to validate a Monte Carlo simulation of the Giant Muon Tracker. The imaging results of simulated samples were reconstructed and compared with those from the experiment, which showed excellent agreement.

Low-enriched-uranium (LEU) reactor systems utilize moderators to improve neutron economy. Solid yttrium hydride is one of the primary moderator candidates for high-temperature (>700 °C) nuclear reactor applications. This is due to its ability to retain hydrogen at elevated temperatures compared to other metal hydrides. For reactor modeling purposes, both neutronic and thermos-mechanical modeling, several high-temperature properties for sub-stoichiometric yttrium hydride (YH2−x) are needed. In this paper, we present an atomistics and a neutron diffraction study of the high-temperature properties of Y  and  YH2−x. Specifically, we focus on the thermal lattice expansion effects in yttrium metal and yttrium hydride, which also govern bulk thermal expansion. Previously reported physical and mechanical properties for sub-stoichiometric yttrium hydride at ambient conditions are expanded using lattice dynamics to take into account high-temperature effects. Accordingly, an array of newly generated properties is presented that enables high-fidelity neutronics, and thermomechanical modeling. These properties include various elastic moduli, thermal expansion parameters for yttrium and yttrium hydride, and single-phase (YH2−x) and two-phase (Y + YH2−x) density as a function of stoichiometry and density.

Among various off-equilibrium microstructures of additively manufactured Ti-6Al-4V alloy, electron beam powder bed fusion, in which three dimensional metallic objects are fabricated by melting the ingredient powder materials layer by layer on a pre-heated bed, results in a specimen that is nearly free of the preferred orientation of the α-Ti phase as well as a low beta phase fraction of ~1 wt%. However, when further heat treatment of up to 1050 °C was applied to the material in our previous study, a strong texture aligning the hexagonal basal plane of α phase with the build direction and about 6% β phase appeared at room temperature. In this study, to understand the mechanism of this heat treatment, the grain level microstructure of the additively manufactured Ti-6Al-4V was investigated using in situ high temperature EBSD up to 1000 °C, which allows the tracking of individual grains during a heat cycle. As a result, we found a random texture originating from the fine grains in the initial material and observed a significant suppression of α phase nucleation in the slow cooling after heating to 950 °C within the α and β dual phase regime but close to the the β-transus temperature at ~980 °C, which led to a coarse microstructure. Furthermore, the texture resulting from phase transformation of the additively manufactured Ti-6Al-4V assuming nucleation at the grain boundaries was modeled, using the double Burgers orientation relationship for the first time. The model successfully reproduced the measured texture, suggesting that the texture enhancement of the α phase by the additional heat treatment derives also from the variant selection during the phase transformation and nucleation on grain boundaries.

Texture memory is a phenomenon in which retention of initial textures occurs after a complete cycle of forward and backward transformations, and it occurs in various phase-transforming materials including cubic and hexagonal metals such as steels and Ti and Zr alloys. Texture memory is known to be caused by the phenomena called variant selection, in which some of the allowed child orientations in an orientation relationship between the parent and child phases are preferentially selected. Without such variant selection, the phase transformations would randomize preferred orientations. In this article, the methods of prediction of texture memory and mechanisms of variant selections in hexagonal metals are explored. The prediction method using harmonic expansion of orientation distribution functions with the variant selection in which the Burgers orientation relationship, {110}β//{0001}α-hex <11¯1>β//21¯1¯0α-hex, is held with two or more adjacent parent grains at the same time, called “double Burgers orientation relation (DBOR)”, is introduced. This method is shown to be a powerful tool by which to analyze texture memory and ultimately provide predictive capabilities for texture changes during phase transformations. Variation in nucleation and growth rates on special boundaries and an extensive growth of selected variants are also described. Analysis of textures of commercially pure Ti observed in situ by pulsed neutron diffraction reveals that the texture memory in CP-Ti is indeed quite well predicted by consideration of the mechanism of DBOR. The analysis also suggests that the nucleation and growth rates on the special boundary of 90° rotation about 21¯1¯0α-hex should be about three times larger than those of the other special boundaries, and the selected variants should grow extensively into not only one parent grain but also other grains in α-hex(hexagonal)→β(bcc) transformation. The model calculations of texture development during two consecutive cycles of α-hex→β→α-hex transformation in CP-Ti and Zr are also shown.

Polycrystalline materials can have complex anisotropic properties depending on their crystallographic texture and crystal structure. In this study, we use resonant ultrasound spectroscopy (RUS) to nondestructively quantify the elastic anisotropy in extruded aluminum alloy 1100-O, an inherently low-anisotropy material. Further, we show that RUS can be used to indirectly provide a description of the material’s texture, which in the present case is found to be transversely isotropic. By determining the entire elastic tensor, we can identify the level and orientation of the anisotropy originated during extrusion. The relative anisotropy of the compressive (c₁₁/c₃₃) and shear (c₄₄/c₆₆) elastic constants is 1.5% ± 0.5% and 5.7% ± 0.5%, respectively, where the elastic constants (five independent elastic constants for transversely isotropic) are those associated with the extrusion axis that defines the symmetry of the texture. These results indicate that the texture is expected to have transversely isotropic symmetry. This finding is confirmed by two additional approaches. First, we confirm elastic constants and the degree of elastic anisotropy by direct sound velocity measurements using ultrasonic pulse echo. Second, neutron diffraction (ND) data confirm the symmetry of the bulk texture consistent with extrusion-induced anisotropy, and polycrystal elasticity simulations using the elastic self-consistent model with input from ND textures and aluminum single-crystal elastic constants render similar levels of polycrystal elastic anisotropy to those measured by RUS. We demonstrate the ability of RUS to detect texture-induced anisotropy in inherently low-anisotropy materials. Therefore, as many other common materials have intrinsically higher elastic anisotropy, this technique should be applicable for similar levels of texture, providing an efficient general diagnostic and characterization tool.

With an increased interest in the use of molten salts in both nuclear and non-nuclear systems, measuring important thermophysical properties of specific salt mixtures becomes critical in understanding salt performance and behavior. One of the more basic and significant thermophysical properties of a given salt system is density as a function of temperature. With this in mind, this work aims to present and layout a novel approach to measuring densities of molten salt systems using neutron radiography. This work was performed on Flight Path 5 at the Los Alamos Neutron Science Center at Los Alamos National Laboratory. In order to benchmark this initial work, three salt mixtures were measured, NaCl, LiCl (58.2 mol%) + KCl (41.8 mol%), and MgCl2 (32 mol%) + KCl (68 mol%). Resulting densities as a function of temperature for each sample from this work were then compared to previous works employing traditional techniques. Results from this work match well with previous literature values for all salt mixtures measured, establishing that neutron radiography is a viable technique to measure density as a function of temperature in molten salt systems. Finally, advantages of using neutron radiography over other methods are discussed and future work in improving this technique is covered.

The US code of Federal Regulations mandates regular inspection of centrifugally cast austenitic stainless steel pipe, commonly used in primary cooling loops in light-water nuclear power plants. These pipes typically have a wall thickness of ~8 cm. Unfortunately, inspection using conventional ultrasonic techniques is not reliable as the microstructure strongly attenuates ultrasonic waves. Work is ongoing to simulate the behavior of acoustic waves in this microstructure and ultimately develop an acoustic inspection method for reactor inspections. In order to account for elastic anisotropy in the material, the texture in the steel was measured as a function of radial distance though the pipe wall. Experiments were conducted on two 10 × 12.7 × 80 mm radial sections of a cast pipe using neutron diffraction scans of 2 mm slices using the HIPPO time-of-flight neutron diffractometer at the Los Alamos Neutron Science Center (LANSCE, Los Alamos, NM, USA). Strong textures dominated by a small number of austenite grains with their (100) direction aligned in the radial direction of the pipe were observed. ODF analysis indicated that up to 70% of the probed volume was occupied by just three single-grain orientations, consistent with grain sizes of almost 1 cm. Texture and phase fraction of both ferrite and austenite phases were measured along the length of the samples. These results will inform the development of a more robust diagnostic tool for regular inspection of this material.

Tl₂LiYCl₆ (TLYC) is an analog to Cs₂LiYCl₆, which is currently an industry-standard inorganic scintillator for radiation detection with good gamma–neutron discrimination. The presence of thallium (Z = 81) instead of cesium (Z = 55) in the elpasolite structure increases the density of the compound and its stopping power for gamma rays. This work investigates the impact of the Tl atom on the elpasolite structure. Single-crystal X-ray diffraction at room temperature and powder neutron diffraction with temperature control were used to characterize the crystal structure of TLYC between 296 and 725 K. The presence of Tl leads to a distortion of the cubic elpasolite structure at room temperature: a tetragonal P4₂ crystal structure (space group 77, a = 10.223, c = 10.338 Å) is identified for TLYC at 296 K. A structural transition to the cubic elpasolite Fm 3 m phase (space group 225) is observed at 464 K. The thermal expansion of the material for each crystal direction is well described by a linear relationship, except for the region between 400 and 464 K where the lattice parameters converge.

Additively-manufactured Ti-6Al-4V (Ti64) exhibits high strength but in some cases inferior elongation to those of conventionally manufactured materials. Post-processing of additively manufactured Ti64 components is investigated to modify the mechanical properties for specific applications while still utilizing the benefits of the additive manufacturing process. The mechanical properties and fatigue resistance of Ti64 samples made by electron beam melting were tested in the as-built state. Several heat treatments (up to 1000 °C) were performed to study their effect on the microstructure and mechanical properties. Phase content during heating was tested with high reliability by neutron diffraction at Los Alamos National Laboratory. Two different hot isostatic pressings (HIP) cycles were tested, one at low temperature (780 °C), the other is at the standard temperature (920 °C). The results show that lowering the HIP holding temperature retains the fine microstructure (~1% β phase) and the 0.2% proof stress of the as-built samples (1038 MPa), but gives rise to higher elongation (~14%) and better fatigue life. The material subjected to a higher HIP temperature had a coarser microstructure, more residual β phase (~2% difference), displayed slightly lower Vickers hardness (~15 HV10N), 0.2% proof stress (~60 MPa) and ultimate stresses (~40 MPa) than the material HIP’ed at 780 °C, but had superior elongation (~6%) and fatigue resistance. Heat treatment at 1000 °C entirely altered the microstructure (~7% β phase), yield elongation of 13.7% but decrease the 0.2% proof-stress to 927 MPa. The results of the HIP at 780 °C imply it would be beneficial to lower the standard ASTM HIP temperature for Ti6Al4V additively manufactured by electron beam melting.

Through in situ electron backscatter diffraction (EBSD) experiments, this paper uncovers dominant damage mechanisms in traditional magnesium alloys exhibiting deformation twinning. The findings emphasize the level of deleterious strain incompatibility induced by twin interaction with other deformation modes and microstructural defects. A double fiber obtained by plane-strain extrusion as a starting texture of AM30 magnesium alloy offered the opportunity to track deformation by EBSD in neighboring grains where some undergo profuse {1 0 1 2} twinning and others do not. For a tensile loading applied along extrusion transverse (ET) direction, those experiencing profuse twinning reveal a major effect of grain boundaries on non-Schmid behavior affecting twin variant selection and growth. Similarly, a neighboring grain, with its ⟨c⟩-axis oriented nearly perpendicular to tensile loading, showed an abnormally early nucleation of {1 0 1 1} contraction twins (2% strain) while the same {1 0 1 1} twin mode triggering under ⟨c⟩-axis uniaxial compression have higher value of critical resolved shear stress exceeding the values for pyramidal ⟨c + a⟩ dislocations. The difference in nucleation behavior of contraction vs. compression {1 0 1 1} twins is attributed to the hydrostatic stresses that promote the required atomic shuffles at the core of twinning disconnections.

Knowledge of the appearance of texture components and fibres in pole figures, in inverse pole figures and in Euler space is fundamental for texture analysis. For cubic crystal systems, such as steels, an extensive literature exists and, for example, the book by Matthies, Vinel & Helming [Standard Distributions in Texture Analysis: Maps for the Case of Cubic Orthorhomic Symmetry, (1987), Akademie-Verlag Berlin] provides an atlas to identify texture components. For lower crystal symmetries, however, equivalent comprehensive overviews that can serve as guidance for the interpretation of experimental textures do not exist. This paper closes this gap by providing a set of scripts for theMTEXpackage [Bachmann, Hielscher & Schaeben (2010).Solid State Phenom.160, 63–68] that allow the texture practitioner to compile such an atlas for a given material system, thus aiding orientation distribution function analysis also for non-cubic systems.

In this work, we conducted in-situ high P-T neutron diffraction experiments on U-7.7Nb. Our results show that the tetragonal γo phase is substantially more compressible than the monoclinic α′′ phase. As the pressure increases, this leads to increased volume collapse and stress relaxation for the reverse martensitic transformation, α′′ → γo. At moderately elevated temperatures, a substantial strain-induced stabilization against transformation into a body centered cubic γ phase was observed in the γo phase. We also found that the ability to retain the metastable γ phase, formed from rapid heating of thermally reset γo, has subtle dependence on the austenitization temperature. The present findings provide a direct test for the hypotheses proposed to explain the low-pressure shock behaviors of the U-Nb alloys.

Crystal preferred orientation of 47 samples of quartzite and eight samples of associated marbles from the Bergell Alps have been analyzed with time-of-flight neutron diffraction and EBSD. The results show a clear distinction of texture types for quartzites transformed from Triassic sandstones and quartz layers in gneiss. Textures of Triassic quartzites are overall weak and display a maximum of c-axes perpendicular to the foliation or a crossed girdle perpendicular to the lineation. Pole figures for positive rhombs {10 1 ¯ 1} show a maximum perpendicular to the foliation and negative rhombs {01 1 ¯ 1} generally display a minimum. Based on polycrystal plasticity models this texture type can be attributed to a combination of basal and rhombohedral slip. Asymmetry of the distributions is attributed to simple shear and local strain heterogeneities. The relatively weak texture is partially caused by muscovite limiting dislocation motion and grain growth, as well as adjacent layers of marble that accommodate significant strain. Most quartz layers in gneiss, including mylonites, display a texture with a-axes parallel to the lineation and a c-axis maximum in the intermediate fabric direction. This texture type can be attributed to dominant prismatic slip. Many samples are recrystallized and recrystallization appears to strengthen the deformation texture. The study shows good agreement of neutron diffraction and EBSD. Neutron diffraction data average over larger volumes and maximum pole densities are generally lower and more representative for the bulk material. With EBSD the microstructure and mechanical twinning can be quantified.

Ferritic alloys are important for nuclear reactor applications due to their microstructural stability, corrosion resistance, and favorable mechanical properties. Nanostructured ferritic alloys having a high density of Y-Ti-O rich nano-oxides (NOs < 5 nm) are found to be extremely stable at high temperatures up to ~1100 °C. This study serves to understand the effect of a high density of nano-particles on texture evolution and recrystallization mechanisms in ferritic alloys of 14YWT (14Cr-3W-0.4Ti-0.21Y-Fe wt %) having a high density of nano-particles and dispersion-free FeCrAl (13Cr-5.2Al-0.05Y-2Mo-0.2Si-1Nb wt %). In order to investigate the recrystallization mechanisms in these alloys, neutron diffraction, electron backscattered diffraction, and in situ and ex situ transmission electron microscopy have been utilized. It has been observed that even though the deformation textures of both the 14YWT and FeCrAl alloys evolved similarly, resulting in either the formation (in FeCrAl alloy) or increase (in 14YWT) in γ-fiber texture, the texture evolution during recrystallization is different. While FeCrAl alloy keeps its γ-fiber texture after recrystallization, 14YWT samples develop a ε-fiber as a result of annealing at 1100 °C, which can be attributed to the existence of NOs. In situ transmission electron microscopy annealing experiments on 14YWT show the combination and growth of the lamellar grains rather than nucleation; however, the recrystallization and growth kinetics are slower due to NOs compared to FeCrAl.

The time-of-flight neutron diffraction data collected in-situ on Oak Ridge National Laboratory’s (ORNL, Oak Ridge, TN, USA) VULCAN and Los Alamos National Laboratory’s (LANL, Los Alamos, NM, USA) High-Pressure-Preferred-Orientation (HIPPO) diffractometers have been analyzed complementarily to show the texture evolution during annealing of a cold-rolled Al-2%Mg alloy. The texture analysis aimed to identify the components present in the initial rolling (or deformation) texture and in the thermally-activated recrystallization texture, respectively. Using a quasi-Monte-Carlo (QMC) approach, a new method has been developed to simulate the weighted texture components, and to obtain inverse pole figures for both rolling and normal directions. As such, distinct recrystallization pathways during annealing in isochronal conditions, can be revealed in terms of the evolution of the texture components and their respective volume fractions. Moreover, the recrystallization kinetics associated with the cube and random texture components are analyzed quantitatively using a similar approach developed for differential scanning calorimetry (DSC).

The coverage of a given diffraction instrument as a percentage of the area 2π of a pole figure hemisphere is a crucial parameter of each diffraction instrument used for texture or strain pole figure determination. On the basis of this knowledge, the number of rotations and rotation angles for a full determination of the orientation distribution function can be optimized. However, the determination of this quantity is non-trivial. This paper presents a method that projects a given detector coverage into pole figure space, i.e. outlines the detector areas in a pole figure, and then determines the fraction of the entire 2π pole figure hemisphere around the sample that is covered. The freely available Generic Mapping Tools (GMT) and ImageJ are utilized for this quantification. With this method, it is shown that the empirically determined rotation angles for the HIPPO neutron time-of-flight diffractometer are close to optimal for a set of three rotations.

Neutron diffraction texture measurements provide bulk averaged textures with excellent grain orientation statistics, even for large-grained materials, owing to the probed volume being of the order of 1 cm³. Furthermore, crystallographic parameters and other valuable microstructure information such as phase fraction, coherent crystallite size, root-mean-square microstrain, macroscopic or intergranular strain and stress, etc. can be derived from neutron diffractograms. A procedure for combined high stereographic resolution texture and residual stress evaluation was established on the pulsed-neutron-source-based engineering materials diffractometer TAKUMI at the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Center, through division of the neutron detector panel regions. Pole figure evaluation of a limestone standard sample with a well known texture suggested that the precision obtained for texture measurement is comparable to that of the established neutron beamlines utilized for texture measurement, such as the HIPPO diffractometer at the Los Alamos Neutron Science Center (New Mexico, USA) and the D20 angle-dispersive neutron diffractometer at the Institut Laue–Langevin (Grenoble, France). A high-strength martensite–austenite multilayered steel was employed for further verification of the reliability of simultaneous Rietveld analysis of multiphase textures and macro stress tensors. By using a texture-weighted geometric mean micromechanical (BulkPathGEO) model, a macro stress tensor analysis with a plane stress assumption showed a rolling direction–transverse direction (RD–TD) in-plane compressive stress (about −330 MPa) in the martensite layers and an RD–TD in-plane tensile stress (about 320 MPa) in the austenite layers. The phase stress partitioning was ascribed mainly to the additive effect of the volume expansion during martensite transformation and the linear contraction misfit between austenite layers and newly transformed martensite layers during the water quenching process.

A tool namedCinema:Debye-Scherrerto visualize the results of a series of Rietveld analyses is presented. The multi-axis visualization of the high-dimensional data sets resulting from powder diffraction analyses allows identification of analysis problems, prediction of suitable starting values, identification of gaps in the experimental parameter space and acceleration of scientific insight from the experimental data. The tool is demonstrated with analysis results from 59 U–Nb alloy samples with different compositions, annealing times and annealing temperatures as well as with a high-temperature study of the crystal structure of CsPbBr₃. A script to extract parameters from a series of Rietveld analyses employing the widely usedGSASRietveld software is also described. Both software tools are available for download.

A uranium-molybdenum alloy clad in 6061 aluminum has the potential to lead to a wide application of low-enriched uranium fuels, replacing highly enriched uranium for research reactors. A Zr coating acts as a diffusion barrier between the fuel and the aluminum cladding. In this study, U-10Mo (mass %) was coated with Zr using a plasma spray technique recognized as a fast and economical coating method. Neutron time-of-flight diffraction was used to study the microstructure evolution by quantifying the phase fractions of involved phases as well as the texture evolution of U-10Mo and Zr during plasma spray coating with Zr. Quantitative texture analysis revealed that the texture was drastically changed for high coating temperatures, likely due to selective grain growth. Furthermore, the Zr coating showed a preferential orientation, which could be correlated with the initial texture of the uncoated U-10Mo. This could be explained by the epitaxial growth of the Zr on the U-10Mo substrate.

BaBrCl:Eu is a promising scintillator material; however, the crystal growth yield must be improved for it to become commercially viable. This study measures strain accumulations in the crystal lattice which can contribute to cracking during post-growth cooling. Neutron diffraction is used to measure the crystal structure of undoped and 5 mol% europium-doped BaBrCl from 303 to 1073 K, approaching the melting point. Rietveld analysis of these data provides the temperature dependence of the thermal and chemical strain in BaBrCl. In particular, anisotropic thermal expansion is measured, with expansion along the b axis nearly double the expansion along the a and c axes. Additionally, the chemical strain from the incorporation of europium atoms peaks around 673 K, explaining cracking frequently observed in that temperature range.

The energy-dependence of the neutron cross section provides vastly different contrast mechanisms than polychromatic neutron radiography if neutron energies can be selected for imaging applications. In recent years, energy-resolved neutron imaging (ERNI) with epi-thermal neutrons, utilizing neutron absorption resonances for contrast as well as for quantitative density measurements, was pioneered at the Flight Path 5 beam line at LANSCE and continues to be refined. Here we present event centroiding, i.e., the determination of the center-of-gravity of a detection event on an imaging detector to allow sub-pixel spatial resolution and apply it to the many frames collected for energy-resolved neutron imaging at a pulsed neutron source. While event centroiding was demonstrated at thermal neutron sources, it has not been applied to energy-resolved neutron imaging, where the energy resolution requires to be preserved, and we present a quantification of the possible resolution as a function of neutron energy. For the 55 μm pixel size of the detector used for this study, we found a resolution improvement from ~80 μm to ~22 μm using pixel centroiding while fully preserving the energy resolution.

In recent years, neutron radiography and tomography have been applied at different beam lines at Los Alamos Neutron Science Center (LANSCE), covering a very wide neutron energy range. The field of energy-resolved neutron imaging with epi-thermal neutrons, utilizing neutron absorption resonances for contrast as well as quantitative density measurements, was pioneered at the Target 1 (Lujan center), Flight Path 5 beam line and continues to be refined. Applications include: imaging of metallic and ceramic nuclear fuels, fission gas measurements, tomography of fossils and studies of dopants in scintillators. The technique provides the ability to characterize materials opaque to thermal neutrons and to utilize neutron resonance analysis codes to quantify isotopes to within 0.1 atom %. The latter also allows measuring fuel enrichment levels or the pressure of fission gas remotely. More recently, the cold neutron spectrum at the ASTERIX beam line, also located at Target 1, was used to demonstrate phase contrast imaging with pulsed neutrons. This extends the capabilities for imaging of thin and transparent materials at LANSCE. In contrast, high-energy neutron imaging at LANSCE, using unmoderated fast spallation neutrons from Target 4 [Weapons Neutron Research (WNR) facility] has been developed for applications in imaging of dense, thick objects. Using fast (ns), time-of-flight imaging, enables testing and developing imaging at specific, selected MeV neutron energies. The 4FP-60R beam line has been reconfigured with increased shielding and new, larger collimation dedicated to fast neutron imaging. The exploration of ways in which pulsed neutron beams and the time-of-flight method can provide additional benefits is continuing. We will describe the facilities and instruments, present application examples and recent results of all these efforts at LANSCE.

The texture of recrystallized straight-rolled α-uranium foils, a component in prospective irradiation target designs for medical isotope production, has been measured by neutron diffraction, as well as X-ray diffraction using both Cu and Mo sources. Variations in the penetration depth of neutron and X-ray radiation allow for determination of both the bulk and surface textures. The bulk α-uranium foil texture is similar to the warm straight-rolled plate texture, with the addition of a notable splitting of the (001) poles along the transverse direction. The surface texture of the foils is similar to the bulk, with an additional (001) texture component that is oriented between the rolling and normal directions. Differences between the surface and bulk textures are expected to arise from shear forces during the rolling process and the influence that distinct strain histories have on subsequent texture evolution during recrystallization.

The evolution of the crystal structure and crystallographic texture of porous synthetic cordierite was studied byin situhigh-temperature neutron diffraction up to 1373 K, providing the firstin situhigh-temperature texture measurement of this technologically important material. It was observed that the crystal texture slightly weakens with increasing temperature, concurrently with subtle changes in the crystal structure. These changes are in agreement with previous work, leading the authors to the conclusion that high-temperature neutron diffraction allows reliable crystallographic characterization of materials with moderate texture. It was also observed that structural changes occur at about the glass transition temperature of the cordierite glass (between 973 and 1073 K). Crystal structure refinements were conducted with and without quantitative texture analysis being part of the Rietveld refinement, and a critical comparison of the results is presented, contributing to the sparse body of literature on combined texture and crystal structure refinements.

Triaminotrinitrobenzene (TATB) is a highly anisotropic molecular crystal used in several plastic-bonded explosive (PBX) formulations. A complete understanding of the orientation distribution of TATB particles throughout a PBX charge is required to understand spatially variable, anisotropic macroscale properties of the charge. Although texture of these materials can be measured after they have been subjected to mechanical or thermal loads, measuring texture evolution in situ is important in order to identify mechanisms of crystal deformation and reorientation used to better inform thermomechanical models. Neutron diffraction measurements were used to estimate crystallographic reorientation while deuterated TATB (d-TATB) powder was consolidated into a cylindrical pellet via a uniaxial die-pressing operation at room temperature. Both the final texture of the pressed pellet and the in situ evolution of texture during pressing were measured, showing that the d-TATB grains reorient such that (001) poles become preferentially aligned with the pressing direction. A compaction model is used to predict the evolution of texture in the pellet during the pressing process, finding that the original model overpredicted the texture strength compared to these measurements. The theory was extended to account for initial particle shape and pore space, bringing the results into good agreement with the data.

Neutron resonance absorption imaging is a non-destructive technique that can characterize the elemental composition of a sample by measuring nuclear resonances in the spectrum of a transmitted beam. Recent developments in pixelated time-of-flight imaging detectors coupled with pulsed neutron sources pose new opportunities for energy-resolved imaging. In this paper we demonstrate non-contact measurements of the partial pressure of xenon and krypton gases encapsulated in a steel pipe while simultaneously passing the neutron beam through high-Z materials. The configuration was chosen as a proof of principle demonstration of the potential to make non-destructive measurement of gas composition in nuclear fuel rods. The pressure measured from neutron transmission spectra (∼739 ± 98 kPa and ∼751 ± 154 kPa for two Xe resonances) is in relatively good agreement with the pressure value of ∼758 ± 21 kPa measured by a pressure gauge. This type of imaging has been performed previously for solids with a spatial resolution of ∼ 100 μm. In the present study it is demonstrated that the high penetration capability of epithermal neutrons enables quantitative mapping of gases encapsulate within high-Z materials such as steel, tungsten, urania and others. This technique may be beneficial for the non-destructive testing of bulk composition of objects (such as spent nuclear fuel assemblies and others) containing various elements opaque to other more conventional imaging techniques. The ability to image the gaseous substances concealed within solid materials also allows non-destructive leak testing of various containers and ultimately measurement of gas partial pressures with sub-mm spatial resolution.

Energy-resolved neutron imaging enables non-destructive analyses of bulk structure and elemental composition, which can be resolved with high spatial resolution at bright pulsed spallation neutron sources due to recent developments and improvements of neutron counting detectors. This technique, suitable for many applications, is demonstrated here with a specific study of ~5–10 mm thick natural gold samples. Through the analysis of neutron absorption resonances the spatial distribution of palladium (with average elemental concentration of ~0.4 atom% and ~5 atom%) is mapped within the gold samples. At the same time, the analysis of coherent neutron scattering in the thermal and cold energy regimes reveals which samples have a single-crystalline bulk structure through the entire sample volume. A spatially resolved analysis is possible because neutron transmission spectra are measured simultaneously on each detector pixel in the epithermal, thermal and cold energy ranges. With a pixel size of 55 μm and a detector-area of 512 by 512 pixels, a total of 262,144 neutron transmission spectra are measured concurrently. The results of our experiments indicate that high resolution energy-resolved neutron imaging is a very attractive analytical technique in cases where other conventional non-destructive methods are ineffective due to sample opacity.

Herein, we report—for the first time—on the additive‐free bulk synthesis of Ti₃SnC₂. A detailed experimental study of the structure of the latter together with a secondary phase, Ti₂SnC, is presented through the use of X‐ray diffraction (XRD), and high‐resolution transmission microscopy (HRTEM). A previous sample of Ti₃SnC₂, made using Fe as an additive and Ti₂SnC as a secondary phase, was studied by high‐temperature neutron diffraction (HTND) and XRD. The room‐temperature crystallographic parameters of the two MAX phases in the two samples are quite similar. Based on Rietveld analysis of the HTND data, the average linear thermal expansion coefficients of Ti₃SnC₂ in the a and c directions were found to be 8.5 (2)·10⁻⁶ K⁻¹ and 8.9 (1)·10⁻⁶ K⁻¹, respectively. The respective values for the Ti₂SnC phase are 10.1 (3)·10⁻⁶ K⁻¹ and 10.8 (6)·10⁻⁶ K⁻¹. Unlike other MAX phases, the atomic displacement parameters of the Sn atoms in Ti₃SnC₂ are comparable to those of the Ti and C atoms. When the predictions of the atomic displacement parameters obtained from density functional theory are compared to the experimental results, good quantitative agreement is found for the Sn atoms. In the case of the Ti and C atoms, the agreement is more qualitative. We also used first principles to calculate the elastic properties of both Ti₂SnC and Ti₃SnC₂ and their Raman active modes. The latter are compared to experiment and the agreement was found to be good.

Neutrons are known to be unique probes in situations where other types of radiation fail to penetrate samples and their surrounding structures. In this paper it is demonstrated how thermal and cold neutron radiography can provide time-resolved imaging of materials while they are being processed (e.g.while growing single crystals). The processing equipment, in this case furnaces, and the scintillator materials are opaque to conventional X-ray interrogation techniques. The distribution of the europium activator within a BaBrCl:Eu scintillator (0.1 and 0.5% nominal doping concentrations per mole) is studiedin situduring the melting and solidification processes with a temporal resolution of 5–7 s. The strong tendency of the Eu dopant to segregate during the solidification process is observed in repeated cycles, with Eu forming clusters on multiple length scales (only for clusters larger than ∼50 µm, as limited by the resolution of the present experiments). It is also demonstrated that the dopant concentration can be quantified even for very low concentration levels (∼0.1%) in 10 mm thick samples. The interface between the solid and liquid phases can also be imaged, provided there is a sufficient change in concentration of one of the elements with a sufficient neutron attenuation cross section. Tomographic imaging of the BaBrCl:0.1%Eu sample reveals a strong correlation between crystal fractures and Eu-deficient clusters. The results of these experiments demonstrate the unique capabilities of neutron imaging forin situdiagnostics and the optimization of crystal-growth procedures.

Triaminotrinitrobenzene (TATB) is a highly anisotropic molecular crystal used in several plastic‐bonded explosive (PBX) formulations. TATB‐based explosives exhibit irreversible volume expansion (“ratchet growth”) when thermally cycled. A theoretical understanding of the relationship between anisotropy of the crystal, crystal orientation distribution (texture) of polycrystalline aggregates, and the intergranular interactions leading to this irreversible growth is necessary to accurately develop physics‐based predictive models for TATB‐based PBXs under various thermal environments. In this work, TATB lattice parameters were measured using neutron diffraction during thermal cycling of loose powder and a pressed pellet. The measured lattice parameters help clarify conflicting reports in the literature as these new results are more consistent with one set of previous results than another. The lattice parameters of pressed TATB were also measured as a function of temperature, showing some differences from the powder. This data is used along with anisotropic single‐crystal stiffness moduli reported in the literature to model the nominal stresses associated with intergranular constraints during thermal expansion. The texture of both specimens were characterized and the pressed pellet exhibits preferential orientation of (001) poles along the pressing direction, whereas no preferred orientation was found for the loose powder. Finally, thermal strains for single‐crystal TATB computed from lattice parameter data for the powder is input to a self‐consistent micromechanical model, which predicts the lattice parameters of the constrained TATB crystals within the pellet. The agreement of these model results with the diffraction data obtained from the pellet is discussed along with future directions of research.

Herein, we report on the crystal structures of Nb₂AlC and TiNbAlC—actual composition (Ti_0.45,Nb_0.55)₂AlC—compounds determined from Rietveld analysis of neutron diffraction patterns in the 300–1173 K temperature range. The average linear thermal expansion coefficients of a Nb₂AlC sample in the a and c directions are, respectively, 7.9(5) × 10⁻⁶ and 7.7(5) × 10⁻⁶ K⁻¹ on one neutron diffractometer and 7.3(3) × 10⁻⁶ and 7.0(2) × 10⁻⁶ K⁻¹ on a second diffractometer. The respective values for the (Ti_0.45,Nb_0.55)₂AlC composition—only tested on one diffractometer—are 8.5(3) × 10⁻⁶ and 7.5(5) × 10⁻⁶ K⁻¹. These values are relatively low compared to other MAX phases. Like other MAX phases, however, the atomic displacement parameters (APDs) show that the Al atoms vibrate with higher amplitudes than the Ti and C atoms, and more along the basal planes than normal to them. When the predictions of the APDs obtained from density functional theory are compared to the experimental results, good quantitative agreement is found for the Al atoms. In case of the Nb and C atoms, the agreement was more qualitative.

Corrections to the paper by Popa, Balzar & Vogel [J. Appl. Cryst.(2014),47, 154–159] are provided.

We studied the phase-transition induced texture changes and strengthening mechanism for zirconium metal under quasi-hydrostatic compression and uni-axial deformation under confined high pressure using the deformation-DIA (D-DIA) apparatus. It is shown that the experimentally obtained texture for ω-phase Zr can be qualitatively described by combining a subset of orientation variants previously proposed in two different models. The determined flow stress for the high-pressure ω-phase is 0.5–1.2 GPa, more than three times higher than that of the α-phase. Using first-principles calculations, we investigated the mechanical and electronic properties of the two Zr polymorphs. We find that the observed strengthening can be attributed to the relatively strong directional bonding in the ω phase, which significantly increases its shear plastic resistance over the α-phase Zr. The present findings provide an alternate route for Zr metal strengthening by high-pressure phase transformation.

Synthetic La_1−xEu_xPO₄ monazite‐type ceramics with 0 ≤ x ≤ 1 have been characterized by ultrasound techniques, dilatometry, and micro‐calorimetry. The coefficients of thermal expansion and the elastic properties are, to a good approximation, linearly dependent on the europium concentration. Elastic stiffness coefficients range from 182(1) to 202(1) GPa for c₁₁ and from 53.8(7) to 61.1(4) GPa for c₄₄. They are strongly dependent on the density of the sample. The coefficient of thermal expansion at 673 K is 8.4(3)  × 10⁻⁶ K⁻¹ for LaPO₄ and 9.9(3)  × 10⁻⁶ K⁻¹ for EuPO₄, respectively. The heat capacities at ambient temperature are between 101.6(8) J·(mol·K)⁻¹ for LaPO₄ and 110.1(8) J·(mol·K)⁻¹ for EuPO₄. The difference between the heat capacity of LaPO₄ and the Eu‐containing solid solutions is dominated by electronic transitions of the 4f‐electrons at temperatures above 75 K.

A complex cerium bearing oxide, Gd₂Ce₂O₇ was synthesized in order to simulate Pu in a fluorite derivative oxide. X-ray diffraction (XRD) data was collected using a lab diffractometer at room temperature and analyzed by Rietveld refinement method using the xnd program. The diffraction pattern obtained from the material could be indexed as a C-type cubic bixbyite crystal structure however several peaks showed peak broadening and could not be accounted for within the single-phase bixbyite model. A full pattern refinement, assuming a possible existence of short order disordered bixbyite regions within an average disordered fluorite phase gave a good fit with the experimental data, providing an estimate for correlation length of those bixbyite regions. Transmission electron microscopy confirms the existence of these correlated domains of disordered bixbyite type phase inside a defect fluorite lattice. Understanding the extent of these domains as a function of composition and the thermal history of the samples may have a profound effect on our understanding of miscibility gaps in Re₂O₃-CeO₂ phase diagrams. These effects could be eventually exploited to design materials with increased radiation resistance, a desired feature for oxide matrices where actinides can be safely disposed.

High-perfection Ni/Co spinel microcrystalline catalysts with extensive faceting show high turnover frequencies in methane dry reforming and good sulfur tolerance.

Piezoelectric materials respond to external stimuli by adjusting atomic positions. In solid-solutions, the changes occurring in atomic scale are very complex since the short- and long-range order are different. Standard methods used in diffraction data analysis fail to model the short-range order accurately. Pressure-induced cation displacements in ferroelectric Pb(Zr0.45Ti0.55)O3 perovskite oxide are modeled by starting from a short-range order. We show that the model gives the average structure correctly and properly describes the local structure. The origin of the microstrain in lead zirconate titanate is the spatially varying Zr and Ti concentration and atomic distances, which is taken into account in the simulation. High-pressure neutron powder diffraction and simulation techniques are applied for the determination of atomic positions and bond-valences as a function of pressure. Under hydrostatic pressure, the material loses its piezoelectric properties far before the transition to the cubic phase takes place. The total cation valence +6 is preserved up to 3.31 GPa by compensating the increasing B-cation valence by decreasing Pb-displacement from the high-symmetry position. At 3.31 GPa, Pb-displacement is zero and the material is no more ferroelectric. This is also the pressure at which the Pb-valence is minimized. The average structure is still tetragonal. The model for microstrain predicts that the transition occurs over a finite pressure range: Pb-displacements are spatially varying and follow the distribution of Zr and Ti ions.

Herein, we report on the temperature‐dependent crystal structures of Ti ₃ AlC ₂ and Ti ₃ Al _0.8 Sn _0.2 C ₂ in the 373–1273 K temperature range, as determined by Rietveld analysis of high‐temperature neutron diffraction time‐of‐flight data. The compositions are 86(1) wt% Ti ₃ AlC ₂ and 14(1) wt% TiC _0.92(2) for the sample with no Sn , and 95(1) wt% Ti ₃( Al _0.8 Sn _0.2) C ₂ and 5(1) wt% Ti ₂ AlC for the solid solution with Sn . The average linear volumetric thermal expansion is 8.0(2) × 10⁻⁶ K ⁻¹ for Ti ₃ AlC ₂ and 8.2(5) × 10⁻⁶ K⁻¹ for Ti ₃( Al _0.8 Sn _0.2) C ₂. The average linear thermal expansion in the a and c directions, respectively, are 7.6(2) × 10⁻⁶ K⁻¹ and 8.9(2) × 10⁻⁶ K⁻¹ for Ti ₃ AlC ₂. For Ti ₃( Al _0.8 Sn _0.2) C ₂, the respective values are 8.0(5) × 10⁻⁶ K⁻¹ and 8.6(6) × 10⁻⁶ K⁻¹. In the case of the solid solution, the quadratic thermal expansion coefficients are also given. Detailed bond lengths analysis shows that the thermal expansions along the a and c directions are controlled by the thermal expansions of the Ti – C , and Ti – Al bond lengths, respectively. The atomic displacement parameters (ADPs) show that the Al and Sn atoms vibrate with a higher amplitude than the Ti and C atoms. Consistent with first‐principles calculations, the ADPs of the Al/Sn site(s) in Ti ₃( Al _0.8 Sn _0.2) C₂ are lower than the ADPs of Al in Ti ₃ AlC ₂.

State-of-the-art neutron time-of-flight diffractometers at modern neutron sources allow sample throughput at rates of much less than one hour per sample. Automated sample changes with a high degree of reliability and flexibility are essential to assure safe operation and efficient use of available neutron flux. At the High-Pressure Preferred Orientation (HIPPO) diffractometer, a previous sample changer measured over 2300 texture and 400 powder samples at ambient conditions to study the properties of crystalline materials at the Lujan neutron scattering facility at the Los Alamos Neutron Science Center. Experience gained during operation of the sample changer for over a decade showed room for improvement and led to a new design using current industrial robot technology. Here, the new HIPPO versatile six-axis robotic sample changer for neutron powder diffraction experiments including texture measurements is presented.

Clathrate hydrates have ice-like crystalline structures typically stabled under low-temperature and high-pressure conditions. They are of great importance as potential materials for energy storage and production and carbon dioxide sequestration. Here the first structural refinement data of neon hydrate, to our knowledge, are presented. Both the experimental observations by in situ neutron diffraction and molecular dynamics simulations demonstrate that neon atoms can be enclathrated to form ice II-structured hydrates. The guest Ne atoms occupy the center of ice channels and have substantial freedom of movement owing to the lack of strong bonding between guest molecules and host lattices. The framework of Ne hydrate can be self-stabilized without the encapsulation of guest atoms, which is very special in the hydrate family.

A new approach for the determination of the elastic macro strain and stress in textured polycrystals by diffraction is presented. It consists of expanding the strain tensor weighted by texture in a series of generalized spherical harmonics where the ground state is defined by the strain/stress state in an isotropic sample in the Voigt model. In contrast to similar expansions already reported by other authors, this new approach provides expressions valid for any sample and crystal symmetries and can easily be implemented in whole powder pattern fitting, including Rietveld refinement. An earlier article [Popa & Balzar (2001).J. Appl. Cryst.34, 187–195] reported a similar model, but with a spherical harmonics expansion around the hydrostatic strain/stress state of the isotropic polycrystal. The availability of several different models is beneficial in order to allow one to select the representation in which the ground state is the closest to the actual stress state in the sample.

The problem of calculating the inverse pole figure (IPF) is analyzed from the perspective of the application of time-of flight neutron diffraction toin situmonitoring of the thermomechanical behavior of engineering materials. On the basis of a quasi-Monte Carlo (QMC) method, a consistent set of grain orientations is generated and used to compute the weighting factors for IPF normalization. The weighting factors are instrument dependent and were calculated for the engineering materials diffractometer VULCAN (Spallation Neutron Source, Oak Ridge National Laboratory). The QMC method is applied to face-centered cubic structures and can be easily extended to other crystallographic symmetries. Examples include 316LN stainless steelin situloaded in tension at room temperature and an Al–2%Mg alloy, substantially deformed by cold rolling andin situannealed up to 653 K.

The magnetic structure of two natural samples of goethite (α-FeOOH) with varying crystallinity was analyzed at 15 and 300 K by neutron diffraction. The well crystallized sample has thePb′nmcolor space group and remained antiferromagnetic up to 300 K, with spins aligned parallel to thecaxis. The purely magnetic 100 peak, identifying this color space group, was clearly resolved. The nanocrystalline sample shows a phase transition to the paramagnetic state at a temperature below 300 K. This lowering of the Néel temperature may be explained by the interaction of magnetic clusters within particles. The nuclear structure, refined with the Rietveld and pair distribution function methods, is consistent with reports in the literature.

The growing demand for electric energy will require expansion of the amount of nuclear power production in many countries of the world. Research and development in this field will continue to grow to further increase safety and efficiency of nuclear power generation. Neutrons are a unique probe for a wide range of problems related to these efforts, ranging from crystal chemistry of nuclear fuels to engineering diffraction on cladding or structural materials used in nuclear reactors. Increased flux at modern neutron sources combined with advanced sample environments allows nowadays, for example, studies of reaction kinetics at operating temperatures in a nuclear reactor. Neutrons provide unique data to benchmark simulations and modeling of crystal structure evolution and thermomechanical treatment. Advances in neutron detection recently opened up new avenues of materials characterization using neutron imaging with unparalleled opportunities especially for nuclear materials, where heavy elements (e.g., uranium) need to be imaged together with light elements (e.g., hydrogen, oxygen). This paper summarizes applications of neutron scattering techniques for nuclear materials. Directions for future research, extending the trends observed over the past decade, are discussed.

Herein we report on the thermal expansions and temperature-dependent crystal structures of select ternary carbide Mn+1AXn (MAX) phases in the Ti–Al–C phase diagram in the 100−1000 °C temperature range. A bulk sample containing 38(±1) wt. % Ti5Al2C3 (“523”), 32(±1) wt. % Ti2AlC (“211”), 18(±1) wt. % Ti3AlC2 (“312”), and 12(±1) wt. % (Ti0.5Al0.5)Al is studied by Rietveld analysis of high-temperature neutron diffraction data. We also report on the same for a single-phase sample of Ti3AlC2 for comparison. The thermal expansions of all the MAX phases studied are higher in the c direction than in the a direction. The bulk expansion coefficients—9.3(±0.1)×10−6 K−1 for Ti5Al2C3, 9.2(±0.1) ×10−6 K−1 for Ti2AlC, and 9.0(±0.1)×10−6 K−1 for Ti3AlC2—are comparable within one standard deviation of each other. In Ti5Al2C3, the dimensions of the Ti–C octahedra for the 211-like and 312-like regions are comparable to the Ti–C octahedra in Ti2AlC and Ti3AlC2, respectively. The isotropic mean-squared atomic displacement parameters are highest for the Al atoms in all three phases, and the values predicted from first-principles phonon calculations agree well with those measured.

We conducted in-situ high-temperature neutron and X-ray diffraction studies on tetragonal PbTiO₃. Using a combination of Rietveld analysis and Maximum Entropy Method, the nuclear and charge density distributions were determined as a function of temperature up to 460 °C. The ionic states obtained from charge density distributions reveal that the covalency of Pb–O₂ bonds gradually weakens with increasing temperature. The spontaneous polarizations calculated from the contributions of ionic state, ionic displacement, and nuclear polarization, are in good agreement with the experimental measurements. This method provides an effective approach to determine spontaneous polarizations in multiferroics with high-current leakage and low resistance.

Differential scanning calorimetry (DSC) has been used to study the phase changes in samples of as-received Zr-2.5Nb pressure tube material by continuous heating and cooling. Two different heating rates (5 and 20°C/min) were used to heat the sample up to 1050°C. After a short time hold at 1050°C, all the samples were continuously cooled to 300°C at a rate of 20°C/min. On continuous heating, the DSC signals obtained showed two endothermic transitions. The low-temperature transition, occurring between about 500 and 650°C, is attributed to a thermal decomposition of metastable niobium-stabilized β-phase. The highertemperature transition, occurring between 600 and 950°C, is due to phase transformations of hcp α-Zr to bcc β-Zr, as previously confirmed in a companion study on the same pressure-tube material that was examined in-situ by neutron diffraction. The neutron diffraction results provided a positive identification of the two phases and also a quantification of the β-phase present in the sample at different heating temperatures, and thus provided a guide to extract the volume fraction of β-phase from the DSC signals obtained in this study. The DSC signals revealed only one exothermic transition which is correlated to the reverse transformation of β-Zr to α-Zr, as previously identified in the companion neutron diffraction study of the same pressure tube material.

A resistive furnace combined with a load frame was built that allows for in situ neutron diffraction studies of high temperature deformation, in particular, creep. A maximum force of 2700 N can be applied at temperatures up to 1000 °C. A load control mode permits studies of, e.g., creep or phase transformations under applied uni-axial stress. In position control, a range of high temperature deformation experiments can be achieved. The examined specimen can be rotated up to 80° around the vertical compression axis allowing texture measurements in the neutron time-of-flight diffractometer HIPPO (High Pressure – Preferred Orientation). We present results from the successful commissioning, deforming a Zr-2.5 wt.% Nb cylinder at 975 °C. The device is now available for the user program of the HIPPO diffractometer at the LANSCE (Los Alamos Neutron Science Center) user facility.

The present study was dedicated to the classical piezoelectric, lead-zirconate-titanate ceramic with composition Pb(Zr0.54Ti0.46)O3 at the Zr-rich side of the morphotropic phase boundary at which two phases co-exists. The pressure-induced changes in the phase fractions were studied by high-pressure neutron powder diffraction technique up to 3 GPa and 773 K. The two co-existing phases were rhombohedral R3c and monoclinic Cm at room temperature and R3c and P4mm above 1 GPa and 400 K. The experiments show that pressure favors the R3c phase over the Cm and P4mm phases, whereas at elevated temperatures entropy favours the P4mm phase. At 1 GPa pressure, the transition to the cubic Pm3¯m phase occurred at around 600 K. Pressure lowers the Cm→P4mm transition temperature. The Cm phase was found to continuously transform to the P4mm phase with increasing pressure, which is inline with the usual notion that the hydrostatic pressure favours higher symmetry structures. At the same time, the phase fraction of the R3c phase was increasing, implying discontinuous Cm→R3c phase transition. This is in clear contrast to the polarization rotation model according to which the Cm would link the tetragonal and rhombohedral phases by being a phase in which the polarization would, more or less continuously, rotate from the tetragonal polarization direction to the rhombohedral direction. Pressure induces large changes in phase fractions contributing to the extrinsic piezoelectricity. The changes are not entirely reversible, as was revealed by noting that after high-pressure experiments the amount of rhombohedral phase was larger than initially, suggesting that on the Zr-rich side of the phase boundary the monoclinic phase is metastable. An important contribution to the intrinsic piezoelectricity was revealed: a large displacement of the B cations (Zr and Ti) with respect to the oxygen anions is induced by pressure.

The effect of manganese doping on the magnetic and structural properties of strontiumtitanate (SrTiO3) was studied. Neutron powder diffraction, x-ray diffraction, magneticmeasurements, scanning electron microscopy and energy dispersive spectroscopy of x-rays wereutilized. Air-sintered Sr(MnxTi1-x)O3 (SMT) with x = 0:02 and x = 0:05 were homogeneoussingle phase orthorhombic (space group Pbnm) perovskite samples. The symmetry was orthorhombicalready at room temperature, and no symmetry change was observed down to 11K. An anomaly in the magnetic susceptibility was observed in x = 0:02 sample at 75 K. Incontrast to earlier reports, no ferromagnetism was observed.

A description of the gsaslanguage software is presented. The software provides input to and processes output from theGSASpackage. It allows the development of scripts for the automatic evaluation of large numbers of data sets and provides documentation of the refinement strategies employed, thus fostering the development of efficient refinement strategies. Use of the bash shell and standard Unix text-processing tools, available natively on Linux and Mac OSX platforms andviathe freecygwinsoftware on Windows systems, make this software platform independent.

The decomposition of hexacarbonyltungsten, W(CO)₆, has been studied. The decomposition was induced by heating W(CO)₆in an autoclave at 523 K and pressures up to 1.8 MPa, and by laser heating in a diamond anvil cell at pressures between 5 and 18 GPa. The products have been characterized using synchrotron X-ray diffraction, pair distribution function analysis, Raman spectroscopy and scanning electron microscopy. Decomposition in the autoclave at the lower pressures resulted in the formation of a metastable tungsten carbide, W₂C, with an average particle size of 1–2 nm, and an unidentified nanocrystalline tungsten oxide and nanocrystalline graphite with average particle sizes of 1–2 and 11 nm, respectively. The existence of nanocrystalline graphite was deduced from micro-Raman spectra and the graphite particle size was extracted from the intensities of the Raman modes. The high-pressure decomposition products obtained in the diamond anvil cell are the monoclinic tungsten oxide phase WO₂and the high-pressure phase W₃O₈(I). The approximate average size of the graphite particles formed here was 6–8 nm. The bulk modulus of W(CO)₆isB₀≃ 13 GPa.

In this work, we report on the temperature‐dependent crystal structures of the isostructural, layered hexagonal phases Ti₂AlN and Cr₂GeC determined by Rietveld analysis of high temperature neutron powder diffraction data of fully dense, polycrystalline, bulk samples in the 100° to 1100°C temperature range. For both phases, the A‐group atoms, Al and Ge, vibrate with the highest amplitude and do so anisotropically within the basal plane. All bonds expand linearly with temperature, with the highest relative thermal expansion occurring in the Ti–Al and Cr–Ge bonds. The thermal expansion coefficients in the a‐ and c‐direction are, respectively, 10.3(±0.2) × 10⁻⁶ and 9.3(±0.2) × 10⁻⁶ K⁻¹ for Ti₂AlN and 12.8(±0.3) × 10⁻⁶ and 14.6(±0.3) × 10⁻⁶ K⁻¹ for Cr₂GeC. The unit cell volume expansions observed by HTND are 10.0(±0.2) × 10⁻⁶ K⁻¹ for Ti₂AlN and 13.4(±0.3) × 10⁻⁶ K⁻¹ for Cr₂GeC.

An automated sample changer with an Eulerian cradle for neutron texture measurements is described. This device has been measuring over 2300 texture and almost 400 powder samples at ambient conditions since it became operational in 2002 for use in the high pressure-preferred orientation diffractometer at the LANSCE neutron scattering facility. Operation for almost a decade resulted in sustained enhancements of mechanics, electronics, and software which significantly improved reliability and resiliency. We also describe in this paper our platform independent computer program POD2K which we use to create publication quality pole figure plots for texture samples.

One of the advantages of a multidetector neutron time-of-flight diffractometer such as the high pressure preferred orientation diffractometer (HIPPO) at the Los Alamos Neutron Science Center is the capability to measure efficiently preferred orientation of bulk materials. A routine experimental method for measurements, both at ambient conditions, as well as high or low temperatures, has been established. However, only recently has the complex data analysis been streamlined to make it straightforward for a noninitiated user. Here, we describe the Rietveld texture analysis of HIPPO data with the computer code Materials Analysis Using Diffraction (MAUD) as a step-by-step procedure and illustrate it with a metamorphic quartz rock. Postprocessing of the results is described and neutron diffraction results are compared with electron backscatter diffraction measurements on the same sample.

We measured the temperature dependence of the structural parameters and the occurrence of magnetism in UPdSn and UCuSn using neutron diffraction. The data were taken in an effort to understand the role of hybridization effects for the development of the uranium magnetic moment and the occurrence of long-range magnetic order in these two compounds. The shortest U–U distance provides a measure of delocalization due to direct 5f-5f overlap, while the U–Pd (or U–Cu, respectively) and U–Sn distances give a measure of the effects of 5f-ligand hybridization. Using Rietveld refinement of our neutron diffraction data, we determined the shortest interatomic distances for temperatures between 15 K and room temperature. The changes in the interatomic distances cause changes in the hybridization effects, which in turn leads to the formation of a magnetic ground state for both compounds.

A study of the reaction of rhenium with carbon at high-(P, T) conditions up to P _max = 67 GPa and T _max = 3800 K is presented. A hexagonal ReC _x was identified as the stable phase at high-(P, T) conditions. A composition of ReC_0.5 is proposed. No evidence for a cubic ReC polymorph with rocksalt structure, as suggested in the literature, or for any other phase was found at the P-T conditions explored. A preliminary P-T rhenium-carbon phase diagram has been derived and properties such as bulk moduli and elastic stiffness coefficients were obtained.

This paper reports neutron diffraction experiments on high temperature Cu–13.1Al–4.0Ni (wt.%) shape memory alloy single crystals. The Cu–13.1%Al–4%Ni (wt.%) single crystal wires having nominal dimensions of 2.0 mm (diameter) and 100 mm (length) were subjected to tensile load at room temperature and at 175°C (well above the austenitic finish temperature). Diffraction patterns were acquired at various stress levels. The growth and decay of different variants during the (β¹₁ 18R monoclinic martensite reorientation under load were identified. Neutron diffraction results at 175 and 200°C were used to study the biased martensitic variant formation during the (β₁) cubic austenite to (β¹₁) 18R monoclinic martensite transformation under load. The observed results are correlated with stress-overall strain data obtained from experiments carried out at different test temperatures in an Instron machine with a high temperature environmental chamber.

The Wilson method was applied for determination of the thermal atomic motions in micro- and nano-crystalline SiC. Limitations of application of this method to examination of complex materials with atoms vibrating with more that one amplitude were discussed. It is shown that a unique interpretation of Wilson plots for crystals with more than one type of atoms and weak vibration component(s) requires measurements performed up to a very large diffraction vector Q (>25 Å^–1). Atomic vibrations in microcrystalline SiC were evaluated based on the diffractograms calculated for models built assuming different mean square atomic displacements (vibration amplitudes) of the component atoms. For nanocrystalline SiC two different temperature atomic factors which describe vibrations of the atoms in the grain interior (B _core) and at its surface (B _shell) were determined.

A structural study of α-AgSCN was carried out using the neutron powder diffractometer HIPPO (high-pressure preferred orientation powder) at ten different temperatures between 25 and 275 K. The structure of α-AgSCN was refined using the Rietveld method and the symmetry elements for the material were found to be: space group No. 15,C2/c,a= 8.7210 (8) Å,b= 7.9318 (8) Å,c= 12.3329 (5) Å, β = 138.750 (3)°, volume = 562.497 (9) ųandZ= 8. The Ag⁺cation has tetrahedral coordination and is surrounded by three –SCN thiocyanate ligands and one isothiocyanate –NCS ligand down to 25 K, with no structural changes. The bond lengths at 275 K are Ag—S1 = 2.749 (10), Ag—S2 = 2.995 (11), Ag—S3 = 2.411 (11), Ag—N = 2.150 (5), S—C = 1.783 (11) and C—N = 1.1447 (35) Å. The bond lengths at 25 K are Ag—S1 = 2.782 (5), Ag—S2 = 2.941 (5), Ag—S3 = 2.431 (5), Ag—N = 2.1526 (26), S—C = 1.749 (5) and C—N = 1.140 (2) Å.

Many projects involving nuclear fuel rest on a quantitative understanding of the co-existing phases at various stages of burnup. Since the fission products have considerably different abilities to chemically associate with oxygen, and the metal-to-oxygen molar ratio is necessarily increasing, the chemical potential of oxygen is a function of burnup. Concurrently, well-recognized small fractions of new phases such as inert gas, noble metals, zirconates, etc. also develop. To further complicate matters, the dominant UO₂ fuel phase may be non-stoichiometric and most of the minor phases themselves have a variable composition dependent on temperature and possible contact with the coolant in the event of a sheathing breach.

A thermodynamic database has been in development to predict the phases in partially burned CANDU (CANada Deuterium Uranium) nuclear fuel containing the major fission products. The building blocks are the standard Gibbs energies of formation of the many possible compounds expressed as a function of temperature. To these data are added mixing terms associated with the appearance of the component species in particular phases. In operational terms, the treatment rests on the ability to minimize the Gibbs energy in a multicomponent system using the algorithms developed by Eriksson. The treatment, considered applicable in the range 300 to 2000 °C, is capable of handling non-stoichiometry in the UO₂ fluorite phase, dilute solution behaviour of significant solute oxides, noble metal inclusions, a second metal solid solution U(Pd – Rh – Ru)₃, zirconate, molybdate, and uranate solutions as well as other minor solid phases, and volatile gaseous species. The paper highlights the current capability of an ongoing project.

The domain‐switching behavior of lead zirconate titanate (PZT) during mechanical cyclic loading between 10 and 150 MPa was investigated by in situ time‐of‐flight neutron diffraction. The domain‐switching behavior was represented by a change of the pole density distribution during cycling. With increasing number of cycles, domain switching becomes saturated, correlating with a decrease in the rate of remnant strain accumulation in the stress–strain curve. Moreover, a relationship was demonstrated between the macroscopic strain and that developed from ferroelastic domain switching. The contribution of ferroelastic strain to the macroscopic strain was calculated from an orientation average of the domain switching distributions and the c/a ratio. The results show that nearly 80% of macroscopic strain arises from ferroelastic domain switching during mechanical cyclic loading.

In situ time-of-flight neutron diffraction was performed to investigate the martensitic phase transformation during quasistatic uniaxial compression testing of 304L stainless steel at 300 and 203K. In situ neutron diffraction enabled the bulk measurement of intensity evolution for various hkl atomic planes during the austenite (fcc) to martensite (hcp and bcc) phase transformation. Based on the neutron diffraction patterns, the martensite phases were observed from the very beginning of the plastic deformation at 203K. However, at 300K, no newly formed martensite, except a small amount of preexisting hcp phase, was observed throughout the test. From the changes in the relative intensities of individual hkl atomic planes, the grain-orientation-dependent phase transformation was investigated. The preferred orientation of the newly formed martensite grains was also investigated for the sample deformed at 203K using neutron diffraction. The results reveal the orientation relationships between the austenite and the newly formed martensites. The fcc grain family diffracting with {200} plane normal parallel to the loading axis is favored for the fcc to bcc transformation and the bcc {200} plane normals are primarily aligned along the loading direction. For the fcc to hcp transformation, the fcc grains with {111} plane normals at an angle in between about 10° and 50° to the loading direction are favored.

We discuss the impact of strong absorption for thermal neutrons on data analysis and compare absorption corrections in the GSAS and MAUD Rietveld codes for texture and structural parameter refinement. Diffraction data were collected on the neutron powder diffractometer HIPPO at LANSCE from dysprosium and erbium, which are moderate-to-strong absorbers for thermal neutrons with absorption cross sections of 159 barns for Er and 994 barns for Dy at λ=1.8 Å. Both elements have hexagonal-close-packed (hcp) crystal structures, and the samples were various thicknesses of rolled foils. The orientation distribution functions (ODF) were fit to the same neutron time-of-flight data sets using two very different full pattern Rietveld analysis procedures. Spherical harmonics functions were fit to the textured data using GSAS. These data were also analyzed by the modified direct method E-WIMV using MAUD. The resulting pole figures from the ODFs determined by both Rietveld analysis packages are qualitatively similar, and the textures were confirmed by X-ray diffraction. Additionally, data from orthorhombic dysprosium and erbium fluoride powders show that atomic positions are not sensitive to absorption. We address inconsistencies and methodologies in data analysis when strong absorption is present.

One of the design goals of the neutron time-of-flight (TOF) diffractometer HIPPO (High Pressure–Preferred Orientation) at LANSCE (Los Alamos Neutron Science Center) was efficient quantitative texture analysis. In this paper, the effects of the HIPPO detector geometry and layout on texture analysis, particularly the shape and dimensions of the detector panels, are investigated in detail. An equal-channel angular-pressed (ECAP) aluminium sample with a strong texture was used to determine the methodological limitations of various methods of quantitative texture analysis. Several algorithms for extracting the orientation distribution function (ODF) from the TOF spectra are compared: discrete orientations at arbitrary positions, harmonic methods in Rietveld codes (MAUD and GSAS) and discrete methods in MAUD. Because of the detector geometry, the sharpest texture peaks that can be represented are 12–15° in width, resulting in an optimal texture resolution of 25–30°. Due to the limited resolution and incomplete pole-figure coverage, harmonic expansions beyond L = 12 (where L is the maximum degree of the harmonic expansion) introduce subsidiary oscillations, which are consistently identified as artifacts. Only discrete methods provide a quantitative representation of the texture. Harmonic methods are adequate for a qualitative description of the main texture component. The results of the analysis establish HIPPO as an efficient instrument to determine preferred orientations in relatively short measuring times.

Repeatable, hysteretic loops in quasi‐static loading measurements on rocks are well known; the fundamental processes responsible for them are not. The grain contact region is usually treated as the site of these processes, but there is little supporting experimental evidence. We have performed simultaneous neutron diffraction and quasi‐static loading experiments on a selection of rocks to experimentally isolate the response of these contact regions. Neutron diffraction measures strain in the lattice planes of the bulk of the grain material, so differences between this strain and the macroscopic response yield information about grain contact behavior. We find the lattice responds linearly to stress in all cases, oblivious to the macroscopic unrecoverable strains, curvature, and hysteresis, localizing these effects to the contacts. Neutron diffraction shows that the more granular rocks appear to distribute stresses so that the same strain appears in all the grains, independent of crystallographic orientation.

The macroscopic stress distribution across a Zircaloy-4 (Zr-4) GTAW weld was measured by time-of-flight neutron diffraction at the SMARTS diffractometer at Los Alamos National Laboratory. Time-of-flight diffraction enabled the measurement of strain for all the available reflections permitted by the rolling texture of the plate and its modification in the weld (melted) and heat-affected zones. Reference lattice spacings were measured on coupons cut from an adjacent section of the weld. A maximum longitudinal stress of 220 ± 40 MPa was observed along the weld centre line, compared with the plate 0.2% proof stress of 390 MPa. A maximum transverse stress of 60 ± 40 MPa was observed on the weld centre-line falling to zero at the edge of the plate.

In this paper we describe the capabilities for texture measurements of the new neutron time-of-flight diffractometer HIPPO at the Los Alamos Neutron Science Center. The orientation distribution function (ODF) is extracted from multiple neutron time-of-flight histograms using the full-pattern analysis first described by Rietveld. Both, the well-established description of the ODF using spherical harmonics functions and the WIMV method, more recently introduced for the analysis of time-of-flight data, are available to routinely derive the ODF from HIPPO data. At ambient conditions, total count time of less than one hour is ample to collect sufficient data for texture analysis in most cases. The large sample throughput for texture measurements at ambient conditions possible with HIPPO requires a robust and reliable, semi-automated data analysis. HIPPO’s unique capabilities to measure large quantities of ambient condition samples and to measure texture at temperature and uni-axial stress are described. Examples for all types of texture measurements are given