X-ray Laue Microdiffraction Research Articles

Multimodal 3D quantification of particle stimulated nucleation in industrially manufactured aluminium AA5182 sheet

Particle stimulated nucleation is a dominant recrystallisation mechanism observed in many industrially relevant aluminium alloys during thermomechanical processing. In this work, we quantify particle stimulated nucleation in 3D in an aluminium AA5182 alloy sheet cold-rolled to 75 % thickness reduction. Second phase particles and nuclei are mapped in the same sample volume by conventional laboratory absorption X-ray tomography and synchrotron X-ray Laue micro-diffraction. The large second phase particles are classified as Fe- and Mg-rich phases. It is found that84 % of the nuclei are particle stimulated and 40 % of the particles stimulate nucleation. The critical particle diameter is found to be 4μm. Deviatoric elastic strains are derived from micro-diffraction data and it is found that elastic strains are present in the recrystallised nuclei. The effects of the different particle types, particle clustering, particle size and aspect ratio as well as strain inheritance are discussed. This work provides a full 3D quantification of particle stimulated nucleation behaviour in AA5182 alloy sheet deformed to high strain.

Stressful crystal histories recorded around melt inclusions in volcanic quartz

Magma ascent and eruption are driven by a set of internally and externally generated stresses that act upon the magma. We present microstructural maps around melt inclusions in quartz crystals from six large rhyolitic eruptions using synchrotron Laue X-ray microdiffraction to quantify elastic residual strain and stress. We measure plastic strain using average diffraction peak width and lattice misorientation, highlighting dislocations and subgrain boundaries. Quartz crystals across studied magma systems preserve similar and relatively small magnitudes of elastic residual stress (mean 53–135 MPa, median 46–116 MPa) in comparison to the strength of quartz (~ 10 GPa). However, the distribution of strain in the lattice around inclusions varies between samples. We hypothesize that dislocation and twin systems may be established during compaction of crystal-rich magma, which affects the magnitude and distribution of preserved elastic strains. Given the lack of stress-free haloes around faceted inclusions, we conclude that most residual strain and stress was imparted after inclusion faceting. Fragmentation may be one of the final strain events that superimposes stresses of ~ 100 MPa across all studied crystals. Overall, volcanic quartz crystals preserve complex, overprinted deformation textures indicating that quartz crystals have prolonged deformation histories throughout storage, fragmentation, and eruption.

Laue microdiffraction on polycrystalline samples above 1500 K achieved with the QMAX-µLaue furnace.

X-ray Laue microdiffraction aims to characterize microstructural and mechanical fields in polycrystalline specimens at the sub-micrometre scale with a strain resolution of ∼10-4. Here, a new and unique Laue microdiffraction setup and alignment procedure is presented, allowing measurements at temperatures as high as 1500 K, with the objective to extend the technique for the study of crystalline phase transitions and associated strain-field evolution that occur at high temperatures. A method is provided to measure the real temperature encountered by the specimen, which can be critical for precise phase-transition studies, as well as a strategy to calibrate the setup geometry to account for the sample and furnace dilation using a standard α-alumina single crystal. A first application to phase transitions in a polycrystalline specimen of pure zirconia is provided as an illustrative example.

Selective growth of recrystallizing grains into well-characterized deformed aluminum at hardness indentation

The selective 3D growth of multiple recrystallization nuclei/grains around a hardness indentation into a deformed Al grain has been quantified through a new approach that combines two synchrotron techniques: 3D X-ray Laue micro-diffraction and diffraction contrast tomography. The former is used to characterize the deformed microstructure and nucleation, while the latter to track the nuclei's growth during interrupted in situ annealing. The combined 4D (x,y,z,t) datasets enable a detailed quantification of the local deformed microstructure consumed by the nuclei/grains and the boundary characteristics between them, including the stored energy and anisotropy of the orientation distribution of the deformation matrix, as well as the misorientation of the moving and non-moving boundary segments. It is found that only certain nuclei can grow into large sizes, and the growth is heterogeneous both among recrystallizing grains and along different directions. Neither the local stored energy nor the boundary misorientation, whether considered individually or in combination, can fully account for the observed growing and shrinking behavior. The growth difference along different directions is related to the deformation microstructure, specifically the geometrical alignment of dislocation boundaries. Furthermore, the effects of impingement of other recrystallizing grains, recovery of the matrix, and elastic strain/stress, on the growth heterogeneities are discussed in detail with a view towards developing advanced modeling with improved predictability of local recrystallization phenomena. The present study demonstrates the effectiveness of the new approach in enabling 3D analysis of recrystallization in complex materials, with potential applications in the development of advanced engineering materials.

Residual strain orientation in rolled titanium determined with synchrotron X-ray Laue microdiffraction

Previously, synchrotron X-ray Laue microdiffraction has been used to measure the magnitudes of residual strain in materials. Recently the method was advanced to determine the orientation of the strain ellipsoid and applied to naturally deformed quartzites; however, the deformation history of these quartzites is ambiguous due to their natural origin. In this study, synchrotron X-ray Laue microdiffraction (µXRD) is used to measure the residual strain for the first time in a sample with known stress history, rolled titanium. A deviatoric strain tensor is calculated from each Laue diffraction image collected with two µXRD scans of a rolled titanium sheet in different sample orientations. The principal strain axes are calculated using an eigen decomposition of the deviatoric strain tensors. The results show that the principal axis of compression is aligned with the normal direction of the titanium sheet, and the principal axis of extension is aligned with the rolling direction. Pole figures are used to represent the 3D distribution of residual strain axes.

Formation of locked-lamellar grains in a slightly hypoeutectic Al-Al2Cu alloy during thin-sample directional solidification

We studied the formation and growth of locked-lamellar microstructures in a thin sample of a slightly hypoeutectic Al-Al2Cu alloy. The coupled-growth dynamics, including early stages and steady-state regimes, was observed optically in real time during directional solidification. The orientation of the α (Al) and θ (Al2Cu) crystals was measured ex situ in a series of eutectic grains by X-ray Laue microdiffraction. A nucleation event of a θ crystal on a pre-existing α crystal, and the subsequent growth of a eutectic grain with a type-C orientation relationship, that is, with a coincidence of {123}-α and {100}-θ planes, were observed in situ. In type-C eutectic grains, lamellar locking occurred parallel to the low-energy coincidence plane. A regular (floating) coupled-growth dynamics was observed in misoriented eutectic grains.

The influence of layer thickness on the deformation and fracture of layered metals: Insights from synchrotron Laue microdiffraction and mechanistic model

Layer thickness behaves as a crucial parameter in determining the mechanical properties of multi-layered composites. Recently, a synchronous improvement in the strength and ductility of Ti/Al layered materials was observed with the thickening of Ti layers. To address the underlying mechanism, Synchrotron Laue X-ray microdiffraction and electron backscatter diffraction were performed to study the dislocation behaviors at the initial and large deformation stages. We also developed a mechanistic model to elucidate the influence of layer thickness, as well as to determine the threshold thickness that governs the transition of deformation and fracture behaviors. Our experimental and model efforts suggest that the contribution of layer thickness lies in its role in the dislocation dynamics and strain distribution, which helps with the design of next-generation high-performance layered composites.

Stress relief during annealing of railway wheel steel characterized by synchrotron X-ray micro-diffraction

Railway wheels in service experience rolling contact fatigue loading, but also need to resist frictional heating on braking, yielding temperatures up to 500 °C. The combination of mechanical and thermal loads leads to changes in the mechanical properties of the material. The focus of this study is to investigate the effect of annealing on local microstructure and residual stresses in railway wheel pearlitic steel (medium carbon steels, ~0.55 wt.% C) using synchroton X-ray Laue micro-diffraction. It is found that the local residual stress releases to a large extent after annealing at 500 °C. The stress formation and relief mechanisms and their relationship to the local microstructure are discussed.

Grain Structure Engineering of NiTi Shape Memory Alloys by Intensive Plastic Deformation.

To explore an effective route of customizing the superelasticity (SE) of NiTi shape memory alloys via modifying the grain structure, binary Ni55Ti45 (wt) alloys were fabricated in as-cast, hot swaged, and hot-rolled conditions, presenting contrasting grain sizes and grain boundary types. In situ synchrotron X-ray Laue microdiffraction and in situ synchrotron X-ray powder diffraction techniques were employed to unravel the underlying grain structure mechanisms that cause the diversity of SE performance among the three materials. The evolution of lattice rotation, strain field, and phase transformation has been revealed at the micro- and mesoscale, and the effect of grain structure on SE performance has been quantified. It was found that (i) the Ni4Ti3 and NiTi2 precipitates are similar among the three materials in terms of morphology, size, and orientation distribution; (ii) phase transformation happens preferentially near high-angle grain boundary (HAGB) yet randomly in low-angle grain boundary (LAGB) structures; (iii) the smaller the grain size, the higher the phase transformation nucleation kinetics, and the lower the propagation kinetics; (iv) stress concentration happens near HAGBs, while no obvious stress concentration can be observed in the LAGB grain structure during loading; (v) the statistical distribution of strain in the three materials becomes asymmetric during loading; (vi) three grain lattice rotation modes are identified and termed for the first time, namely, multi-extension rotation, rigid rotation, and nondispersive rotation; and (vii) the texture evolution of B2 austenite and B19′ martensite is not strongly dependent on the grain structure.

LaueNN: neural-network-based hkl recognition of Laue spots and its application to polycrystalline materials.

A feed-forward neural-network-based model is presented to index, in real time, the diffraction spots recorded during synchrotron X-ray Laue microdiffraction experiments. Data dimensionality reduction is applied to extract physical 1D features from the 2D X-ray diffraction Laue images, thereby making it possible to train a neural network on the fly for any crystal system. The capabilities of the LaueNN model are illustrated through three examples: a two-phase nano-structure, a textured high-symmetry specimen deformed in situ and a polycrystalline low-symmetry material. This work provides a novel way to efficiently index Laue spots in simple and complex recorded images in <1 s, thereby opening up avenues for the realization of real-time analysis of synchrotron Laue diffraction data.

Grain Boundaries and Dislocations in Layered Cathodes

Crystallographic defects exist in many redox active energy materials, e.g., battery and catalyst materials, which significantly alter their chemical properties for energy storage and conversion. In this presentation, we will address how these defects, e.g., grain boundaries and geometrically necessary dislocations, govern the charge distribution and battery performance of layered oxide cathodes. Architecting grain crystallographic orientation can modulate charge distribution and chemomechanical properties for enhancing the performance of polycrystalline battery materials. However, probing the interplay between charge distribution, grain crystallographic orientation, and performance remains a daunting challenge. Herein, we elucidate the spatially resolved charge distribution in lithium layered oxides with different grain crystallographic arrangements and establish a model to quantify their charge distributions. While the holistic “surface-to-bulk” charge distribution prevails in polycrystalline particles, the crystallographic orientation-guided redox reaction governs the charge distribution in the local charged nanodomains. Compared to the randomly oriented grains, the radially aligned grains exhibit a lower cell polarization and higher capacity retention upon battery cycling. The radially aligned grains create less tortuous lithium ion pathways, thus improving the charge homogeneity as statistically quantified from over 20 million nanodomains in polycrystalline particles. This study provides an improved understanding of the charge distribution and chemomechanical properties of polycrystalline battery materials. Crystallographic defects, such as geometrically necessary dislocations, are reported to influence the redox reactions in battery particles through single-particle, multimodal, in situ synchrotron measurements. Through Laue X-ray microdiffraction, many crystallographic defects are spatially identified and statistically quantified from a large quantity of diffraction patterns in many layered oxide particles, including geometrically necessary dislocations, tilt boundaries, and mixed defects. The in situ and ex situ measurements, combining microdiffraction and X-ray spectroscopic imaging, reveal that LiCoO2 particles with a higher concentration of geometrically necessary dislocations provide deeper charging reactions, indicating that dislocations may facilitate redox reactions in layered oxides during initial charging. The present study illustrates that a precise control of crystallographic defects and their distribution can potentially promote and homogenize redox reactions in battery materials.

(Invited) Grain Boundaries and Dislocations in Layered Cathodes

Crystallographic defects exist in many redox active energy materials, e.g., battery and catalyst materials, which significantly alter their chemical properties for energy storage and conversion. In this presentation, we will address how these defects, e.g., grain boundaries and geometrically necessary dislocations, govern the charge distribution and battery performance of layered oxide cathodes.Architecting grain crystallographic orientation can modulate charge distribution and chemomechanical properties for enhancing the performance of polycrystalline battery materials. However, probing the interplay between charge distribution, grain crystallographic orientation, and performance remains a daunting challenge. Herein, we elucidate the spatially resolved charge distribution in lithium layered oxides with different grain crystallographic arrangements and establish a model to quantify their charge distributions. While the holistic “surface-to-bulk” charge distribution prevails in polycrystalline particles, the crystallographic orientation-guided redox reaction governs the charge distribution in the local charged nanodomains. Compared to the randomly oriented grains, the radially aligned grains exhibit a lower cell polarization and higher capacity retention upon battery cycling. The radially aligned grains create less tortuous lithium ion pathways, thus improving the charge homogeneity as statistically quantified from over 20 million nanodomains in polycrystalline particles. This study provides an improved understanding of the charge distribution and chemomechanical properties of polycrystalline battery materials.Crystallographic defects, such as geometrically necessary dislocations, are reported to influence the redox reactions in battery particles through single-particle, multimodal, in situ synchrotron measurements. Through Laue X-ray microdiffraction, many crystallographic defects are spatially identified and statistically quantified from a large quantity of diffraction patterns in many layered oxide particles, including geometrically necessary dislocations, tilt boundaries, and mixed defects. The in situ and ex situ measurements, combining microdiffraction and X-ray spectroscopic imaging, reveal that LiCoO2 particles with a higher concentration of geometrically necessary dislocations provide deeper charging reactions, indicating that dislocations may facilitate redox reactions in layered oxides during initial charging. The present study illustrates that a precise control of crystallographic defects and their distribution can potentially promote and homogenize redox reactions in battery materials.

Huge local elastic strains in bulk nanostructured pure zirconia materials

From the liquid state to room temperature, two successive solid-state phase transitions occur in pure zirconia. It is well-known that the last one (tetragonal to monoclinic) is martensitic and induces large volume variations and shear strains. Elastic and inelastic behaviors of zirconia-based materials are strongly influenced by this transition and the associated strain fields that it induces. Knowledge of strain and stress at the crystal scale is thus a crucial point. Using fully dense pure zirconia polycrystals obtained by a fuse casting process, we have determined at a sub-micrometric scale, by X-ray Laue microdiffraction, the strains map at room temperature in as-cast specimens and after a post elaboration high temperature thermal treatment. We observed that the fluctuation of deviatoric elastic strain is huge, the standard deviation of normal component being in the range of 1–2%. The heat treatment tends to even further increase this range of fluctuation, despite the development of a multiscale crack network formed during the cooling. Correspondingly, the associated stress level is also huge. It lies in the 5 GPa range with stress gradient amounting 1 GPa μm−1.

Enhanced strength in pure Ti via design of alternating coarse- and fine-grain layers

The yield strength of metals is typically governed by the average grain size through the Hall-Petch relation, and it usually follows the rule of mixture (ROM) for layered composite materials. In the present study, an extraordinarily high yield strength, far beyond the predicted values from the Hall-Petch relation and the ROM, is achieved in a specially designed layered titanium that is characterized by alternating coarse- and fine-grain layers (C/F-Ti) where the grain sizes match the layer thicknesses in both the coarse- and fine-grained layers. The strengthening mechanism of such a layered C/F-Ti is investigated based on detailed experimental characterizations, including nanoindentation tests of local hardness, in-situ synchrotron Laue X-ray microdiffraction (μXRD) measurement of the lattice strain distribution during tensile testing, and transmission electron microscopy (TEM) analysis of the dislocation structure after yielding. In the coarse-grain layers, significantly higher hardness values are observed next to the layer interfaces compared to the layer center regions, and <c+a> dislocations and densely populated pile-ups of <a> dislocations are exclusively observed in the interface regions after yielding. These experimental results point to an enhanced interface constraint effect on the deformation mechanism in hexagonal close-packed (hcp) materials with a large difference in the critical resolved shear stress between <a> slip and <c+a> slip. The C/F-Ti combines the strength of fine grains and the ductility of coarse grains, demonstrating a new structural design strategy for property optimization of single-phase hcp materials.

Charging Reactions Promoted by Geometrically Necessary Dislocations in Battery Materials Revealed by In Situ Single-Particle Synchrotron Measurements.

Crystallographic defects exist in many redox active energy materials, e.g., battery and catalyst materials, which significantly alter their chemical properties for energy storage and conversion. However, there is lack of quantitative understanding of the interrelationship between crystallographic defects and redox reactions. Herein, crystallographic defects, such as geometrically necessary dislocations, are reported to influence the redox reactions in battery particles through single-particle, multimodal, and in situ synchrotron measurements. Through Laue X-ray microdiffraction, many crystallographic defects are spatially identified and statistically quantified from a large quantity of diffraction patterns in many layered oxide particles, including geometrically necessary dislocations, tilt boundaries, and mixed defects. The in situ and ex situ measurements, combining microdiffraction and X-ray spectroscopy imaging, reveal that LiCoO2 particles with a higher concentration of geometrically necessary dislocations provide deeper charging reactions, indicating that dislocations may facilitate redox reactions in layered oxides during initial charging. The present study illustrates that a precise control of crystallographic defects and their distribution can potentially promote and homogenize redox reactions in battery materials.

X-ray Laue Microdiffraction and Raman Spectroscopic Investigation of Natural Silicon and Moissanite

Moissanite, SiC, is an uncommon accessory mineral that forms under low oxygen fugacity. Here, we analyze natural SiC from a Miocene tuff-sandstone using synchrotron Laue microdiffraction and Raman spectroscopy, in order to better understand the SiC phases and formation physics. The studied crystals of SiC consist of 4H- and 6H-SiC domains, formed from either, continuous growth or, in one case, intergrown, together with native Si. The native Si is polycrystalline, with a large crystal size relative to the analytical beam dimensions (&gt;1–2 μm). We find that the intergrown region shows low distortion or dislocation density in SiC, but these features are comparatively high in Si. The distortion/deformation observed in Si may have been caused by a mismatch in the coefficients of thermal expansion of the two materials. Raman spectroscopic measurements are discussed in combination with our Laue microdiffraction results. Our results suggest that these SiC grains likely grew from an igneous melt.

Data-driven approach for synchrotron X-ray Laue microdiffraction scan analysis.

A novel data-driven approach is proposed for analyzing synchrotron Laue X-ray microdiffraction scans based on machine learning algorithms. The basic architecture and major components of the method are formulated mathematically. It is demonstrated through typical examples including polycrystalline BaTiO3, multiphase transforming alloys and finely twinned martensite. The computational pipeline is implemented for beamline 12.3.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory. The conventional analytical pathway for X-ray diffraction scans is based on a slow pattern-by-pattern crystal indexing process. This work provides a new way for analyzing X-ray diffraction 2D patterns, independent of the indexing process, and motivates further studies of X-ray diffraction patterns from the machine learning perspective for the development of suitable feature extraction, clustering and labeling algorithms.

Dislocation density distribution at slip band-grain boundary intersections

We study the mechanisms of slip transfer at a grain boundary, in titanium, using Differential Aperture X-ray Laue Micro-diffraction (DAXM). This 3D characterisation tool enables measurement of the full (9-component) Nye lattice curvature tensor and calculation of the density of geometrically necessary dislocations (GNDs). We observe dislocation pile-ups at a grain boundary, as the neighbour grain prohibits easy passage for dislocation transmission. This incompatibility results in local micro-plasticity within the slipping grain, near to where the slip planes intersect the grain boundary, and we observe bands of GNDs lying near the grain boundary. We observe that the distribution of GNDs can be significantly influenced by the formation of grain boundary ledges that serve as secondary dislocation sources. This observation highlights the non-continuum nature of polycrystal deformation and helps us understand the higher order complexity of grain boundary characteristics.

High Resolution Mapping of Orientation and Strain Gradients in Metals by Synchrotron 3D X-ray Laue Microdiffraction

Synchrotron 3D X-ray Laue microdiffraction, available at beamline 34-ID-E at Advanced Photon Source in Argonne National Laboratory, is a powerful tool for 3D non-destructive mapping of local orientations and strains at sub-micron scale in the bulk. With this technique, it is possible to study local residual stresses developed during manufacturing or while in service due to interactions between, for example, different phases and/or grains with different orientations in materials containing multiple or single phase(s). Such information is essential for understanding mechanical properties and designing advanced materials, but is largely non-existent in the current generation of materials models. In the present paper, the principle and experimental set-up of the 3D microdiffraction are introduced, followed by a description of a method for quantification of the local plastic deformation based on high-angular-resolution orientation maps. The quantification of local residual stresses in two model materials, ductile cast iron (two phases) and partially recrystallized pure nickel (single phase), using 3D microdiffraction will then be presented. The results show that 3D microdiffraction is important for understanding the origin of local residual stresses and to relate them to the microstructural evolution. Finally, the limitations of the 3D microdiffraction on the current generation synchrotron source and new possibilities after the synchrotron upgrade are discussed.

Microstructure and residual elastic strain at graphite nodules in ductile cast iron analyzed by synchrotron X-ray microdiffraction

The microstructure and residual elastic strain at graphite nodules (GNs) in ductile cast iron produced using either a fast or slow cooling rate have been characterized using synchrotron 3D X-ray Laue microdiffraction. The results show that thermal stress is introduced during cooling and that part of this stress is relaxed by plastic deformation of the polycrystalline ferrite matrix. It is found that the plastic deformation is accommodated by the formation of dislocations and dislocation boundaries, which are organized in a cell structure. The dislocation density quantified based on the microstructure is most pronounced at the GN/matrix interface around small GNs in the fast cooled sample. Residual elastic strain is also present, which is mainly compressive with a maximum of 6.0–9.9 × 10−4 near the GNs. Gradients of plastic deformation and elastic strain field around the GNs are observed. The results document for the first time that both the elastic strain field and the plastic strain field averaged over the grains around the GNs is approximately scaling with GN size and not affected by the cooling rate. The experimental data are compared with simulations by a finite element method, and agreement and disagreement are discussed in detail.