Imaging of Orientation and Geometry in Microstructures: Development and Applications of High Energy X-ray Diffraction Microscopy

Near-field High Energy X-ray Diffraction Microscopy (HEDM) is a synchrotron based imaging technique capable of resolving crystallographic orientation in a bulk, polycrystalline material non-destructively. Recent advances in data acquisition and analysis methods have led to micron-scale spatial resolution and ≤ 0.1º angular resolution of the measured volumetric orientation maps across millimeter sized samples. This is a significant improvement over the previous generation of three-dimensional X-ray techniques, which provides us with the access of statistically significant microstructure volumes. Combined with the use of state-of-the-art surface mesh generation algorithms, this markedly improved resolution results in the capability to directly measure geometrical evolution, such as grain boundary motion, and material deformation in the form of lattice rotations. In this thesis, the algorithms and analysis methods recently developed for HEDM are discussed. This includes the descriptions of the robust geometrical extraction methods used for microstructure feature characterization. A set of validation tests for the Forward Modeling Method and the newly developed orientation reconstruction algorithm, the Stratified Monte Carlo Pruning method, is also detailed. By using HEDM to measure the annealing of high purity nickel, grain boundary motion for different boundary types are measured and presented. Moreover, the use of HEDM enabled us to observe the first ever spatially resolved lattice rotation in a high purity copper wire under uni-axial tension, thus demonstrating HEDM’s applicability to defected materials.</p

Modeling the Effects of Grain and Porosity Structure on Copper Spall Response

Ongoing efforts to characterize the incipient spallation of copper have increased the experimental fidelity at which the material’s microstructure is measured. Various imaging techniques have allowed for 3D characterization of the structure of inclusions, porosity, and crystallographic grains. This work employs a combined crystal mechanics and porosity model that, for the first time, addresses the influence of three different types of spatial distributions of second phase particles, relative to features in both experimentally-measured and synthetically-generated microstructures. With these features, the model can probe the sensitivity of copper spall response to both grain and porosity structures. The sensitivity of the model to various nucleation and porosity growth parameters is also shown. These sensitivity studies illustrate where increased experimental accuracy can most readily affect modeling results. Likewise, the model’s fidelity captures many of the key features measured experimentally and is a step toward a model capable of predicting and improving the spall resistance in many materials

Shock induced damage in copper: A before and after, three-dimensional study

We report on the microstructural features associated with the formation of incipient spall and damage in a fully recrystallized, high purity copper sample. Before and after ballistic shock loading, approximately 0.8 mm3 of the sample's crystal lattice orientation field is mapped using non-destructive near-field High Energy Diffraction Microscopy. Absorption contrast tomography is used to imagevoids after loading. This non-destructive interrogation of damage initiation allows for novel characterization of spall points vis-a-vis microstructural features and a fully 3D examination of microstructural topology and its influence on incipient damage. The spalled region is registered with and mapped back onto the pre-shock orientation field. As expected, the great majority of voids occur at grain boundaries and higher order microstructural features; however, we find no statistical preference for particular grain boundary types. The damaged region contains a large volume of Σ–3 (60°⟨111⟩) connected domains with a large area fraction of incoherent Σ-3 boundaries

Annealing twins in nickel nucleate at triple lines during grain growth

International audienc

Shock induced damage in copper: A before and after, three-dimensional study

We report on the microstructural features associated with the formation of incipient spall and damage in a fully recrystallized, high purity copper sample. Before and after ballistic shock loading, approximately 0.8 mm3 of the sample's crystal lattice orientation field is mapped using non-destructive near-field High Energy Diffraction Microscopy. Absorption contrast tomography is used to imagevoids after loading. This non-destructive interrogation of damage initiation allows for novel characterization of spall points vis-a-vis microstructural features and a fully 3D examination of microstructural topology and its influence on incipient damage. The spalled region is registered with and mapped back onto the pre-shock orientation field. As expected, the great majority of voids occur at grain boundaries and higher order microstructural features; however, we find no statistical preference for particular grain boundary types. The damaged region contains a large volume of Σ–3 (60°⟨111⟩) connected domains with a large area fraction of incoherent Σ-3 boundaries

Observation of annealing twin nucleation at triple lines in nickel during grain growth

International audienceThree-dimensional near-field high-energy X-ray diffraction microscopy has been used to observe the formation of new twinned grains in high purity Ni during annealing at 800 °C. In the fully recrystallized microstructure annealed at 800 °C, twinned grains form along triple lines. Both the grain boundary character and the grain boundary dihedral angles were measured before and after the twin formed. These measurements make it possible to show that although each new twinned grain increases the total grain boundary area, it reduces the total grain boundary energy

Combined near- and far-field high-energy diffraction microscopy dataset for Ti-7Al tensile specimen elastically loaded in situ

High-energy diffraction microscopy (HEDM) constitutes a suite of combined X-ray characterization methods, which hold the unique advantage of illuminating the microstructure and micromechanical state of a material during concurrent in situ mechanical deformation. The data generated from HEDM experiments provides a heretofore unrealized opportunity to validate meso-scale modeling techniques, such as crystal plasticity finite element modeling (CPFEM), by explicitly testing the accuracy of these models at the length scales where the models predict their response. Combining HEDM methods with in situ loading under known and controlled boundary conditions represents a significant challenge, inspiring the recent development of a new high-precision rotation and axial motion system for simultaneously rotating and axially loading a sample. In this paper, we describe the initial HEDM dataset collected using this hardware on an alpha-titanium alloy (Ti-7Al) under in situ tensile deformation at the Advanced Photon Source, Argonne National Laboratory. We present both near-field HEDM data that maps out the grain morphology and intragranular crystallographic orientations and far-field HEDM data that provides the grain centroid, grain average crystallographic orientation, and grain average elastic strain tensor for each grain. Finally, we provide a finite element mesh that can be utilized to simulate deformation in the volume of this Ti-7Al specimen. The dataset supporting this article is available in the National Institute of Standards and Technology (NIST) repository (http://hdl.handle.net/11256/599)

Combined near- and far-field high-energy diffraction microscopy dataset for Ti-7Al tensile specimen elastically loaded in situ

High-energy diffraction microscopy (HEDM) constitutes a suite of combined X-ray characterization methods, which hold the unique advantage of illuminating the microstructure and micromechanical state of a material during concurrent in situ mechanical deformation. The data generated from HEDM experiments provides a heretofore unrealized opportunity to validate meso-scale modeling techniques, such as crystal plasticity finite element modeling (CPFEM), by explicitly testing the accuracy of these models at the length scales where the models predict their response. Combining HEDM methods with in situ loading under known and controlled boundary conditions represents a significant challenge, inspiring the recent development of a new high-precision rotation and axial motion system for simultaneously rotating and axially loading a sample. In this paper, we describe the initial HEDM dataset collected using this hardware on an alpha-titanium alloy (Ti-7Al) under in situ tensile deformation at the Advanced Photon Source, Argonne National Laboratory. We present both near-field HEDM data that maps out the grain morphology and intragranular crystallographic orientations and far-field HEDM data that provides the grain centroid, grain average crystallographic orientation, and grain average elastic strain tensor for each grain. Finally, we provide a finite element mesh that can be utilized to simulate deformation in the volume of this Ti-7Al specimen. The dataset supporting this article is available in the National Institute of Standards and Technology (NIST) repository (http://hdl.handle.net/11256/599)