Using a large-scale, experimentally captured 3D microstructure data set, we implement the generative adversarial network (GAN) framework to learn and generate 3D microstructures of solid oxide fuel cell electrodes.The generated microstructures are visually, statistically, and topologically realistic, with distributions of microstructural parameters, including volume fraction, particle size, surface area, tortuosity, and triple-phase boundary density, being highly similar to those of the original microstructure.These results are compared and contrasted with those from an established, grain-based generation algorithm (DREAM.3D). Importantly, simulations of electrochemical performance, using a locally resolved finite element model, demonstrate that the GAN-generated microstructures closely match the performance distribution of the original, while DREAM.3D leads to significant differences. The ability of the generative machine learning model to recreate microstructures with high fidelity suggests that the essence of complex microstructures may be captured and represented in a compact and manipulatable form.

The laser melting process is accompanied by rapid evolution in temperature,phase, structure, and strain because of its high heating and cooling rates. In this study, the evolution of grains within a thin solid plate of Ni alloy 718 during laser processing was probed with in situ high-energy x-ray diffraction experiments. The high temporal and spatial resolution available in the measurement allowed us to study the rapid evolution of the melted region beneath the surface of the sample. The characterization of the evolution of secondary phases, i.e., Laves and carbide, was captured despite the weak diffracted peaks caused by small volume fractions. Thermal history was estimated based on changes in the lattice spacing from the thermal contraction upon cooling. The temporal variation in 2θwith azimuthal direction revealed the evolution in anisotropy of lattice spacing and thus of the mechanical state during laser processing.

The microstructures of Ti-6Al-4V following laser processing depend primarily on the phase transformation of beta to alpha, but their development is constrained by the rapidly changing temperature in the small fusion zone. In-situ synchrotron X-ray diffraction was utilized to probe the rapid phase evolution in single melt tracks with high angular and temporal resolution. Both fully martensitic and mixed alpha+alpha +beta microstructures were confirmed by microscopy. Cooling rates were inferred from the lattice parameter history and complementary thermal simulation. It was found that the threshold cooling rate for fully martensitic transformation is in the range between 2900 and 6500 degrees C/s. IMPACT STATEMENT High-speed synchrotron X-ray diffraction during operando laser processing suggests a new threshold between martensitic and diffusional phase transformation in Ti-6Al-4V occurring at higher cooling rates than previously reported.

Metal additive manufacturing is a fabrication method that forms a part by fusing layers of powder to one another. An energy source, such as a laser, is commonly used to heat the metal powder sufficiently to cause a molten pool to form, which is known as the melt pool. The melt pool can exist in the conduction or the keyhole mode where the material begins to rapidly evaporate. The interaction between the laser and the material is physically complex and difficult to predict or measure. In this article, high-speed X-ray imaging was combined with immersion ultrasound to obtain synchronized measurements of stationary laser-generated melt pools. Furthermore, two-dimensional and three-dimensional finite-element simulations were conducted to help explain the ultrasonic response in the experiments. In particular, the time-of-flight and amplitude in pulse-echo configuration were observed to have a linear relationship to the depth of the melt pool. These results are promising for the use of ultrasound to characterize the melt pool behavior and for finite-element simulations to aid in interpretation.

A set of IF steel specimens, at several stages of recrystallization, were subjected to EBSD analysis to provide data for a study of primary recrystallization. First, a criterion was defined for detecting the recrystallized grains that combines multiple parameters. The new approach pays particular attention to ensuring that reasonable recrystallized fractions are obtained in both the early and late stages of recrystallization. Using this to partition orientations maps into recrystallized and non-recrystallized grains, the distribution and density of nuclei, their correlation with EBSD parameters and stored energy, and their texture were determined. The evolution of the grain size distribution, microstructure and texture is then discussed in terms of the balance of the two main mechanisms (growth of the recrystallized grains into the deformed matrix and grain growth competition between already recrystallized grains) which occur during recrystallization.

A set of IF steel specimens, at several stages of recrystallization, were subjected to EBSD analysis to provide data for a study of primary recrystallization. First, a criterion was defined for detecting the recrystallized grains that combines multiple parameters. The new approach pays particular attention to ensuring that reasonable recrystallized fractions are obtained in both the early and late stages of recrystallization. Using this to partition orientations maps into recrystallized and non-recrystallized grains, the distribution and density of nuclei, their correlation with EBSD parameters and stored energy, and their texture were determined. The evolution of the grain size distribution, microstructure and texture is then discussed in terms of the balance of the two main mechanisms (growth of the recrystallized grains into the deformed matrix and grain growth competition between already recrystallized grains) which occur during recrystallization.

In this paper, an original approach is proposed to compare modeling and relevant statistical experiments using β-Ti21S Body Centered Cubic (BCC) metal as a challenging benchmark. Our procedure allows the evolution of microstructural defects to be tracked in situ with excellent spatial resolution, while observing a bulk sample region sufficiently large to be statistically representative of the material. We identify multiple mechanisms such as slip transfer, slip traces, pencil glide, etc. We demonstrate that for small plastic strains (<0.25 %) under uniaxial tensile loading, the Schmid law is satisfied statistically. Under these circumstances, changes in Critical Resolved Shear Stress (CRSS) are minimal and accommodation of incompatible deformation between grains has not yet become important. The majority of the observed slip plane traces at the mesoscale corresponds to the 123 family. Fully automated while precise, the reported approach compares this data with four crystal plasticity models, and provides a methodology for similar analyses in other materials.

The elastoplastic transition of a metastable β-Ti alloy, Timetal-18, is studied using in-situ high energy synchrotron X-ray diffraction microscopy (HEDM). The measured evolutions of the complete elastic strain (and stress) tensor(s), resolved shear stress, lattice rotation and rotation of the stress state of the grains are compared with the predictions of the elasto-viscoplastic Micromechanical Analysis of Stress-Strain Inhomogeneities with fast Fourier transform (MASSIF) code instantiated with an experimentally measured microstructure which matched that of the sample. The preferred glide plane of dislocations with ½<111> Burgers vectors of the BCC alloy was explored. It was found that the polycrystalline stress-strain response could be equally well described by any of the candidate glide planes or combinations thereof (i.e., pencil glide). However, simulations involving slip on 112 planes yielded a marginally better description of the individual grain-level responses, as compared to the simulation involving only the 110 planes. The small (typically <1$\,^\circ$) crystallographic reorientations that the grains undergo during the elastoplastic transition, are insufficient to permit discrimination between candidate slip modes. The resolved shear stress (RSS) distributions showed a sharp increase in skewness around macroscopic yield and it was found that the hardening during the elastoplastic transition is primarily due to intergranular interactions. Analysis of hard and soft grains suggests non-Schmid effects may be present, even in these low strain rate, room temperature experiments. Finally, examination of the individual responses revealed strain softening in some of the grains. Intragranular heterogeneity in the orientation and stress state are highlighted as important areas for future investigations, which may reveal answers to unresolved questions in this research.

This work focuses on the use of x-ray computed tomography for non-destructive characterization of additively manufactured parts. Ti-6Al-4V parts manufactured using electron beam melting were used. Within this context a comparative study between laboratory and synchrotron-based x-ray computed tomography (LXCT and SXCT) is presented showing the advantages of both techniques. Additionally, the interplay between field-of-view, resolution and sub-sample extraction is systematically presented both qualitatively and quantitatively for LXCT. Overall, it was concluded that laboratory based μXCT offered a compelling alternative to SXCT for static measurements involving defect characterization in AM parts while synchrotron-based techniques offered unmatched performance for dynamic and sub-micron studies.