@article {1686, title = {Electron backscattered diffraction using a new monolithic direct detector: High resolution and fast acquisition}, journal = {Ultramicroscopy}, volume = {220}, year = {2021}, pages = {113160}, abstract = {

A monolithic active pixel sensor based direct detector that is optimized for the primary beam energies in scanning electron microscopes is implemented for electron back-scattered diffraction (EBSD) applications. The high detection efficiency of the detector and its large array of pixels allow sensitive and accurate detection of Kikuchi bands arising from primary electron beam excitation energies of 4 keV to 28 keV, with the optimal contrast occurring in the range of 8\–16 keV. The diffraction pattern acquisition speed is substantially improved via a sparse sampling mode, resulting from the acquisition of a reduced number of pixels on the detector. Standard inpainting algorithms are implemented to effectively estimate the information in the skipped regions in the acquired diffraction pattern. For EBSD mapping, an acquisition speed as high as 5988 scan points per second is demonstrated, with a tolerable fraction of indexed points and accuracy. The collective capabilities spanning from high angular resolution EBSD patterns to high speed pattern acquisition are achieved on the same detector, facilitating simultaneous detection modalities that enable a multitude of advanced EBSD applications, including lattice strain mapping, structural refinement, low-dose characterization, 3D-EBSD and dynamic in situ EBSD.

}, keywords = {Direct detection, EBSD, Indexing, Inpainting, SEM, Sparse sampling}, issn = {18792723}, doi = {10.1016/j.ultramic.2020.113160}, url = {https://doi.org/10.1016/j.ultramic.2020.113160}, author = {Wang, Fulin and Echlin, Mclean P. and Taylor, Aidan A. and Shin, Jungho and Bammes, Benjamin and Levin, Barnaby D.A. and De Graef, Marc and Pollock, Tresa M. and Gianola, Daniel S.} } @conference {1596, title = {3D Characterization of the Columnar-to-Equiaxed Transition in Additively Manufactured Inconel 718}, booktitle = {Superalloys 2020}, year = {2020}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {

Additive manufacturing (AM) provides enormous process- ing flexibility, enabling novel part geometries and opti- mized designs. Access to a local heat source further per- mits the potential for local microstructure control on the scale of individual melt pools, which can enable local con- trol of part properties. In order to design tailored process- ing strategies for target microstructures, models predict- ing the columnar-to-equiaxed transition must be extended to the high solidification velocities and complex thermal histories present in AM. Here, we combine 3D charac- terization with advanced modeling techniques to develop a more complete understanding of the solidification pro- cess and evolution of microstructure during electron beam melting (EBM) of Inconel 718. Full calibration of existing microstructure prediction models demonstrates the differ- ences between AM processes and more conventional weld- ing techniques, underlying the need for accurate deter- mination of key parameters that can only be measured directly in 3D. The ability to combine multisensor data in a consistent 3D framework via data fusion algorithms is essential to fully leverage these advanced characteriza- tion approaches. Thermal modeling provides insight on microstructure development within isolated solidification events and demonstrates the role of Marangoni effects on controlling solidification behavior.

}, keywords = {Additive manufacturing, Microstructure, Solidification, Tomography}, isbn = {9783030518349}, doi = {10.1007/978-3-030-51834-9}, url = {http://dx.doi.org/10.1007/978-3-030-51834-9_65}, author = {Polonsky, Andrew T. and Raghavan, Narendran and Echlin, Mclean P. and Kirka, Michael M. and Dehoff, Ryan R. and Pollock, Tresa M.}, editor = {Tin, Sammy and Hardy, Mark and Clews, Justin and Cormier, Jonathan and Feng, Qiang and Marcin, John and O{\textquoteright}Brien, Chris and Suzuki, Akane} } @inbook {1531, title = {Acquisition of 3D Data for Prediction of Monotonic and Cyclic Properties of Superalloys}, booktitle = {Integrated Computational Materials Engineering (ICME): Advancing Computational and Experimental Methods}, year = {2020}, pages = {1{\textendash}18}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, address = {Cham}, abstract = {

The component design and fatigue life prediction of turbine disk alloys are critically dependent on the thermomechanical properties of the material. The TriBeam microscope provides a pathway to capture large, targeted 3D microstructural data volumes from turbine disk alloys in order to instantiate models that are used to simulate mechanical loading and assess material properties. The TriBeam experiments used to capture the microstructure, the analysis methods, data requirements, and future needs for 3D infrastructure will be discussed.

}, isbn = {978-3-030-40562-5}, doi = {10.1007/978-3-030-40562-5_1}, url = {https://doi.org/10.1007/978-3-030-40562-5_1}, author = {Echlin, Mclean P. and Lenthe, William C. and Stinville, Jean-Charles and Pollock, Tresa M.}, editor = {Ghosh, Somnath and Woodward, Christopher and Przybyla, Craig} } @article {1566, title = {Serial sectioning in the SEM for three dimensional materials science}, journal = {Current Opinion in Solid State and Materials Science}, year = {2020}, pages = {100817}, abstract = {

Here we explore the range of serial sectioning techniques that have evolved over the past decade, providing a comprehensive toolkit for capturing rich 3D microstructures, chemistries and crystallographic information, with sub-micron resolution at volumes that extend out to mm3 or even cm3. In each case we consider the challenges associated with their application, the volumes they can analyze, the damage to the surface they impart, and their suitability for different materials. In certain cases these warrant hybrid methods, motivating workflows that leverage multiple sectioning modes within the same instrument. Finally, we provide a perspective on their future development, including advances in data collection, segmentation, registration, data fusion, and correlative microscopy. Furthermore, the exploitation of 3D techniques for a better understanding of existing materials, and the design of new ones, is discussed through their use in multiscale modelling, digital twinning, material informatics and machine learning frameworks.

}, keywords = {Biology, Life sciences, Materials science, Scanning electron microscopy, Serial sectioning}, issn = {13590286}, doi = {10.1016/j.cossms.2020.100817}, url = {https://doi.org/10.1016/j.cossms.2020.100817}, author = {Echlin, Mclean P. and Burnett, Timothy L. and Polonsky, Andrew T. and Pollock, Tresa M. and Withers, Philip J.} } @article {1406, title = {Solidification-driven orientation gradients in additively manufactured stainless steel}, journal = {Acta Materialia}, volume = {183}, year = {2020}, pages = {249{\textendash}260}, abstract = {

A sample of 304L stainless steel manufactured by Laser Engineered Net Shaping (LENS) was characterized in 3D using TriBeam tomography. The crystallographic, structural, and chemical properties of the as-deposited microstructure have been studied in detail. 3D characterization reveals complex grain morphologies and large orientation gradients, in excess of 10o, that are not easily interpreted from 2D cross-sections alone. Misorientations were calculated via a methodology that locates the initial location and orientation of grains that grow during the build process. For larger grains, misorientation increased along the direction of solidification. For grains with complex morphologies, K-means clustering in orientation space is demonstrated as a useful approach for determining the initial growth orientation. The gradients in misorientation directly tracked with gradients in chemistry predicted by a Scheil analysis. The accumulation of misorientation is linked to the solutal and thermal solidification path, offering potential design pathways for novel alloys more suited for additive manufacturing.

}, keywords = {Additive manufacturing, Microstructure, Solidification, Tomography, Tribeam}, issn = {13596454}, doi = {10.1016/j.actamat.2019.10.047}, author = {Polonsky, Andrew T. and Lenthe, William C. and Echlin, Mclean P. and Livescu, Veronica and Gray, George T. and Pollock, Tresa M.} } @article {1586, title = {Twin related domain networks in Ren{\'e} 88DT}, journal = {Materials Characterization}, volume = {165}, year = {2020}, pages = {110365}, abstract = {

Annealing twins in wrought fcc materials have historically been characterized using simple 2D measures including morphology and volume fraction. Accurately describing twin related domain microstructure requires accounting for their complex 3D structure. A large microstructural volume of a nickel-base alloy Ren\é 88DT has been collected using TriBeam tomography for full characterization of a large number of complete twin related domains. A network based approach enables visualization of twin domain structures. Metrics adapted from graph theory enable the first quantitative 3D microstructure descriptions. The implications for fatigue properties in twinned nickel-base alloys are discussed.

}, keywords = {3D EBSD, Annealing twin boundaries, Graph theory, Nickel-base superalloy, Recrystallization, Tribeam, Twins}, issn = {10445803}, doi = {10.1016/j.matchar.2020.110365}, url = {https://doi.org/10.1016/j.matchar.2020.110365}, author = {Lenthe, William C. and Echlin, Mclean P. and Stinville, Jean C. and De Graef, Marc and Pollock, Tresa M.} } @article {1386, title = {Computational homogenization for multiscale forward modeling of resonant ultrasound spectroscopy of heterogeneous materials}, journal = {Materials Characterization}, volume = {158}, year = {2019}, pages = {109945}, abstract = {

We present a computational framework for multiscale forward modeling of ultrasound resonance in heterogeneous materials that accounts for microstructure. The approach includes two steps. The first step is the accurate determination of the elastic properties of heterogeneous materials with finite element simulations on a representative volume element of the microstructure at the mesoscopic length scale. The second step is modeling resonance frequencies of a macroscopic component made of an effective homogeneous medium having the same elastic properties as the actual material with microstructure. The approach is validated in a case study on a Cu\–W two-phase composite, for which resonance frequencies predicted with the proposed framework are compared against the experimental measurements. The present multiscale modeling approach, involving computational homogenization and leveraging 3D microstructure data, showed better accuracy compared to classical Voigt/Reuss bounds often used for forward modeling of resonant ultrasound spectroscopy.

}, keywords = {Computational homogenization, Finite elements, Forward modeling, Non-destructive evaluation, Resonant ultrasound spectroscopy}, issn = {10445803}, doi = {10.1016/j.matchar.2019.109945}, url = {https://doi.org/10.1016/j.matchar.2019.109945}, author = {Latypov, Marat I. and Charpagne, Marie Agathe and Souther, Mason and Goodlet, Brent R. and Echlin, Mclean P. and Beyerlein, Irene J. and Pollock, Tresa M.} } @article {1356, title = {Dislocation dynamics in a nickel-based superalloy via in-situ transmission scanning electron microscopy}, journal = {Acta Materialia}, volume = {168}, year = {2019}, pages = {152{\textendash}166}, abstract = {

Micro-tensile specimens of nickel-based superalloy oligocrystals were tested in-situ in an scanning electron microscope in transmission mode (TSEM) enabling observation of dislocations. The dynamics of dislocation motion during tensile loading were captured and correlated with the measured intermittencies during plastic flow recorded by high load- and temporal-resolution sensors. This investigation in particular focused on the dislocation behavior near twin boundaries with different slip configurations. A multiplicity of deformation mechanisms at the dislocation scale were observed within individual slip bands, including precipitate shearing, dislocation decorrelation and antiphase boundary-coupled shearing. These processes affect strain localization near twin boundaries and provide new defect-level insights on plastic localization and fatigue crack initiation in these alloys.

}, keywords = {Dislocations dynamic, In-situ transmission scanning electron microscopy (TSEM), Nickel-based superalloy ren{\'e} 88DT, Plastic localization, STEM detector, Twin boundary}, issn = {13596454}, doi = {10.1016/j.actamat.2018.12.061}, url = {https://doi.org/10.1016/j.actamat.2018.12.061}, author = {Stinville, J. C. and Yao, Eric R. and Callahan, Patrick G. and Shin, Jungho and Wang, Fulin and Echlin, Mclean P. and Pollock, Tresa M. and Gianola, Daniel S.} } @article {1496, title = {Short crack propagation from cracked non-metallic inclusions in a Ni-based polycrystalline superalloy}, journal = {Acta Materialia}, volume = {165}, year = {2019}, pages = {241{\textendash}258}, abstract = {

Fatigue cracks initiating from surface and sub-surface non-metallic inclusions (NMIs) have recently been demonstrated to be a necessary but not sufficient explanation for atypically short low-cycle fatigue life in Inconel 718 alloy at intermediate temperature. Therefore, the early stages of short crack propagation from surface NMIs were investigated in a crystallographic and two-dimensional versus three-dimensional morphological manner after room temperature low cycle fatigue (LCF) testing. In the present investigation, NMIs were purposely pre-cracked using different techniques to suppress the natural crack initiation period and thus the incubation period prior to the early stages of crack propagation. Under such fatigue testing conditions, different mechanisms of crack transmission from pre-cracked NMIs were identified: (i) no propagation, (ii) NMI/adjacent metallic grain interfacial debonding, (iii) transgranular crack propagation within the adjacent metallic grain. Focused-ion-beam cross-section observations of numerous fatigue tested NMIs aimed to define a morphological criterion for non-propagating NMIs. Large cracked NMIs at the surface (2c) with limited extension into the depth (a) did not propagate under such fatigue conditions for 2c/a ratio higher than 3. Furthermore, specific crystallographic relationships between NMIs and the adjacent metallic grain explained different crack propagation configurations from pre-cracked NMIs, i.e. interfacial debonding and transgranular crack propagation involving single or multiple-slip activity.

}, keywords = {Focus-ion-beam cross-section (FIB-cross section), Low cycle fatigue, Non-metallic inclusions, Short crack propagation, Superalloy 718DA}, issn = {13596454}, doi = {10.1016/j.actamat.2018.11.051}, author = {Texier, Damien and Stinville, Jean Charles and Echlin, Mclean P. and Pierret, St{\'e}phane and Villechaise, Patrick and Pollock, Tresa M. and Cormier, Jonathan} } @article {1431, title = {Advanced detector signal acquisition and electron beam scanning for high resolution SEM imaging}, journal = {Ultramicroscopy}, volume = {195}, year = {2018}, pages = {93{\textendash}100}, abstract = {

The advancement of materials science at the mesoscale requires improvements in both sampling volumes/areas and spatial resolution in order to make statistically significant measurements of microstructures that influence higher-order material properties, such as fatigue and fracture. Therefore, SEM-based techniques have become desirable due to improvements in imaging resolution, large sample handling capability, and flexibility for in-situ instrumentation. By using fast sampling of SEM electron detector signals, intrinsic beam scanning defects have been identified that are related to the response time of the SEM electron beam deflectors and electron detectors. Mitigation of these beam scanning defects using detector sampling approaches and an adaptive model for settling time is shown to produce higher resolution SEM images, at faster image acquisition times, with a means to quantify the different response functions for various beam deflectors and detectors including those for electrons and ions.

}, keywords = {High resolution digital image correlation, Image processing, Imaging defects, Scan generator, Scanning electron microscopy, SEM}, issn = {18792723}, doi = {10.1016/j.ultramic.2018.08.025}, url = {https://doi.org/10.1016/j.ultramic.2018.08.025}, author = {Lenthe, William C. and Stinville, Jean Charles and Echlin, Mclean P. and Chen, Zhe and Daly, Samantha and Pollock, Tresa M.} } @article {1326, title = {Defects and 3D structural inhomogeneity in electron beam additively manufactured Inconel 718}, journal = {Materials Characterization}, volume = {143}, year = {2018}, pages = {171{\textendash}181}, abstract = {

Material structure and defects created during additive manufacturing contribute to the variability in mechanical properties of these parts, limiting their use for critical applications. Three-dimensional crystallographic, structural, and chemical information in electron beam melted Inconel 718 was collected from the sub-micron to the millimeter scale using the TriBeam tomography system. The relationship of defects to the surrounding microstructure has been studied in detail. Lack of fusion defects created sharp discontinuities in the grain morphology that extended several build layers beyond the layer where the defect originated. Nitrides and carbides in the size range of 1.25 \μm to 10 \μm were observed throughout the volume, with pronounced nitride clustering. The similarities between solidification in additive manufacturing and traditional manufacturing processes are demonstrated by the comparable size and distribution of carbides measured for industrial-scale samples of 718. Defects created during additive manufacturing cannot be easily remedied via standard post-processing techniques, and will likely diminish the mechanical performance of additively manufactured parts.

}, keywords = {Additive manufacturing, Electron beam melting, Lack of fusion, Microstructure, Tomography}, issn = {10445803}, doi = {10.1016/j.matchar.2018.02.020}, author = {Polonsky, Andrew T. and Echlin, Mclean P. and Lenthe, William C. and Dehoff, Ryan R. and Kirka, Michael M. and Pollock, Tresa M.} } @article {1346, title = {Fatigue deformation in a polycrystalline nickel base superalloy at intermediate and high temperature: Competing failure modes}, journal = {Acta Materialia}, volume = {152}, year = {2018}, pages = {16{\textendash}33}, abstract = {

The microstructural configurations that favor early strain localization and fatigue crack initiation at intermediate and high temperature (400 \°C\–650 \°C) have been investigated using novel experimental techniques, including high resolution digital image correlation and transmission scanning electron microscopy. Cyclic fatigue experiments in the high and low cycle fatigue regimes have been performed on a Ren\é 88DT polycrystalline nickel-base superalloy at temperatures up to 650 \°C and compared to previous fatigue results obtained from tests in the very high cycle fatigue regime. Competing failure modes are observed along with an inversion in the temperature fatigue life dependence of fatigue strength from the low to high cycle fatigue regime. Oxidation-assisted processes are dominant at high applied stresses while cyclic plastic localization and accumulation govern fracture at low applied stresses. In addition, a second competing mode exists in the high and very high cycle fatigue regime from non-metallic inclusions as compared to internal intrinsic initiation sites. The grain-scale features that exhibit strain localization and crack initiation were investigated in detail. Transmission electron microscopy (TEM), transmission scanning electron microscopy (TSEM) and electron channeling contrast imaging have been conducted on samples removed from targeted regions with microstructural configurations that favor crack initiation to characterize the associated dislocation sub-structure and its evolution with temperature. Plasticity is observed to be less localized during cyclic loading at high temperature compared to room temperature. The microstructural features that drive initiation across the temperature range investigated are: twin-parent grains pairs that are at the upper end of the size distribution, are oriented for near maximum elastic modulus mismatch, and have high stresses along planes parallel to the twin boundaries.

}, keywords = {Coherent twin boundary, Elastic anisotropy, Fatigue crack initiation at intermediate and high temperature, High resolution digital image correlation, Microstructural effect, Polycrystalline microstructure, Ren{\'e} 88DT polycrystalline superalloy, Strain localization}, issn = {13596454}, doi = {10.1016/j.actamat.2018.03.035}, url = {https://doi.org/10.1016/j.actamat.2018.03.035}, author = {Stinville, Jean Charles and Martin, Etienne and Karadge, Mallikarjun and Ismonov, Shak and Soare, Monica and Hanlon, Tim and Sundaram, Sairam and Echlin, Mclean P. and Callahan, Patrick G. and Lenthe, William C. and Miller, V. M. and Miao, Jiashi and Wessman, Andrew E. and Finlay, Rebecca and Loghin, Adrian and Marte, Judson and Pollock, Tresa M.} } @article {1486, title = {Femtosecond laser rejuvenation of nanocrystalline metals}, journal = {Acta Materialia}, volume = {156}, year = {2018}, pages = {183{\textendash}195}, abstract = {

Nanocrystalline metals are distinct from traditional engineering materials due to their high concentration of grain boundaries and corresponding structural disorder at grain boundaries. The effect of local disorder in nanocrystalline materials manifests in ways reminiscent of fully amorphous materials, such as mesoscale shear localization and pressure-dependent yielding, owing to the high concentration of grain boundaries and their predominance in governing plasticity. Relaxation processes in nanocrystalline materials that facilitate reconfigurations of grain boundaries and lower their energy, such as low temperature annealing, have been shown to enhance mechanical strength. However, processes that raise the energy of a nanocrystalline metal have not been observed, limiting the tunability of properties and the prospect for suppressing shear localization. Here, we use femtosecond laser processing as a unique non-equilibrium process that can generate complex stress states due to ultrafast electronic excitation and subsequent relaxation events. Experiments on nanocrystalline Al-O and Cu-Zr alloys indicate that sub-ablation femtosecond laser pulses cause up to an 87\% reduction in hardness with no change in grain size, which can be ascribed to grain boundary-mediated processes. Parallels between our results and rejuvenation processes in glassy systems will be discussed in the context of controlling metastable structural configurations through novel processing routes.

}, keywords = {Femtosecond lasers, Grain boundaries, Nanocrystalline, Rejuvenation}, issn = {13596454}, doi = {10.1016/j.actamat.2018.06.027}, url = {https://doi.org/10.1016/j.actamat.2018.06.027}, author = {Balbus, Glenn H. and Echlin, Mclean P. and Grigorian, Charlette M. and Rupert, Timothy J. and Pollock, Tresa M. and Gianola, Daniel S.} } @article {1481, title = {Prediction of tensile stiffness and strength of Ti-6Al-4V using instantiated volume elements and crystal plasticity}, journal = {Acta Materialia}, volume = {157}, year = {2018}, pages = {21{\textendash}32}, abstract = {

Based on simulations of tensile tests, the macroscopic stiffness and strength of the \α phase of Ti-6Al-4V are estimated. Sets of virtual samples are instantiated using characterization data from three-dimensional electron back-scattered diffraction (EBSD) scans collected with the TriBeam microscope and local properties extracted from in situ loading high-energy x-ray diffraction (HEXD) experiments. The simulations use a crystal-scale finite element framework to compute the mechanical response of the virtual samples under tensile loading. From the simulation data, mechanical properties are extracted from volume elements ranging in size from a fraction of the gage section to its entire length. To detect macroscopic yield, a flood-fill algorithm is used to identify a zone of plastically deformed finite elements extending through a volume element. Trends in the estimated properties as functions of the volume element size are examined. The lower bound of volume element size necessary to replicate experimentally measured macroscale properties is indicated. The technique and results provide a guideline for estimating macroscale property values in components designed with size smaller than the lower bound due to constraint.

}, keywords = {Crystal plasticity finite element, Stiffness, Titanium, Volume element size, Yield detection}, issn = {13596454}, doi = {10.1016/j.actamat.2018.07.011}, url = {https://doi.org/10.1016/j.actamat.2018.07.011}, author = {Chatterjee, Kamalika and Echlin, Mclean P. and Kasemer, Matthew and Callahan, Patrick G. and Pollock, Tresa M. and Dawson, Paul} } @article {1446, title = {Electrically pumped continuous wave quantum dot lasers epitaxially grown on patterned, on-Axis (001) Si}, journal = {Optics Express}, volume = {25}, year = {2017}, pages = {3927{\textendash}3934}, keywords = {III-V on Silicon, Monolithic Integration, Quantum dot lasers, Silicon Photonics}, isbn = {9784885523069}, issn = {08999406}, doi = {10.1364/ol.42.000338}, author = {Norman, Justin and Kennedy, M.J. and Selvidge, Jennifer and Li, Quang and Wan, Yating and Liu, Alan Y. and Callahan, Patrick G. and Echlin, Mclean P. and Pollock, Tresa M. and Lau, Kei May and Gossard, Arthur C. and Bowers, John E.} } @article {1256, title = {Modelling the elastic properties of bi-continuous composite microstructures captured with TriBeam serial-sectioning}, journal = {Computational Materials Science}, volume = {131}, year = {2017}, pages = {187{\textendash}195}, doi = {10.1016/j.commatsci.2017.01.026}, author = {Mignone, Paul J. and Echlin, Mclean P. and Pollock, Tresa M. and Finlayson, Trevor R. and Riley, Daniel P. and Sesso, Mitchell L. and Franks, George V.} } @article {1201, title = {Reconstruction of Laser-Induced Surface Topography from Electron Backscatter Diffraction Patterns}, journal = {Microscopy and Microanalysis}, volume = {23}, year = {2017}, pages = {730{\textendash}740}, doi = {10.1017/s1431927617012326}, author = {Callahan, Patrick G. and Echlin, Mclean P. and Pollock, Tresa M. and Graef, Marc De} }