@article {2366, title = {Direct electron detection for EBSD of low symmetry \& beam sensitive ceramics}, journal = {Ultramicroscopy}, volume = {268}, year = {2025}, pages = {114079}, abstract = {

Electron backscatter diffraction (EBSD) is a powerful tool for determining the orientations of near-surface grains in engineering materials. However, many ceramics present challenges for routine EBSD data collection and indexing due to small grain sizes, high crack densities, beam and charge sensitivities, low crystal symmetries, and pseudo-symmetric pattern variants. Micro-cracked monoclinic hafnia, tetragonal hafnon, and hafnia/hafnon composites exhibit all such features, and are used in the present work to show the efficacy of a novel workflow based on a direct detecting EBSD sensor and a state-of-the-art pattern indexing approach. At 5 and 10 keV primary beam energies (where beam-induced damage and surface charge accumulation are minimal), the direct electron detector produces superior diffraction patterns with 10x lower doses compared to a phosphor-coupled indirect detector. Further, pseudo-symmetric variant-related indexing errors from a Hough-based approach (which account for at least 4\%-14\% of map areas) are easily resolved by dictionary indexing. In short, the workflow unlocks fundamentally new opportunities to characterize materials historically unsuited for EBSD.

}, keywords = {Beam sensitive materials, Ceramics, Dictionary indexing, Direct electron detection, Electron backscatter diffraction}, author = {Della Ventura, Nicol{\`o} M and Ericks, Andrew R and Echlin, McLean P and Moore, Kalani and Pollock, Tresa M and Begley, Matthew R and Zok, Frank W and De Graef, Marc and Gianola, Daniel S} } @article {2416, title = {Energy-resolved EBSD using a monolithic direct electron detector}, year = {2025}, abstract = {

Accurate quantification of the energy distribution of backscattered electrons (BSEs) contributing to electron backscatter diffraction (EBSD) patterns remains as an active challenge. This study introduces an energy-resolved EBSD methodology based on a monolithic active pixel sensor direct electron detector and an electron-counting algorithm to enable the energy quantification of individual BSEs, providing direct measurements of electron energy spectra within diffraction patterns. Following detector calibration of the detector signal as a function of primary beam energy, measurements using a 12 keV primary beam on Si(100) reveal a broad BSE energy distribution across the diffraction pattern, extending down to 3 keV. Furthermore, an angular dependence in the weighted average BSE energy is observed, closely matching predictions from Monte Carlo simulations. Pixel-resolved energy maps reveal subtle modulations at Kikuchi band edges, offering insights into the backscattering process. By applying energy filtering within spectral windows as narrow as 2 keV centered on the primary beam energy, significant enhancement in pattern clarity and high-frequency detail is observed. Notably, electrons in the 2\–8 keV range, despite having undergone substantial energy loss (\ΔE = 4\–10 keV), still produce Kikuchi patterns. By enabling energy determination at the single-electron level, this approach introduces a versatile tool-set for expanding the quantitative capabilities of EBSD, thereby offering the potential to deepen the understanding of diffraction contrast mechanisms and to advance the precision of crystallographic measurements.

}, author = {Della Ventura, Nicol{\`o} M and Moore, Kalani and Echlin, McLean P and Begley, Matthew R and Pollock, Tresa M and De Graef, Marc and Gianola, Daniel S} } @article {2391, title = {Orientation-Adaptive Virtual Imaging of Defects using EBSD}, year = {2025}, abstract = {

EBSD is a foundational technique for characterizing crystallographic orientation, phase distribution, and lattice strain. Embedded within EBSD patterns lies latent information on dislocation structures, subtly encoded due to their deviation from perfect crystallinity - a feature often underutilized. Here, a novel framework termed orientation-adaptive virtual apertures (OAVA) is introduced. OAVAs enable the generation of virtual images tied to specific diffraction conditions, allowing the direct visualization of individual dislocations from a single EBSD map. By dynamically aligning virtual apertures in reciprocal space with the local crystallographic orientation, the method enhances contrast from defect-related strain fields, mirroring the principles of diffraction-contrast imaging in TEM, but without sample tilting. The approach capitalizes on the extensive diffraction space captured in a single high-quality EBSD scan, with its effectiveness enhanced by modern direct electron detectors that offer high-sensitivity at low accelerating voltages, reducing interaction volume and improving spatial resolution. We demonstrate that using OAVAs, identical imaging conditions can be applied across a polycrystalline field-of-view, enabling uniform contrast in differently oriented grains. Furthermore, in single-crystal GaN, threading dislocations are consistently resolved. Algorithms for the automated detection of dislocation contrast are presented, advancing defect characterization. By using OAVAs across a wide range of diffraction conditions in GaN, the visibility/invisibility of defects, owing to the anisotropy of the elastic strain field, is assessed and linked to candidate Burgers vectors. Altogether, OAVA offers a new and high-throughput pathway for orientation-specific defect characterization with the potential for automated, large-area defect analysis in single and polycrystalline materials.

}, author = {Della Ventura, Nicol{\`o} M and Lamb, James D and Lenthe, William C and Echlin, McLean P and P{\"u}rstl, Julia T and Trageser, Emily S and Quevedo, Alejandro M and Begley, Matthew R and Pollock, Tresa M and Gianola, Daniel S and De Graef, Marc} } @inbook {2336, title = {3D characterization of defects and microstructure in high density LPBF prints of a CoNi alloy}, booktitle = {The Minerals, Metals \& Materials Series}, series = {The minerals, metals \& materials series}, year = {2024}, pages = {811{\textendash}821}, publisher = {Springer Nature Switzerland}, organization = {Springer Nature Switzerland}, address = {Cham}, author = {Lamb, James D and Raeker, Evan B and Pusch, Kira M and Echlin, McLean P and Forsik, Stephane A J and Zhou, Ning and Dicus, Austin D and Pollock, Tresa M} } @article {2286, title = {Deformation mechanisms and defect structures in Heusler intermetallic MnCu2Al}, journal = {Acta Mater.}, volume = {268}, year = {2024}, pages = {119711}, author = {Rhodes, Bailey E and Mayer, Justin A and Xu, Shuozhi and Lamb, James D and Wendorf, Joe and Echlin, McLean P and Pollock, Tresa M and Eggeler, Yolita M and Beyerlein, Irene J and Gianola, Daniel S} } @article {2296, title = {Quantification of melt pool dynamics and microstructure during simulated additive manufacturing}, journal = {Scr. Mater.}, volume = {245}, year = {2024}, pages = {116036}, author = {Lamb, James and Ochoa, Ruben and Eres-Castellanos, Adriana and Klemm-Toole, Jonah and Echlin, McLean P and Sun, Tao and Fezzaa, Kamel and Clarke, Amy and Pollock, Tresa M} } @article {2341, title = {Resolving crystallographic geometrically necessary dislocations in three dimensions in a hexagonal close packed titanium alloy}, journal = {Model. Simul. Mat. Sci. Eng.}, volume = {32}, year = {2024}, pages = {065035}, abstract = {

Abstract Geometrically necessary dislocation (GND) content is measured from mm3-scaled Ti7Al three-dimensional (3D) microstructural data using a theory extended for hexagonal close packed crystals, which accounts for basal, prismatic and pyramidal \⟨ c + a \⟩ type dislocation content. The Ti7Al samples have been mechanically pre-strained to two different strain levels, and will then be strained along the same axis in uniaxial tension during simulation. Both inter- and intragranular GNDs across the microstructures have been characterized, with a large contribution of pyramidal \⟨ c + a \⟩ GNDs, consistent with the relative slip activity involved in pre-straining. The spatially resolved crystallographic GND distributions within the 3D microstructures are used to instantiate a microstructure model for forward modeling deformation simulations by a dislocation density hardening elasto-viscoplastic fast Fourier transform framework. Coarsening the voxel resolution during the initial microstructure construction procedure is shown to strongly impact both the magnitude and spatial distribution of the GNDs and in turn the forward deformation response of the pre-strained material. This study indicates that the voxel resolution desired when transferring from measured to model microstructures need not only be proportionally scaled with the microstructure but also sufficiently fine to capture the subgranular orientation gradients that may already be present in the material.

}, author = {Witzen, Wyatt A and Lamb, James D and Arul Kumar, Mariyappan and Echlin, McLean P and Pollock, Tresa M and Beyerlein, Irene J} } @article {2311, title = {Resolving crystallographic geometrically necessary dislocations in three dimensions in a hexagonal close packed titanium alloy}, journal = {Model. Simul. Mat. Sci. Eng.}, volume = {32}, year = {2024}, pages = {065035}, abstract = {

Abstract Geometrically necessary dislocation (GND) content is measured from mm3-scaled Ti7Al three-dimensional (3D) microstructural data using a theory extended for hexagonal close packed crystals, which accounts for basal, prismatic and pyramidal \⟨ c + a \⟩ type dislocation content. The Ti7Al samples have been mechanically pre-strained to two different strain levels, and will then be strained along the same axis in uniaxial tension during simulation. Both inter- and intragranular GNDs across the microstructures have been characterized, with a large contribution of pyramidal \⟨ c + a \⟩ GNDs, consistent with the relative slip activity involved in pre-straining. The spatially resolved crystallographic GND distributions within the 3D microstructures are used to instantiate a microstructure model for forward modeling deformation simulations by a dislocation density hardening elasto-viscoplastic fast Fourier transform framework. Coarsening the voxel resolution during the initial microstructure construction procedure is shown to strongly impact both the magnitude and spatial distribution of the GNDs and in turn the forward deformation response of the pre-strained material. This study indicates that the voxel resolution desired when transferring from measured to model microstructures need not only be proportionally scaled with the microstructure but also sufficiently fine to capture the subgranular orientation gradients that may already be present in the material.

}, author = {Witzen, Wyatt A and Lamb, James D and Arul Kumar, Mariyappan and Echlin, McLean P and Pollock, Tresa M and Beyerlein, Irene J} } @article {2316, title = {On the role of geometrically necessary dislocations in void formation and growth in response to shock loading conditions in wrought and additively manufactured Ta}, journal = {J. Mater. Res. Technol.}, volume = {31}, year = {2024}, pages = {3035{\textendash}3049}, author = {Lamb, James D and Mullin, Kaitlyn M and Christodoulou, Paul G and Witzen, Wyatt A and Echlin, McLean P and Beyerlein, Irene J and Pollock, Tresa M} } @article {echlin2016incipient, title = {Incipient slip and long range plastic strain localization in microtextured Ti-6Al-4V titanium}, journal = {Acta Materialia}, volume = {114}, year = {2016}, pages = {164{\textendash}175}, publisher = {Pergamon}, author = {Echlin, McLean P and Stinville, Jean Charles and Miller, Victoria M and Lenthe, William C and Pollock, Tresa M} } @article {lenthe2016prediction, title = {Prediction of Fatigue-Initiating Twin Boundaries in Polycrystalline Nickel Superalloys Informed by TriBeam Tomography}, journal = {Microscopy and Microanalysis}, volume = {22}, number = {S3}, year = {2016}, pages = {1732{\textendash}1733}, publisher = {Cambridge University Press}, author = {Lenthe, William C and Stinville, Jean-Charles and Echlin, McLean P and Pollock, Tresa M} } @article {titus2015dislocation, title = {Dislocation injection in strontium titanate by femtosecond laser pulses}, journal = {Journal of Applied Physics}, volume = {118}, number = {7}, year = {2015}, pages = {075901}, publisher = {AIP Publishing}, author = {Titus, Michael S and Echlin, McLean P and Gumbsch, Peter and Pollock, Tresa M} } @article {douglas2015three, title = {Three-dimensional multimodal imaging and analysis of biphasic microstructure in a Ti{\textendash}Ni{\textendash}Sn thermoelectric material}, journal = {APL Materials}, volume = {3}, number = {9}, year = {2015}, pages = {096107}, publisher = {AIP Publishing}, author = {Douglas, Jason E and Echlin, McLean P and Lenthe, William C and Seshadri, Ram and Pollock, Tresa M} } @article {echlin2015tribeam, title = {The TriBeam system: Femtosecond laser ablation in situ SEM}, journal = {Materials Characterization}, volume = {100}, year = {2015}, pages = {1{\textendash}12}, publisher = {Elsevier}, author = {Echlin, McLean P and Straw, Marcus and Randolph, Steven and Filevich, Jorge and Pollock, Tresa M} } @article {echlin2014three, title = {Three-dimensional characterization of the permeability of W{\textendash}Cu composites using a new {\textquotedblleft}TriBeam{\textquotedblright} technique}, journal = {Acta Materialia}, volume = {64}, year = {2014}, pages = {307{\textendash}315}, publisher = {Pergamon}, author = {Echlin, McLean P and Mottura, Alessandro and Wang, Michael and Mignone, Paul J and Riley, Daniel P and Franks, George V and Pollock, Tresa M} } @article {echlin2014three, title = {Three-dimensional sampling of material structure for property modeling and design}, journal = {Integrating Materials and Manufacturing Innovation}, volume = {3}, number = {1}, year = {2014}, pages = {1}, publisher = {Springer Berlin Heidelberg}, author = {Echlin, McLean P and Lenthe, William C and Pollock, Tresa M} } @article {echlin2013statistical, title = {A statistical sampling approach for measurement of fracture toughness parameters in a 4330 steel by 3-D femtosecond laser-based tomography}, journal = {Acta Materialia}, volume = {61}, number = {15}, year = {2013}, pages = {5791{\textendash}5799}, publisher = {Elsevier}, author = {Echlin, McLean P and Pollock, Tresa M} } @article {echlin2012new, title = {A new TriBeam system for three-dimensional multimodal materials analysis}, journal = {Review of Scientific Instruments}, volume = {83}, number = {2}, year = {2012}, pages = {023701}, publisher = {AIP Publishing}, author = {Echlin, McLean P and Mottura, Alessandro and Torbet, Christopher J and Pollock, Tresa M} } @article {echlin2011new, title = {A New Femtosecond Laser-Based Tomography Technique for Multiphase Materials}, journal = {Advanced Materials}, volume = {23}, number = {20}, year = {2011}, pages = {2339{\textendash}2342}, publisher = {Wiley Online Library}, author = {Echlin, McLean P and Husseini, Naji S and Nees, John A and Pollock, Tresa M} }