@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.} } @article {1661, title = {Influence of plastic deformation on the magnetic properties of Heusler MnAu2Al}, journal = {Phys. Rev. Materials}, volume = {5}, year = {2021}, month = {01/2021}, chapter = {014408}, abstract = {

The Heulser intermetallic\ MnAu2Al\ is shown to undergo a dramatic change in net magnetization in response to plastic deformation. A mechanism is proposed involving antiferromagnetic interactions in the otherwise ferromagnetic compound (when ordered) that arise due to chemical changes at the antiphase boundaries created by the deformation. The coupling between chemical and magnetic order across antiphase boundaries is likely to occur in other ordered magnetic systems and may provide an explanation for otherwise anomalous magnetic behavior across several systems, including other Heusler intermetallics.

}, doi = {https://doi.org/10.1103/PhysRevMaterials.5.014408}, url = {https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.5.014408}, author = {Levin, Emily E. and Kitchaev, Daniil A. and Eggeler, Yolita M and Mayer, Justin A. and Behera, Piush and Gianola, Daniel S. and Van der Ven, Anton and Pollock, Tresa M. and Seshadri, Ram} } @article {1691, title = {Multiplicity of dislocation pathways in a refractory multiprincipal element alloy}, journal = {Science}, volume = {370}, year = {2020}, pages = {95{\textendash}101}, abstract = {

Refractory multiprincipal element alloys (MPEAs) are promising materials to meet the demands of aggressive structural applications, yet require fundamentally different avenues for accommodating plastic deformation in the body-centered cubic (bcc) variants of these alloys. We show a desirable combination of homogeneous plastic deformability and strength in the bcc MPEA MoNbTi, enabled by the rugged atomic environment through which dislocations must navigate. Our observations of dislocation motion and atomistic calculations unveil the unexpected dominance of nonscrew character dislocations and numerous slip planes for dislocation glide. This behavior lends credence to theories that explain the exceptional high temperature strength of similar alloys. Our results advance a defect-aware perspective to alloy design strategies for materials capable of performance across the temperature spectrum.

}, issn = {10959203}, doi = {10.1126/science.aba3722}, author = {Wang, Fulin and Balbus, Glenn H. and Xu, Shuozhi and Su, Yanqing and Shin, Jungho and Rottmann, Paul F. and Knipling, Keith E. and Stinville, Jean Charles and Mills, Leah H. and Senkov, Oleg N. and Beyerlein, Irene J. and Pollock, Tresa M. and Gianola, Daniel S.} } @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 {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.} }