@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 {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 {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 {1426, title = {Bayesian inference of elastic properties with resonant ultrasound spectroscopy}, journal = {The Journal of the Acoustical Society of America}, volume = {143}, year = {2018}, pages = {71{\textendash}83}, abstract = {

\© 2018 Acoustical Society of America. Bayesian modeling and Hamiltonian Monte Carlo (HMC) are utilized to formulate a robust algorithm capable of simultaneously estimating anisotropic elastic properties and crystallographic orientation of a specimen from a list of measured resonance frequencies collected via Resonance Ultrasound Spectroscopy (RUS). Unlike typical optimization procedures which yield point estimates of the unknown parameters, computing a Bayesian posterior yields probability distributions for the unknown parameters, and HMC is an efficient way to compute this posterior. The algorithms described are demonstrated on RUS data collected from two parallelepiped specimens of structural metal alloys. First, the elastic constants for a specimen of fine-grain polycrystalline Ti-6Al-4 V with random crystallographic texture and isotropic elastic symmetry are estimated. Second, the elastic constants and crystallographic orientation for a single crystal Ni-based superalloy CMSX-4 specimen are accurately determined, using only measurements of the specimen geometry, mass, and resonance frequencies. The unique contributions of this paper are as follows: the application of HMC for sampling the Bayesian posterior of a probabilistic RUS model, and the procedure for simultaneous estimation of elastic constants and lattice-specimen misorientation. Compared to previous approaches these algorithms demonstrate superior convergence behavior, particularly when the initial parameterization is unknown, and enable substantially simplified experimental procedures.

}, issn = {0001-4966}, doi = {10.1121/1.5017840}, author = {Bales, Ben and Petzold, Linda and Goodlet, Brent R. and Lenthe, William C. and Pollock, Tresa M.} } @article {1441, title = {Competing Modes for Crack Initiation from Non-metallic Inclusions and Intrinsic Microstructural Features During Fatigue in a Polycrystalline Nickel-Based Superalloy}, journal = {Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science}, volume = {49}, year = {2018}, pages = {3865{\textendash}3873}, abstract = {

Cyclic fatigue experiments in the high and very high cycle fatigue regimes have been performed on a Ren\é 88DT polycrystalline nickel-based superalloy. The microstructural configurations that favor early strain localization and fatigue crack initiation at high temperature from 400\ \°C to 650\ \°C have been investigated. Competing failure modes are observed in the high to the very high cycle fatigue regime. Fatigue cracks initiate from non-metallic inclusions and from intrinsic internal microstructural features. Interestingly, as stresses are reduced into the very high cycle regime, there is a transition to initiation only at crystallographic facets. At higher stress in the high cycle fatigue regime, a significant fraction of specimens initiate cracks at non-metallic inclusions. This transition is analyzed with regard to microstructural features that favor strain localization and accumulate damage early during cycling.

}, isbn = {1166101847803}, issn = {10735623}, doi = {10.1007/s11661-018-4780-3}, url = {https://doi.org/10.1007/s11661-018-4780-3}, 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 L.P. and Callahan, Patrick G. and Lenthe, William C. and Miao, Jiashi and Wessman, Andrew E. and Finlay, Rebecca and Loghin, Adrian and Marte, Judson 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 {1451, title = {Grain size effects on NiTi shape memory alloy fatigue crack growth}, journal = {Journal of Materials Research}, volume = {33}, year = {2018}, pages = {91{\textendash}107}, abstract = {

Fatigue cracking in polycrystalline NiTi was investigated using a multiscale experimental framework for average grain sizes (GS) from 10 to 1500 nm for the first time. Macroscopic fatigue crack growth rates, measured by optical digital image correlation, were connected to microscopic crack opening and closing displacements, measured by scanning electron microscope DIC (SEM-DIC) using a high-precision external SEM scan controller. Among all grain sizes, the 1500 nm GS sample exhibited the slowest crack growth rate at the macroscale, and the largest crack opening level (stress intensity at first crack opening) and minimum crack opening displacements at the microscale. Smaller GS samples (10, 18, 42, and 80 nm) exhibited nonmonotonic trends in their fatigue performance, yet the correlation was strong between macroscale and microscale behaviors for each GS. The samples that exhibited the fastest crack growth rates (42 and 80 nm GS) showed a small crack opening level and the largest crack opening displacements. The irregular trends in fatigue performance across the nanocrystalline GS samples were consistent with nonmonotonic values in the elastic modulus reported previously, both of which may be related to the presence of residual martensite only evident in the small GS samples (10 and 18 nm).

}, keywords = {fatigue, nanostructure, scanning electron microscopy (SEM)}, issn = {20445326}, doi = {10.1557/jmr.2017.395}, author = {Lepage, William S. and Ahadi, Aslan and Lenthe, William C. and Sun, Qing Ping and Pollock, Tresa M. and Shaw, John A. and Daly, Samantha H.} }