@article {1846, title = {Inducing skyrmion flop transitions in Co 8 Zn 8 Mn 4 at room temperature}, journal = {Physical Review Materials}, volume = {7}, year = {2023}, month = {04}, doi = {10.1103/PhysRevMaterials.7.044401}, author = {Meynell, Simon and Eggeler, Yolita and Bocarsly, Joshua and Kitchaev, Daniil and Rhodes, Bailey and Pollock, Tresa and Wilson, Stephen and Ven, Anton and Seshadri, Ram and Graef, Marc and Jayich, Ania and Gianola, Daniel} } @article {2026, title = {Development of grain-scale slip activity and lattice rotation fields in Inconel 718}, journal = {Acta Materialia}, volume = {226}, year = {2022}, month = {01}, pages = {117627}, doi = {10.1016/j.actamat.2022.117627}, author = {Hestroffer, Jonathan and Latypov, Marat and Stinville, Jean-Charles and Charpagne, Marie-agathe and Valle, Valery and Miller, Matthew and Pollock, Tresa and Beyerlein, Irene} } @article {1956, title = {Heterogeneous slip localization in an additively manufactured 316L stainless steel}, journal = {International Journal of Plasticity}, volume = {159}, year = {2022}, month = {09}, pages = {103436}, doi = {10.1016/j.ijplas.2022.103436}, author = {Bean, Christopher and Wang, Fulin and Charpagne, Marie-agathe and Villechaise, P. and Valle, Valery and Agnew, S.R. and Gianola, D.S. and Pollock, T.m. and Stinville, Jean-Charles} } @article {1966, title = {Multi-modal Dataset of a Polycrystalline Metallic Material: 3D Microstructure and Deformation Fields}, journal = {Scientific Data}, volume = {9}, year = {2022}, month = {08}, doi = {10.1038/s41597-022-01525-w}, author = {Stinville, Jean-Charles and Hestroffer, Jonathan and Charpagne, Marie-agathe and Polonsky, Andrew and Echlin, M. and Torbet, Chris and Valle, Valery and Nygren, K. and Miller, M. and Klaas, Ottmar and Loghin, Adrian and Beyerlein, I. and Pollock, T.} } @article {2006, title = {Observation of bulk plasticity in a polycrystalline titanium alloy by diffraction contrast tomography and topotomography}, journal = {Materials Characterization}, volume = {188}, year = {2022}, month = {04}, pages = {111891}, doi = {10.1016/j.matchar.2022.111891}, author = {Stinville, Jean-Charles and Ludwig, Wolfgang and Callahan, P.G. and Echlin, M.P. and Valle, Valery and Pollock, T.m. and Proudhon, Henry} } @article {1951, title = {On the origins of fatigue strength in crystalline metallic materials}, journal = {Science}, volume = {377}, year = {2022}, month = {09}, pages = {1065-1071}, doi = {10.1126/science.abn0392}, author = {Stinville, Jean-Charles and Charpagne, Marie-agathe and Cervellon, Alice and H{\'e}mery, Samuel and Wang, Fulin and Callahan, P. and Valle, Valery and Pollock, T.} } @article {1811, title = {Single crystal elastic constants of additively manufactured components determined by resonant ultrasound spectroscopy}, journal = {Materials Characterization}, volume = {192}, year = {2022}, pages = {112244}, abstract = {

Bayesian inference with Sequential Monte Carlo was used to determine the single crystal elastic constants of additively manufactured (AM) cobalt-nickel-based superalloy specimens from only the resonant frequencies and texture data. This novel framework enables the quantification of the single crystal elastic constants for AM and polycrystalline specimens using only electron backscatter diffraction (EBSD) and Resonant Ultrasound Spectroscopy (RUS), avoiding the expense of bulk single crystal fabrication or synchrotron experiments. A parallelizable and open-source Python package (SMCPy) was used to perform Bayesian inference of the single crystal elastic constants from resonant frequencies of AM specimens. The single crystal elastic constants determined from AM cobalt-nickel-base superalloy specimens were validated with measurements of the single crystal elastic constants on a bulk single crystal specimen. EBSD texture data was used to determine the single crystal elastic constants from the resonant frequencies of AM specimens, and validated with neutron diffraction data by considering the experimental uncertainty in both the EBSD and neutron diffraction data. The robustness of this framework for varied texture orientations relative to the build direction (BD) was demonstrated for AM specimens printed at 0\° and 20\° BD-inclinations.

}, issn = {1044-5803}, doi = {https://doi.org/10.1016/j.matchar.2022.112244}, url = {https://www.sciencedirect.com/science/article/pii/S1044580322005265}, author = {Jeff Rossin and Patrick Leser and Kira Pusch and Carolina Frey and Sven C. Vogel and Alec I. Saville and Chris Torbet and Amy J. Clarke and Samantha Daly and Tresa M. Pollock} } @article {2096, title = {High-throughput approach for estimation of intrinsic barriers in FCC structures for alloy design}, journal = {Scripta Materialia}, volume = {204}, year = {2021}, month = {07}, pages = {114126}, doi = {10.1016/j.scriptamat.2021.114126}, author = {Vamsi, K V and Charpagne, Marie-agathe and Pollock, Tresa} } @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 {1761, title = {Precipitate Shearing, Fault Energies, and Solute Segregation to Planar Faults in Ni-, CoNi-, and Co-Base Superalloys}, journal = {Annual Review of Materials Research}, volume = {51}, year = {2021}, pages = {209-240}, abstract = {

The mechanical properties of superalloys are strongly governed by the resistance to shearing of ordered precipitates by dislocations. In the operating environments of superalloys, the stresses and temperatures present during thermomechanical loading influence the dislocation shearing dynamics, which involve diffusion and segregation processes that result in a diverse array of planar defects in the ordered L12 \γ\′ precipitate phase. This review discusses the current understanding of high-temperature deformation mechanisms of \γ\′ precipitates in two-phase Ni-, Co-, and CoNi-base superalloys. The sensitivity of planar fault energies to chemical composition results in a variety of unique deformation mechanisms, and methods to determine fault energies are therefore reviewed. The degree of chemical segregation in the vicinity of planar defects reveals an apparent phase transformation within the parent \γ\′ phase. The kinetics of segregation to linear and planar defects play a significant role in high-temperature properties. Understanding and controlling fault energies and the associated dislocation dynamics provide a new pathway for the design of superalloys with exceptional properties.

}, doi = {10.1146/annurev-matsci-102419-011433}, url = {https://doi.org/10.1146/annurev-matsci-102419-011433}, author = {Eggeler, Y.M. and Vamsi, K.V. and Pollock, T.m.} } @article {2106, title = {Slip localization in Inconel 718: A three-dimensional and statistical perspective}, journal = {Acta Materialia}, volume = {215}, year = {2021}, month = {06}, pages = {117037}, doi = {10.1016/j.actamat.2021.117037}, author = {Charpagne, Marie-agathe and Hestroffer, Jonathan and Polonsky, Andrew and Echlin, M.P. and Texier, Damien and Valle, Valery and Beyerlein, I.J. and Pollock, T.m. and Stinville, Jean-Charles} } @article {2071, title = {Strain Localization and Fatigue Crack Formation at ( 0001 ) Twist Boundaries in Titanium Alloys}, journal = {Acta Materialia}, volume = {219}, year = {2021}, month = {08}, pages = {117227}, doi = {10.1016/j.actamat.2021.117227}, author = {H{\'e}mery, Samuel and Stinville, Jean-Charles and Wang, Fulin and Charpagne, Marie-agathe and Emigh, M.G. and Pollock, T.m. and Valle, Valery} } @article {1416, title = {Automated and quantitative analysis of plastic strain localization via multi-modal data recombination}, journal = {Materials Characterization}, volume = {163}, year = {2020}, pages = {110245}, issn = {10445803}, doi = {10.1016/j.matchar.2020.110245}, url = {https://linkinghub.elsevier.com/retrieve/pii/S1044580319335569}, author = {Charpagne, M.A. and Stinville, J.C. and Callahan, P.G. and Texier, D. and Chen, Z. and Villechaise, P. and Valle, V. and Pollock, T.m.} } @article {1571, title = {Design of Nickel-Cobalt-Ruthenium Multi-Principal Element Alloys}, journal = {Acta Materialia}, year = {2020}, pages = {16013}, keywords = {Alloy design, Density functional theory, High Entropy Alloys, planar fault energies, TRIP, TWIP}, issn = {1359-6454}, doi = {10.1016/j.actamat.2020.05.003}, url = {https://doi.org/10.1016/j.actamat.2020.05.003}, author = {Charpagne, M A and Vamsi, K V and Eggeler, Y M and Murray, S P and Frey, C and Kolli, S K and Pollock, T M} } @article {1411, title = {Direct measurements of slip irreversibility in a nickel-based superalloy using high resolution digital image correlation}, journal = {Acta Materialia}, volume = {186}, year = {2020}, pages = {172{\textendash}189}, abstract = {

Fatigue crack nucleation in crystalline materials typically develops due to highly localized cyclic slip. During a fatigue cycle, reverse slip differs locally from slip in the forward direction particularly in precipitate-containing materials such as superalloys. In this paper we report the first direct measurements of irreversibility at the scale of individual slip bands by high-resolution digital image correlation (DIC) in a polycrystalline nickel-based superalloy. Quantitative measurements of the slip irreversibility are challenging for regions of material that have a size that captures the microstructure and its variability. High spatial resolution at the nanometer scale during experimental measurements is needed to observe slip localization during deformation. Moreover, large fields are also needed to obtain the material response over statistically representative populations of microstructural configurations. Recently, high resolution scanning electron microscope (SEM) digital image correlation (DIC) has been extended for quantitative analysis of discontinuities induced by slip events using the Heaviside-DIC method. This novel method provides quantitative measurements of slip localization at the specimen surface. In this paper, the Heaviside-DIC method is used to measure slip irreversibility and plastic strain accumulation in a nickel-based superalloy. The method detects bands with high levels of irreversibility early in cycling that ultimately form fatigue cracks upon further cycling. The local microstructural configurations that induce large amounts of plasticity and slip irreversibility are correlated to crack nucleation locations.

}, keywords = {Heaviside-digital image correlation, High resolution digital image correlation, Low cycle fatigue, Polycrystalline Ren{\'e} 88DT nickel-based superalloy, Scanning electron microscopy digital image correlation, Slip irreversibility, Strain localization and accumulation}, issn = {13596454}, doi = {10.1016/j.actamat.2019.12.009}, url = {https://doi.org/10.1016/j.actamat.2019.12.009}, author = {Stinville, J. C. and Callahan, P. G. and Charpagne, M. A. and Echlin, M. P. and Valle, V. and Pollock, T. M.} } @article {1626, title = {Measurement of elastic and rotation fields during irreversible deformation using Heaviside-digital image correlation}, journal = {Materials Characterization}, volume = {169}, year = {2020}, month = {11/2020}, pages = {110600}, abstract = {

The recent development of the high resolution and discontinuity-tolerant digital image correlation technique enables the extraction of discontinuities within a displacement field. The technique provides quantitative analysis of discontinuities arising from slip, shear bands, cracks, and grain boundary sliding in a variety of material systems, including polycrystalline metallic materials. The discontinuity-tolerant digital image correlation method can be implemented to retrieve not only quantitative discontinuity analysis but also the local strain and rotation fields that operate near these discontinuities. The present implementation includes high-resolution digital image correlation (HR-DIC) measurements collected in a scanning electron microscope for analysis of both the plastic and elastic fields that develop during deformation of polycrystalline metallic materials. The combination of the discontinuity-tolerant DIC technique with the computation of internal gradients enables extraction of non-localized strain and rotation fields during plastic deformation of a nickel-based superalloy. Therefore the lattice rotation/expansion and plastic localization that occur during deformation can be determined in a single experiment. This method is validated using synthetic images with preset deformation, and experimental measurements using the electron back scatter diffraction (EBSD) technique.

}, doi = {https://doi.org/10.1016/j.matchar.2020.110600}, url = {https://www.sciencedirect.com/science/article/abs/pii/S1044580320320714}, author = {J.C. Stinville and M.A. Charpagne and F. Bourdin and P.G. Callahan and Z. Chen and M.P. Echlin and D. Texier and J. Cormier and P. Villechaise and T.M. Pollock and V. Valle} } @article {1331, title = {A new proximate structure for the APB (111) in L12 compounds}, journal = {Scripta Materialia}, volume = {182}, year = {2020}, pages = {38{\textendash}42}, abstract = {

A new approach which involves a diffuse multi-layer fault model coupled with a cluster approach to statistical mechanics (CASM) infrastructure has been developed to identify the proximate structure for the antiphase boundary (APB) on {111} planes in L12. We report a new structure, \‘\γa\′\&$\#$39; which approximates the bonding environment of an APB better than a previously reported structure, \‘\ω\&$\#$39;. Density functional theory calculations were employed to predict the APB energies from structural energies of \γa\′ and L12 and were validated against estimations from supercell methods for several binary compounds. The implications of the discovery of the \γa\′ are discussed.

}, keywords = {Antiphase boundaries, Density functional theory, High-throughput calculations, Planar faults energies, Superalloys}, issn = {13596462}, doi = {10.1016/j.scriptamat.2020.02.038}, url = {https://doi.org/10.1016/j.scriptamat.2020.02.038}, author = {Vamsi, K. V. and Pollock, Tresa M.} } @conference {1606, title = {Role of Non-metallic Inclusions and Twins on the Variability in Fatigue Life in Alloy 718 Nickel Base Superalloy}, booktitle = {Superalloys 2020}, year = {2020}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {

Non-metallic inclusions (NMIs) and slip bands parallel to and slightly offset from twin boundaries are observed to be preferential sites for fatigue crack nucleation in wrought superalloys. Potential interactions between NMI cracking and slip activity within neighboring grains or at twin boundaries were investigated under monotonic tensile loading (up to 1.3\% total strain) at room temper- ature. High resolution- and Heaviside-digital image correlation measurements were performed during inter- rupted tensile loading to identify strain localization, associated slip systems, and damage initiation. Different mechanisms and scenarios were identified: (1) Microplas- ticity generally starts at twin boundaries even at stresses as low as 70\% of the macroscopic yield strength, (2) transgranular slip activity intensively develops above the macroscopic yield stress, (3) intense slip activity develops near and parallel to 21\% of the twin boundaries intercepting NMIs, (4) 7\% of the twin boundaries inter- cepting NMIs lead to slip-assisted NMI cracking, (5) no transgranular slip activity participates in NMI cracking, (6) the fraction of cracked NMIs progressively increases with the load, and (7) within the NMIs that initiated cracks, 67\% cracked below 90\% of the macroscopic yield strength without the presence of slip activity in the neighboring grains. While slip-assisted NMI cracking was evidenced in the present study, most NMI cracking is due to strain incompatibility between NMIs and neighboring grains at the high end of the elastic regime without slip interaction.

}, keywords = {fatigue, High Resolution-Digital Image Correlation (HR-DIC), In-situ tensile testing, Non-metallic inclusions (NMIs), Twin boundary}, isbn = {9783030518349}, doi = {10.1007/978-3-030-51834-9}, url = {http://dx.doi.org/10.1007/978-3-030-51834-9_65}, author = {Texier, Damien and Stinville, Jean-Charles and Charpagne, Marie-agathe and Chen, Zhe and Valle, Valery and Villechaise, Patrick and Pollock, Tresa M. and Cormier, Jonathan}, 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} } @conference {1616, title = {Tuning Strain Localization in Polycrystalline Nickel-Based Superalloys by Thermomechanical Processing}, booktitle = {Superalloys 2020}, year = {2020}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {

Thermomechanical processing routes are used to produce microstructures that minimize plastic strain localization at the sub-grain scale in a polycrystalline \γ \− \γ\&$\#$39; nickel- based superalloy. This novel approach is made possible by the use of innovative experimental tools and statistical data analysis that capture slip events over large represen- tative fields of view. Results are correlated to conventional observations of fatigue crack initiation and early stage of propagation. The effect of coherent twin boundaries and primary \γ\&$\#$39; precipitates on fatigue properties and plastic localization is detailed.

}, keywords = {3D microstructure, Annealing twin boundaries, Nickel-based superalloy, Primary γ{\textquoteright} precipitates, Slip bands}, isbn = {9783030518349}, doi = {10.1007/978-3-030-51834-9}, url = {http://dx.doi.org/10.1007/978-3-030-51834-9_65}, author = {Charpagne, M. A. and Stinville, J. C. and Polonsky, A. T. and Echlin, M. P. and Murray, S. P. and Chen, Z. and Bozzolo, N. and Cormier, J. and Valle, V. and Pollock, T. 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} } @conference {1601, title = {The Yield Strength Anomaly in Co-Ni Design Space}, booktitle = {Superalloys 2020}, year = {2020}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {

A new computational approach to model precipitate compositions and properties in the CoNi-design space for yield strength anomaly prediction is presented. The antiphase boundary (APB) energies on {111} and {010} and the degree of elastic anisotropy are known to influence the yield strength anomaly. APB energies were estimated by a diffuse multi-layer fault (DMLF) model using the structural energies of proximate structures: L12, ca\′, and D023. The elastic moduli were calculated via the energy-strain approach using density functional theory calculations. (Ni1\−xCox)3(Al1\−yWy) was chosen as the model system, and Yoo\&$\#$39;s criterion is evaluated over the entire range ofcompositions to identify regions that exhibit the yield strength anomaly. (Ni0.65Co0.35)3(Al0.5W0.5) has the maximum APB (111) and any two-phase alloy (c + c') in Ni\–Co\–Al\–W system with this precipitate composition might exhibit higher strength upon shearing by a matrix dislocation. ThermoCalc was employed to identify stable L12 regions in (Ni1\−xCox)3(Al1\−yWy). The effect of Co on the yield strength anomaly was investigated experimen- tally in three (Ni1\−xCox)3Al alloys with L12 structure. All three alloys exhibited the yield strength anomaly, validat- ing the computational approach. The addition of Co provides solid solution strengthening to Ni3Al at room temperature; however, this contribution to the overall strength diminished as a function of temperature. CoNi-alloys displayed strengths similar to Ni3Al at elevated temperatures with Co addition resulting in a marginal increase in strength at the peak temperature. The present study elucidates that APB energies from a DMLF model combined with elastic moduli can be employed to predict yield strength anomaly using Yoo\&$\#$39;s criteria.

}, keywords = {Antiphase boundaries, CoNi-based superalloys, Yield strength anomaly}, isbn = {9783030518349}, doi = {10.1007/978-3-030-51834-9}, url = {http://dx.doi.org/10.1007/978-3-030-51834-9_65}, author = {Vamsi, K. V. and Murray, Sean P. 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} } @article {1511, title = {A 3D analysis of the onset of slip activity in relation to the degree of micro-texture in Ti{\textendash}6Al{\textendash}4V}, journal = {Acta Materialia}, volume = {181}, year = {2019}, pages = {36{\textendash}48}, abstract = {

The mechanical properties of titanium alloys result from their complex multi-scale microstructural features, including micron scale precipitates and millimeter scale microtextured regions (MTRs). While previous investigations have revealed that the presence of mm-scale MTRs can degrade mechanical properties, particularly fatigue, the accompanying strain localization processes that operate at the microscale within the \α grains in MTRs are not well understood. The present work is a mechanistic investigation of MTRs using crystal plasticity simulations of mm3-scale experimentally captured and synthetically generated 3D microstructure datasets. The explicit modeling of both the \α grains and MTRs in Ti\–6Al\–4V enables assessment of the effect of microtexture and local structure variations within the MTR on overall deformation behavior and the onset of plastic slip in MTRs. The presence of MTRs with a dominant [0001] orientation results in both stress and plastic strain hotspots during the early stages of straining. Crystal plasticity predictions are compared to previous digital image correlation studies on early strain localization. The influence of MTRs on the local stress and strain fields is discussed with regard to the monotonic tension, fatigue and dwell-fatigue behavior of titanium alloys.

}, keywords = {3D EBSD, Crystal plasticity, Macrozones, Microtexture, Titanium alloys}, issn = {13596454}, doi = {10.1016/j.actamat.2019.09.028}, url = {https://doi.org/10.1016/j.actamat.2019.09.028}, author = {H{\'e}mery, S. and Na{\"\i}t-Ali, A. and Gu{\'e}guen, M. and Wendorf, J. and Polonsky, A. T. and Echlin, M. P. and Stinville, J. C. and Pollock, T. M. and Villechaise, P.} } @article {1371, title = {The evolving landscape for alloy design}, journal = {MRS Bulletin}, volume = {44}, year = {2019}, pages = {238{\textendash}246}, abstract = {

The discovery, design, and development of new alloys have long been critical elements of advanced engineering systems. Challenged by their chemical and structural complexity, this design process is, however, often too slow. This article highlights progress in theory, computation, data, and advanced experimental techniques that are advancing our capabilities for rapid discovery and design of new multicomponent alloys. Applied across the length scales, these new capabilities support exploration across broad composition spaces; examples of new materials and associated advances in the understanding of underlying thermochemical and thermomechanical phenomena are presented. We highlight current challenges, gaps, and specific areas that, if further developed, could have future high payoff.

}, keywords = {alloys, crystallographic structure, electronic structure, phase equilibria, simulation}, issn = {08837694}, doi = {10.1557/mrs.2019.69}, author = {Pollock, Tresa M. and Van der Ven, Anton} } @article {1501, title = {In-plane and out-of-plane deformation at the sub-grain scale in polycrystalline materials assessed by confocal microscopy}, journal = {Acta Materialia}, volume = {169}, year = {2019}, pages = {260{\textendash}274}, abstract = {

High-resolution digital image correlation (HR-DIC) techniques have become essential in material mechanics to assess strain measurements at the scale of the elementary mechanisms responsible of the deformation in polycrystalline materials. The purpose of this study is to demonstrate the use of laser scanning confocal microscopy (LSCM) coupled with DIC techniques to deepen knowledge on the deformation process of a polycrystalline nickel-based superalloy at room temperature. The LSCM technique is capable of detecting both in-plane and out-of-plane strain localization within slip bands at the sub-grain level. The LSCM observations are consistent with previous in-situ scanning electron microscopy (SEM) studies: The onset of crystal plasticity occurs primarily near \Σ3 twin boundaries with macroscopic loading in the elastic domain (macroscopic stress as low as 80\% of the 0.2\% offset yield strength (Y.S. 0.2\% )). This intense irreversible strain localization occurs with either a high Schmid factor (\μ \> 0.43) or a significant elastic modulus difference between the pair of twins (\Δ\Ε \> 100 GPa). In the plastic deformation domain, transgranular slip activity following slip systems with the highest Schmid factor is mostly responsible for the deformation at the grain level, thus leading to strain percolation. The simultaneous in-plane and out-of-plane deformation assessment via the HR-LSCM-DIC technique was found to be essential for the identification of active slip systems. Finally, the HR-LSCM-DIC technique enabled the quantification of the glide amplitude involved in the three-dimensional shearing process at the grain level that solely in-plane measurements cannot provide.

}, keywords = {High Resolution-Digital Image Correlation (HR-DIC), In-situ tensile testing, Laser scanning confocal microscopy (LSCM), Nickel-based polycrystalline superalloy, Strain localization}, issn = {13596454}, doi = {10.1016/j.actamat.2019.03.001}, url = {https://doi.org/10.1016/j.actamat.2019.03.001}, author = {Liu, J. H. and Vanderesse, N. and Stinville, J. C. and Pollock, T. M. and Bocher, P. and Texier, D.} } @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 {1316, title = {Creep Behavior of Quinary γ'-Strengthened Co-Based Superalloys}, journal = {Metallurgical and Materials Transactions A}, volume = {49}, year = {2018}, pages = {4090{\textendash}4098}, issn = {1073-5623}, doi = {10.1007/s11661-018-4768-z}, url = {http://link.springer.com/10.1007/s11661-018-4768-z}, author = {Rhein, Robert K. and Callahan, Patrick G. and Murray, Sean P. and Stinville, Jean-Charles and Titus, Michael S. and Van der Ven, Anton and Pollock, Tresa M.} } @article {1436, title = {Measurements of plastic localization by heaviside-digital image correlation}, journal = {Acta Materialia}, volume = {157}, year = {2018}, pages = {307{\textendash}325}, abstract = {

In polycrystalline metallic materials, quantitative and statistical assessment of the plasticity in relation to the microstructure is necessary to understand the deformation processes during mechanical loading. Plastic deformation often localizes into physical slip bands at the sub-grain scale. Detrimental microstructural configurations that result in the formation and evolution of slip bands during loading require advanced strain mapping techniques for the identification of these atomically sharp discontinuities. A new discontinuity-tolerant DIC method, Heaviside-DIC, has been developed to account for discontinuities in the displacement field. Displacement fields have been measured at the scale of the physical slip bands over large areas in nickel-based superalloys by high resolution scanning electron microscopy digital image correlation (SEM DIC). However, conventional DIC methods cannot quantitatively measure plastic localization in the presence of discontinuous kinematic fields such as those produced by slip bands. The Heaviside-DIC technique can autonomously detect discontinuities, providing information about their location, inclination, and identify slip systems (in combination with orientation mapping). Using Heaviside-DIC, discontinuities are physically evaluated as sharp shear-localization events, allowing for the quantitative measure of strain amplitude nearby the discontinuities. Measurements using the new Heaviside-DIC technique are compared to conventional DIC methods for identical materials and imaging conditions.

}, keywords = {Discontinuities measurements, High resolution digital image correlation, Ren{\'e} 88DT polycrystalline superalloy, Scanning electron microscopy, Slip band offset, Slip band shearing, Slip system identification, Strain localization}, issn = {13596454}, doi = {10.1016/j.actamat.2018.07.013}, url = {https://doi.org/10.1016/j.actamat.2018.07.013}, author = {Bourdin, F. and Stinville, J. C. and Echlin, M. P. and Callahan, P. G. and Lenthe, W. C. and Torbet, C. J. and Texier, D. and Bridier, F. and Cormier, J. and Villechaise, P. and Pollock, T. M. and Valle, V.} } @article {1476, title = {Shearing of γ{\textquoteright} particles in Co-base and Co-Ni-base superalloys}, journal = {Acta Materialia}, volume = {161}, year = {2018}, pages = {99{\textendash}109}, abstract = {

Shearing mechanisms of the primary strengthening phase in cobalt-base and cobalt-nickel-base superalloys, \γ\′ (L12), are investigated at the elementary defect level by using a combination of generalized-stacking-fault energy (GSF) calculations and phase field simulations. The GSF energy surfaces of the \γ and \γ\′ phases, as determined from available experimental data and ab initio calculations, are used in the phase field simulations. Sophisticated deformation pathways leading to various planar defects including antiphase boundaries (APB), remnant superlattice intrinsic stacking faults (SISF), APB-SISF-APB ribbons and SISF islands are predicted as a function of alloy composition and particle shapes. The predicted stacking fault configurations for both alloys are consistent with recent transmission electron microscopy observations. Effects of dislocation line tension difference in \γ and \γ\′ phases and planar defect energy variation due to segregation at the planar defects are discussed. The detailed dislocation core structures, effects of dislocation line tension differences on deformation mechanisms, and unique deformation mechanisms uncovered, which include stacking fault ribbon shearing, antiphase boundary shearing, and mixed modes, could be used to improve constitutive microstructure-property relationships in advanced crystal plasticity modeling and to assist in alloy design.

}, keywords = {Ab initio calculation, Dislocation creep, Phase field simulation, Precipitation hardening, Stacking fault ribbon}, issn = {13596454}, doi = {10.1016/j.actamat.2018.09.013}, author = {Feng, L. and Lv, D. and Rhein, R. K. and Goiri, J. G. and Titus, M. S. and Van der Ven, A. and Pollock, T. 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