Segregation and η phase formation along stacking faults during creep at intermediate temperatures in a Ni-based superalloy

Smith, Timothy M.; Esser, Bryan D.; Antolin, Nikolas; Viswanathan, G.B.; Hanlon, Timothy; Wessman, Andrew; Mourer, D. P.; Windl, Wolfgang; McComb, David W.; Mills, Michael J.

doi:10.1016/j.actamat.2015.08.053

Cited by 144 publications

(44 citation statements)

References 48 publications

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“…Some of the interaction spots and fault ending points present a higher intensity in the HAADF-STEM image which might be related with a higher concentration of heavier elements. This observation is consistent with the previous work in ME3 alloy by Smith et al [24] The rationalization of these higher density regions associated with the fault growth is discussed in the following section.…”

Section: B Intrinsic and Extrinsic Stacking Faults: Cisf/sisf And Cesupporting

confidence: 82%

Segregation-Assisted Plasticity in Ni-Based Superalloys

Barba

Smith

Miao

et al. 2018

Metall Mater Trans A

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Correlative high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy are used to study deformation-induced planar faults in the single-crystal superalloy MD2 crept at 800°C and 650 MPa. Segregation of Cr and Co at microtwins, anti-phase boundaries (APB), and complex/superlattice extrinsic and intrinsic stacking faults (CESF/SESF and CISF/SISF) is confirmed and quantified. The extent of this is found to depend upon the fault type, being most pronounced for the APB. The CESF/SESF is studied in detail due to its role as a precursor of the microtwins causing the majority of plasticity under these conditions. Quantitative modeling is carried out to rationalize the findings; the experimental results are consistent with a greater predicted velocity for the lengthening of the CESF/ SESF-compared with the other types of fault-and hence confirm its role in the diffusion-assisted plasticity needed for the microtwinning mechanism to be operative.

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Section: B Intrinsic and Extrinsic Stacking Faults: Cisf/sisf And Cesupporting

confidence: 82%

Segregation-Assisted Plasticity in Ni-Based Superalloys

Barba

Smith

Miao

et al. 2018

Metall Mater Trans A

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“…In both cases, a distinct local composition at the faults is observed. As described in a preliminary study8, the ordering observed along the fault in ME501 can be attributed to a shear-induced phase transformation from γ′ to η phase along the fault. Bulk η phase possesses a hexagonal D0 24 crystal structure (P6 3 /mmc, a =0.5096, c=0.8304, α = β =90°, γ =120°), the same found locally along a SESF89.…”

Section: Resultsmentioning

confidence: 56%

“…As described in a preliminary study8, the ordering observed along the fault in ME501 can be attributed to a shear-induced phase transformation from γ′ to η phase along the fault. Bulk η phase possesses a hexagonal D0 24 crystal structure (P6 3 /mmc, a =0.5096, c=0.8304, α = β =90°, γ =120°), the same found locally along a SESF89. In ME3, brighter contrast, attributed to a larger average atomic number at the SESFs is also observed; however, the lack of atomic ordering along the fault implies that a different segregation event has occurred101112.…”

Section: Resultsmentioning

confidence: 56%

Phase transformation strengthening of high-temperature superalloys

et al. 2016

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Decades of research has been focused on improving the high-temperature properties of nickel-based superalloys, an essential class of materials used in the hot section of jet turbine engines, allowing increased engine efficiency and reduced CO2 emissions. Here we introduce a new ‘phase-transformation strengthening' mechanism that resists high-temperature creep deformation in nickel-based superalloys, where specific alloying elements inhibit the deleterious deformation mode of nanotwinning at temperatures above 700 °C. Ultra-high-resolution structure and composition analysis via scanning transmission electron microscopy, combined with density functional theory calculations, reveals that a superalloy with higher concentrations of the elements titanium, tantalum and niobium encourage a shear-induced solid-state transformation from the γ′ to η phase along stacking faults in γ′ precipitates, which would normally be the precursors of deformation twins. This nanoscale η phase creates a low-energy structure that inhibits thickening of stacking faults into twins, leading to significant improvement in creep properties.

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confidence: 99%

“…For the first time, using a double aberration corrected FEI Themis™ with a Super-X™ XEDS detector compositional mapping of a Ni-based superalloy (commercially available HL-11) was collected at atomic resolution across a stacking fault, as seen in Figure . Individual spectra in the atomic resolution XEDS maps exhibit low signal-to-noise, usually having very few counts per channel. Based on previous characterization of the fault structure determining structural periodicity [4], the data was summed over a repeating unit cell of the fault structure along the [110] projection, resulting in almost an order of magnitude increase in the peak maxima of the XEDS spectra and even larger increase in integrated peak counts. These modified 3D data cubes were then fed into the Bruker Esprit software package and quantified using experimentally determined Cliff-Lorimer k-factors from a solutionized sample of the same material.…”

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confidence: 99%

Quantifying Ordering Phenomena Through High-Resolution Electron Microscopy, Spectroscopy, and Simulation

et al. 2016

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Advances in aberration corrected scanning transmission electron microscopy (STEM) have allowed researchers to investigate structure-property relationships at the atomic scale [1][2][3][4]. In many systems, ordering phenomena at the atomic level can have a dramatic impact on the structural, electronic, and magnetic properties of the material. By combining experiment, simulation, and data processing, these ordering phenomena can be studied in a quantitative way, opening the door for new insights into the structure-property relationships of a wide variety of material systems. Experimentally, high angle annular dark field (HAADF) STEM and energy dispersive X-ray spectroscopy (EDX) are two very powerful techniques for probing compositional variations at the Ångstrom scale. In order to fully understand and quantify these techniques, image simulation and ionization calculations using the quantum excitation of phonons model can be used [5,6]. For the first time, using a double aberration corrected FEI Themis™ with a Super-X™ XEDS detector compositional mapping of a Ni-based superalloy (commercially available HL-11) was collected at atomic resolution across a stacking fault, as seen in Figure . Individual spectra in the atomic resolution XEDS maps exhibit low signal-to-noise, usually having very few counts per channel. Based on previous characterization of the fault structure determining structural periodicity [4], the data was summed over a repeating unit cell of the fault structure along the [110] projection, resulting in almost an order of magnitude increase in the peak maxima of the XEDS spectra and even larger increase in integrated peak counts. These modified 3D data cubes were then fed into the Bruker Esprit software package and quantified using experimentally determined Cliff-Lorimer k-factors from a solutionized sample of the same material. By preprocessing these data before quantification, the error in the quantification was significantly reduced, allowing for site-specific determination of solute segregation in and around the fault structure in this Ni-based superalloy, leading to the determination of a novel high temperature strengthening mechanism.In addition to using spectroscopy to quantify compositional variations at the Ångstrom scale, there have been many reports of using HAADF-STEM images to quantitatively understand ordering phenomena [7][8][9]. Double perovskite thin films with the general formula A 2 BB′O 6 have been studied extensively for their interesting electronic and magnetic properties [10][11][12]. These properties, however, can be highly dependent on the degree of cation ordering, especially B and B′ atoms due to superexchange between them across bridging O atoms [10]. A structural characterization of Sr 2 CrReO 6 (SCRO) films was performed using HAADF-STEM imaging and diffraction leading to the identification of highly prevalent antiphase domains. To further confirm these findings images and diffraction patterns were simulated for SCRO models with antiphase domains present.Extending the us...

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Segregation and η phase formation along stacking faults during creep at intermediate temperatures in a Ni-based superalloy

Cited by 144 publications

References 48 publications

Segregation-Assisted Plasticity in Ni-Based Superalloys

Segregation-Assisted Plasticity in Ni-Based Superalloys

Phase transformation strengthening of high-temperature superalloys

Quantifying Ordering Phenomena Through High-Resolution Electron Microscopy, Spectroscopy, and Simulation

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