@article{ff2a65de7e11486fa27732655bb6860e,
title = "γ{\textquoteright}-(L12) precipitate evolution during isothermal aging of a Co–Al–W–Ni superalloy",
abstract = "The coarsening kinetics and elemental partitioning behavior of γ{\textquoteright}-(L12) precipitates in a γ(f.c.c.)-matrix for a model quaternary Co-8.8Al-8.9W-9.9Ni at.% superalloy are investigated utilizing isothermal aging conditions at 650, 800 and 900 °C. The γ′-precipitate mean radius, number density, and volume fraction, at 800 and 900 °C, were studied using scanning electron microscopy; the calculated temporal exponents associated with coarsening of γ′-precipitates display good agreement with model predictions for quasi-stationary coarsening. An atom probe tomographic (APT) investigation of the aged γ/γ′ microstructure at 650 °C demonstrates that the compositions and volume fractions of both phases vary continuously up to 4096 h. The aged microstructure at 650 °C consists of interconnected nanoscale γ′-precipitates, corroborated utilizing SEM for the 4096 h aged-specimen. The activation energy for coarsening is estimated for the temperature range 650–900 °C to be 283 kJ mol−1, in reasonable agreement with activation energies for diffusion of Al, W, and Ni in Co, suggesting that coarsening of γ′-precipitates is limited by bulk-diffusion. APT measurements of specimens aged for 1024 h at 800 and 900 °C demonstrate that the isothermal aging temperature has a significant effect on the compositions and partitioning behavior of Co, Al, W and Ni between the γ- and γ′-phases. The partitioning ratio of the concentrations between the γ′- and γ-phases is largest for W, decreasing linearly from 5.3 ± 0.1 at 650 °C to 2.1 ± 1.2 at 900 °C, and smallest for Co, decreasing from 0.86 ± 0.01 at 650 °C to 0.73 ± 0.01 at 900 °C.",
keywords = "Atom-probe tomography (APT), Coarsening kinetics, Cobalt-base superalloys, Microstructure",
author = "Sauza, {Daniel J.} and Dunand, {David C.} and Noebe, {Ronald D.} and Seidman, {David N.}",
note = "Funding Information: This work was performed in part under the financial assistance award 70NANB14H012 from U.S. Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD). Atom-probe tomography was performed at the Northwestern University Center for Atom-Probe Tomography (NUCAPT). The local-electrode atom-probe tomograph at NUCAPT was acquired and upgraded with equipment grants from the MRI program of the National Science Foundation (NSF DMR-0420532) and the DURIP program of the Office of Naval Research (N00014-0400798, N00014-0610539, N00014-0910781). NUCAPT received support from the MRSEC program (NSF DMR-1121262) of the Materials Research Center, the SHyNE Resource (NSF NNCI-1542205), and the Initiative for Sustainability and Energy at Northwestern (ISEN). This work also made use of the shared facilities at the Materials Research Center of Northwestern University (DMR-1121262). We also gratefully thank Mr. Robert Schuld (NU) for assistance with the preparation and heat treatments. Funding Information: This work was performed in part under the financial assistance award 70NANB14H012 from U.S. Department of Commerce , National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD). Atom-probe tomography was performed at the Northwestern University Center for Atom-Probe Tomography (NUCAPT). The local-electrode atom-probe tomograph at NUCAPT was acquired and upgraded with equipment grants from the MRI program of the National Science Foundation ( NSF DMR-0420532 ) and the DURIP program of the Office of Naval Research ( N00014-0400798 , N00014-0610539 , N00014-0910781 ). NUCAPT received support from the MRSEC program ( NSF DMR-1121262 ) of the Materials Research Center, the SHyNE Resource ( NSF NNCI-1542205 ), and the Initiative for Sustainability and Energy at Northwestern (ISEN). This work also made use of the shared facilities at the Materials Research Center of Northwestern University ( DMR-1121262 ). We also gratefully thank Mr. Robert Schuld (NU) for assistance with the preparation and heat treatments. Publisher Copyright: {\textcopyright} 2018 Acta Materialia Inc.",
year = "2019",
month = feb,
day = "1",
doi = "10.1016/j.actamat.2018.11.014",
language = "English (US)",
volume = "164",
pages = "654--662",
journal = "Acta Materialia",
issn = "1359-6454",
publisher = "Elsevier Limited",
}