@article{8115f60b00de4e57aef7db253ebcc50b,
title = "Effect of Cr additions on a γ-γ{\textquoteright} microstructure and creep behavior of a Co-based superalloy with low W content",
abstract = "Nickel- and cobalt-based superalloys derive their excellent oxidation and corrosion resistance from the surface oxidation of Al and Cr, which form protective oxide layers. Starting from an existing Cr-free cobalt-based superalloy (Co–30Ni–7Al–4Ti–3Mo–2W–1Nb–1Ta-0.1B at. %) with a γ-γ′ microstructure, we create three alloys with 4, 8 and 12 at. % Cr additions. Chromium lowers the γ′ solvus temperature (from 1129 °C for 0% Cr to 1075 °C for 12 at. % Cr) and alters the γ′ precipitate morphology (from cuboidal-to-spherical), but does not affect the coarsening kinetics (which follow the Lifshitz-Slyozov-Wagner model). The alloys with 8 and 12 at. % Cr exhibit minor amounts of a Mo-rich intermetallic phase at grain boundaries after homogenization, and the 12 at. % Cr alloy displays an additional ~3 vol % intragranular refractory-rich secondary precipitates upon aging at 850 °C for 168 h. Atom-probe tomography reveals that Cr partitions strongly to the γ-matrix, with a partitioning coefficient of κ γ'/γ = 0.33 and 0.26 for Cr additions of 4 and 8%, respectively. These additions halve the creep rate of the original alloy at stresses between 275 and 400 MPa, reflecting significant changes in γ{\textquoteright} precipitate composition, volume fraction, morphology, and rafting tendency.",
keywords = "Atom-probe tomography, Coarsening kinetics, Creep, Partitioning, Rafting, Superalloys",
author = "Ng, {Daniel S.} and Chung, {Ding Wen} and Toinin, {Jacques P.} and Seidman, {David N.} and Dunand, {David C.} and Lass, {Eric A.}",
note = "Funding Information: This study was performed 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 Material Design (CHiMaD). Scanning electron microscopy was done in the EPIC facility of Northwestern University's NU ANCE Center. Atom-probe tomography and sample preparation were performed at the Northwestern University Center for Atom-Probe Tomography (NUCAPT). We thank research associate professor Dieter Isheim for maintaining 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 has also received support from the MRSEC program ( NSF DMR-1720139 ) of the Materials Research Center, the SHyNE Resource ( NSF NNCI-1542205 ), and the Initiative for Sustainability and Energy at Northwestern (ISEN) . The authors would also like to thank Dr. Fei Xue for his valuable contributions during the revision of this publication. Funding Information: This study was performed 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 Material Design (CHiMaD). Scanning electron microscopy was done in the EPIC facility of Northwestern University's NUANCE Center. Atom-probe tomography and sample preparation were performed at the Northwestern University Center for Atom-Probe Tomography (NUCAPT). We thank research associate professor Dieter Isheim for maintaining 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 has also received support from the MRSEC program (NSF DMR-1720139) of the Materials Research Center, the SHyNE Resource (NSF NNCI-1542205), and the Initiative for Sustainability and Energy at Northwestern (ISEN). The authors would also like to thank Dr. Fei Xue for his valuable contributions during the revision of this publication. Publisher Copyright: {\textcopyright} 2020 Elsevier B.V.",
year = "2020",
month = mar,
day = "19",
doi = "10.1016/j.msea.2020.139108",
language = "English (US)",
volume = "778",
journal = "Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing",
issn = "0921-5093",
publisher = "Elsevier BV",
}