Effect of Cr additions on a γ-γ′ microstructure and creep behavior of a Co-based superalloy with low W content

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:778

Article

Ng, Daniel S.¹  Chung, Ding-Wen¹  Toinin, Jacques P.^1,5  Seidman, David N.^1,2  Dunand, David C.¹  Lass, Eric A.^3,4 

[1] Northwestern Univ, Dept Mat Sci & Engn, 2200 Campus Dr, Evanston, IL 60208 USA

[2] Northwestern Univ, NUCAPT, Evanston, IL 60208 USA

[3] Univ Tennessee, Dept Mat Sci & Engn, 1508 Middle Dr, Knoxville, TN 37996 USA

[4] NIST, Mat Sci & Engn Div, 100 Bur Dr, Gaithersburg, MD 20899 USA

[5] Rhein Westfal TH Aachen, Inst Phys 1, Sommerfeldstr 14, D-52074 Aachen, Germany

关键词: Superalloys;    Coarsening kinetics;    Atom-probe tomography;    Partitioning;    Creep;    Rafting;   

DOI  :  10.1016/j.msea.2020.139108

来源: Elsevier

【 摘 要 】

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 gamma-gamma' microstructure, we create three alloys with 4, 8 and 12 at. % Cr additions. Chromium lowers the gamma' solvus temperature (from 1129 degrees C for 0% Cr to 1075 degrees C for 12 at. % Cr) and alters the gamma' 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 similar to 3 vol % intragranular refractory-rich secondary precipitates upon aging at 850 degrees C for 168 h. Atom-probe tomography reveals that Cr partitions strongly to the.-matrix, with a partitioning coefficient of kappa(gamma'/gamma) = 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 gamma' precipitate composition, volume fraction, morphology, and rafting tendency.

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