Low-density, W-free Co-Nb-V-Al-based superalloys with γ/γ′ microstructure

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

卷:796

Article

Tirado, Fernando L. Reyes¹  Taylor, Spencer, V¹  Dunand, David C.^1,2 

[1] Northwestern Univ, Dept Mat Sci & Engn, 2220 Campus Dr, Evanston, IL 60208 USA

[2] Rice Univ, Dept Mat Sci & Nanoengn, 6100 Main St MS 325, Houston, TX 77005 USA

关键词: Cobalt-base superalloys;    Atom probe tomography (APT);    Microstructure;    Creep;    Precipitates;   

DOI  :  10.1016/j.msea.2020.139977

来源: Elsevier

【 摘 要 】

Previously-reported metastable gamma'-L1(2)CO(3)(Nb0.65V0.35) precipitates in the Co-6Nb-6V (at. %) ternary alloy are stabilized by additions of Al, Ti, Ni and Cr to the alloy. We identify two such multinary gamma/gamma' alloys - with compositions of Co-10Ni-6Ti-5Al-xCr-3Nb-3V-0.04B at.% (with x = 0 and 4% Cr) - with gamma'-precipitates remaining stable for up to 1000 h at 850 degrees C, with no additional phases present. Decreasing the Ti concentration from 6 to 2%, two more gamma/gamma' superalloys - Co-10Ni-5Al-xCr-3Nb-3V-2Ti-0.04B (with x = 4 and 8% Cr) - are created with stable gamma'-precipitates (measured for 168 hat 850 degrees C) with morphologies more cuboidal than for the first two alloys with 6%Ti. These submicron cuboidal gamma' precipitates are arranged into crystallographically-oriented sheets with small (<50 nm) gamma'-spacing within sheets and larger (similar to 100 nm) gamma'-spacing between sheets. The alloy with the highest 8% Cr concentration shows, after aging at 850 degrees C for 24 h, gamma'-nanoprecipitates with (Co0.85Ni0.15)(3)(Ti0.13Al0.25Nb0.24Cr0.21V0.16B0.01) composition (assuming full segregation onto the two sublattices), with Al and Ti replacing at a similar rate both Nb and V in the ternary Co-3(Nb0.65V0.35). This high-Cr alloy exhibits the best oxidation resistance, as seen by a reduction in the parabolic growth rate constant and surface oxide thickness. Also, the present W- and Ta-free, Cr-containing superalloys show good creep resistance at 850 degrees C, which is comparable to other recent Cr-containing Co-base gamma/gamma' superalloys with higher densities: (i) W-containing Co-9W-9Al-8Cr (at.%), and (ii) Ta-containing Co-10Ni-5Al-4Cr-3Ta-3V-2Ti-0.04B (at.%). This is the first report of a family of Co-Nb-V-Al-based gamma/gamma'-superalloys with low density (<8.0 g/cm(3)).

【 授权许可】

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