Microstructural and creep properties of boron- and zirconium-containing cobalt-based superalloys

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

卷:682

Article

Bocchini, Peter J.¹  Sudbrack, Chantal K.²  Noebe, Ronald D.²  Dunand, David C.^1,2  Seidman, David N.^1,3 

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

[2] NASA, Glenn Res Ctr, Mat & Struct Div, 21000 Brookpk Rd, Cleveland, OH 44135 USA

[3] Northwestern Univ, Ctr Atom Probe Tomog, 2220 Campus Dr, Evanston, IL 60208 USA

关键词: Cobalt-base superalloys;    Gamma prime;    Atom-probe tomography (APT);    Grain boundaries;    Creep;   

DOI  :  10.1016/j.msea.2016.10.124

来源: Elsevier

【 摘 要 】

The effects of micro-additions of boron and zirconium on grain-boundary (GB) structure and strength in polycrystalline y(f.c.c.) plus y'(L1(2)) strengthened Co-9.5A1-7.5W-X at% alloys (X=0-Ternary, 0.05B, 0.01B, 0.05Zr, and 0.005B-0.05Zr at%) are studied. Creep tests performed at 850 degrees C demonstrate that GB strength and cohesion limit the creep resistance and ductility of the ternary B- and Zr-free alloy due to intergranular fracture. Alloys with 0.05B and 0.005B-0.05Zr both exhibit improved creep strength due to enhanced GB cohesion, compared to the baseline ternary Co-9.5A1-7.5W alloy, but alloys containing 0.01B or 0.05Zr additions display no benefit. Atom-probe tomography (APT) is utilized to measure GB segregation, where B and Zr are demonstrated to segregate at GBs. A Gibbsian interfacial excess of 5.57 +/- 1.04 atoms nm(-2) was found for B at a GB in the 0.01B alloy and 2.88 +/- 0.81 and 2.40 +/- 0.84 atoms nm(-2) for B and Zr, respectively, for the 0.005B-0.05Zr alloy. The GBs in the highest B-containing (0.05B) alloy exhibit micrometer-sized boride precipitates with adjacent precipitate denuded-zones (PDZs), whereas secondary precipitation at the GBs is absent in the other four alloys. The 0.05B alloy has the smallest room temperature yield strength, by 6%, which is attributed to the PDZs, but it exhibits the largest increase in creep strength (with an similar to 2.5 order of magnitude decrease in the minimum strain rate for a given stress at 850 degrees C) over the baseline Co-9.5A1-7.5W alloy.

【 授权许可】

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