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Research Papers

Precipitate Microstructure as an Indicator of Stress and Temperature Distributions in a Serviced Gas Turbine Blade

[+] Author and Article Information
Mehmet Guclu Akkoyun

Department of Mechanical Engineering,
Bogazici University,
South Campus,
Bebek 34342, Istanbul, Turkey
e-mail: mehmet.akkoyun@boun.edu.tr

Ercan Balikci

Department of Mechanical Engineering,
Bogazici University,
South Campus,
Bebek 34342, Istanbul, Turkey
e-mail: ercan.balikci@boun.edu.tr

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received February 27, 2017; final manuscript received June 22, 2017; published online August 8, 2017. Assoc. Editor: Curt Bronkhorst.

J. Eng. Mater. Technol 140(1), 011001 (Aug 08, 2017) (6 pages) Paper No: MATS-17-1062; doi: 10.1115/1.4037275 History: Received February 27, 2017; Revised June 22, 2017

Superalloys are high temperature materials which are indispensable in many high temperature applications such as the gas turbines. IN738LC is a nickel-based superalloy that is extensively used in the hot sections of the gas turbines. The strengthening in this alloy is provided mainly by the γ′ precipitates. In this research, precipitate size and morphology of a serviced IN738LC polycrystalline turbine blade is investigated. Specimens from the trailing edge, middle, and leading edge positions of the tip, middle, and root sections on their hot (exterior) and cooled (interior) surfaces are analyzed for the precipitate size and morphology. The size and morphology are then linked to the temperature and stress/strain distribution in the blade. In general, the hot surfaces have larger precipitates that indicate a higher temperature exposure. In particular, the precipitate size is larger in the tip and middle sections than the root section, implying that the latter has a lower temperature. As the precipitates transforms to rafts at high temperature and stress/strain, the middle positions of the tip and middle sections, the trailing edge of the tip section, and the leading edge of the middle section are predicted to have high temperature–stress/strain coupling.

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Figures

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Fig. 1

Pressure side of the serviced turbine blade

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Fig. 2

A representative mount for tip section-middle position specimens. The cube on the right schematically shows sample planes. The cooling channel is between the planes “suction cold” and “pressure cold.”

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Fig. 3

Precipitate size for specimens in the tip, middle, and root sections. PT, pressure side-trailing edge; PM, pressure side-middle; PL, pressure side-leading edge; OL, stagnation point; SL, suction side-leading edge; SM, suction side-middle; ST, suction side-trailing edge.

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Fig. 4

Precipitate morphology in the tip section. The scale bar is only for the precipitates, and the blade outline is not to scale.

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Fig. 5

Precipitate morphology in the middle section. The scale bar is only for the precipitates, and the blade outline is not to scale.

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Fig. 6

Precipitate morphology in the root section. The scale bar is only for the precipitates, and the blade outline is not to scale.

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Fig. 7

Precipitate morphology in the firtree specimen

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