This title appears in the Scientific Report :
2014
Interdiffusion between vacuum plasma-sprayed protective bond coats and γ`-strengthened Cobalt-base superalloys during thermal treatment
Interdiffusion between vacuum plasma-sprayed protective bond coats and γ`-strengthened Cobalt-base superalloys during thermal treatment
γ`-strengthened Ni-base superalloys are commonly used for high-temperature, high-load applications in gas turbine blades. The recent discovery of a γ/γ` microstructure in the ternary Co-Al-W alloy system [1] led to intensive research in the design of γ`-strengthened Co-base superalloys. They promise...
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Personal Name(s): | Terberger, Philipp (Corresponding Author) |
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Sebold, Doris / Quadakkers, Willem J. / Vassen, Robert | |
Contributing Institute: |
Werkstoffstruktur und -eigenschaften; IEK-2 Werkstoffsynthese und Herstellungsverfahren; IEK-1 |
Published in: | 2014 |
Imprint: |
2014
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Conference: | Thermal Barrier Coatings IV, Kloster Irsee, Irsee (Germany), 2014-06-22 - 2014-06-27 |
Document Type: |
Poster |
Research Program: |
Helmholtz Interdisciplinary Doctoral Training in Energy and Climate Research (HITEC) Power Plants |
Publikationsportal JuSER |
γ`-strengthened Ni-base superalloys are commonly used for high-temperature, high-load applications in gas turbine blades. The recent discovery of a γ/γ` microstructure in the ternary Co-Al-W alloy system [1] led to intensive research in the design of γ`-strengthened Co-base superalloys. They promise higher operating temperatures compared to Ni-base superalloys. [2] As a new candidate for a turbine blade construction material, Co-base superalloys have to be compatible with state of the art protective bond coats. Vacuum plasma-sprayed (VPS) MCrAlY bond coats (M=Co,Ni) are commonly used for this application in gas-fired industrial turbines.In the present investigation the interaction of VPS bond coats with γ`-strengthened Co-base superalloys during isothermal heat treatment is studied. Hence, the focus is on the interdiffusion processes and the resulting phase changes at the interface between coating and base material. Interdiffusion can lead to depletion or enrichment of certain elements that induce phase changes and thus influence properties of the bond coat and the superalloy substrate. Knowledge about these processes will help to anticipate detrimental effects that can arise during service of the new superalloys.Co-9Al-9W (in at%) single crystal samples were coated with either a Ni-base or Co-base MCrAlY bond coat using vacuum plasma-spraying. They were heat treated in vacuum at 1080 °C and subsequently thermally treated in air at 900 °C for up to 500 hours. Phases formed in the interdiffusion zone were identified and analysed using SEM and EDX, complemented by thermodynamic simulations. It was observed that the γ` phase quickly dissolves due to the enrichment of Cr and the depletion of Al. The interdiffusion zone shows a large amount of W-rich precipitates, mainly consisting of Co7W6 and Co23Cr15W15. At the interface of γ/γ` microstructure and interdiffusion zone, thin needle-like precipitates were found that may be Co3W and that serve as nucleation sites for the above mentioned W-rich phases. In direct comparison the Co-base bond coat shows better compatibility with the substrate than the Ni-base bond coat, because it exhibits fewer and smaller W-rich precipitates and thinner interdiffusion zones. This may be due to the higher Co content, the lower Cr activity, and the higher W-solubility of the Co-base bond coat. |