Microtensile creep testing of freestanding MCrAlY bond coats
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Microtensile creep testing of freestanding MCrAlY bond coats Sven Giese1,a), Steffen Neumeier1, Doris Amberger-Matschkal1, Jan Bergholz2, Robert Vaßen2, Mathias Göken1,b) 1
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Materials Science & Engineering, Institute I, Erlangen 91058, Germany IEK-1: Materials Synthesis and Processing, Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research, Jülich 52425, Germany a) Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs.org/editor-manuscripts/. 2
Received: 25 February 2019; accepted: 23 April 2019
Bond coats are essential in gas turbine technology for oxidation protection. Freestanding MCrAlY (M = Ni, Co) bond coats were investigated with respect to their creep strength at elevated temperatures. Three types of MCrAlY, a Ni-based bond coat Amdry 386, a Co-based bond coat Amdry 9954 and Amdry 9954 + 2 wt% Al2O3 (ODS = oxide dispersion strengthened) produced by low pressure plasma spraying, were analyzed. The two phase microstructure of the bond coats consists of a fcc c-Ni solid solution and a B2 b-NiAl phase. Constant load experiments were performed in a thermomechanical analyzer at temperatures between 900 and 950 °C. Microtensile test specimens with a diameter of 450 lm were produced by a high-precision grinding and polishing process. Creep rupture was mainly due to void nucleation along the b–c interfaces and grain boundaries. The time to failure is larger in Ni-based Amdry 386 compared to that in Co-based Amdry 9954 due to a higher fraction of the high-strength b-NiAl phase at test temperatures. The addition of ODS-particles in the Co-based bond coat Amdry 9954 resulted in a better creep resistance but lower ductility in comparison to ODSparticle-free Amdry 9954.
Introduction The continuous improvement of aero engines and land-based gas turbines leads to increasing gas inlet temperatures and the demands for new materials. Such increased temperatures are possible with thermal barrier coating (TBC) systems consisting of Al- and Cr-containing bond coatings for enhanced oxidation- and corrosion resistance and ceramic TBCs, which are essential for thermal isolation [1]. The difference in thermal expansion coefficients between the metal substrate and the TBC would lead to delamination. A metallic bond coat can improve the bonding between substrate and TBC and can reduce the risk of spallation of the ceramic top coat. Therefore, MCrAlY overlay coatings are applied to superalloy components, tailored to provide protection against high-temperature oxidation and hot corrosion [2, 3, 4, 5, 6, 7]. Studies have investigated hardness, Young’s modulus, diffusion or the influence of bond coats with different chemical compositions on the mechanical properties of the superalloys so far [8, 9, 10,
11]. However, less information about the mechanical prop
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