Microtensile creep testing of freestanding MCrAlY bond coats

Abstract

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 γ-Ni solid solution and a B2 β-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 m were produced by a high-precision grinding and polishing process. Creep rupture was mainly due to void nucleation along the β-γ 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 β-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 ODS-particle-free Amdry 9954.