Thermal stability of microstructural phases in commercial NiCoCrAlY bond coats

Martensite in a ‘two-phase’ NiCoCrAlY bond coat was observed to transform to the parent β-phase < ∼150 °C during in situ transmission electron microscopy heating. At these low temperatures, the transformation does not promote bond coat plasticity or rumpling of the thermally grown oxide that would lead to significant stresses in the top coat. A lower limit of 800 °C was measured for the γ′ solvus temperature. Dissolution of γ′ does not produce a volume change, owing to the coherent nature of the precipitates.