Martensitic transformation in CVD NiAl and (Ni,Pt)Al bond coatings

The martensitic phase transformation in single-phase β-NiAl and (Ni,Pt) Al coatings was investigated. After isothermal exposure to 1150 °C for 100 h, the β phase in both types of coatings was transformed to a martensite phase during cooling to room temperature. Martensitic transformation was also observed in the (Ni,Pt)Al bond coat with and without a YSZ top layer after thermal cycling at 1150 °C (700 1-h cycles). The transformation took place due to Al depletion in the coating from the formation of the Al O scale and interdiffusion between the coating and superalloy substrate. The effects of the martensitic transformation 2 3 on coating surface stability ('rumpling') via volume changes during the phase transformation are discussed with regard to TBC failure.