Long-term oxidation tests on a Re-containing MCrAlY coating

The oxidation and interdiffusion properties of Re-containing NiCoCrAlY-coatings for application in gas turbines were studied in the temperature range from 950 °C to 1000 °C. For this purpose cylindrical specimens of IN 738 were coated with a number of NiCoCrAlYs by vacuum plasma spraying and subsequently exposed in air under isothermal as well as thermocycling conditions. After exposure, the oxidation products, subsurface depletion layer as well as interdiffusion zone, with the IN 738 substrate were analysed by optical metallography and SEM/EDX. Very high amounts of Re led to extensive precipitation of Cr-rich phases, causing an embrittlement of the coating. Optimized coatings in respect to Re-, Cr-, and Al-content appeared to possess excellent performance even up to exposure times of 20 000 h.