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 temperat ure range from 950 degrees C to 1000 degrees C. For this purpose cylin drical specimens of IN 738 were coated with a number of NiCoCrAlYs by vacuum plasma spraying and subsequently exposed in air under isotherma l as well as thermocycling conditions. After exposure, the oxidation p roducts, subsurface depletion layer as well as interdiffusion zone wit h 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 i n respect to Re-, Cr-, and Al-content appeared to possess excellent pe rformance even up to exposure times of 20 000 h. (C) 1997 Elsevier Sci ence S.A.