EFFECT OF MCRALY OVERLAY COATINGS ON OXIDATION RESISTANCE OF TIAL INTERMETALLICS

The effects of Co-30Cr-6Al-0.5Y and Ni-30Cr-6Al-0.5Y overlay coatings on oxidation resistance of TiAl intermetallics were studied at 900-100 0 degrees C in static air. The TiAl alloys showed poor oxidation resis tance due to the formation of mixed Al2O3 + TiO2 scale which is easily spalled off. CoCrAlY and NiCrAlY coatings could remarkably improve th e oxidation resistance of TiAl owing to the formation of protective Al 2O3 scale. Due to the inward diffusion of Co and Ni to the substrate, two brittle and hard diffusion layers formed between the CoCrAlY and N iCrAlY coatings and the substrate. TiO, appeared on both of CoCrAlY an d NiCrAlY coatings, which may result in the acceleration of the oxidat ion rate at 1000 degrees C. (C) 1998 Elsevier Science S.A.