Effect of rhenium addition to a nickel-base single crystal superalloy on isothermal oxidation of the aluminide coating

The alummide difftision coating was prepared by the low-pressure gas phase deposition on two single crystal Ni-base superalloys, DD32 containing 4.0 wt.% rhenium and DD32M without rhenium. For the as-deposited coating, the Al concentration in p-phase on the coated DD32 was higher than that on the coated DD32M. The isothermal oxidation at 1273 K of the coated DD32 and DD32M was investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Re addition decreases the oxidation rate of the coating and obviously improves the oxidation resistance of the aluminide coating. Re addition influences the oxide growth in the long-term oxidation and accelerates the theta-alpha phase transformation. After long-term oxidation at 1273 K, a continuous white layer (Re-rich precipitate phase) occurring in the interdiffusion zone may play a role as an effective "diffusion barrier", inhibiting both outward and inward diffusion of Ni and Al. (c) 2004 Elsevier B.V All rights reserved.