Microstructural Observations on Oxidized Ni-Based Superalloy TMS-75 and PGM-Doped Derivatives

Abstract

The isothermal oxidation behavior of experimental third and fourth generation Ni-based superalloys was studied at temperatures between 900 and . It was found that the lower Cr concentration in third and fourth generation alloys compared to second generation alloys negatively affects the ability of the alloy to form and maintain a protective alumina scale especially at lower temperatures . An extensive internal reaction zone comprised of oxide and nitride phases is observed underneath a nonprotective external oxide scale. At higher temperatures, a continuous alumina scale forms underneath (Ni,Co)O and spinel layers. Due to the low level of reactive element (RE) additions in these experimental alloys, scale adhesion is poor. An increase of Cr content is necessary to ensure formation of a protective alumina scale at lower temperatures. Addition of Y and/or Zr is recommended for improved oxide adhesion, resulting in better overall oxidation performance.