The Effects of Water Vapor on the Oxidation of Nickel-Base Superalloys and Coatings at Temperatures from 700C to 1100C

The oxidation of superalloys that rely upon the development of Al2O3 or Cr2O3 scales for oxidation resistance in air containing water vapor are compared at temperatures from 700°C to 1100°C. It is shown that water vapor affects the oxidation of such alloys in different ways. Water vapor adversely affects the selective oxidation of aluminum in the -Al2O3-formers, and also affects the adherence of these oxide scales. The major effect of water vapor on the chromia-formers is enhanced vaporization of Cr2O3. Aluminide coated superalloys are also examined in these cyclic oxidation tests, and it will be shown that water vapor caused spalling of the -Al2O3 scales, but the effect is small for strongly adherent -Al2O3 scales.