文摘
The effects of steam on the oxidation behavior of model Al2O3-scale forming Ni-base alloys at 1000?°C were studied. This was done by conducting tests using dry air and air +30?% H2O (“wet air-in short) gas environments. It was found that the critical concentration of Al (N Al * ) to form a continuous and protective alumina scale on Ni–Al–Cr alloys is increased when the environment is wet air. Based on a rigorous assessment of the parameters contained in Maak’s modification (Z Met 52:545, 1961) of Wagner’s criterion (Z Elektrochem 63:772, 1959) for the transition from internal oxidation to external scale formation, it was deduced that the factor that can change the critical concentration N Al * to the extent measured is the critical volume fraction f v * .