STUDIES ON THE OXIDATION BEHAVIOR OF INCONEL-625 BETWEEN 873 AND 1523K

The oxidation behavior of Inconel 625 during the early stages (<150 mi n) has been studied at oxygen pressures (P-O2) of 0.12 kPa (0.9 torr) and 101.3 kPa (760 torr) in the temperature range of 1323 K to 1523 K by using TGA and between 873 and 1523 K by using XPS, AES, and EDS. Th e TGA results correlated well with those obtained by surface analysis of the oxide films. The results of XPS and AES analysis suggested that two distinctly different oxidation mechanisms operate, depending on t he temperature of oxidation. Enrichment of the oxide films with respec t to Cr2O3 occurs above 873 K, the degree of enrichment peaking at abo ut 1200 K such that the oxide films formed at temperatures close to th is consist almost exclusively of Cr2O3. At temperatures above 1300 K, the oxides of two minor alloying components, Nb and Ti, have been foun d to be present in the oxide films in significant proportions. The res ults have been discussed on the basis of the relative thermodynamic st abilities of the competing oxide phases and the diffusivities of the a lloying elements in Inconel 625.