Nickel base alloys are widely used in high temperature oxidative atmospheres, such as heat exchangers and land-based gas turbines. To mitigate the deleterious effects of oxidation, chromium and aluminum additions, which promote the development of a protective layer of chromia or alumina, are made to these alloys. In dry air, the behavior of chromia- and alumina-forming alloys can be predictable. However, in several instances, high temperature applications contain a significant amount of water vapor, which can lead to adverse effects on the oxidation process. The effects of water vapor are not completely understood and thus, a comparative study was conducted on the oxidation behavior of a chromia- and an alumina- former in dry and wet air.

UNS N06230, a chromia-former, and UNS N07214, an alumina former, were oxidized at 1000°C in dry and wet air (15 volume% H2O) for times of 1 minute, 10 minutes, 1, 5, 10 and 100 hours using thermogravimetric analysis. The oxidized coupons were characterized using X-ray diffraction and scanning electron microscopy. In these early stage oxidation experiments, the UNS N07214 (alumina former) had a lower oxidation rate relative to the UNS N06230 (chromia former). The alumina former showed a more complex behavior in these early stages of oxidation relative to the chromia former.

Subject
Scanning electron microscopy, X-ray diffraction, Water, Nickel based alloys, Oxide formation, Chromium, Oxide layers, Oxidation behavior, Vapors, Oxide surfaces, Aluminum alloys, Alloys, Oxidation
Keywords:
oxidation, water vapor, chromia-former, alumina-former, nickel base alloys
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2019
Association for Materials Protection and Performance (AMPP)
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