Selective oxidation behavior of ferritic martensitic Fe-Cr base alloys, exposed in various atmospheres containing combinations of O 2 , CO 2 , and H 2 O, were studied at various temperatures relevant to oxy-fuel combustion. This paper begins with a discussion of the required Cr content to form a continuous external chromia scale on a simple binary Fe-Cr alloy exposed in oxygen or air based on experiments and calculations using the classic Wagner model. Then, the effects of the exposure environment and Cr content on the selective oxidation of Fe-Cr alloys are evaluated. Finally, the effects produced by alloying additions of Si, commonly present in various groups of commercially available ferritic steels, are described. The discussion compares the oxide scale formation on simple binary and ternary Fe-Cr base model alloys with that on several commercially available ferritic steels.

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This paper reports results from a larger study that has focused on the development of novel Pt+Hf-modified γ-Ni+γ′-Ni 3 Al-based compositions for high temperature bond coatings with improved reliability and durability. The effects of Pt, Hf and Cr contents on resistance to both isothermal and cyclic oxidations at 1150°C in air were analyzed. It was found that Pt contents of up to 20at.% significantly enhanced the selective oxidation of aluminum so as to suppress the formation of less-protective NiO and NiAl 2 O 4 . The Pt also served to decrease the reactivity of Hf in the γ′ phase, to the extent that unwanted HfO 2 formation could be suppressed. Balanced Pt+Hf-modified γ+γ′ compositions exhibited remarkably slow oxidation kinetics. Moreover, γ+γ′ coatings were shown to offer clear potential advantages over β-NiAl-based coatings, with the former exhibiting excellent surface stability (i.e., no rumpling) and compatibility with the superalloy substrate (i.e., no SRZ formation).