| Abstract Scope |
As power generation systems move towards higher operating temperatures to increase their efficiency, there is an increasing need for alumina-scale forming alloys. The presence of H2O and CO2 has been shown to disrupt protective oxide scale formation, imposing further constraints on alloy compositions in these environments. To explore this important aspect, a commercial alumina forming Ni-based superalloy (Rene N5) and homogenized model Ni-6Al-XCr (X: 2, 4, 6, 8, 10 at.%) alloys were exposed to Ar, Ar+20% H2O, Ar+4%CO2, Ar+20%H2O+4%CO2, Ar+20% H2O+4%CO2+10%O2, and air environments at 1200 °C. Preliminary results show that while the lower Cr containing model alloys are predicted to exhibit internal oxidation behavior in air, the low PO2 of the Ar atmosphere causes a significant reduction in the critical aluminum concentration necessary for the transition between internal-external oxidation behavior. This is further complicated in the steam and CO2-containing environments, which are shown to affect the transient chromia’s microstructure. |