Effect of Minor Alloying Elements on the Oxidation Behavior of Ni-Base Alloys in a High-Temperature Steam Environment

Model alloys based on Alloy 617 were fabricated with modified minor alloying elements for improvement in oxidation resistance in high-temperature steam environments. Model alloys were grouped as one with Ti and Al and the other without. Mn content was varied from 0 to 2 wt% for the alloys within each group. The alloys were subjected to oxidation testing in steam at 900 °C for up to 1000 h. Alloys with Ti and Al showed high weight gains due to fast oxide growth on top of grain boundaries and internal oxidation. Mn addition caused formation of Mn-rich spinels and contributed somewhat to weight gain. On the other hand, for the alloys without Ti and Al, Mn content greater than 0.5 wt% prevented oxide spallation. Tensile properties were not significantly affected by the minor alloying element modifications, and one of the model alloys exhibited comparable creep rupture life to Alloy 617.