Use of Precious Metal-Modifed Nickel-Base Superalloys for Thin Gage Applications (Preprint)

Precious metal-modified nickel-base superalloys are being investigated for use in thin gage applications, such as thermal protection systems or heat exchangers, due to their strength and inherent oxidation resistance at temperatures in excess of 1050 deg C. This overview paper summarizes the Air Force Research Laboratory (AFRL) and Rolls-Royce North America interest in experimental two phase gamma-Ni + gamma'-Ni3Al superalloys. AFRL is interested in alloys with a base composition of Ni-15Al-5Cr (atomic %) with C, B, and Zr additions for grain-boundary refinement and strengthening. The alloys currently being evaluated also have 4-5 atomic % total of platinum-group metals, in this case platinum and iridium. The feasibility of hot rolling these alloys to a final thickness of 175-250 micron and obtaining a nearly fully recrystallized microstructure was demonstrated. However, an anomalous grain-growth behavior was also observed at the surface in the intermediate and final rolled products. Future work will include evaluating alloys with a combination of rhenium and tantalum (up to 2 atomic % total) in place of the platinum and iridium. Journal article submitted to the Journal of the Minerals, Metals & Materials Society (JOM).