Additively manufactured nickel superalloys for aerospace and power generation applications require a combination of strength, ductility, and stress rupture resistance to resist elevated stress loads at operating temperature. Additionally, they must develop a protective layer of alumina oxide when exposed to air to withstand environmental damage up to 1050 °C. In 2020, Carpenter Technology designed a novel alumina-forming high-γ’ Ni superalloy for additive manufacturing with tension and stress rupture properties approaching those of CM 247 LC®. At the time, the novel alloy was lacking ductility at intermediate temperatures (700 °C – 800 °C) [1]. A careful composition rebalance was conducted using a combination of thermodynamic modeling, high-throughput screening, and experimental melting to strengthen grain boundaries to mitigate the hot ductility dip. Printing of density coupons and complex parts with fine internal features demonstrate that the new alloy can be processed by both laser powder bed fusion (L-PBF) and electron beam melting (EBM) with a wide printability window. An extensive design of experiment (DOE) was performed to characterize its recrystallization behavior.

The new alloy has between 55 vol.% and 60 vol.% of γ’ precipitate and in the horizontal direction generates 1150 MPa yield strength (Ys)/1550 MPa ultimate tensile strength (UTS) at room temperature and 1050 MPa Ys/1100 MPa UTS at 760 °C. Ductility is at least 5 El% at 760 °C in both horizontal and vertical directions. Atom probe tomography (APT) was used to characterize the grain boundary structure and explain the improved hot ductility. The composition profile across the γ/γ’ interface was reconstructed and the γ/γ’ partition coefficient was calculated using the APT data. X-Ray diffraction data indicates a slightly positive γ/γ’ misfit puts the γ matrix in a state of compressive stress and provides the alloy with resistance to strain-age cracking. Long-term exposure at 871 °C confirms the presence of a 3 µm – 5 µm layer of alumina on top of the base metal.