Developments in wrought nb containing superalloys (718 + 100°f)

Alloy 718, developed and patented by International Nickel Company in 1962, has become the most widely used, superalloy. It is available in all product forms, including ingot, billet, bar, rod, wire, sheet, strip, plate and castings. The alloy's popularity is due to its excellent combination of mechanical properties, moderate price and good processability, including weldability. Its maximum use temperature, however, is restricted to about 1200DGF. Above this temperature the gamma" (Ni3Nb) precipitation hardening phase responsible for the alloy's outstanding properties rapidly overages and properties, particularly creep resistance, fall dramatically. There has been a substantial amount of work by numerous investigators over the years to increase the temperature capability of 718. But until now, the only commercially significant choices for structural applications above 1200DGF were gamma' (Ni3A1, Ti) hardened alloys such as Waspaloy and Rene 41. These alloys, however, are more costly and difficult to fabricate and weld than 718. This paper reviews some of the past efforts to improve the performance of 718-type alloys, including current work by Allvac on a newly developed alloy, Allvac 718Plus. The chemistry, mechanical properties and processing characteristics of alloy 718P1us will be compared in detail to both 718 and Waspaloy and the relative cost of these alloys will be discussed. Data will be presented from full scale, production sized ingots which show a 100DGF temperature advantage for 718P1us alloy over 718, while maintaining its good processing characteristics. (AU)