Alloy 718: Part I, Quintessential Aero-Engine Superalloy

Abstract

The first installment of a three-part series traces the origins and early aerospace adoption of Inconel alloy 718, the highest-volume nickel-base superalloy in aircraft engines today. Invented in the mid-1950s by Herbert Eiselstein at Huntington Alloys — originally for coal-fired power plant tubing — the alloy’s niobium-induced gamma double prime strengthening phase delivered superior yield strength and weldability compared to incumbent superalloys, while its slow aging kinetics enabled forming and welding reliability that Waspaloy and René 41 could not match. Inco’s decision to freely license the patent drove competitive process innovation across the supply chain, rapidly maturing vacuum melting, remelting, and forging technologies. Early engine programs, from the SR-71 Blackbird’s J58 diffuser case to GE’s TF39 and Pratt & Whitney’s JT9D, established alloy 718 as the structural workhorse of aero-engines — a position reinforced by its cobalt-free composition, lower intrinsic cost, and broad fabricability that continue to sustain its dominance today.