ADVANCED MATERIALS & PROCESSES | MAY 2026 16 The highest volume nickel-base superalloy used in aircraft engines is Inconel alloy 718 UNS N07718, yet its origin was not in the aerospace sector. In the mid-1950s, designs were progressing for an advanced coal-fired power plant using ultra-supercritical steam technology[1]. Austenitic stainless steels such as AISI 316 were leading candidates for boiler tubing. INSPIRATION AND SYNERGY Herbert Eiselstein, FASM, a metallurgist at the Huntington Alloys Division of the International Nickel Co. (Inco) in Huntington, West Virginia, thought that a nickel-base alloy, solid solution strengthened by molybdenum, tungsten or niobium, would provide a stronger and weldable tubing alloy that would also be more resistant to sigma phase formation than stainless steel[2]. Using a series of designed experiments, he was surprised to find that compositions within a limited range of nickel, chromium, iron, aluminum, and titanium, 4-6% niobium induced an intense age hardening reaction by a precipitate that was stable to about 1200°F (649°C). This aging reaction was different from the Al/Ti based gamma prime phase that strengthened legacy superalloys in that it was not only more intense, but also sluggish in its development. Huntington Alloys and its sister company Wiggin Alloys in the U.K. had pioneered the development of gamma prime strengthened alloys beginning with Nimonic alloy 80 in 1941 and was familiar with the difficulty of forming and welding them[3]. This new age hardening system appeared to offer a path to a more versatile alloy for fabricated aircraft engine structures. Eiselstein shared his information with General Electric Aviation (he was a 1941 graduate of University of Cincinnati, joining Inco in 1946 after service in the Navy) and many others in the aerospace industry. With their encouragement, Eiselstein redirected his development work with new goals stated in the patent appli- cation that was filed in 1958: “an alloy with a yield strength of at least 100 ksi at room temperature and 100hour rupture strength of at least 90 ksi at 1200°F”[4]. Over the succeeding four years until the patent issued, Eiselstein refined the composition through additional designed experiments and provided material for evaluation to aircraft and rocket engine manufacturers[5,6]. Inco decided to freely license the patent in the United States, thereby enabling companies such as Latrobe Steel, Special Metals, Carpenter, and Allvac to develop the capability to produce and enhance the alloy. The competition between the producers significantly accelerated acceptance through the development of modern melting, remelting, and forging tech- HERBERT LEWIS EISELSTEIN, FASM (1919-2011) An ASM member for 74 years, Herbert Eiselstein, FASM, received the ASM William Hunt Eisenman award in 2005 for his unique ability to apply the principles of physical metallurgy to the solution of real engineering problems. His inventive genius was responsible for many nickel-base superalloys that make commercial air safer and more economical. In 1988, the superalloy industry recognized his contributions by dedicating the Sixth International Symposium on Superalloys and the 1989 Symposium on Inconel 718 to Herbert L. Eiselstein for his contributions involving alloy design, development, and processing. Patents that bear his name include those for Inconels 718, 625, 903, 617, 601, 706, and 618; Monel 502; and Incoloy 840 and 802. Inconel 718 continues to be one of the main components of the military and commercial aircraft engines 65 years after it was invented by Herb Eiselstein. Eiselstein TABLE 1 — NOMINAL COMPOSITION OF ALLOYS, WT% Alloy/Element Ni Cr Co Fe Mo Al Ti Nb C 718 52.5 19 NA 18.5 3 0.5 0.9 5.1 0.03 A286 26 15 NA 54 1.3 0.2 2 NA 0.05 80A 76 19.5 NA NA NA 1.4 2.4 NA 0.06 René 41 55 18 11 NA 10 1.5 3.1 NA 0.09 Waspaloy 58 19.5 13.5 NA 4.3 1.3 3 NA 0.08 Note: Table refers only to alloys mentioned in this article. NA represents elements that are not specified or intentionally added but may be present in residual quantities. Alloy 718 has many special chemistry grades within the broad UNS N07718 definition. First 50-lb 718 casting for compressor rear frame of J93 engine[11].
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