ADVANCED MATERIALS & PROCESSES | JULY 2026 23 The aircraft turbine engine has consistently been the principal market for alloy 718 following its invention by Inco in 1958. But its unique combination of mechanical, physical, and chemical properties and its wide commercial availability have engendered many other applications. Ironically, one of the first alternate uses was for containment, transport, and mixing of cryogenic liquids, initially in rocket engines, and then in a multitude of other cryogenic enabled machinery. Herbert Eiselstein’s patent claimed high yield strength at room tempera- ture and stress rupture strength at 1200°F (649°C) as the defining attributes[1]. There was no mention of weldability, or notch ductility and toughness at cryogenic temperatures although they are cited in his landmark 1965 paper[2]. Inco along with NASA, Battelle, and others conducted full spectrum characterization in the 1960s that showed alloy 718 also has resistance to general pitting and stress corrosion, is relatively resistant to hydrogen embrittlement, does not have a ductile/ brittle transition temperature, and is non-magnetic except at extremely low temperatures. These attributes when combined with high yield strength made it a candidate for the non-aero engine applications described in this article and in a keynote presentation at the 9th Superalloy 718 Conference[3]. POWER TURBINES Industrial power gas turbines were ALLOY 718: PART II A VERSATILE ALLOY FOR CRITICAL APPLICATIONS This second installment in a three-part series explores how the uses for 718 expanded beyond the aero-engine industry. John deBarbadillo, FASM,* Barboursville, West Virginia *Member of ASM International in general use prior to the development of the aircraft turbine in the early years of World War II. Some of these turbines used nickel and cobalt-base alloys for vanes and buckets. The use of alloy 718 in static and rotating parts in small power turbines followed quickly after its qualification for aircraft engines. Some of these turbines are classified as aeroderivative while others are custom designed for specific platforms. These turbines are widely used as vehicular, marine, and industrial power sources. Solidification segregation restricted the size of alloy 718 ingots precluding its use for wheels, spacers, and shafts in the much larger steam and large frame power turbines. In the early 1990s, GE Power (now GE Vernova) introduced a new class of large turbine that used alloy 706 (a 718 derivative also invented by Eiselstein) that could be cast into much larger ingots without segregation[4]. The qualification of alloy 706 was achieved through innovations in melting, remelting, forging, handling, and inspection by GE and its melting and forging suppliers. These new manufacturing capabilities followed by a decade of turbine operational success inspired a reconsideration of alloy 718 for use in large frame turbine rotors. GE and its supply chain Herbert Eiselstein, FASM. Alloy 718 (UNS N07719) perforated sheet superplastically formed for an aircraft gas turbine tail cone skin. Courtesy of Special Metals Corp. and ASM Handbook, Volume 14B, Metalworking: Sheet Forming.
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