ADVANCED MATERIALS & PROCESSES | MAY 2026 18 alloy 718 at GE in both commercial and military engines[10,12,14]. Pratt & Whitney introduced alloy 718 into commercial engines with a fabricated diffuser case in the JT9D engine in 1968[12]. During this period, the engine OEMs developed their initial material specifications, and the supply chain made significant improvements in material quality and manufacturing reliability. WAS THE SUCCESS OF ALLOY 718 INEVITABLE? From its initial relatively small volume use in the Blackbird, the consumption of the alloy grew exponentially in the 1970s and 1980s, not only at GE and P&W, but at virtually every U.S. turbine producer[14]. By 1989, alloy 718 had become so successful that it spawned its own dedicated technical symposium that will host its 11th conference in 2026. J.F. Barker stated at the seminal conference that nickel- base superalloys constituted 48% of the weight of GE’s high volume CF6 commercial engine and that 71% of that weight was alloy 718[10]. In the 5th conference in 2001, Shafrik reported that 56% of all alloys used in forgings was alloy 718[15]. Clearly the mechanical properties provided operational advantages over the gamma prime strengthened alloys within their temperature capability range. Initially this was expressed in terms of yield strength, but later fatigue strength became defining for engine life critical parts. But other factors both inherent and external influenced the rapid adoption of the alloy. Alloy 718, while stiff, is much more amenable to hot and cold rolling of sheet in coil and plate mill products as well as forging into complex configurations than Waspaloy. The slow aging kinetics enable suppression of pre- cipitation during cooling after solution annealing and provide resistance to stress relief cracking of fusion welds in complex casings and weld repair of castings[10,12,16,17]. Another advantage is the relative ease in which an ultra-fine grain size can be generated using delta phase stabilization within hot working and heat treatment cycles. Grain size of ASTM 8-12 in forged parts is critical on the X211 nuclear engine program replacing A286. Both aircraft programs were cancelled, but GE gained valuable experience in fabricating these components[10]. Meanwhile Pratt & Whitney (P&W) was developing their JT11 (later J58) for the supersonic SR-71 Blackbird surveillance and reconnaissance aircraft. Waspaloy was initially specified for the diffuser case which required extensive welding. This part proved difficult to produce due to strainage cracking. The problem was solved by substitution of alloy 718, thus becoming the first military application using the alloy[12]. Qualification of alloy 718 for turbine rotors was hindered by the difficulty of developing uniform properties in contoured forgings[10,12]. This was solved by the forgers in time for first use in limited production of the GE4 engine designed for the U.S. supersonic transport project SCAT-15F. The Boeing 2707-390 SST was cancelled due to economics and concern about sonic boom, but the forging and heat treatment data were applied to the GE-1 demonstrator that was to become the core of the TF39 for the Air Force C5A Heavy Transport and CF6 commercial engine. Components included forged rotors, welded cases, and investment cast parts. The application for an alloy 718 casting was a 50-pound rear frame hub[13]. These developments led to large scale use of Cutaway drawing of GE J93. Courtesy of Wikimedia Commons. GE YJ93 turbojet was designed to handle bombers at speeds of 2000 mph and at altitudes of 70,000 ft. Courtesy of the National Museum of the United States Air Force. GE’s TF39 was the world’s first high-bypass engine. Courtesy of GE Aerospace. Electric Co. (GE), these included the turbine frame and compressor rear frame for the J93 engine intended for the XB70 Supersonic Bomber replacing René 41, and frames and casings
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