The phase evolution of Allvac® alloy 718Plus® has been determined experimentally via construction of time-temperaturetransformation (TTT) and continuous-cooling-transformation (CCT) curves based on identifying the various phases, their sizes and volume fractions along with distributions as they evolved during thermal treatment. The solution temperature range of interand intra-granular  phases and of have been characterized via detailed microstructural investigations. The phase solvus of alloy 718Plus determined by dissolution during isothermal hold for 0.1 hours ranges between 1010-1071C, with clear distinctions between solutioning of grain boundary and complete solutioning. The temperature where the intergranular or grain boundary particles dissolve after 0.1 hours in the investigated material is 1015C. At this temperature, grain growth occurs owing to a lack of pinning by grain boundary phase particles. However, it is only at 1065C, that a complete dissolution of all particles has been observed. The nose of the TTT curve for  occurs at about 843C for start (25 % transformation) and end of transformation (100% transformation). The temperature ranges at which precipitation hardening (704-788C), coarsening (843C) and over aging (898C) take place in the alloy have been located by correlating the TTT and the time-temperature-hardness (TTH) curves. This investigation provides a solid basis for practical processing of the alloy, to be used as a candidate material for 700C applications.Allvac and 718Plus are registered trademarks of ATI Properties, Inc.

Mechanical property balance, malleability, and weldability of Alloy 718 have driven widespread utilization across the aerospace and non-aerospace industries for nearly 50 years. However, the metastability of the primary strengthening gamma double prime phase is typically unacceptable for applications above about 650°C. As a result, other more costly and difficult to process alloys, like Waspaloy, are used in such applications. The latter alloys, strengthened primarily by gamma prime, are also more sensitive to weld-related cracking than Alloy 718. As part of the Metals Affordability Initiative CORE Program, several alternate alloys were identified and evaluated for aircraft engine static structural component applications for use temperatures of at least 700°C. The application-integrated project team consisting of engine manufacturers, General Electric, Honeywell, and Pratt & Whitney; forgers Firth-Rixson and Ladish Co., Inc.; primary metal producers, Allvac and Carpenter Technology; and the Air Force Research Laboratory, selected the Allvac-developed 718Plus® alloy composition for scale-up and validation. Subscale and full-scale experiments confirmed that processability and weldability of this alloy were significantly improved relative to Waspaloy, approaching that of Alloy 718. Complex rolled rings varying in size from less than 25 to nearly 250 kg have been processed validating the advantages of this alloy. Assessment suggests capability similar to Waspaloy to 704°C has been achieved along with an acceptable balance of other properties. This paper will summarize the processing, weldability, and mechanical property evaluations successfully performed in this project, as well as progress toward industrial implementation of this alloy.

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Significant effort has been exerted to develop a cast version of the ATI 718Plus® alloy for aerospace applications with use temperatures approximately 42°C (75°F) higher than conventional alloy 718. Current alternatives to alloy 718 for low cost, hightemperature investment-cast structural components are limited. The target technology application is gas turbine structural components, including combustor plenums, stator cases, diffuser cases, turbine cases, turbine frames, and various other highstrength/high-temperature structural castings. An overview of the results from the castability and weldability studies, compositional selection and heat treatment selection, select mechanical properties, and cast component trials will be discussed. 718Plus is a registered trademark of and 718Plus® alloy is a patented proprietary alloy ATI Properties, Inc.