Metals Affordability Initiative: Application of Allvac Alloy 718Plus for Aircraft Engine Static Structural Components

Abstract

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.

Evolution of secondary phases in alloy ATI 718Plus®during processing

“…The tensile and stress rupture properties of 718Plus have been extensively studied, as the alloy was first optimised for static applications [4][5][6]. However, its use in rotating components demands a fine balance between strength and resistance to fatigue crack initiation vs damage tolerance and creep resistance.…”

Effect of Temperature and Strain during Forging on Subsequent Delta Phase Precipitation during Solution Annealing in ATI 718Plus® Alloy

“…The alloy has been characterized and evaluated by many OEM's, both independently and as part of a Metals Affordability Initiative funded project [2,3,4]. Alloy development at ATI Allvac is complete, and commercial application of the alloy began in earnest in 2010.…”

Comparison between Microstructure Evolution in IN718 and ATI Allvac® 718Plus^TM – Simulation and Trial Forgings

“…This newly developed alloy shows an approximately 55 °C improved thermal stability. [1][2][3][4][5][6][7] The chemical composition of IN718 and Allvac® 718Plus TM is listed in Table 1 and Table 2 TM suppresses the precipitation of γ'' and favors the precipitation of γ' as primary hardening phase. In both superalloys δ phase is used to control grain growth [12].…”

“…This newly developed alloy shows an approximately 55 °C improved thermal stability. [1][2][3][4][5][6][7] The chemical composition of IN718 and Allvac® 718Plus TM is listed in Table 1 and Table 2, respectively. …”