Papers by Keyword: ATI 718Plus

Abstract: As aerospace engines advance to obtain higher thermal efficiencies, it is imperative to develop high temperature materials. Inconel 718 is a nickel-based superalloy that has been used for decades in aero-engine parts as it allows for use in high temperature applications. ATI 718Plus is a newer nickel-based superalloy that has been developed with a 55°C higher temperature capability over Inconel 718. ATI 718Plus components are manufactured by forging a wrought billet in stages to obtain the desired geometry and microstructure. Parts are heat treated to optimised proportions of γ’ and η phases. η phase is an acicular phase that precipitates on the grain boundaries, whereas γ’ is the primary strengthening phase. η phase is an important phase to understand as it is utilised in controlling the grain size during hot working processes at temperatures below its solvus temperature. When η phase is fully solutioned, the grain size is free to increase and hence the material mechanical properties can become detrimental. The short-term precipitation kinetics of η phase in strain-free ATI 718Plus is still not completely understood. In this study, the aims and objectives were to study the η precipitation kinetics in strain-free material as well as studying η phase precipitation in equilibrium conditions. TTT diagrams were produced for the η phase in strain-free material and compared to the limited data available in the open literature. In addition, the equilibrium η phase content, aspect ratio, length and width were determined and compared to the very little data that is currently published.

Abstract: ATI 718Plus components are manufactured by forging a wrought billet in stages to obtain the desired geometry and microstructure. Parts are then heat treated to optimized proportions of γ’ and η phases. η phase is a plate-like phase that precipitates on the grain boundaries of ATI 718Plus, similar to δ phase in Inconel 718. However, the complete kinetic behaviour of η phase precipitation during forging and heat treatment is still not fully understood. This paper investigates the effects of strain hardening on η phase precipitation kinetics in ATI 718Plus. This is achieved through the use of isothermal hot compression tests and heat treatment. Strain hardening was found to affect the η precipitation kinetics considerably. The results reported are a contribution to a fuller understanding of this important process

Abstract: Complex shaped, ultra thin-walled parts can be manufactured using superplastic forming. Hot working temperature for the production of fine-grained billets (d=5-15 μm) out of ATI Allvac 718Plus^® superalloy is in the range of 982-1038°C. An ultrafine-grained structure (d=0.3 μm) was produced by multi-axial forging with a gradual decrease of the forging temperature from 950 to 700°C. Superplastic properties of the alloy were carried out in the temperature interval of 700-950°C. It has been revealed that the fine-grained alloy provided superplastic elongations about 300% at 950°C and strain rate of 10^-4 s^-1. The highest elongation of ultrafine-grained alloy was about 1450% and very low flow stresses were reached at 900°C and strain rate of 3×10^-4 s^-1. The ultrafine-grained alloy showed superplastic properties also at 700°C (0.62T_m). The microstructure and superplastic properties of the alloys 718 and 718Plus are compared.

Abstract: ATI 718Plus^® alloy is a new, cast and wrought, Ni-base superalloy with a maximum use temperature approximately 55°C higher than alloy 718. The mechanical properties have been well characterized by turbine engine OEM’s and the alloy has been specified for use as static components and blades in gas turbine engines. Broader use of ATI 718Plus alloy in engine disk applications requires detailed understanding of the damage tolerance under creep and cyclic loading conditions. The results of a large testing program to evaluate the crack growth behavior of ATI 718Plus alloy at temperatures between 649°C and 704°C under conditions of fatigue, dwell-fatigue, and creep are presented. Crack growth rates in ATI 718Plus alloy in this temperature range are lower than alloy 718 and comparable to Waspaloy under non-dwell-fatigue conditions, and comparable to alloy 720 in dwell-fatigue tests.