The Versatile Affordable Advanced Turbine Engine (VAATE) program has been supporting the development of Alloy 10, a gasatomized powder metal (PM) superalloy. Funding for the program was provided by U.S. Air Force Research Laboratory (AFRL).Honeywell International, Rolls Royce -Allison Advanced Development Company (AADC), and Williams International have been jointly developing Alloy 10 for small and large gas turbine engine applications. Alloy 10 is a demonstrated industry leader in high temperature creep resistance, and has been produced using production-scale equipment for high pressure turbine disk applications. To address cost issues, the VAATE Alloy 10 project evaluated the relative differences between material densified by hot isostatic pressing (as-HIP) and material produced by extrusion followed by isothermal forging. The program was completed as a series of four tasks: (i) chemistry optimization, (ii) as-HIP compaction, (iii) HIP compaction plus isothermal forging for small engine applications, and (iv) extrusion plus isothermal forging for large engine applications. This report provides the status of the program, microstructures typical of the various Alloy 10 product forms, and a summary of initial mechanical properties data.
The 718 family of nickel-base superalloys is used extensively in the design of critical aerospace components, namely in the hot section disks of gas turbine engines. The reliability of such components is often dependent upon, among other factors, their as-machined surface integrity. Surface integrity is often related to tool-surface interactions. The interactions may result in varying degrees of carbide cracking (possibly resulting in matrix cracking), carbide pull-outs, surface tearing, surface roughness, and grain distortion.
Fine Grain Alloy 718 is a relatively cost effective turbine and compressor disk alloy with superior yield strength and low cycle fatigue properties. An understanding of Alloy 718's response to environmental and temperature conditions under sustained peak or dwell conditions is a requirement for assessing actual in-service capability. This is especially critical when the disk operating conditions exceed historical engine experience with Alloy 718. This paper presents a detailed review of experimental dwell low cycle fatigue and cyclic crack growth results for fine grain alloy 718. The experimental fatigue results combined with the observed physical initiation and propagation mechanisms were used to develop a comprehensive life prediction system for fine grain Alloy 718 turbine disk.
Alloy 10 is a third generation powder metal nickelbased superalloy developed by Honeywell for higher temperature turbine and compressor disk applications. Turbine disk blade attachments experience concentrated stresses at elevated temperatures for extended periods of time. Therefore, the notch dwell fatigue capability of an alloy is critical in determining the durability of a turbine disk. A dwell notch lowcycle fatigue (LCF) program was conducted to assess the high temperature capability of Alloy 10 under different geometric stress concentration conditions. The initial intent was not to significantly revise or develop new life prediction methods, but to determine practical operating conditions and temperature limits that minimize the detrimental effects of sustained peak loading. The test program consisted of uniaxially loaded flat double edge notch specimens with geometric stress concentration factors (Kt) of 2 and 3 evaluated under various sustained peak loading conditions. The Kt 2 and 3 specimens were selected to represent the range of stress gradients for turbine disk blade attachment locations. The test temperatures ranged from 650⁰C to 704⁰C with a typical peak tensile hold time of 90 seconds. Conventional non-dwell notch fatigue and creep rupture tests were also conducted to determine baseline properties.An elastic/plastic finite element model with additional creep visco-plasticity was also developed to better understand the potential mechanisms that influence fatigue crack initiation. The empirical and analytical results indicate that stress gradient, creep-induced stress relaxation, cyclic stress state, and environmental factors such as oxidation-assisted crack closure contribute to the elevated temperature dwell fatigue performance of Alloy 10.
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