Advancing Current and State-of-the-Art Application of Ni- and Co-based Superalloys: Processing – Casting, Forging, Heat Treatment
Sponsored by: TMS Structural Materials Division, TMS: High Temperature Alloys Committee, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Chantal Sudbrack, National Energy Technology Laboratory; Mario Bochiechio, Pratt & Whitney; Kevin Bockenstedt, ATI Specialty Materials; Katerina Christofidou, University of Sheffield; James Coakley, Chromalloy; Martin Detrois, National Energy Technology Laboratory; Laura Dial, Ge Research; Bij-Na Kim; Victoria Miller, University of Florida; Kinga Unocic, Oak Ridge National Laboratory
Tuesday 8:30 AM
February 25, 2020
Room: 11B
Location: San Diego Convention Ctr
Session Chair: Chantal Sudbrack, Northwestern University Center for Atom-Probe Tomography; Martin Detrois, National Energy Technology Laboratory
8:30 AM Introductory Comments
8:35 AM Keynote
Advancing The State of the Art of Superalloys by Balancing Performance with Repairability: Eric Huron1; 1GE Aircraft Engines
The expansion of commercial aviation has been enabled by advances in gas turbine technology. These advances have in turn been enabled by improvements in materials, including superalloys. The aviation propulsion community has developed new superalloy compositions and new processing methods, with the new alloys informally referred to as “generations” of superalloys. The early generation advances were focused primarily on high temperature mechanical properties such as creep, but it has become more critical to develop a “Life Cycle” understanding to extend operating lives and improve economics for superalloy components. Higher temperature strength and creep capability remain important but must be coupled with a more balanced development approach, with cyclic fatigue capability, environmental resistance, and repair methodology also critical to success. This presentation will discuss how interactive improvements in alloy composition, processing, environmental resistance, and repair technology are driving the aviation gas turbine industry forward and advancing the state of the art.
9:15 AM Invited
Considerations for Homogenizing Alloys: Paul Jablonski1; Jeffery Hawk1; 1National Energy Technology Laboratory
Chemical inhomogeneities result naturally as a by-product of alloy solidification. Thermal or thermo-mechanical treatments are often used to reduce these inhomogeneities. The question remains exactly how to achieve this and to what level. Traditionally, the homogenization heat treatment is based upon past practice on related alloys or trial and error laboratory experiments. If the chemical inhomogeneity profile is known a-priory, kinetic modeling software such as DICTRA (Diffusion Controlled TRAnsformations) can be used to model the homogenization kinetics of an alloy. In this study, the Scheil module within the Thermo-Calc software was used to predict the as-cast segregation of alloys. The segregation profiles were determined based on the remaining liquid chemistries and were read into DICTRA to refine the homogenization heat treatment. The thermodynamic and kinetic modeling of the computationally predicted heat treatment, and subsequent experimental verifications on real castings is presented along with a set of decision criteria.
9:45 AM
Creep Resistant Cast INCONEL Alloy 740H using an Alternative Casting Technique: Martin Detrois1; Kyle Rozman1; Paul Jablonski1; Jeffrey Hawk1; 1National Energy Technology Laboratory
Increasing performance requirements of power plant designs require the use of Ni-based superalloys to replace steels. To date, Ni-based superalloy INCONEL 740H has been shown to be appropriate for use in A-USC power plants as boiler components in a wrought product. However, using the alloy in its cast form would be significantly valuable in terms of range of component size, geometry and complexity. Previous investigations revealed short creep lives of the cast alloy. Here, an alternative casting route was developed to control the grain size, grain boundary structure and minimize chemistry variability and segregation. More than 30,000 h worth of combined creep testing has been performed to date. A better than 38% increase was obtained for this material in comparison to the creep life obtained from the best performing conventionally cast material. Furthermore, the alternate casting route resulted in the Larson-Miller plot that coincided with that of wrought alloy 740.
10:05 AM Break
10:25 AM Invited
Experimental Assessment and Numerical Simulation of Recrystallization Phenomena in Nickel based Superalloy Forgings: Nathalie Bozzolo1; Marc Bernacki1; 1MINES ParisTech
The most usual phenomenon controlling the final grain size while forging nickel based superalloys is known to be dynamic recrystallization proceeding discontinuously through necklace nucleation. Post-dynamic evolutions may nevertheless also be of utmost importance in the control of the final microstructure in a large forging after cooling down to room temperature. Apart from this usual behavior, more exotic phenomena can also take place under specific thermomechanical conditions, among which : - critical static recrystallization leading to the overgrowth of few grains, - or heteroepitaxial recrystallization of 𝛾 grains on 𝛾’ primary precipitates, - or the formation of 𝛾’ precipitates close to a twin relationship with the matrix grain as a result of the interaction between a recrystallization front with preexisting precipitates.Both the experimental assessment of these phenomena and their simulation will be illustrated in the talk.
10:55 AM
On the Formation of Heating and Cooling Precipitates from a Superalloy Powder: David Collins1; Neil D'Souza2; Chinnapat Panwisawas3; Paraskevas Kontis4; 1University of Birmingham; 2Rolls-Royce plc; 3University of Oxford; 4Max-Planck-Institut für Eisenforschung GmbH
Contemporary powder-based polycrystalline nickel-base superalloys inherit microstructures and properties that are heavily determined by the initial condition of the powder particles. A combination of atom probe tomography and in-situ neutron diffraction was used to study the formation of gamma-prime precipitates during different thermal cycles. The behaviour was assessed from powder comprising single-phase supersaturated gamma only, then tracking the gamma-prime volume fraction and lattice misfit evolution. Subsolvus heat treatments yielded a unimodal gamma-prime distribution, formed during heating, with evidence to suggest these had formed via spinodal decomposition. A supersolvus heat treatment led to the formation of this same gamma-prime population during heating, but dissolves as the temperature increases further. The gamma-prime then reprecipitates as a multimodal population during cooling. Atom probe characterisation provided intriguing precipitate characteristics, including clear differences in morphology, size distribution and chemistry, depending on whether the gamma-prime formed during heating or cooling.
11:15 AM
Microstructure Evolution in a P/M Ni-based Super Alloy: Taisuke Sasaki1; Akihiro Suzuki2; Motoki Okuno3; Daisuke Nagahama3; Masato Ohnuma2; Kazuhiro Hono1; 1National Institute for Materials Science; 2Hokkaido University; 3Honda R&D Co.,Ltd.
P/M Ni-based superalloys for turbine disk are subjected to a post-forging heat treatment to precipitate γ’ phase. Because stability of the γ’ phase depends on the heat treatment temperature, the γ’ phase in the P/M Ni-based superalloys exhibit a complicated growth behavior. In this work, we analyzed the mechanism of this anomalous microstructure evolution by SEM, TEM and 3DAP and SAXS. In the early stage of the heat treatment, tertiary γ’ phase with a few nm in diameter precipitates, and are coarsened monotonically while it is not the case for secondary γ’ phase with ~20 nm in diameter. The size of the secondary γ’ does not change significantly in the early stage, and is mostly identical to that of the tertiary γ’ phase at 200 h. The reason for the different growth behavior can be explained by the compositional change within the precipitates during the heat treatment.
11:35 AM
Optimising Creep Resistance of a Powder Metallurgy Nickel Superalloy via Tailoring of γ΄ Precipitates Using Different Heat Treatments: Chrysanthi Papadaki1; Wei Li2; Alexander Korsunsky1; 1University of Oxford; 2Rolls-Royce plc
A series of advanced experimental techniques have been used to examine the morphological, compositional and structural characteristics of the intergranular and intragranular secondary and tertiary γ’ precipitates as a function of the cooling rate after solution heat treatment, in a high gamma prime content powder metallurgy (P/M) nickel superalloy, Alloy 11. First, a power law dependence of the γ′ precipitate size on the cooling rate was observed experimentally, and then validated and explained by a model developed on the basis of McLean’s theory of precipitate growth. Next, high-resolution scanning and transmission electron microscopy techniques combined with energy-dispersive X-ray spectroscopy (STEM-EDX analysis) for elemental mapping of the γ′ precipitates in the nanoscale were employed to obtain insights into local variations between different populations of gamma prime precipitates formed at different cooling regimes. Eventually, a link with creep resistance was established, by performing interrupted creep tests and subsequent microstructural examination.