Alloy Phase Transformations at Elevated Temperatures: Session I
Sponsored by: TMS High Temperature Alloys Committee, TMS Phase Transformations Committee
Program Organizers: Dinc Erdeniz, University of Cincinnati; Benjamin Adam, Oregon State University; Jonah Klemm-Toole, Colorado School of Mines; Eric Lass, University of Tennessee-Knoxville; Ashley Paz y Puente, University of Cincinnati; Sophie Primig, University of New South Wales; Chantal Sudbrack, National Energy Technology Laboratory
Monday 2:00 PM
October 10, 2022
Room: 326
Location: David L. Lawrence Convention Center
Session Chair: Dinc Erdeniz, University of Cincinnati
2:00 PM Invited
The Optimization of Local Phase Transformation Strengthening in Next Generation Superalloys: Timothy Smith1; Nikolai Zarkevich2; Mikhail Mendelev2; Valery Borovikov2; Ashton Egan3; Timothy Gabb1; John Lawson2; Michael Mills3; 1NASA Glenn Research Center; 2NASA Ames Research Center; 3The Ohio State University
NASA is currently developing novel disk superalloys (TSNA-#) that leverage a recently discovered phase transformation strengthening mechanism. This local phase transformation (LPT) strengthening provided TSNA-1 with a 3x improvement in creep strength over similar disk superalloys and comparable strength compared to the single crystal blade alloy CMSX-4 at 760 °C. Through ultra-high-resolution chemical mapping of the stacking faults induced by creep deformation, it was discovered that the improvement in creep strength was a result of atomic-scale η (D024) and χ (D019) formation along superlattice stacking faults. To understand these results, the energy differences between the L12 and competing D024 and D019 stacking fault structures and their dependence on composition were then computed from first principles using density functional theory and molecular dynamic models. Other properties beyond creep strength will also be discussed with relations to these atomic scale deformation processes.
2:30 PM Invited
Microstructure Evolution and Mechanical Properties of α′/α″-Strengthened Ferritic Superalloys: Christopher Zenk1; Luis Morales1; Andreas Bezold1; Andreas Förner1; Steffen Neumeier1; Carolin Körner1; 1Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Ferritic superalloys are an emerging class of materials based on the Fe-Al-Ni system. A coherent bcc-derived α/α′ (A2/B2) microstructure can be established, analogous to the γ/γ′ (A1/L12) microstructure of Ni-base superalloys. With Fe as their base element (∼50at.%) and a high Al-content (∼18at.%) these materials have a major cost advantage over Ni-base superalloys. The addition of Ti facilitates the partial transformation of α′ into L21 (based on Ni2AlTi, henceforth α″) and significantly improves the creep resistance of these alloys. Our alloy development efforts led to an α′/α″-strengthened alloy that was additively manufactured via Laser Metal Deposition. In-situ synchrotron diffraction reveals insights into the complex phase transformation pathway through which a variety of different microstructures can be designed. The elemental partitioning between the three phases is measured in TEM and APT. The high-temperature mechanical properties will be discussed on the basis of compressive and tensile tests as well as creep tests.
3:00 PM
Single-step Aging Treatment on Cast Haynes 282 Ni-based Alloy – Microstructure and Mechanical Behavior: Timothy Lach1; Xiang Chen1; 1Oak Ridge National Laboratory
Haynes® 282® alloy is a Ni-based superalloy designed for excellent high-temperature strength and creep resistance. This improved performance is attributed to its chemical composition and microstructural features (e.g., γ' precipitates, soluble species, and metal carbides). To maximize high-temperature strength, Haynes-282 is typically subjected to a solution-annealing heat treatment followed by a two-step age-hardening treatment. However, this is a time-intensive and expensive process. A simplified single-step aging treatment was successfully completed for the wrought version of Haynes-282 and yielded microstructural features that produced strengthening behavior normally associated with more complex thermal processing. For cast Haynes-282, the behavior is made complicated by casting heterogeneities and defects. In this work, high-resolution analytical electron microscopy and high temperature mechanical behavior testing were used to evaluate the microstructural evolution of the single-step aging treatment on cast Haynes-282 alloy. Detailed comparisons will be made with the standard aging treatment and with aging of the wrought alloy.
3:20 PM
Effect of Grain Boundary Phases on Creep Properties of a Novel Ni-Co Based Superalloy: Yoshiki Kumagai1; David Dunand2; 1Daido Steel Co Ltd.; 2Northwestern University
In some wrought Ni-based superalloys, grain-boundary precipitates strongly influence creep properties. Recently, we developed a novel Ni-Co-based superalloy with high W content which exhibits precipitation of several grain-boundary phases: γ', Cr-carbide, W-carbide and μ. In this study, the role of the grain-boundary phases on the creep properties is investigated. Two microstructures with different dominant grain-boundary phases are produced by multi-step aging treatments, without changing the amount and the size of γ' precipitates within grain interior. Metallographic analysis shows that dense precipitation of grain-boundary Cr-carbide, together with grain-boundary γ', reduces the minimum creep rate under compressive creep conditions, but at the expense of ductility and rupture life under tensile creep conditions, as compared to precipitation of grain-boundary W-carbide and μ.
3:40 PM Break
4:00 PM
Microstructure and Mechanical Properties of W-free γ + γ' Co-based Superalloys with Ni, Cr, and Fe Additions: Brandon Ohl1; Howard Stone2; David Dunand1; 1Northwestern University; 2University of Cambridge
The effects of adding Ni (0-30 at.%),Cr (4-8 at.%), and Fe (0-18 at.%) to a W-free, Co-based superalloy's phase evolution are investigated. Most alloys maintain a stable FCC + L12 microstructure upon aging 1000 h at 850ºC, with some formation of other intermetallic phases in alloys with high Fe and Cr. In addition to precipitate microscopy analysis as samples age, neutron diffraction and synchrotron X Ray diffraction are used to determine the γ/γ' lattice misfit, and differential scanning calorimetry is used to determine γ' solvus and γ solidus/liquidus temperatures. Microstructure is then connected to mechanical properties, as measured by compressive creep tests at 850ºC and by compressive yield measurements between room temperature and 950 ºC.
4:20 PM Cancelled
Concurrent Precipitation of Nb(C,N), M23C6, and Sigma Phases in Alloy 347H with and without Ancillary Additions of Boron and Nitrogen: Michael Glazoff1; Jianguo Yu1; Laurent Capolungo2; Michael Gao3; Gabriel Ilevbare1; 1Idaho National Laboratory; 2Los Alamos National Laboratory; 3National Energy Technology Laboratory
We present efforts to develop quantitative models of precipitation in alloy 347H using PRISMA. Precipitation models provide data for the development of chemistry- and precipitation-informed creep theory (LANL) and facilitate developing alloys for extreme environments (ORNL). Results for the XMAT-generated precipitation data (750°C) and literature sources at 600-800°C, are presented. Research sponsored by the U.S. Department of Energy, Office of Fossil Energy and Carbon Management, the Crosscutting Technology High Performance Materials Research Program.
4:40 PM
Hyper Duplex Stainless Steel: A Study on the Sigma Phase Formation: Andres Acuna1; Antonio Ramirez1; 1Ohio State University
The high alloying content of the recently developed hyper duplex stainless steel (HDSS) provides remarkable corrosion resistance, PREn > 49, and a balanced ferrite austenite microstructure. However, due to the Cr and Mo content, this alloy is susceptible to sigma phase formation. An extensive sigma phase formation study was conducted on HDSS developing precipitation experimental data, JMAK analytical calculations, and a computational kinetic model. Isothermal heat treatments produced specimens for SEM characterization. The quantified sigma volume fraction developed a TTT map to adjust and validate the computational model and the JMAK calculations. We found that sigma kinetics is highest at 900 oC -920oC in isothermal conditions. However, in conditions of continuous cooling processes, cooling rates faster than 4oC/s do not cause sigma precipitation. The established kinetic model allows the prediction of sigma formation based on the applied cooling rates. Hence, allowing optimization of the welding parameters to avoid sigma presence.
5:00 PM Cancelled
In-situ and Ex-situ Evaluation of Phase Transformation and Its Impact on the Hot Ductility of Steel during Continuous Casting Processes: Alyssa Stubbers1; John Balk1; 1University of Kentucky
Phase transformation of steel during continuous casting may cause low ductility behavior that can lead to cracking and other quality concerns during steel production. Ex-situ evaluation of these phase transformations has proven challenging due to austenite transformation to martensite upon quenching and difficulty differentiating BCT martensite from BCC ferrite using XRD and other traditional characterization methods. Using a Gleeble 3500 at University of Kentucky, in-situ measurements can be coupled with ex-situ characterization in order to develop a better understanding of the mechanics of phase transformations at casting relevant temperatures. Methodology in this study focuses on using dilatometry and EBSD techniques to reconstruct pre-quenched austenite microstructures and gather phase dependent property information. This data is then used to make conclusions about phase transformation progression and its direct impact on the material property profile of steels during continuous casting.