Advanced Characterization of High-temperature Alloys: Phase Evolution during Manufacturing and Service-induced Deformation: Role of Deformation in Phase Transformations and Microstructural Evolution
Sponsored by: TMS Structural Materials Division, TMS: High Temperature Alloys Committee
Program Organizers: Katerina Christofidou, University of Sheffield; Benjamin Adam, Oregon State University; Stoichko Antonov, Max-Planck Institut für Eisenforschung GmbH; James Coakley, Chromalloy; Martin Detrois, National Energy Technology Laboratory; Paraskevas Kontis, Norwegian University of Science and Technology; Stella Pedrazzini, Imperial College London; Sophie Primig, University of New South Wales
Tuesday 2:30 PM
March 21, 2023
Room: 29D
Location: SDCC
Session Chair: Stella Pedrazzini, Imperial College London; Paraskevas Kontis, Norwegian University of Science and Technology; Cynthia Rodenkirchen, Imperial College London
2:30 PM Invited
Leveraging Local Phase Transformation Strengthening to Achieve Superior Next Generation Superalloys: Timothy Smith1; Timothy Gabb1; Nikolai Zarkevich2; Mikhail Mendelev2; Valery Borovikov2; Christopher Kantzos1; Ashton Egan3; John Lawson2; Michael Mills3; 1NASA Glenn Research Center; 2NASA Ames Research Center; 3The Ohio State University
For this study, multiple new disk superalloys (TSNA 1-6) specifically designed to take advantage of strengthening atomic-scale dynamic complexions were investigated. This local phase transformation (LPT) strengthening provided newly acquired and forged superalloy TSNA-1 with almost 10x better creep strength over similar forged disk superalloys and over a 2x improvement compared to the single crystal blade alloy CMSX-4 at 760 °C. Ultra-high-resolution chemical mapping of the creep induced superlattice stacking faults confirmed this improvement was the result of atomic-scale η (D024) and χ (D019) local phase transformations as, notably, microstructural differences could not explain the observed differences in creep strength. To better understand these results, density functional theory and molecular dynamic modelling were used to explore the effect chemistry has on activating these strengthening phase transformations along stacking faults. In addition, the effect these atomic-scale mechanisms have on other important properties will be examined.
3:00 PM
Quantifying Creep Deformation Behavior of Optimized Local Phase Transformation Strengthened Next Generation Superalloys: Ashton Egan1; Longsheng Feng1; Timothy Smith2; Yunzhi Wang1; Michael Mills1; 1Ohio State University; 2NASA Glenn Research Center
Planar defects and microtwins become dominant shearing mechanisms during high temperature deformation of superalloys owing to diffusion mediated segregation/reordering. Local Phase Transformation (LPT) is employed to strengthen alloys via formation of η/χ at defects, preventing subsequent deformation. Two remarkable alloys, single-crystal NA1 and polycrystalline TaTi1, are exemplary. A NA1 polycrystalline variant had been shown to compare well with behavior of CMSX-4; this work seeks to determine activation energy and stress exponents used to describe/model this behavior using a matrix of SX NA1 subjected to various stresses/temperatures in {001}. Alloy TaTi1 was created utilizing computation-aided design to optimize LPT strengthening beyond NA1 while remaining practical for service; their creep behavior and LPT characteristics are quantified and juxtaposed. Advanced characterization of deformation structures was conducted utilizing controlled Electron Channeling Contrast Imaging (cECCI) and probe-corrected Scanning Transmission Electron Microscopy (STEM), with atomic resolution Energy Dispersive X-Ray Spectroscopy (EDS) quantifying local segregation/ordering.
3:20 PM
Microstructural Control of LPBF Inconel 718 through Post Processing of Intentionally Placed AM Discontinuity Distributions: Elaine Livera1; Katerina Christofidou1; Daniel Ryan2; Iain Todd1; 1University of Sheffield; 2Solar Turbines
A major untapped potential of laser powder bed fusion (LPBF) is the ability to additively manufacture (AM) parts with site-specific properties. However, robust methods of improving performance and manufacturing efficiency via spatial variations in microstructure are underexplored. This work introduces a novel method of creating multi-modal microstructures in IN718 by performing a Hot Isostatic Pressing (HIP) procedure on characteristic LPBF discontinuities such as keyhole and lack of fusion porosity, as well as large powder filled voids. Observed using electron backscattered diffraction, this approach enables the formation of site-specific variations in microstructure and extreme bi-modal microstructures in which grains differ in area by 194%. Additionally, as opposed to the typical anisotropic AM microstructures, this method facilitates the production of fully dense, equiaxed and strain free materials culminating in a 62% energy saving, and 47% time saving per layer.This work was supported by the UK Engineering and Physical Sciences Research Council [EP/L016273/1] and Solar Turbines Incorporated.
3:40 PM
Temporal Evolution of γ′ Precipitate in HAYNES 282 during Ageing: Growth and Coarsening Kinetics, Solute Partitioning and Lattice Misfit: Shreya Mukherjee1; Bibhu Sahu2; Aniruddha Biswas3; Sujoy Kar4; Soumitra Tarafder5; 1Indian Institute of Science; 2University of Michigan; 3BARC, Mumbai; 4IIT Kharagpur; 5CSIR NML
Elemental partitioning across the precipitate/matrix interface controls the kinetics of precipitate evolution, during growth and coarsening. We present the first comprehensive analysis of evolutions of microstructure, as well as the lattice misfit, in light of elemental partitioning, applied to a Ni-based superalloy, HAYNES 282. In this work, experimental analyses by APT, TEM, and XRD are combined with thermo-kinetic modelling using ThermoCalc and TC-PRISMA. The current study has isolated the growth and the coarsening regimes analyzed the respective kinetics and identified their individual rate-controlling processes. Diffusive growth and coarsening kinetics are found to closely match with the data of Cr and Ti for growth, and Mo for coarsening, respectively. For the coarsening kinetics, we have used the thermodynamic parameter corresponding to the non-dilute, non-ideal γ solid solution phase in the modified LSW equation. Constrained misfit has been found to be positive and decreased with ageing time.
4:00 PM Break
4:30 PM Invited
Effect of Temperature, Stress and Environment on Preferential and Internal Oxidation of Ni-base Alloys: Karen Kruska1; Elizabeth Kautz1; Ziqing Zhai1; Matthew Olszta1; Daniel Schreiber1; 1PNNL
Ni-base alloys are frequently employed in high-temperature applications due to their excellent resistance to corrosion and stress corrosion over a wide range of conditions. With increasing temperature, the oxidation mechanism shifts from passivation to preferential intergranular oxidation to internal oxidation. To assess the effects of temperature (360°C - 800°C), stress and aqueous environment on the degradation of such Ni-base alloys, stressed and unstressed samples were exposed to hydrogenated water and low pO2 gas. Subsequently, the corrosion products were analyzed with scanning electron microscopy, analytical transmission electron microscopy and atom-probe tomography. Low solute alloys that formed passivating oxide films in gas exhibited preferential intergranular oxidation in hydrogenated water. Applied stress alone did not cause passivity break-down under originally passivating conditions. However, enhanced diffusion accelerated oxide penetration in all stressed samples. These distinctions highlight the importance of isolating parameters in the pursuit of a mechanistic understanding of the oxidation behavior in Ni-base alloys.
5:00 PM
Local Phase Transformation Strengthening in CoNi-base Superalloys: Andreas Bezold1; Nicolas Karpstein1; Erdmann Spiecker1; Mathias Goken1; Steffen Neumeier1; 1Friedrich-Alexander-Universität Erlangen-Nürnberg
Polycrystalline CoNi-base superalloys exhibit a promising property profile consisting of excellent creep strength, good oxidation resistance and a sufficiently large processing window for hot working. In this work, the overall defect structure as well as the atomic structure and chemistry of planar defects in this alloy system are investigated after creep deformation at 750 °C using high resolution scanning transmission electron microscopy. Depending on alloy composition, either γ-like or χ/η-like local phase transformations (LPT) are observed along stacking faults and microtwin boundaries. Similar to their Ni-base counterparts, the occurrence of χ/η-like LPTs is accompanied by a significant increase in creep strength. Atomic-scale energy dispersive X-ray spectroscopy investigations reveal that especially Ta, W and Cr are enriched at these planar defects and trigger the favourable χ/η-like LPTs in complex polycrystalline CoNi-base superalloys. Based on these investigations, potential guidelines for future alloy design are proposed.
5:20 PM
Microstructural Characterization of Cost-effective Inconel 738LC Superalloy after Tensile Deformation at Various Temperatures: Hyo Ju Bae1; Kwang Kyu Ko1; Eun Hye Park1; Joong Eun Jung2; Jung Gi Kim1; Hyokyung Sung1; Jae Bok Seol1; 1Gyeongsang National University; 2Korea Institute of Materials Science
Inconel 738LC has been used in gas turbines as blades at high temperatures because of its excellent high-temperature mechanical properties. However, high cost due to the high addition of Co (8.00-9.00 wt%) limits their wide application. Herein, with the aim of reducing the Co contents in Inconel 738LC alloy, the chemical composition of typical Inconel 738LC is modified while increasing the tensile strength by 12% at various temperatures (room temperature-932 ℃). The mechanical properties significantly depend on the morphology and composition of Ni3(Al,Ti,Nb)-type precipitates(γ′). Nevertheless, atomic scale chemical composition changes during tensile deformation in constituent phases such as primary/secondary γ′ and matrix have not been reported. Therefore, the characterization of the modified Inconel 738LC after tensile deformation at various temperatures was investigated with comparing typical Inconel 738LC. To analyze the microstructure, multi-scale analyses were conducted using SEM/EDS, HRTEM, and APT. Details of the property-microstructure relations will be explained.