Phase Stability in Extreme Environments II: Oxidation and Hydrogen influence on Phase Changes
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee, TMS: Alloy Phases Committee, TMS: Nuclear Materials Committee
Program Organizers: David Frazer, Idaho National Laboratory; Andrew Hoffman, Catalyst Science Solutions; Kinga Unocic, Oak Ridge National Laboratory; Janelle Wharry, Purdue University; Kaila Bertsch, Lawrence Livermore National Laboratory; Raul Rebak, GE Global Research; Tianyi Chen, Oregon State University; Marie Romedenne, Oak Ridge National Laboratory
Thursday 8:30 AM
March 7, 2024
Room: Bayhill 18
Location: Hyatt
Session Chair: Marie Romedenne, ORNL
8:30 AM Invited
Impact of Build/Print Variations on Steam Oxidation Performance of 316L Stainless Steel: Elizabeth Sooby1; Scott Schier1; Ana Stevanovic1; Brian Jaques2; Patrick Warren1; 1University of Texas at San Antonio; 2Boise State University
Additive manufacturing (AM) has emerged as a promising solution for the high-throughput fabrication of unique and complex geometries required in the construction of nuclear reactors. The inherent complexities of the AM process can result in unexpected material properties and performance, necessitating further research. In this study, we investigate the effects of various build conditions (laser energy and spatter deposition) on defect formation and steam oxidation kinetics, while implementing in-situ part identification throughout the entire process. Our focus is on characterizing oxidized AM 316LSS samples subjected to high-temperature steam environments (<65% pH2O) at 800°C using both surface and cross-sectional characterization techniques like Scanning Electron Microscopy (SEM) and Raman. SEM provides detailed microstructural characterization of surface and cross-sectional features, including oxide films and pitting defects. Raman spectroscopy analysis is employed to determine the chemical composition of the polished/passivated surface oxides that form on the samples. By correlating materials characterization and testing with print parameters, print orientation, sample history, and thermal conditions, we aim to enhance our understanding of the relevant performance properties for high temperature steam exposed applications. The findings of this study highlight the potential of AM in the construction of reliable and safe nuclear reactors, leveraging in-situ part qualification.
9:00 AM
Degradation Mechanisms of Steels and Ni-based Alloys in Hydrogen/Water Vapor High Temperature Environments: David Kniep1; Mario Rudolphi1; Mathias Galetz1; 1DECHEMA-Forschungsinstitut
Hydrogen-rich high temperature environments are becoming more prevalent due to the need to substitute natural gas. Many chemical processes, including solid oxide electrolyzer cells (SOECs) and their periphery, are facing hydrogen and water vapor degradation. Candidate materials, e.g. for interconnects, for these environments require high electrical conductivity, creep resistance, and microstructure and phase stability at temperatures above 825°C. As potential materials, six ferritic interconnect materials with decreasing amounts of chromium (AISI446, Crofer 22 APU, Crofer 22 H, AISI442, AISI410, P91) and three Ni-based alloys (Haynes 244, Haynes 233, Haynes 230) were evaluated for their stability in 10% H2/90% H2O and 50% H2/50% H2O between 700-900°C up to 1000 hours. The degradation mechanisms of these selected candidate materials for SOEC components were investigated and characterized. The materials show different behavior in terms of scale growth, changes in the subsurface zone and changes in the mechanical properties from hydrogen uptake.
9:20 AM Invited
The Less Understood Impact of Environmental Degradation on Phase Stabilities in High Temperature Alloys: Rishi Pillai1; Marie Romedenne1; 1Oak Ridge National Laboratory
High temperature alloys typically rely on solid solution or precipitation strengthening for their mechanical properties. However, exposure in corrosive environments drives compositional changes in the alloy subsurface which consequently results in critical depletion of alloy constituents or dissolution of strengthening phases. This work will demonstrate the role of environment and key chemical interactions between alloying constituents in governing these degradation processes through various case studies with uncoated and coated Fe- and Ni-base alloys tested in a wide range of environments such as O2, CO2, H2O, molten halide salts and liquid metals. Advanced thermokinetic modeling will be employed to understand the underlying mechanisms and predict the impact of corrosion-induced degradation on stabilities of strengthening phases and in turn on mechanical properties. The modeling results will be compared with experimental data and microstructural characterization findings.
9:50 AM Break
10:10 AM Invited
Atomic-scale Understanding of the Hydrogen Embrittlement Mechanism in Model and Commercial Austenitic Steels Using Cryogenic Transfer Atom Probe Tomography: Zehao Li1; Semanti Mukhopadhyay1; Tingkun Liu1; Dallin Barton1; Arun Devaraj1; 1Pacific Northwest National Laboratory
For the future hydrogen-based clean energy economy, austenitic stainless steels (γ-SS) are increasingly demanded for transporting and storing hydrogen due to their excellent corrosion and fracture resistance. However, γ-SSs may suffer from significant hydrogen-induced degradation, i.e., hydrogen embrittlement (HE) depending on the austenite stability, local H concentration, and H-induced deformation mechanisms. In order to establish a basis for the rational design and fabrication of γ-SSs with improved HE resistance, it is essential to gain insight into the HE mechanism by clarifying the interaction of hydrogen with various microstructure features in γ-SSs at the atomic scale. In this talk, we will highlight our results on visualizing and quantifying the hydrogen trapping sites in model and commercial γ-SSs using a state-of-the-art cryogenic transfer atom probe tomography (LEAP 6000XR). The effects of deformation and H concentration on the HE in γ-SSs will be elucidated based on detailed microstructure analysis.
10:40 AM
Effect of Hydrogen on the Phase Stability of Steels: Tilmann Hickel1; Ali Tehranchi2; Joerg Neugebauer2; 1BAM Federal Institute for Materials Research and Testing; 2Max-Planck-Institut fuer Eisenforschung
In this work, we studied the role of extreme hydrogen concentrations on the relative stability of the fcc/bcc/hcp phases using the ab initio thermodynamics. The results indicate that at low hydrogen chemical potentials the stability of the fcc phase, which can be representative of retained austenite (RA) in steels, is slightly enhanced by the presence of H atoms. In contrast, at high hydrogen chemical potentials the bcc phase is stabilized by H. Moreover, since the excess volume of the hydrogen-rich bcc phase is significantly larger than that of the fcc phase, the presence of a stress field can change the relative stability of these phases in the coexistence regions of the phase diagram. This feature is particularly important for cyclic loading conditions: during loading cycles forward and reverse phase transformations occur and the H released by these transformations can damage the material.
11:00 AM
Non-ideality of Hydrogen Isotope Permeation in Metals & Alloys: Kacie Breeding1; Steven Zinkle1; Weicheng Zhong2; 1University of Tennessee, Knoxville; 2Oak Ridge National Laboratory
Tritium extraction from breeder blanket hot working fluids is a key technological feasibility issue for fusion energy. A leading extraction method utilizes vacuum permeators, where tritium selectively permeates through tubing material with high hydrogen isotope permeability. Group V metals & alloys have the highest reported permeability, however experimental results can vary wildly by orders of magnitude (including positive and negative slopes for permeability versus inverse temperature). We have performed experimental permeation tests on V and Nb alloys over a wide range of pressures and temperatures and analyzed the conditions that lead to apparent deviation from Sievert’s law for diatomic gas solubility. In general, key phenomena such as time constants for molecule dissociation and reattachment as well as the time to approach solubility limits need to be considered when setting up test temperatures and pressures. Additional factors include uninvestigated phase transitions, permeate formation, hydrogen trapping & non-ideal gaseous permeate behavior.