Phase Stability in Extreme Environments: Phase Stability in Nuclear Environments II
Sponsored by: TMS Structural Materials Division, TMS Materials Processing and Manufacturing Division, TMS: Corrosion and Environmental Effects Committee, TMS: Nuclear Materials Committee, TMS: Phase Transformations Committee
Program Organizers: 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
Monday 2:00 PM
March 20, 2023
Room: 28C
Location: SDCC
Session Chair: Andrew Hoffman, GE Research; Jia-Hong Ke, Idaho National Laboratory
2:00 PM Introductory Comments
2:10 PM Invited
Effect of α` Chromium-rich Precipitates on the Tensile Properties of Commercial FeCrAl Alloy: Hamdy Abouelella1; Andrew Hoffman2; Rajnikant Umretiya2; Nathan Almirall2; Benjamin Beeler1; Raul Rebak2; 1North Carolina State University; 2Ge Research
FeCrAl alloys have been considered a candidate for accident tolerant fuel-cladding and structural materials because of their high-temperature strength and superior oxidation resistance. However, the tendency to form α` chromium-rich precipitates increases the hardness and decreases the ductility of the alloy. Kanthal APMT tubes, an advanced FeCrAl alloy, were thermally aged at 450℃ for 1000 hours to form α` precipitates. Subsequently, tensile tests were performed at two different temperatures with as-received and aged tubes to understand the effect of α` chromium-rich precipitates on tensile properties. The results show that α` precipitates will indeed increase the strength and slightly decrease the ductility. However, the tensile strength concomitantly increases, offsetting that ductility drop. The results indicated that alpha prime precipitates do not preclude FeCrAl use as a cladding material.
2:40 PM
Reduced Alpa-prime Precipitation during Thermal Annealing and Irradiation in Ultrafine-grained or Nanocrystalline FeCrAl Alloys: Haiming Wen1; Maalavan Arivu1; Rinat Islamgaliev2; 1Missouri University of Science and Technology; 2Ufa State Aviation Technical University
FeCrAl alloys are leading candidate materials for cladding of accident tolerant fuels in light water reactors replacing Zircaloy owing to their high temperature strength and corrosion resistance in steam environments. However, FeCrAl alloys suffer from embrittlement after long-term thermal aging at ~500 oC and lower, due to α’ Cr precipitation, which is detrimental to the structural performance and corrosion resistance. Another major issue for FeCrAl alloys in nuclear reactors is the irradiation-enhanced α′ precipitation, leading to irradiation-induced hardening and embrittlement. Bulk ultrafine-grained and nanocrystalline alloys possess drastically higher strength than their conventional coarse-grained counterparts, and are anticipated to have significantly enhanced irradiation tolerance. In this study, ultrafine-grained and nanocrystalline FeCrAl alloys were manufactured by equal-channel angular pressing and high-pressure torsion, respectively. The thermal aging and irradiation behavior of these materials were carefully studied. Results indicated that reducing grain size can hinder both thermally induced and irradiation enhanced α’ Cr precipitation.
3:00 PM
Aging-Induced α' Precipitates in FeCrAl Alloys and Its Effects on Corrosion Behavior: Rupesh Rajendran1; Rajnikant Umretiya2; Andrew Hoffman2; Richard Blair2; Christopher Perlee2; Raul Rebak2; 1Georgia Institute of Technology; 2GE Global Research
FeCrAl alloys are candidate materials for accident tolerant fuel (ATF) cladding applications in light water reactors (LWR) owing to their high resistance to hydrothermal corrosion, high temperature steam oxidation, fretting, and creep properties. Although these alloys were previously used in high temperature applications, Cr-rich α' phase can be precipitated at temperatures below the miscibility gap. The effect of volume fraction and morphology of α' phase on the material behavior of FeCrAl alloys is not clearly understood. In this work, we study the effects of aging temperature and duration of Fe-Cr-Al-Mo-based advanced powder metallurgy tube (APMT) specimens on the α' phase and its effect on electrochemical behavior in 3.5%NaCl environment. Preliminary results show an increase in α' phase increases the polarization resistance and reduces the corrosion rate, enhancing corrosion performance in chloride environments. Hydrothermal corrosion and high temperature steam oxidation results are found not to be affected by the α' phase.
3:20 PM Break
3:50 PM Invited
Effects of Aluminum Addition and Point Defects on Cr-rich α' Phase Stability in FeCrAl Alloys: Jia-Hong Ke1; Andrea Jokisaari1; 1Idaho National Laboratory
FeCrAl alloys have been considered as candidate accident-tolerant fuel cladding materials for nuclear reactor applications. Recent experimental studies showed radiation-accelerated formation of α' in FeCrAl contributing to hardening and embrittlement, but it remains unclear how the ternary solute element affects the stability of α’ precipitates compared to the binary FeCr. In this work, the non-dilute chemical effect of Al on FeCr phase stability is studied by density functional theory and cluster expansion approaches. The simulation result shows a pronounced change of Cr solubility in bcc Fe by adding Al and the rejection of Al from the α’ precipitate. We also use the model to explore the vacancy defect as a potential nucleation site of Cr-rich clusters. The atomistic insight and the limitation of the study will be discussed.
4:20 PM
Atom Probe Characterization of Al/Mo Effects on α’ Precipitation in FeCrAl Cladding Alloys: Nathan Almirall1; Andrew Hoffman1; Rajnikant Umretiya1; Michael Worku1; Christopher Perlee1; Raul Rebak1; Hamdy Abouelella1; 1GE Research
FeCrAl alloys possess high temperature strength and oxidation resistance desirable for nuclear fuel cladding in loss of coolant accident scenarios. In order to qualify the next generation of UO2 fuel cladding, the safe operation of neutron irradiated FeCrAl alloys must be verified. One outstanding issue in the FeCrAl alloy system is the irradiation-enhanced Cr-rich α’ precipitation causing hardening and corresponding embrittlement. Crucially, the thermo-kinetic effect of Al & Mo alloying additions on the α’ precipitation is not fully understood. Al and Cr additions provide corrosion resistance by forming passive oxides. However, recent aging studies observed that while Al suppresses the α’ precipitation by lowering the miscibility gap, it may simultaneously enhance precipitation kinetics. This presentation covers results from Atom Probe Tomography (APT) to characterize the GRC key fuel cladding alloy FA-SMT (Fe21Cr5Al3Mo) to gain a better understanding of the Al/Mo effect on α’ precipitation.
4:40 PM
Determining the Phase Boundary between α and α+α’ at Low-temperatures with Proton Irradiations and APT: Yajie Zhao1; Pengcheng Zhu1; Jonathan Poplawsky2; Arunodaya Bhattacharya2; Jean Henry3; Steven Zinkle4; 1University of Tennessee, Knoxville; 2Oak Ridge National Laboratory; 3CEA, DEN, Service de Recherches Métallurgiques Appliquées, Laboratoire d’Analyse Microstructurale des Matériaux, Université Paris-Saclay; 4University of Tennessee, Knoxville; Oak Ridge National Laboratory
FeCr binary alloys are useful model alloy representations of ferritic-martensitic steels, which are important structural materials for various applications. The phase separation to form Cr-rich alpha prime precipitates (á’) can induce severe hardening and embrittlement. However, accurate experimental á/á+á’ phase boundary assessments at low-intermediate temperatures are not available due to slow diffusivity of Cr atoms at temperatures below 450 °C that inhibits achievement of thermal equilibrium by annealing alone, and contradictory predictions exist from computational modeling. In order to accelerate the kinetics, proton irradiations were conducted at 250-450 °C up to 2 dpa. Thermal aging at 450-500 °C was also performed to expand the investigated temperature region. The temperature-dependent precipitate formation and matrix solute concentration after irradiations and thermal treatments were measured through atom probe tomography. á’ precipitates were observed in various specimens containing 6-18% Cr. The possible correlation of Cr-enriched clusters and dislocations was revealed by STEM-EDX technique.
5:00 PM
Phase-field Modeling of Laves Phase Precipitate in Accident Tolerant Cladding: Jeonghwan Lee1; Kunok Chang1; 1Kyung Hee University
Fe-Cr-Al alloy has been studied as a candidate material for accident-resistant cladding because of its superior high-temperature oxidation resistance. Recently, it has been experimentally reported that the Laves phase is precipitated when the Fe-13.5Cr-4.7Al alloy is irradiated with Fe+ ions, which governs irradiation embrittlement. Phase-field modeling has been widely used to simulate stable phase precipitation, but recently, it is also possible to simulate precipitation behavior that occurs in situations quite far from equilibrium, such as ion irradiation. The phase-field modeling is being improved to simulate the precipitate process even if the thermodynamic stable phase is not confirmed. In this study, the precipitation behavior was simulated in the Fe+ ion irradiation environment for the Laves phase, which is not confirmed as a thermodynamically stable phase, and the effects of the material damage expressed and temperature on precipitate behavior were evaluated. The simulation results were validated through the experimental results.