Mechanical Behavior of Nuclear Reactor Components: Early Career
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Nanomechanical Materials Behavior Committee, TMS: Nuclear Materials Committee
Program Organizers: Clarissa Yablinsky, Los Alamos National Laboratory; Assel Aitkaliyeva, University of Florida; Eda Aydogan, Middle East Technical University; Laurent Capolungo, Los Alamos National Laboratory; Khalid Hattar, University of Tennessee Knoxville; Kayla Yano, Pacific Northwest National Laboratory; Caleb Massey, Oak Ridge National Laboratory
Wednesday 8:30 AM
March 17, 2021
Room: RM 50
Location: TMS2021 Virtual
8:30 AM Invited
On the Role of Material Pedigree to Predict Engineering Material Properties: Andrea Rovinelli1; Mark Messner1; T.-L. Sham1; 1Argonne National Laboratory
Mesoscale material models are generally developed with the goal to predict macroscopic properties of engineering materials and alloys while accounting for the inherent microstructure variability. The parameters for these models are often calibrated to best fit the available experimental results. Once calibrated, the mesoscale models are used to construct bounding curves used by engineers to estimate failure under the assumption of a unique material pedigree. A material pedigree refers to the different attributes such as material texture, chemical composition, processing parameters, grain size, etc. However, the calibration of these mesoscopic model parameters is generally done using data from open literature, such that it can be used across a wide range of stresses and temperatures. This calibration process thus violates the assumption of a unique material pedigree. In this work we perform a sensitivity study to establish the influence of material pedigree on extrapolated macroscopic material properties.
8:50 AM Invited
A Model for Dislocation Climb and Precipitate Interactions Applied to Creep in Ferritic Steel: Aaron Kohnert1; Laurent Capolungo1; 1Los Alamos National Laboratory
Creep deformation is a primary concern for structural materials, which can lead to rupture and is often accelerated by radiation in reactor conditions. In the present study, discrete dislocation dynamics is applied to examine the dislocation creep regime using a unique methodology developed to describe the 3d transport of point defects between dislocations in a general network. Accordingly, this model can address the kinetics of climb in both thermal and irradiation environments. The kinematics of motion by climb for both edge and mixed character dislocations are considered to allow a full description of the climb in tangled dislocation networks which may include junctions. These realistic networks are evolved at a variety of ambient temperatures and applied loads to simulate creep deformation. Creep rate, activity, and density recovery are compared between single phase material and crystals with varying second phase dispersions to quantify the contribution of precipitates to the creep strength.
9:10 AM Invited
Atom-probe Study of Nano-hardening Features in Neutron Irradiated RAFM Steels: Arunodaya Bhattacharya1; Philip Edmondson1; Hiroyasu Tanigawa2; Takashi Nozawa2; Josina Geringer1; Yutai Katoh1; Michael Rieth3; 1Oak Ridge National Laboratory; 2National Institutes for Quantum and Radiological Science and Technology; 3Karlsruhe Institute of Technology
Reduced activation ferritic-martensitic (RAFM) steels are currently the most promising structural material candidates for the plasma-near components of fusion energy systems. A critical concern is the irradiation-induced low-temperature hardening/embrittlement (LTHE) causing fracture toughness loss in RAFM steels. LTHE is historically attributed to hardening by dislocation loops, and other potential nano-clustering features such as Cr rich clusters. However, a fundamental mechanistic understanding of LTHE is not well-established. At ORNL, numerous RAFM steel concepts such as F82H/Eurofer97 were neutron irradiated at the High Flux Isotope Reactor (HFIR) at 300 °C to a variety of doses ranging from <5 dpa to >60 dpa. Using atom-probe tomography (APT), we will elucidate the nano-clustering behavior in the neutron irradiated RAFM steels to reveal the key solute nano-clustering mechanisms contributing to the LTHE phenomenon. Research sponsored the U.S. Department of Energy, Office of Fusion Energy Sciences under contract DE-AC05-00OR22725 with UT-Battelle LLC.
9:30 AM Invited
Microstructural Effects on the Mechanical Behavior of FeCrAl Alloys: Andrew Hoffman1; Shenyan Huang1; Steve Buresh1; Michael Schuster1; Evan Dolley1; Raul Rebak1; 1GE Research
Due to their excellent resistance to high temperature steam oxidation, FeCrAl alloys are excellent candidates for Accident Tolerant Fuel (ATF) cladding material. Although FeCrAl alloys have been used in industry for several decades, historical applications have been high temperature operation environments and therefore more work is needed to understand the mechanical properties of these alloys at room temperature and light water reactor operating conditions. It has been shown that non-optimized FeCrAl alloys are susceptible to cracking and brittle failures which can significantly affect fracture and impact toughness, strain to failure, and alloy strength. This can cause concerns with fabrication, transport, and stress corrosion cracking in these alloys. Development work on commercial FeCrAl alloys has shown that a fine-grained microstructure can significantly improve mechanical properties of these alloys. This study will go through historical development and optimization of FeCrAl microstructures, and the impact of this microstructure on various mechanical properties.
9:50 AM Invited
Novel Small Scale Mechanical Testing Techniques for Nuclear Materials: Jonathan Gigax1; Hyosim Kim1; Calvin Lear1; Matthew Chancey1; Peter Hosemann2; Yongqiang Wang1; Stuart Maloy1; Nan Li1; 1Los Alamos National Lab; 2University of California-Berkeley
Mechanical property evaluation of neutron irradiated materials is the technique of choice for understanding degradation in service. However, the limited number of facilities and long irradiation times severely restricts the testing throughput. Ion irradiation is one approach to screening candidates quickly as the irradiation times are orders of magnitude less, with the limited ion penetration depth as a major drawback to the technique. In light of this, we have developed novel techniques for extracting additional information from this region. Our studies have focused on improving existing nanoindentation approaches, developing microshear compression testing, and expanding mechanical testing to the mesoscale. These techniques span the ranges typically achieved by light and heavy ions, and have provided new insights into the effects of radiation damage on materials.
10:10 AM Invited
Probing the Mechanical Behavior of Irradiated Materials through Micromechanical Testing: Sezer Ozerinc1; 1Middle East Technical University
Combining the recent advances in micromechanical testing with accelerated ion beam testing capabilities provide new opportunities for gaining insight into the mechanical behavior of materials under irradiation conditions. We have developed an in-situ irradiation-induced creep setup that enables direct measurements on micropillar specimens under MeV-heavy ion irradiation. The results show that irradiation-induced creep is mediated by point defects in a wide range of amorphous materials. We also probe irradiation-induced effects in nanostructures, which provides a deeper understanding of interface-dominated mechanical behavior. MeV-heavy ion irradiation on Cu-Nb nanolayers results in a competition between ion beam-induced mixing and phase separation. As irradiation temperature decreases, the effect of mixing starts to dominate, forming rougher interfaces. Micropillar compression on these irradiated specimens shows that ion-beam mixing enhances the shear strength of the interface. The findings quantify the mechanical behavior of irradiated interfaces through direct measurements for the first time in the literature.
10:30 AM Invited
Small Scale Mechanical Testing of Nuclear Fuel and Cladding: David Frazer1; Joshua White2; Tarik Saleh2; Fabiola Cappia1; Fei Teng1; Daniel Murray1; Cameron Howard1; Colin Judge1; 1Idaho National Lab; 2LANL
A thorough knowledge of the mechanical properties of fuel and cladding is important for understanding the pellet cladding mechanical interaction during operation of a nuclear reactor. A challenge with researching the mechanical properties of irradiated materials, particularly fuel, is that the high levels of radioactivity make testing the specimens difficult: usually requiring the use of time consuming and expensive hot-cells. Small scale mechanical testing (SSMT) enables probing the mechanical properties on highly irradiated materials using minute volumes of material which greatly reduces the radiation dose to workers and allowing testing without the use of hot-cells which reduces both expense and process time. Due to the small volume of the specimens required for testing SSMT also enables targeting specific microstructural features such as grain boundaries. Measurements of fresh fuel samples over temperature, the implementation of these techniques to irradiated fuels, and advanced cladding materials and concepts, will be addressed and evaluated.
10:50 AM Invited
Atomistic Simulations and Theoretical Modelling of the Yield Behavior of Industrial Tantalum Alloys: Divya Singh1; Satish Rao2; Jaafar El-Awady1; 1Johns Hopkins University; 2UES Inc.
Tantalum and its alloys, in particular those with Tungsten and Hafnium (Ta-10W-2.5Hf (T-222) and Ta-8W-2Hf (T-111)) are of significant interest for high temperature space and nuclear applications. These alloys demonstrate outstanding strength, along with improved corrosion and creep properties at high temperature. However, the high-temperature mechanical and fracture properties of these alloys are not fully understood. We first present molecular dynamics simulations to determine the core structure and mobility of a/2[111] dislocations using Johnson-Zhou interatomic potentials in both these alloys. The Suzuki model of solid solution strengthening, adapted for concentrated BCC alloys, is then utilized to predict the yield strength of these alloys as a function of temperature. Such model results are then compared with direct molecular dynamics simulation data on the mobility of a/2[111] dislocations as well as experimental data on the yield behavior of these alloys as a function of temperature and shown to be in good correspondence.
11:10 AM Invited
The Merit of In-situ Environmental TEM for the Study of Tungsten under Fusion-relevant Conditions: Maanas Togaru1; Rajat Sainju1; Yuanyuan Zhu1; 1University of Connecticut
Tungsten has been selected as the plasma-facing divertor material at the ITER. With a view to transient events, air ingress accidents and future DEMO PFM safety, engineering tungsten with enhanced oxidation resistance and mechanical performance including ductility and DBTT has attracted an increasing attention in the fusion community. However, significant knowledge gaps exist in the understanding of the oxidation mechanism and kinetics of tungsten and associated alloys, and how passivating elements conflict and/or compromise the mechanical properties. In this talk, we demonstrate how the novel MEMS-based in-situ environmental TEM, capable of mimicking the actual air ingress scenario at atmospheric pressure, can be utilized to directly access scale phases evolution and elucidate the mechanisms underpinning oxidation onset and kinetics. New insights on irradiation-assisted tungsten and tungsten alloy oxidation hold a great promise for reinforcing design criteria that balance mechanical properties with oxidation resistance for the development of next-generation tungsten-based PFMs.