Mechanical Behavior of Nuclear Reactor Components: Small Scale Testing
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
Tuesday 8:30 AM
March 16, 2021
Room: RM 50
Location: TMS2021 Virtual
8:30 AM Invited
In-situ Micro-tensile Studies on the Effects of Ion Irradiation on the Mechanical Properties of Small-grained Alloys: Dhriti Bhattacharyya1; Alan Xu1; Mihail Ionescu1; Tao Wei1; Michael Saleh1; 1Australian Nuclear Science and Technology Organization
Ion irradiation is an attractive alternative to neutron irradiation for studying the effects of radiation damage on materials as it imparts relatively high doses (several dpa) in a short time frame (days) without activating the samples. However, the thin layer of material radiated by this technique requires the employment of small-scale testing methods such as micro-mechanical testing.Micro-mechanical testing is more suitable for the assessment of mechanical properties when the grain size is small compared with the sample size. Here, an overview of a series of studies on the effects of ion irradiation on the mechanical properties of three different materials with small grains (<2 μ m) is presented. These studies on an oxide dispersion strengthened (ODS) steel MA957, pure Ni and Ni-SiC dispersion strengthened alloy employ in situ micro-tensile testing inside the scanning electron microscope. The results are discussed in terms of their relevance to bulk mechanical properties.
9:00 AM
Bridging the Length Scales via Femtosecond Laser Machining of Micro-mesoscale Tensile Specimens: Andrew Dong1; Hi Vo1; Peter Hosemann1; Stuart Maloy2; 1University of California, Berkeley; 2Los Alamos National Laboratory
Small scale mechanical testing has significant benefits in probing microstructural features and in producing greater numbers of samples from finite volumes of material. In the nuclear field, smaller length scale specimens are necessary to account for the limited penetration depths of irradiations as well as to minimize overall radioactivity per specimen. Femtosecond laser machining is becoming an increasingly popular technique for rapidly and consistently fabricating micro to meso length scale test samples. Presently, the body of literature in this domain is sparse, and the utility of this technique, as well as small scale testing in general, is limited by the fidelity of the results. In this experiment, reduced geometry micro-mesoscale tensile samples were prepared via femtosecond laser machining to a range of gauge thicknesses and aspect ratios. The samples were pulled and analyzed in comparison to previous micro-mesoscale work in efforts to bridge the length scales in material property evaluation.
9:20 AM
α’ Precipitation and Hardness Change in Ion Irradiated High Purity FeCr Alloys: Yajie Zhao1; Arunodaya Bhattacharya2; Cristelle Pareige3; Pengcheng Zhu1; Caleb Massey2; Philip Edmondson2; Jean Henry4; Steven Zinkle1; 1The University of Tennessee; 2Oak Ridge National Laboratory; 3GPM, Université et INSA de Rouen; 4CEA, DEN, Service de Recherches Métallurgiques Appliquées, Laboratoire d’Analyse Microstructurale des Matériaux, Université Paris-Saclay
FeCr based ferritic-martensitic steels suffer from radiation-enhanced Cr-rich alpha prime phase (α’) separation which induces severe hardening and embrittlement. However, the α’ phase separation was seldom reported after high-dose rate ion irradiations. To study the hardening response of non-equilibrium α’, high-purity Fe(10-18%)Cr alloys were irradiated at varying dose rates (10-5-10-3 dpa/s) and temperatures (300-450 °C) to 0.35 or 3.5 dpa. The post-irradiation characterization, performed using atom probe tomography, revealed homogeneously distributed α’ precipitates, for temperatures down to 300 °C and up to a damage rate of 10-3 dpa/s, after ion irradiations. Most measured clustered Cr concentrations were below the equilibrium values suggested by the phase diagram, while clusters with higher Cr concentration were observed at lower dose rates or high temperatures. By combining the APT results with hardness changes measured by nano-indentation and using theoretical hardening models, the contribution of α’ to the hardening of FeCr alloys will be quantified.
9:40 AM Invited
Nanomechanical Assessment of a Neutron Irradiated U-10Zr Fuel: Maria Okuniewski1; Jonova Thomas1; Alejandro Figueroa1; Fei Tang2; Daniel Murray2; Xiang Liu2; 1Purdue University; 2Idaho National Laboratory
Uranium-zirconium (U-Zr) fuels have been investigated for decades as fast reactor fuels. However, little was previously known about the nanomechanical evolution within these fuels, in particular the fuel-cladding chemical interaction (FCCI) region and the cladding. Recent advances in nanomechanical and nanochemical characterization of nuclear fuels have furthered the nuclear community’s understanding of neutron irradiated materials. Nanoindentations were performed on an U-10 wt.% Zr fuel clad with HT-9 and irradiated in the Fast Flux Test Reactor to a burn-up of 5.7 atom %. Nanomechanical disparities were observed in the HT-9, HT-9 infiltrated with fission products, and the FCCI region. The FCCI region demonstrated the largest increase in nanohardness. The nanomechanical results will be correlated to the microstructural features observed via electron microscopy and synchrotron micro-computed tomography.
10:10 AM
Challenges to Accurate Evaluation of Bulk Hardness with Nanoindentation Testing at Low Indent Depths: Pengcheng Zhu1; Yajie Zhao1; Shradha Agarwal1; Steven Zinkle1; 1University of Tennessee
Ferritic/martensitic steels are promising structural materials for Generation IV fission and fusion reactors. High purity Fe and Fe-(3-25%)Cr in annealed and aged (100-900 hours at 475 °C) conditions were tested using nanoindentation to estimate the bulk hardness in nanoscale volumes. The effect of different test modes (constant strain rate, constant loading rate), surface preparation, and pileup corrections were evaluated; in all cases curvatures of Nix-Gao linear fitting model occurred below ~250 nm indent depths. Pile-up corrections by AFM improve the accuracy of the data and provide better correlation between nanoindentation and Vickers hardness. TEM and APT characterization of Cr-rich α’ precipitates was used to compare predicted (dispersed barrier hardening superposition) vs. measured strength values of the aged specimens. The nanoindentation responses of dual ion irradiated T91 (9MeV Fe3+ and 3.42MeV He2+, 16.6 dpa at 445 and 500 °C) will be analyzed using optimized test protocol based on aged specimen testing.
10:30 AM
High Throughput Assessment of Creep Behavior of Advanced Alloys for Model Development and Validation: Moujhuri Sau1; Zezhou Li1; Eric Hintsala2; Douglas Stauffer2; Laurent Capolungo3; Nathan Mara1; 1University of Minnesota; 2Bruker Corporation; 3Los Alamos National Labs
The mechanical performance of materials used in extreme conditions must be well-understood to facilitate materials design. Recent advancements in nanomechanical testing have proven effective in determining the interplay of strain-rate sensitivity, activation volume, activation energy and applied stress to understand time-dependent deformation from small volumes (~1μm3), for complex loading geometries, and at higher throughput than traditional creep testing. These datasets will guide and validate polycrystalline deformation models via determination of mechanism-specific parameters from nanoindentation testing of advanced steels. Elevated temperature nanoindentation tests were carried out in both inert gas and vacuum environments on two reactor steel candidates –T91 and MA957. The constitutive creep parameters of these materials were quantified using indentation-based stress relaxation tests, strain rate jump tests and electron microscopy. Datasets arising from these studies provide a fundamental understanding of creep at diminished length scales, and will be benchmarked to bulk tensile creep tests.
10:50 AM
Creep Behavior of Helium Implanted Submicron Films under Irradiation: Nargisse Khiara1; Michaël Coulombier2; Fabien Onimus1; Jean-Pierre Raskin2; Thomas Pardoen2; Yves Bréchet3; 1CEA Saclay; 2Ecole Polytechnique de Louvain; 3Science et Ingénierie des MAtériaux et Procédés
The materials used for nuclear applications undergo intense neutron irradiation that induces the formation of irradiation defects, the production of helium and the emergence of physical phenomena such as irradiation creep. The irradiation creep deformation, and the underlying mechanisms, in the presence of helium has been little investigated. The mechanical behavior of 1% and 7% helium implanted copper is first determined using both a novel approach based on the testing of on-chip thin freestanding structures developed at Université catholique de Louvain and nano-indentation. The on-chip He-implanted structures are then used to determine the irradiation creep behaviour under heavy ion irradiation. The small thickness of the material, below a few hundreds nanometers, allow full and homogenous irradiation by helium ions and heavy ions of a few hundreds keV. In parallel to these nanomechanical tests, the microstructure of the copper film before and after irradiation is characterized by Transmission Electron Microscopy.