Accelerated Materials Evaluation for Nuclear Applications Utilizing Irradiation and Integrated Modeling: Accelerated Materials Evaluation
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: Assel Aitkaliyeva, University of Florida; Peter Hosemann, University of California - Berkeley; Samuel Briggs, Oregon State University; David Frazer, Los Alamos National Laboratory
Wednesday 8:30 AM
February 26, 2020
Room: Theater A-8
Location: San Diego Convention Ctr
Session Chair: Samuel Briggs, Oregon State University
8:30 AM
A Comparative Study of Two Nanoindentation Approaches for Assessing Mechanical Properties of Ion-irradiated Stainless Steel 316: Dhriti Bhattacharyya1; Michael Saleh1; Alan Xu1; Zain Zaidi2; Christopher Hurt2; Mihail Ionescu1; 1Australian Nuclear Science and Technology Organization; 2University of New South Wales
Nanoindentation is a commonly used method to measure the hardness of surfaces with thin layers, especially in studying the change in mechanical properties of ion irradiated materials. This research compares two different methods of nanoindentation to study the changes in hardness resulting from ion irradiation of SS316 alloy using He2+ ions at beam energies of 1, 2 and 3 MeV, respectively. The first method involves the indentation of the irradiated surface perpendicular to it using the continuous stiffness mode (CSM), while the second applies the indents on an oblique surface, accessing an inclined cross-section of the irradiated material. Finite element modelling has been used to further illuminate the deformation processes below the indents in the two methods. The hardness profiles obtained from the two nanoindentation methods reveal the differences in the outcomes and advantages of the respective procedures, and provide a useful guideline for their applicability to various experimental conditions.
8:50 AM
A Comparison of Ring Pull and Axial Tensile Tests of HT-9 and 14YWT Thin-walled Tubes: Thomas Nizolek1; James Valdez1; Calvin Lear1; Cheng Liu1; Benjamin Eftink1; Tarik Saleh1; Stuart Maloy1; 1Los Alamos National Laboratory
Mechanical testing of thin-walled tubes and cladding materials is challenging, particularly for activated materials that must be handled in a hot cell environment. While tensile properties along a tube axis are easily determined using miniature dog-bone tensile samples, assessing flow strength and ductility in the hoop stress direction of a short tube is significantly more difficult. Here we develop design criteria and data analysis methods for ring pull tests, comparing ring pull versus axial tensile tests for two candidate fuel cladding materials: HT-9 ferritic/martensitic steel and 14YWT nanostructured ferritic alloy. The impact of geometry-driven bending strains on ring pull tests varies with material ductility, as shown through digital image correlation strain mapping of both alloys. The outlook for determining ultimate tensile strength and elongation to failure using ring pull tests for materials with limited ductility will be discussed.
9:10 AM
Small Scale Mechanical Testing of Ceramic Interfaces in Nuclear Materials: Characterizing the Impact of Elastic Mismatch on Stress Intensity and Property Extraction: Joseph Kabel1; Peter Hosemann1; 1University of California, Berkeley
SiC/SiC composites have gained significant attention as an accident tolerant fuel cladding for nuclear reactors to improve safety and efficiency. Component functionality depends on interfacial performance; from weak PyC at the fiber/matrix interface for toughness, to strong bonding of the environmental barrier coating to prevent corrosion and fission product release. Small scale mechanical testing has been used to probe the relevant interface properties, often applying simplified analytical analyses for strength values. However, bi-material interfaces with elastic mismatch are known to evolve a stress intensity at the free surface. Numerical analyses were applied to capture the bi-material stress intensity factor for micro-pillar and -cantilever testing. An experimental case study on SiC/PyC/SiC micro-pillars shows a shear strength dependence on PyC thickness; however, the numerical analysis reveals that increased thickness reduces the stress intensity, ultimately normalizing the failure strength property. Similarly, the stress evolution in micro-cantilevers containing SiC/Cr and SiC/CrN interfaces is presented.
9:30 AM
Multiple Scale Mechanical Testing of Neutron Irradiated FeCrAl Alloys: Benjamin Eftink1; David Frazer1; Todd Steckley1; Matthew Quintana1; Paul Caccamise1; Tobias Romero1; Stuart Maloy1; Tarik Saleh1; 1Los Alamos National Laboratory
Mechanical tests of irradiated materials rely on small sample volumes due to i) limited space in test reactors and ii) limited damage depth for accelerator irradiations. Understanding the connection between the micro- and nano- scale to bulk testing techniques is therefore valuable. As part of an effort to extract useful mechanical response from limited volumes of irradiated materials, multiple mechanical testing techniques were performed on neutron irradiated FeCrAl alloys. Techniques spanning bulk miniature tensile, shear punch, micro-hardness, nano-indentation, and micro-pillar compression tests were conducted. Merits of the techniques and relationships comparing the bulk tensile properties to the micro- and nano-scale testing will be discussed.
9:50 AM
In-situ Studies on the Mechanical Properties of He Ion Irradiated Nanotwinned Ag: Tongjun Niu1; Jin Li1; Jie Ding1; Yifan Zhang1; Ruizhe Su1; Jaehun Cho1; Sichuang Xue1; Zhongxia Shang1; Di Chen2; Yongqiang Wang3; Haiyan Wang1; Xinghang Zhang1; 1Purdue University; 2University of Houston; 3Los Alamos National Laboratory
Recent studies show that twin boundaries are effective defect sinks in eliminating radiation-induced defects. However, the influence of radiation-induced defects on the mechanical behavior of nanotwinned (NT) materials is less well understood. In this study, we investigate the mechanical properties of He ion irradiated NT Ag using in-situ micropillar compression tests. Post-compression TEM analysis of deformed pillars shows that deformation induces prominent detwinning in as-deposited NT Ag, whereas He bubbles and stacking faults (SFs) generated during irradiation leads to much less detwinning in irradiated Ag. The radiation hardening mechanism and the influence of He bubbles on the deformation behavior of NT Ag are discussed.
10:10 AM Break
10:25 AM
A Virtual Experiment Approach to Positron Annihilation Spectroscopy: Aaron Kohnert1; Laurent Capolungo1; 1Los Alamos National Laboratory
Positron annihilation lifetime spectroscopy is a technique used to analyze the vacancy and vacancy cluster content of irradiated materials, providing a unique means to measure radiation damage features too small for direct observation in electron microscopes. On the other hand, lifetime spectra require interpretation to extract quantitative information. This study uses an integrated modeling approach to generate lifetime spectra from fully representative vacancy cluster size distributions obtained under a variety of damage conditions from cluster dynamics modeling. The virtual spectra are compared to experimental datasets and analyzed to determine how reliably spectrum fitting techniques such as the two trap method can extract quantitative information in the case of complex size distributions. Finally, the effects of uncertainty in key parameters such as trapping coefficients and trapped positron lifetimes are explored systematically.
10:45 AM
Rapid Investigation of Irradiation Temperature Sensitivity Using Charged Particles: Andrew London1; Chris Hardie1; Joven Lim1; Tonci Tadić2; 1UK Atomic Energy Authority; 2Ruđer Bošković Institute, Croatia
In service, materials experience neutron irradiation over a wide range of temperatures. The evolution of irradiation damage is particularly sensitive to the material’s temperature. Therefore, there is a need to develop, evaluate and screen materials for these sensitivities. Experimental validation of the mechanisms of irradiation damage is also required with high temperature fidelity. Ion irradiation can quickly reproduce most features of the damage caused by high-energy neutrons. We report the development of a new technique which uses ion irradiation and linear thermal gradient to produce a wealth of data over a range of irradiation temperatures from a single irradiation experiment. We applied this new technique to an age hardened CuCrZr alloy, Fe-Cr alloys and Fe9Cr steels. Nanoindentation revealed the mechanical response as a function of irradiation temperature and the microstructure was characterized using site-specific microscopy. A wide range of responses were quantified with high temperature accuracy at moderate irradiation doses.
11:05 AM
Mechanical Characterization of Three Neutron Irradiated HT-9 Heats (ORNL, LANL and EBR II) at LWR and Fast Reactor Relevant Temperatures: Ramprashad Prabhakaran1; Mychailo Toloczko1; Kumar Sridharan2; 1Pacific Northwest National Laboratory; 2University of Wisconsin-Madison
9-12 weight% ferritic-martensitic steels such as HT-9 are being considered as candidate structural materials for fast, advanced LWR, and fusion reactors due to their excellent resistance to radiation-induced void swelling, good irradiation creep properties, microstructural stability, and thermal conductivity. However, the extreme hardening and low fracture toughness that occur at irradiation temperatures below 430°C is a serious issue. To address this concern, systematic investigations on the mechanical behavior and microstructure of HT-9 with slight variations in chemical composition and heat treatment are needed over a wide range of doses and temperatures to better understand the source of hardening. Mechanical characterization was performed on three HT-9 heats with different processing conditions irradiated to 6 dpa (Advanced Test Reactor, Idaho) at 291°C, 360°C and 431°C to understand the effects of radiation damage, and to provide insight on desirable HT-9 processing conditions.
11:25 AM
Direct Measurement of Radiation Damage Through the Energy Stored in Defects: Simulations and Experiments: Charles Hirst1; Penghui Cao2; Michael Short1; 1Massachusetts Institute of Technology; 2University of California, Irvine
From the ashes of the 1957 Windscale nuclear disaster, new scientific understanding emerged; the thermally-activated migration and annihilation of defects resulted in a significant energy release. Fast forward 60 years and this phenomenon may be harnessed to directly measure radiation damage within a material. Current characterisation techniques, such as Transmission Electron Microscopy, have fundamental limitations that restrict analysis to a subset of the defects in a sample. This can result in oversight of the defects responsible for irradiation-induced changes in properties. We propose to leverage the Windscale findings, to measure defect populations through their characteristic energy release upon annealing. This has been successfully simulated, using molecular dynamics, to visualise the defect recovery mechanism and to predict the macroscopic stored energy release. Current experiments are focussed on developing differential scanning calorimetry as an analytical technique for radiation damage evaluation which has the potential to greatly accelerate progress in nuclear materials science.
11:45 AM
Recent Applications of Ex-situ Transient Grating Spectroscopy to the Study of Radiation-induced Degradation of Nuclear Materials: Sara Ferry1; Cody Dennett2; Angus Wylie1; Pär Olsson3; Michael Short1; 1Massachusetts Institute of Technology; 2Idaho National Laboratory; 3KTH Royal Institute of Technology
Transient grating spectroscopy (TGS) is a non-contact, non-destructive optical heterodyne detection technique used to quickly obtain acoustic and thermal transport properties in irradiated materials. TGS is a useful tool for detecting and characterizing radiation damage induced changes in nuclear materials with greater ease and speed than is afforded by traditional post-irradiation examination (PIE) techniques, and can be used both in situ and ex situ. Here, we present recent results from two ongoing ex situ studies. In the first, we expand upon previous work examining irradiation-induced thermal diffusivity changes in single crystal niobium by repeating the experiment with additional metals, and supplementing the experimental results for all tested metals with density functional theory (DFT) studies. In the second, we demonstrate that TGS can be used to detect the onset of “fuzz” development in plasma-exposed polycrystalline tungsten. This radiation damage mode is of particular concern for first-wall materials in fusion devices.