Tarik A Saleh

·Understanding the comparability of gaugeless ring pull testing across studies.·Strength and ductility are measured for FeCrAl in the hoop direction.·A mechanics analysis is performed for bending strains in gaugeless ring pull.·A preferred region of mandrel diameters exists for consistent results.·Digital image correlation is used to evaluate ring contact slip. Inconsistencies in ring-pull testing methods for thin-walled tubes make it difficult to compare a material's mechanical properties in the hoop direction presented in past publications. The effect of test setup, specifically mandrel diameter, was investigated for nuclear fuel cladding tubes of the iron-chromium-aluminium (FeCrAl) alloy, C26M (Fe-12Cr-6Al-2Mo). Mandrel diameter for ring-pull testing can change how the ring deforms and friction effects, further convoluting the results from testing. To address the impact of mandrel size in relation to ring diameter, gaugeless ring-pull samples were tested across a range of mandrel diameters and compared to uniaxial tensile tests from the same tube of material. Two groups of samples were tested: an as-received, low ductility sample set and an annealed, high ductility sample set, both cut from the same extruded tube. By pairing systematic variation of mandrel geometry with analysis of local strain gradients using digital image correlation, this study investigates the effect of test fixture geometry on apparent mechanical properties and effective strain fields and provides guidance for comparing previously published data. Certain features in uniaxial stress-strain curves (namely the yield strength, ultimate tensile strength, and uniform elongation) appeared to have analogies in the effective stress-strain curves from ring-pull testing. These corresponding features are compared to expose biases in the analysis of material properties using gaugeless ring-pull and to provide novel guidance on test setup during experimental design.

Continuing to refine our knowledge of the evolving mechanical properties of nuclear fuel over the entire fuel service cycle is necessary to understand the pellet-clad mechanical interaction that occurs in the fuel rods during the operation. A challenge with measuring the mechanical properties of irradiated fuels is their high levels of radioactivity that usually require the use of hot cells making testing time consuming and expensive. Nanoindentation based techniques can be employed on minute volumes of material to measure mechanical properties, including Young ' s modulus, hardness, and creep stress exponents. Increasing the mixed oxide fuels mechanical properties database through a variety of testing techniques should enhance modelers ' abilities to predict failure mechanisms in the fuel/clad interface. A current challenge to testing mixed oxide fuels is the plutonium component in the fuel. Mixed fluorite type oxides with ceria (CeO 2 ) can be used as a surrogate for mixed oxide fuels. In this study, (U,Ce)O 2 solid solutions samples are used to develop elevated temperature nanoindentation and nanoindentation creep testing methods for use on mixed oxide fuels. Nanoindentation testing was performed on 3 separate (U x-1 ,Ce x )O 2 compounds ranging from x equals 0.1 to 0.3 in equal steps at temperatures up to 800 degrees C: their Young ' s modulus, hardness, and creep stress exponents were evaluated. The Young ' s modulus decreases in the expected linear manner while the hardness decreases in the expected exponential manner. The nanoindentation creep experiments at 800 degrees C give stress exponent values, n = 4.7 - 6.9, that suggests dislocation motion as the deformation mechanism.

The fabrication of bulk delta-phase Zirconium Hydride (delta-ZrHx) using Zircaloy-4 as a precursor is herein reported. Characterization using electron-microscopy methods indicate that the fabricated material is of a single-phase. Sn-rich segregation zones have been observed to form as a direct result of the hydriding process. These findings experimentally validate previous ab initio calculations on the influence H incorporation in Zircaloy-4 constitutional elements such as Sn, Fe and Cr. The effect of hydriding and Sn segregation on pre-existing Zr(Fe,Cr)(2) Laves phases is also evaluated. Major implications on the development of moderators for use in microreactors within the nuclear industry are discussed.

The next generation of nuclear materials must withstand severe operating conditions including high temperatures and irradiation exposure. Oxide dispersion strengthened steels, especially 14YWT, have shown promise as a durable material under these conditions. Understanding the irradiation-enhanced creep of structural components is fundamental to evaluating their suitability for applications in reactor environments. Ion irradiations can be used to expedite irradiation testing, but they have a restricted depth of penetration, limiting the characterization of changes to the material’s properties. Small-scale mechanical testing combined with ion beam irradiations has the potential to evaluate the irradiation-enhanced creep of materials. In this study, in-situ transmission electron microscopy nanopillar creep studies on 14YWT were performed with simultaneous ion beam irradiation. The irradiation increases the measured strain rate by an order of magnitude. Variable temperature ex-situ nanoindentation creep studies were performed between room temperature and 1073 K on control samples of 14YWT; observations indicated that there was a change in the deformation mechanism between 873 K and 1073 K, which agrees well with macro-scale mechanical testing. These results validate continued research into applying these meso-scale testing techniques to nuclear materials in the future.

Two new refractory amorphous high-entropy alloys (RAHEAs) within the W–Ta–Cr–V and W–Ta–Cr–V–Hf systems were herein synthesized using magnetron-sputtering and tested under high-temperature annealing and displacing irradiation using in situ Transmission Electron Microscopy. While the 14W-41Ta-26Cr-19V in at.% RAHEA (defined as WTaCrV RAHEA) was found to be unstable under such tests, additions of Hf in this system composing a new quinary 24W-40Ta-18Cr-5V-13Hf in at.% RAHEA (defined as WTaCrVHf RAHEA) was found to be a route to achieve stability both under annealing and irradiation. A new effect of nanoprecipitate reassembling observed to take place within the WTaCrVHf RAHEA under irradiation indicates that a duplex microstructure composed of an amorphous matrix with crystalline nanometer-sized precipitates enhances the radiation response of the system. It is demonstrated that tunable chemical complexity arises as a new alloy design strategy to foster the use of novel RAHEAs within extreme environments. New perspectives for the alloy design and application of chemically-complex amorphous metallic alloys in extreme environments are presented with focus on their thermodynamic phase stability when subjected to high-temperature annealing and displacing irradiation. •Two new Refractory Amorphous High Entropy Alloys (RAHEAs) were synthesized.•Extensive tests under high temperature annealing and irradiation were performed.•The quaternary WTaCrV RAHEA was found the thermodynamic unstable.•The quinary WTaCrVHf RAHEA presented excellent thermodynamic stability.•Crystalline radiation-induced defects are absent in RAHEAs.

High-entropy materials represent the state-of-the-art on the alloy design strategy for future applications in extreme environments. Recent data indicates that high-entropy alloys (HEAs) exhibit outstanding radiation resistance in face of existing diluted alloy counterparts due to suppressed damage formation and evolution. An extension of the HEA concept is presented in this paper towards the synthesis and characterization of novel high-entropy ceramics as emergent materials for application in environments where energetic particle irradiation is a major concern. A novel carbide within the quinary refractory system CrNbTaTiW has been synthesized using magnetron-sputtering. The material exhibited nanocrystalline grains, single-phase crystal structure and C content around 50 at.%. Heavy-ion irradiation with in-situ Transmission Electron Microscopy was used to assess the irradiation response of the new high-entropy carbide (HEC) at 573 K and a comparison with the HEA within the system is made. No displacement damage effects appear within the microstructures of both HEA and HEC up to a dose of 10 displacements-per-atom. Surprisingly, the HEC has not amorphized under the investigated conditions. Xe was implanted in both materials and bubbles nucleated, but smaller sizes compared with conventional nuclear materials shedding light they are potential candidates for use in nuclear energy. [Display omitted]

We developed an automated tool, Nanoindentation Neo package for the analysis of nanoindentation load–displacement curves using a Genetic Algorithm (GA) applied to the Oliver-Pharr method (Oliver et al.,1992). For some materials, such as polycrystalline isotropic graphites, Least Squares Fitting (LSF) of the unload curve can produce unrealistic fit parameters. These graphites exhibit sharply peaked unloading curves not easily fit using the LSF, which tends to overestimate the indenter tip geometry parameter. To tackle this problem, we extended our general materials characterization tool Neo for EXAFS analysis (Terry et al., 2021) to fit nanoindentation data. Nanoindentation Neo automatically processes and analyzes nanoindentation data with minimal user input while producing meaningful fit parameters. GA, a robust metaheuristic method, begins with a population of temporary solutions using model parameters called chromosomes; from these we evaluate a fitness value for each solution, and select the best solutions to mix with random solutions producing the next generation. A mutation operator then modifies existing solutions by random perturbations, and the optimal solution is selected. We tested the GA method using Silica and Al reference standards. We fit samples of graphite and a high entropy alloy (HEA) consisting of BCC and FCC phases. [Display omitted] •Developed machine learning algorithm for nanoindentation using Oliver-Pharr method.•Automated analysis of measurements.•Extension of our Neo Genetic Algorithm package to another surface science technique.