The fabrication of bulk delta-phase Zirconium Hydride (δ-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.

Refractory High-Entropy Alloys (RHEAs) hold promising potential to be used as structural materials in future nuclear fusion reactors, where W and its alloys are currently leading candidates. Fusion materials must be able to withstand extreme conditions, such as (i) severe radiation-damage arising from highly-energetic neutrons, (ii) embrittlement caused by implantation of H and He ions, and (iii) exposure to extreme high-temperatures and thermal gradients. Recent research demonstrated that two RHEAs - the WTaCrV and WTaCrVHf - can outperform both coarse-grained and nanocrystalline W in terms of its radiation response and microstructural stability. Chemical complexity and nanocrystallinity enhance the radiation tolerance of these new RHEAs, but their multi-element nature, including low-melting Cr, complicates bulk fabrication and limits practical applications. We demonstrate that reducing the number of alloying elements and yet retain high-radiation tolerance is possible within the ternary system W-Ta-V via synthesis of two novel nanocrystalline refractory medium-entropy alloys (RMEAs): the W$_{53}$Ta$_{44}$V$_{3}$ and W$_{53}$Ta$_{42}$V$_{5}$ (in at.\%). We experimentally show that the radiation response of the W-Ta-V system can be tailored by small additions of V, and such experimental result was validated with theoretical analysis of chemical short-range orders (CSRO) from combined ab-initio atomistic Monte-Carlo modeling. It is predicted from computational analysis that a small change in V concentration has a significant effect on the Ta-V CRSO between W$_{53}$Ta$_{44}$V$_{3}$ and W$_{53}$Ta$_{42}$V$_{5}$ leading to radiation-resistant microstructures in these RMEAs from chemistry stand-point of views. We deviate from the original high-entropy alloy concept to show that high radiation resistance can be achieved in systems with simplified chemical complexity.

The development of microreactor technology presents an efficient solution for providing portable electricity, catering to both human space exploration needs within our solar system and supplying power to remote Earth-bound areas. The miniaturization of nuclear reactors poses immediate new challenges for materials science with respect to the capability for controlling nuclear reactions via thermalization of highly-energetic neutrons. In a microreactor, neutron moderation takes place in compact geometries, thus new moderator materials are required to exhibit high moderating power per unit of volume. This challenge is currently being addressed through the development of transition metal hydrides, known for their strong nuclear moderation capability but to date, research on their irradiation response is limited, specifically regarding phase stability, hydrogen in-lattice retention, and their dependence on irradiation temperature and dose. Herein, we present a detailed investigation on the response of yttrium dihydride (YH2) 2 ) to heavy ion irradiation. The experiments indicate that YH2 2 is stable up to an irradiation dose of 2 dpa and below 800 degrees C, degrees C, identified herein as a critical temperature for YH2. 2 . Our study detected the nucleation and growth of voids as a function of the irradiation temperature. They were the predominant type of radiation damage present in the microstructure of YH2 2 that was distinguishable from pre-existing defects in the pristine YH2 2 samples. Below the critical temperature, no phase transformation (degassing/dehydriding) nor amorphization occurred. Experimental results with concomitant density functional theory calculations allowed us to elaborate and propose new strategies to enhance the metal hydride performance in extreme environments.

Ceramic matrix composites exhibit excellent high temperature properties and are candidate materials for structural applications from jet engines to nuclear fuel cladding. The strength and deformation behavior of these composites are intrinsically tied to the properties of the fiber/matrix interface. This research introduces a novel technique to evaluate the fundamental friction and wear characteristics of these interfaces. A case study on SiCf/ PyC/SiCm composites applies in situ fiber fretting to investigate the kinetic friction coefficient and cyclic wear characteristics of the interphase. The experimental methodology is presented in explicit detail to encourage other researchers to explore the capabilities of this technique. Testing was carried out as a function of fiber roughness, PyC thickness (approximate to 10, 500, 1200 nm), cycle count (10, 100, 1000), and frequency (1, 5, and 10 Hz). The friction coefficient and wear behavior changed with cycle length due to a transition from adhesive to abrasive mechanisms. SEM fractography provided insights to tribological evolution from adhesive sliding to three-body abrasive wear. The structural disorder at the tribo-surface relating to graphitic content and dangling bond density was investigated using Raman spectroscopy. Properties are contextualized with comparison to uniaxial tensile behavior of the parent composite.

This paper presents the polarization characteristics of electrochemical oxygen pumps (EOPs) during transfer oxygen from/to liquid lead-bismuth eutectic (LBE). A thick-walled (1.5 mm) one-end closed tube of yttria partially stabilized zirconia was used as a solid electrolyte. Three different electrode of air/LSM (lanthanum strontiummanganite), air/LSCF (lanthanum strontium cobalt ferrite) and LBE/PbO were compared. The polarization characteristics were obtained by linear sweep voltammetry in LBE at 450 degrees C at various dissolved oxygen concentrations in LBE. The EOP with LBE/PbO electrode showed negligible activation polarization compared to EOPs with other electrodes. However, with the LBE/PbO electrode a significant concentration polarization occurred at low current density, limiting its capacity for oxygen transfer from EOP to LBE. The oxygen transfer from LBE to EOP is limited by oxygen mass transfer from the LBE bulk to the solid electrolyte surface of EOPs, especially under low dissolved oxygen condition. (C) 2019 The Electrochemical Society.