arXiv subjects

Steven J. Zinkle

Publications and source records attributed to Steven J. Zinkle.

4 recordsLinked to original sources

arXiv2024

Object kinetic Monte Carlo simulations on the difference between fission neutron and heavy ion irradiation induced void evolution in Fe-Cr alloys

Experimental results show significant difference between neutrons and ions irradiation of alloys, while the underlying reasons remain unclear. Herein, we performed object kinetic Monte Carlo (OKMC) simulations on void evolution in Fe-Cr alloys under neutron and ion irradiations, focusing on the effects of dose rate, irradiation particle type and temperature. Binary Collision Approximation and Molecular Dynamics are applied to obtain the cascade morphology of ion irradiation in order to study the effect of spatial correlation of cascades along the ion track, which is considered as a significant difference between the neutron and ion irradiations. Systematic OKMC simulations were performed at a wide range of dose rate from $10^{-7}$ to $10^{-3}$ dpa/s and temperature from 300 to 500$^\circ C$. Simulation results show that both a higher dose rate and a lower temperature can lead to a higher density and a smaller average size of voids. High dose rate greatly promotes the interaction frequency between small defects and inhibit the absorption of vacancies by one vacancy cluster, thus enhancing the nucleation of vacancy clusters. This dose rate effect explains the major difference of microstructure between fission neutron and heavy ion irradiation. High temperature enhances the migration of small defects and the absorption of vacancies by vacancy clusters, and thus enlarge the vacancy clusters. The impact of irradiation particle types that has influence on the primary knock-on atom spectrum and cascade morphology is less important to void evolution compared with dose rate and irradiation temperature. This work provides fundamental insights into the difference in void evolution between fission neutron and heavy ion irradiations that are important to the application of ion irradiations in study irradiation effects of nuclear materials.

physics.app-ph↗

arXiv2022

Model-based quantitative methods to predict irradiation-induced swelling in alloys

Predicting volume swelling of structural materials in nuclear reactors under high-dose neutron irradiations based on existing low-dose experiments or irradiation data with high-dose-rate energetic particles has been a long-standing challenge for safety evaluation and rapidly screening irradiation-resistant materials in nuclear energy systems. Here, we build an Additional Defect Absorption Model that describes the irradiation-induced swelling effects produced by energetic electrons, heavy-ions, and neutrons by considering additional defect sinks inherent in the irradiation process. Based on this model, we establish quantitative methods to predict high-dose swelling from low-dose behavior and obtain the equivalent irradiation dose for different energetic particles when the dose rates differ by several orders of magnitude. Furthermore, we propose a universal parameter to characterize the swelling resistance of various alloys and predict their radiation tolerances under different radiation conditions. This work provides quantitative prediction methods for evaluating irradiation-induced swelling effects of structural materials, which is critical to the safety and material development for advanced nuclear reactors.

cond-mat.mtrl-sci↗

arXiv2018

On the Study of Chaos and Memory Effects in the Bonhoeffer-van der Pol Oscillator with a Non-Ideal Capacitor

In this paper, the voltage fluctuations of the Bonhoeffer van der pol oscillator system with a non-ideal capacitor were investigated. Here, the capacitor was modeled, using a fractional differential equation in which the order of the fractional derivative is also a measure of the memory in the dielectric. The governing fractional differential equation was derived using two methods, namely a differential and integral approach. The former method utilized a hierarchical resistor-capacitor (RC) ladder model while the latter utilized the theory of the universal dielectric-response. The dynamical behavior of the potential across the capacitor was found to be affected by this parameter, and, therefore, the memory of the system. Additionally, findings indicate that an increase in the memory parameter was associated with an increase in the energy stored in the dielectric. It was found that oscillation death resulted in a higher amount of stored energy in the dielectric over time, as compared to behavior, which displayed relaxation oscillations or chaotic fluctuations. The relatively-lower stored energy resulting from the latter types of dynamical behavior appeared to be a consequence of the memory effect, where present accumulations of energy in the capacitor are affected by previous decreases in the potential. Hence, in this type of scenario, the dielectric material can be thought of as remembering the past behavior of the voltage, which leads to either a decrease, or an enhancement in the stored energy. The non-ideal capacitor was also found to have a transitory nature, where it behaves more like a resistor as α approaches 0, and conversely, more like a capacitor as α goes to 1. Here, a decrease in α was linked to an enhanced metallic character of the dielectric.

physics.data-an↗

arXiv2017

High pressure synthesis of a hexagonal close-packed phase of the high-entropy alloy CrMnFeCoNi

High-entropy alloys, near-equiatomic solid solutions of five or more elements, represent a new strategy for the design of materials with properties superior to those of conventional alloys. However, their phase space remains constrained, with transition metal high-entropy alloys exhibiting only face- or body-centered cubic structures. Here, we report the high-pressure synthesis of a hexagonal close-packed phase of the prototypical high-entropy alloy CrMnFeCoNi. This martensitic transformation begins at 14 GPa and is attributed to suppression of the local magnetic moments, destabilizing the initial fcc structure. Similar to fcc-to-hcp transformations in Al and the noble gases, the transformation is sluggish, occurring over a range of >40 GPa. However, the behaviour of CrMnFeCoNi is unique in that the hcp phase is retained following decompression to ambient pressure, yielding metastable fcc-hcp mixtures. This demonstrates a means of tuning the structures and properties of high-entropy alloys in a manner not achievable by conventional processing techniques.

cond-mat.mtrl-sci↗