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2. Understanding the mechanical properties of reduced activation steels

Author

Li, Xiaojie, Li, Xiaoqing, Schönecker, Stephan, Li, Ruihuan, Zhao, Jijun, and Vitos, Levente

Subjects
Condensed Matter - Materials Science
Abstract

Reduced activation ferritic/martensitic (RAFM) steels are structural materials with potential application in Generation-IV fission and fusion reactors. We use density-functional theory to scrutinize the micro-mechanical properties of the main alloy phases of three RAFM steels based on the body-centered cubic FeCrWVMn solid solution. We assess the lattice parameters and elastic properties of ferromagnetic $\alpha$-Fe and Fe$_{91}$Cr$_{9}$, which are the main building blocks of the RAFM steels, and present a detailed analysis of the calculated alloying effects of V, Cr, Mn, and W on the mechanical properties of Fe$_{91}$Cr$_{9}$. The composition dependence of the elastic parameters is decomposed into electronic and volumetric contributions and studied for alloying levels that cover the typical intervals in RAFM steels. A linear superposition of the individual solute effects on the properties of Fe$_{91}$Cr$_{9}$ is shown to provide an excellent approximation for the \emph{ab initio} values obtained for the RAFM steels. The intrinsic ductility is evaluated through Rice's phenomenological theory using the surface and unstable stacking fault energies, and the predictions are contrasted with those obtained by empirical criteria. Alloying with V or W is found to enhance the ductility, whereas additional Cr or Mn turns the RAFM base alloys more brittle., Comment: 29 pages, 4 figures

Published
2018
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7. Stacking fault energy of face-centered cubic metals: thermodynamic and ab initio approaches

Author

Li, Ruihuan, Lu, Song, Kim, Dongyoo, Schönecker, Stephan, Zhao, Jijun, Kwon, Se Kyun, and Vitos, Levente

Subjects
Condensed Matter - Materials Science
Abstract

The formation energy of the interface between face-centered cubic (fcc) and hexagonal close packed (hcp) structures is a key parameter in determining the stacking fault energy (SFE) of fcc metals and alloys using thermodynamic calculations. Often the contribution of the planar fault energy to the SFE has the same order of magnitude as the bulk part, and thus the lack of a precise information about it can become the limiting factor in thermodynamic predictions. Here, we differentiate between the actual interfacial energy for the coherent fcc(111)/hcp(0001) interface and the "pseudo-interfacial energy" that enters the thermodynamic expression for the SFE. Using first-principles calculations, we determine the coherent and pseudo- interfacial energies for six elemental metals (Al, Ni, Cu, Ag, Pt, and Au) and for three paramagnetic Fe-Cr-Ni alloys. Our results show that the two interfacial energies significantly differ from each other. We observe a strong chemistry dependence of both interfacial energies. The calculated pseudo-interfacial energies for the Fe-Cr-Ni steels agree well with the available literature data.

Published
2015
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16. First-Principles Study of the Stability of TinOmClusters and He Behavior Inside TinO2Va1Clusters in Vanadium Alloy

Author

Li, Ruihuan, Zhang, Bo, Sun, Dan, Cao, Xiaoxiao, and Zhao, Jijun

Abstract

AbstractIn order to characterize the behaviors of interstitial oxygen (O) in the vanadium (V) alloy, the interactions between O and Ti with respect to atomic separation distance have been investigated using first-principles calculations. We observe an attractive interaction between Ti and O within the third nearest neighbor (nn) (3nn) distance. The stability of the Ti-vacancy (Ti-Va) clusters has been studied by calculating the binding energy between Ti and monovacancy in the vanadium alloy, and our results show that the stable configurations are Ti1Va1, Ti2Va1, and Ti4Va1clusters. The TinVa1clusters prefer to trap two O atoms and form stable Ti1O2Va1, Ti2O2Va1, and Ti4O2Va1clusters. Furthermore, the self-trapping energies of the Hexclusters by the TinO2Va1clusters have been calculated. When four He atoms are trapped, the Hexclusters are stable. Furthermore, the trapping energies for the multiple He atoms captured by the TinO2Va1clusters are calculated, and the TinO2clusters are found to impede the vacancy trapping of He atoms to form He bubbles.

Published
2024
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21. Dynamics of nutrients and bacterial metabolism in dipole eddies in an oligotrophic ocean

Author

Li, Ruihuan, Li, Xiangfu, Zhou, Shengqi, Shi, Zhen, and Xu, Jie

Abstract

The vertical turbulent fluxes of nitrate to the base of the euphotic zone and effect of changing environmental conditions on bacterial metabolism were examined inside a cyclonic eddy (CE) and an anticyclonic eddy (AE) in an oligotrophic ocean, in order to better understand dynamics of nutrients and plankton in eddies. The turbulent nitrate flux at the base of the euphotic zone inside the CE was higher than inside the AE, while this flux contributed to 19.7‒76.3% of new production in the AE and only < 4.94% in the CE where new production was primarily driven by upwelling. Turbulent nitrate flux in the AE edge was higher than in the AE center, which was the most likely attributed to submesoscale processes. In contrast, the reverse pattern occurred in the CE, primarily due to difference in turbulent diffusivity. In addition, changes in environmental conditions in eddies mediate bacterial metabolism. The upwelling improved nutrient availability and bacterial production in CE. The enhanced temperature induced by downwelling in AE increased the cell-specific bacterial respiration. Our findings improved our understanding of biogeochemical processes in eddies in oceans., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Published
2023

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