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He-enhanced heterogeneity of radiation-induced segregation in FeNiCoCr high-entropy alloy

Journal of Materials Science & Technology 2022年第6期101卷 226-233页

作者： W.T.Lin G.M.Yeli G.Wang J.H.Lin S.J.Zhao D.Chen S.F.Liu F.L.Meng Y.R.Li F.He Y.Lu J.J.Kai Department of Mechanical Engineering City University of Hong KongHong KongChina Institute of Nuclear&New energy Technology Tsinghua UniversityBeijingChina Department of Physics Southern University of Science and TechnologyShenzhenChina Centre for Advanced Nuclear Safety and Sustainable Development City University of Hong KongHong KongChina School of Environmental Science and Engineering Southern University of Science and TechnologyShenzhenChina School of Materials Science and Engineering Shanghai UniversityShanghaiChina Nano-Manufacturing Laboratory(NML) City University of Hong Kong Shenzhen Research InstituteShenzhenChina

Radiation-induced segregation(RIS) is a typical non-equilibrium process that can dramatically alter the behavior of defect sinks and material properties under irradiation. However, RIS mechanisms have been rarely studied around small He bubbles owing to the technical challenges involved in direct measurements of local chemistry. Here, using state-of-the-art atom probe tomography, we report the RIS behavior near He bubbles in the Fe Ni Co Cr high-entropy alloy that indicates Co segregates most strongly, followed by weaker Ni segregation, whereas Fe and Cr are depleted almost to the same degree. Exceptionally, the magnitude of Co segregation around He bubbles is higher than previously measured values at voids and dislocation loops. electron energy-loss spectroscopy was used to measure the He density and pressure inside individual bubbles. We demonstrate that He bubbles are over-pressurized at the irradiation temperature that could result in the vacancy bias and the subsequent vacancy-dominated RIS mechanism.First-principles calculations further reveal that there are repulsive interactions between He and Co atoms that may reduce the frequency of Co-vacancy exchange. As a result, He atoms likely retard Co diffusion via the vacancy mechanism and enhance the heterogeneity of RIS in Co-containing multicomponent alloys. These insights could provide the basis for understanding He effects in nuclear materials and open an avenue for tailoring the local chemical order of medium-and high-entropy alloys.

关键词： High-entropy alloy Radiation-induced segregation He bubbles Atom probe tomography electron energy-loss spectroscopy

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Initial nucleation of amorphous Si–B–C–N ceramics derived from polymer-precursors

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Journal of Materials Science & Technology 2019年第12期35卷 2851-2858页

作者： Ling-yan Li Hui Gu Vesna Srot Peter van Aken Joachim Bill Materials Genome Institute School of Materials Science and EngineeringShanghai University99 Shangda RoadShanghai200444China Stuttgart Center for electron Microscopy Max-Planck-lnstitute for Solid-State ResearchHeisen bergs trasse 370569StuttgartGermany Institute of Materials Science University of StuttgartHeisenbergstrasse 570569StuttgartGermany

Nucleation behavior of amorphous Si–B–C–N ceramics derived from boron-modified polyvinylsilazane procusors was systematically investigated by transmission electron microscopy(TEM) combined with spatially-resolved electron energy-loss spectroscopy(EELS) analysis. The ceramics were pyrolyzed at1000℃ followed by further annealing in N2, and SiC nano-crystallites start to emerge at 1200℃ and dominate at 1500℃. Observed by high-angle annular dark-field imaging, bright and dark clusters were revealed as universal nano-structured features in ceramic matrices before and after nucleation, and the growth of cluster size saturated before reaching 5 nm at 1400℃. EELS analysis demonstrated the gradual development of bonding structures successively into SiC, graphetic BNCxand Si3N4 phases, as well as a constant presence of unexpected oxygen in the matrices. Furthermore, EELS profiling revealed the bright SiC clusters and less bright Si3N4-like clusters at 1200–1400℃. Since the amorphous matrix has already phase separated into SiCN and carbon clusters, another phase separation of SiCN into SiC and Si3N4-like clusters might occur by annealing to accompany their nucleation and growth, albeit one crystallized and another remained in amorphous structure. Hinderance of the cluster growth and further crystallization was owing to the formation of BNCxlayers that developed between SiC and Si3N4-like clusters as well as from the excessive oxygen to form the stable SiO2.

关键词： Precursor derived ceramics Si–B–C–N Nucleation High-angle annular dark-field imaging electron energy-loss spectroscopy

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