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Strength enhancement of high entropy alloy HfNbTaTiZr by severe plastic deformation
x10c,í,x17e,ek, J.,Haux161,ild, P.,Cieslar, M.,Melikhova, O.,Vlasá,k, T.,Janex10d,ek, M.,Krá,l, R.,Harcuba, P.,Luká,x10d,, F.,Zý,ka, J.,Má,lek, J.,Moon, J Elsevier 2018 Journal of alloys and compounds Vol.768 No.-
<P><B>Abstract</B></P> <P>Refractory metal high entropy alloy HfNbTaTiZr with ultrafine grained structure and grain size of ≈80 nm was processed by high pressure torsion. The development of microstructure, lattice defects and mechanical properties with increasing strain was examined. Grain refinement of HfNbTaTiZr alloy deformed up to the equivalent strain <I>e</I> ≈ 50 resulted in a significant enhancement of strength while keeping sufficient ductility. However, further straining <I>e</I> > 100 led to a decrease of strength and the loss of ductility due to the decomposition of solid solution facilitated by vacancies introduced by severe plastic deformation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High entropy alloy HfNbTaTiZr was nanostructured by high pressure torsion. </LI> <LI> Grain size of 80 nm was achieved by deformation to the equivalent strain e = 5. </LI> <LI> Structure refinement resulted in remarkable enhancement of strength of the alloy. </LI> <LI> Ductility remains sufficient for good workability. </LI> <LI> Further deformation to very high strains resulted in loss of strength. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
x10c,í,x17e,ek, J.,Janex10d,ek, M.,Krajx148,á,k, T.,Strá,ská,, J.,Hrux161,ka, P.,Gubicza, J.,Kim, H.S. Elsevier 2016 Acta materialia Vol.105 No.-
<P>Interstitial free steel with ultrafine-grained (UFG) structure was prepared by high-pressure torsion (HPT). The development of the microstructure as a function of the number of HPT turns was studied at the centre, half-radius and periphery of the HPT-processed disks by X-ray line profile analysis (XLPA), positron annihilation spectroscopy (PAS) and electron microscopy. The dislocation densities and the dislocation cell sizes determined by XLPA were found to be in good agreement with those obtained by PAS. The evolution of the dislocation density, the dislocation cell and grain sizes, the vacancy cluster size, as well as the high-angle grain boundary (HAGB) fraction was determined as a function of the equivalent strain. It was found that first the dislocation density saturated, then the dislocation cell size reached its minimum value and finally the grain size got saturated. For very high strains after the saturation of grain size the HAGB fraction further increased. The PAS investigations revealed that vacancies introduced by severe plastic deformation agglomerated into small clusters consisting of 9-14 vacancies. The evolution of the yield strength calculated from the microhardness as a function of strain was explained by the development of the defect structure. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.</P>
Synthesis and Magnetic Properties of Hematite Particles in a “Nanomedusa” Morphology
Lee, Jin Bae,Kim, Hae Jin,Lux17e,nik, Janez,Jelen, Andreja,Pajix107,, Damir,Wencka, Magdalena,Jaglix10d,ix107,, Zvonko,Meden, Anton,Dolinx161,ek, Janez Hindawi Limited 2014 Journal of nanomaterials Vol.2014 No.-
<P>We present the synthesis, characterization, and magnetic properties of hematite particles in a peculiar “nanomedusa” morphology. The particles were prepared from an iron-silica complex by a hydrothermal process in a solution consisting of ethyl acetate and ethanol. The particles’ morphology, structure, and chemical composition were investigated by transmission electron microscopy, powder X-ray diffraction, and scanning electron microscope equipped with an energy-dispersive X-ray spectrometer. The “hairy” particles consist of a spherical-like core of about 100 nm diameter and fibrous exterior composed of thin “legs” of 5 nm diameter grown along one preferential direction. The particles’ cores are crystalline and undergo a magnetic phase transition to a weakly ferromagnetic state at a temperature of 930 K that matches reasonably the Néel temperature of bulk hematite. However, unlike bulk hematite that undergoes Morin transition to an antiferromagnetic state around room temperature and small hematite nanoparticles that are superparamagnetic, the “nanomedusa” particles remain weakly ferromagnetic down to the lowest investigated temperature of 2 K. Each particle thus represents a nanodimensional “hairy” ferromagnet in a very broad temperature interval, extending much above the room temperature. Such high-temperature ferromagnetic nanoparticles are not frequently found among the nanomaterials.</P>
Hayakawa, Kazuhide,Pham, Loc-Duyen D,Seo, Ji Hae,Miyamoto, Nobukazu,Maki, Takakuni,Terasaki, Yasukazu,Sakadž,ix107,, Sava,Boas, David,van Leyen, Klaus,Waeber, Christian,Kim, Kyu-Won,Arai, Ken,L SAGE Publications 2016 Journal of cerebral blood flow and metabolism Vol.36 No.4
<P> There are numerous barriers to white matter repair after central nervous system injury and the underlying mechanisms remain to be fully understood. In this study, we propose the hypothesis that inflammatory macrophages in damaged white matter attack oligodendrocyte precursor cells via toll-like receptor 4 signaling thus interfering with this endogenous progenitor recovery mechanism. Primary cell culture experiments demonstrate that peritoneal macrophages can attack and digest oligodendrocyte precursor cells via toll-like receptor 4 signaling, and this phagocytosis of oligodendrocyte precursor cells can be inhibited by using CD200-Fc to downregulate toll-like receptor 4. In an in vivo model of white matter ischemia induced by endothelin-1, treatment with CD200-Fc suppressed toll-like receptor 4 expression in peripherally circulating macrophages, thus restraining macrophage phagocytosis of oligodendrocyte precursor cells and leading to improved myelination. Taken together, these findings suggest that deleterious macrophage effects may occur after white matter ischemia, whereby macrophages attack oligodendrocyte precursor cells and interfere with endogenous recovery responses. Targeting this pathway with CD200 may offer a novel therapeutic approach to amplify endogenous oligodendrocyte precursor cell-mediated repair of white matter damage in mammalian brain. </P>
Fluid-enhanced surface diffusion controls intraparticle phase transformations
Li, Yiyang,Chen, Hungru,Lim, Kipil,Deng, Haitao D.,Lim, Jongwoo,Fraggedakis, Dimitrios,Attia, Peter M.,Lee, Sang Chul,Jin, Norman,Mox161,kon, Jox17e,e,Guan, Zixuan,Gent, William E.,Hong, Jihyun,Yu Springer Science and Business Media LLC 2018 Nature Materials Vol.17 No.10