Refinement of the eutectic composition in the LaB6–VB2 system (original) (raw)
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Work function characterization of directionally solidified LaB6-VB2 eutectic
Ultramicroscopy, 2017
With its low work function and high mechanical strength, the LaB6/VB2 eutectic system is an interesting candidate for high performance thermionic emitters. For the development of device applications, it is important to understand the origin, value, and spatial distribution of the work function in this system. Here we combine thermal emission electron microscopy and low energy electron microscopy with Auger electron spectroscopy and physical vapor deposition of the constituent elements to explore physical and chemical conditions governing the work function of these surfaces. Our results include the observation that work function is lower (and emission intensity is higher) on VB2 inclusions than on the LaB6 matrix. We also observe that the deposition of atomic monolayer doses of vanadium results in surprisingly significant lowering of the work function with values as low as 1.1eV.
Consolidation of B4C–VB2 eutectic ceramics by spark plasma sintering
Journal of the Ceramic Society of Japan, 2015
The in situ synthesis and consolidation of B 4 CVB 2 eutectic composites by spark plasma sintering (SPS) is reported. The microstructure properties were determined for composites with the B 4 CVB 2 eutectic composition as functions of the VB 2 content and the VB 2 VB 2 interlamellar spacing. A change of VB 2 concentration from 45 to 48 mol.% resulted in the formation of the rodlike eutectic microstructure. Indentation fracture toughness values higher than 4 MPa•m 1/2 were identified for eutectic composites with interlamellar spacings between 0.9 and 1.2¯m. The composites obtained by SPS with a composition of 45 mol.% VB 2 exhibited a lower Vickers hardness (2324 GPa) and higher indentation fracture toughness (up to 4.5 MPa•m 1/2) than the eutectic composites with 48 mol.% of VB 2 .
Boride morphology in A (Fe, V, B) Ti-alloy containing B2-phase
Acta Metallurgica et Materialia, 1995
The morphology of borides grown from the melt in a Ti-A1 (Fe, V, B) alloy has been investigated. Flake-like dispersoids are shown by energy dispersive X-ray spectroscopy and electron energy loss boron maps to consist of interleaved titanium boride and B2 grains, with selected area diffraction analysis identifying the boride phase as TiB2. High resolution electron microscopy reveals that the TiB2 and B2 are very high aspect ratio plates, reflecting the overall morphology of the dispersoids, with the interfacial and orientational relationship being { 1010}x~B2//{001 } B2 and < 0001 > r,B:// < 010 > nz. Growth methods of the TiB2/B2 dispersoids are discussed in light of the surprisingly fine nano-scale of the interleaving plates. R6sum6-La morphologie des borures primaires form6s fi partir d'un alliage Ti-A1 (Fe, V, B) fondu a 6td 6tudi6e. Par spectrom6trie des rayons X en s61ection d'6nergie et par des cartes chimiques obtenues en spectroscopie des pertes d'6nergie, les dispersoides, ayant une forme de plaquettes, sont compos6s d'un empilement de grains lamellaires de borure de titane et de la phase B2. Avecla diffraction des ~lectrons en s61ection d'aire, le borure a 6t6 identifi6 comme ~tant TiB2. La microscopie 61ectronique en haute r6solution revile que les phases TiB2 et B2 ont un facteur de forme 61ev6 repercutant la morphologie g6n6rale des dispersoides. Les relations d'orientations et d'interface entre ces deux phases sont { 10T0}Tm2 // {001 }s2 et < 0001 > TiB2 // < 010 > SZ. Les m~canismes de croissance des dispersoides TiB2/B2 sont discut6s/l la lumi~re de la surprenante structure tr6s fine (/l l'6chelle nanom6trique) et al ternante des plaquettes. Zusammenfassung-Die Morphologie von prim~iren, aus der Schmelze gewachsenen Boriden in einer Ti-A1 (Fe, V, B)-Legierung ist untersucht worden. Die Analyse flockenartiger Ausscheidungsphasen mit energiedispersiver R6ntgenspektroskopie und Bor-spezifischer Elektronenenergieverlustspektroskopie zeigte, dab diese aus ineinander geschobenen Titanborid-und B2-Phasen bestanden, wobei durch Elektronenbeugungsbilder die Boride als TiB2 identifizert wurden. Hochaufl6sende Elektronenmikroskopie offenbarte die Gestalt der TiB2-und B2-Phasen als lang-gestreckte Platten mit Orientierungen { 10T0}r~B2// {001 }B2 und < 0001 > T~B2 // < 010 > B2, die Morphologie der Ausscheidungspartikel reflektierend. Das Wachstum der TiB2/B2-Ausscheidungsphasen wird im Hinblick auf deren strukturelle Feinheit im Nanometer-Bereich diskutiert.
Consolidation of B4C–VB2 eutectic ceramics by spark plasma sintering
Journal of the Ceramic Society of Japan, 2015
The in situ synthesis and consolidation of B 4 CVB 2 eutectic composites by spark plasma sintering (SPS) is reported. The microstructure properties were determined for composites with the B 4 CVB 2 eutectic composition as functions of the VB 2 content and the VB 2 VB 2 interlamellar spacing. A change of VB 2 concentration from 45 to 48 mol.% resulted in the formation of the rodlike eutectic microstructure. Indentation fracture toughness values higher than 4 MPa•m 1/2 were identified for eutectic composites with interlamellar spacings between 0.9 and 1.2¯m. The composites obtained by SPS with a composition of 45 mol.% VB 2 exhibited a lower Vickers hardness (2324 GPa) and higher indentation fracture toughness (up to 4.5 MPa•m 1/2) than the eutectic composites with 48 mol.% of VB 2 .
Microhardness of Czochralski-Grown Single Crystals of VB2
Journal of Solid State Chemistry, 1997
Single crystals of congruent melting hexagonal VB 2 were grown using a triarc furnace applying the Czochralski technique. Orientation dependent microhardness measurements on a single crystal reveal quasi similar hardness in the crystallographic directions 1 100.12 2 and 1 110.02 2 , whereas the 1 110.12 2 shows slightly lower values.
Properties and behaviour of 83Pb17Li eutectic
Fusion Engineering and Design, 1991
This article presents some test results of 83Pb-17Li euteetic properties. This eutectic was produced by induction melting in the form of ingots with a volume of 30 I. It should be noted that inhomogeneity of eutectic composition and structure was revealed within one and the same ingot. Annealing at temperatures below melting point changes the micro structure i.e. increasing of the size of the/]'-phase-particles takes place. The following values of euteetic thermal-physical properties were determined: enthalpy, specific heat capacity, thermal expansion, latent heat of melting. Some peculiarities of eutectic mechanical properties changing in the temperature range of 293 K to 473 K were investigated. * Here and further the values are presented in weight percents, unless specified otherwise. 0920-3796/91/$03.50 © 1991 -Elsevier Science Publishers B.V. (North-Holland)
On the stability of the V5B6-phase
Journal of Alloys and Compounds, 2004
The currently assessed V-B phase diagram indicates a peritectoid formation at 1727 • C (V 3 B 4 + VB ⇔ V 5 B 6) for the V 5 B 6 boride. The observation of this phase in several as-cast V-B alloys has lead us to a systematic evaluation of its stability, specially its possible formation from the liquid. In this work, V-B alloys (52-56 at.% B range) were produced through arc melting and heat-treated under high vacuum at 2000 • C for 2 h. The materials in both as-cast and heat-treated conditions were characterized through scanning electron microscopy (SEM) (backscattered electron (BSE) images) and X-ray diffraction (XRD). The features observed in the as-cast samples allowed us to conclude that this phase should be formed from the liquid through the L + V 3 B 4 ⇔ V 5 B 6 peritectic reaction. In spite of not reaching equilibrium condition during heat-treating, the results from the characterization of heat-treated samples have indicated the stability of the V 5 B 6-phase at 2000 • C, in disagreement with the currently accepted V-B phase diagram.
KfK 4]44 THERMOPHYSICAL PROPERTIES IN THE SYSTEM Li-Pb Part I: Preparation andcharacterization of Li(17)Pb(83) eutectic alloy and the Lipb intermetallic compound U. Jauch, V. Karcher, B. Schulz Part 11: Thermophysical properties of Li(17)Pb(83) eutectic alloy Abstract Part I: Preparation and Characterization of Li(17)Pb(83) eutectic alloy and the LiPb intermetallic compound Part 11: Thermophysical properties of Li(17)Pb(83) eutectic alloy Part 111: Estimation of the thermophysical properties in the system Li-Pb page 2 25 45 -1 -General Abstract This report describes the work performed on the determination of the thermophysical properties of alloys in the binary system lithium-lead, within the frame of theKfK-project of nuclear fusion technology. The preparation of the Li(J7)Pb(83) alloy and the intermetallic compound Lipb from the pure elements determines the contents of part I of the report, which includes too the characterization of the materials using chemical analysis, metallography, thermal and thermal differential analysis. The great importance of the characterization especially of the metallography is shown in presenting some results of the eutectic alloy fabricated by different producers under technical conditions. Because of the great importance of the thermophysical behaviour of the liquid eutectic Li(17)Pb(83) for the design of a liquid metal breeder blanket in the next European Torus, part 11 of the report describes the measurements and results of the thermodynamic properties (latent heat of fusion, specific heat, density, thermal expansion and surface energy) of this alloy. The results of the determination of the transport properties (thermal and electrical conductivity and viscosity) are presented, too. In part 111 the methods are given, which lead to an estimation of thermophys ical properties of Li-compounds with high Li-contents (> 50 at.%) in the solid state. -2 -THERMOPHYSICAL PROPERTIES IN THE SYSTEM Li-Pb Part I Preparation and Characterization of the Li(17)Pb(83) eutectic &lloy and the LiPb intermetallic compound U. Jauch, V. Karcher, B. Schu1z Kernforschungszentrum Kar1sruhe Institut für Materia1-und Festkörperforschung Abstract Li(17)Pb(83) and LiPb were prepared from the pure elements in amounts of seve-ra1 hundred grams. The reso1idified samp1es were characterized by me1ting points (eutectic temperature), chemica1 analysis and meta110graphy. Using differential thermal analysis the heats of fusion were determined and the behaviour of the intermetallic phase LiPb in vacuum and high purified He was studied. The resu1ts from these investigations were app1ied to characterize Contents List of figures List of tables page 47 48 1 •
Materials Characterization, 2018
Under directional growth, the eutectic transformation L ⇄ Al 3 Nb + Nb 2 Al + Nb(Ni 1−x Al x) 2 resulted in a very organized three phase microstructure. While many features of this eutectic have already been explored, crystallographic details of its phases are still missing. This paper aims to investigate composition and crystallographic features of a directionally solidified eutectic made up of the Al 3 Nb, Nb 2 Al and Nb(Ni 1−x Al x) 2 phases. It was observed that the Nb(Ni 1−x Al x) 2 intermetallic phase has the C14 structure, with composition 56.91 ± 0.43 at.% Al, 10.11 ± 0.12 at.% Ni and 32.98 ± 0.53 at.% Nb. Selected area diffraction in a transmission electron microscope permitted interplanar spacings to be determined and values obtained are consistent with those in the literature. Accurate lattice parameters were determined using powder X-ray diffraction combined with Rietveld refinement. It was found that the lattice parameters of the Nb(Ni 1−x Al x) 2 (x = 0.85) phase are a = 5.031 Å and c = 8.298 Å and these lattice parameters depend on Al content.