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Kartavykh A.V.,Technological Institute for Superhard and Novel Carbon Materials TISNCM | Tcherdyntcev V.V.,National University of Science and Technology "MISIS" | Stepashkin A.A.,National University of Science and Technology "MISIS" | Gorshenkov M.V.,National University of Science and Technology "MISIS"
Russian Metallurgy (Metally) | Year: 2013

The temperature dependence of the linear thermal expansion coefficient K L of the intermetallic Ti-46Al-8Nb (at %) alloy is experimentally determined for the first time within the temperature range from 373 to 1773 K (solidus point). The determined boundaries of phase fields are compared with the results of differential thermal analysis and the calculated phase diagram of the alloy. The high-temperature limit (1384 K) of the alloy structure thermostability is detected from signs of the α2 + γ ⇆ α + γ phase transition in dilatometric curves. The restructuring mechanism in the α + γ field is studied by scanning electron microscopy. It is shown that the α2 + γ → α + γ phase transition is accompanied by selective structural degradation of single-crystalline α2 lamellae and the related destruction of a fine lamellar α2-Ti3Al(Nb) + γ-TiAl(Nb) texture. The average values of K L of the alloy are calculated within 100-K ranges in the low-temperature α2 + γ phase field, which is of interest from a practical viewpoint, according to the State Standard GOST 8.018-2007. © 2013 Pleiades Publishing, Ltd.


Moya J.S.,CSIC - Institute of Materials Science | Torrecillas R.,University of Oviedo | Diaz L.A.,University of Oviedo | Rodriguez-Suarez T.,University of Oviedo | And 3 more authors.
Journal of the European Ceramic Society | Year: 2013

A small fraction (5vol.%) of detonation nanodiamonds, or DND, acts as a remarkably effective boundary pinning agent in alumina throughout a wide sintering temperature range (from 1200 up to 1700°C). This is the first time that such a strong grain growth inhibitory effect is observed for any of the alumina based composites of similar characteristics reported in the literature. These nanocomposites were consolidated by pulsed electric current sintering (PECS) and present bending strength (550MPa) and toughness (5.2MPam1/2) values significantly higher than the ones corresponding to alumina compacts obtained under the same sintering conditions. © 2013 Elsevier Ltd.


Kartavykh A.V.,Technological Institute for Superhard and Novel Carbon Materials TISNCM | Ginkin V.P.,RAS Institute of Physics and Power Engineering | Ganina S.M.,RAS Institute of Physics and Power Engineering
Advances in Applied Mechanics Research, Conference Proceedings - 7th Australasian Congress on Applied Mechanics, ACAM 2012 | Year: 2012

The work is aimed at the study of the formation and refinement of primary microstructure appearing in the refractory lightweight structural TiAl-based intermetallics during their solidification from the melt. The alloy with Ti-46Al-8Nb (at.%) nominal composition is selected for applied study in microstructure engineering. For tailored microstructure development, the Directional Solidification (DS) of pre-synthesized alloy was performed in the vertical multizone electro-furnace by Vertical Gradient Freezing (VGF) power-down technique in pure argon environment. Both columnar-dendrite, and equiaxed-granular reproducible as-cast microstructures have been produced in DS ingots, basing onto Columnar-to-Equiaxed Transition (CET) diagram exploration. Particular attention was paid further to equiaxed microstructure improvement by combination of modifying doping of alloy with boron grain refiner and VGF processing. As a result the perfect inoculated microstructure of Ti-44Al-7Nb-2B (at.%) ingots was produced with 120 μm mean grain diameter, low scattering of dimensional characteristics and high tolerance to DS process parameters variation. DS samples were examined by SEM microanalysis along with EBSD and Auger spectrometry of boride particles in the alloy matrix. The nature, state and exact composition of precipitated borides are discussed along with the nucleation mechanism in relation to the literature data.


Al Rifai S.A.,Voronezh State University | Kulnitskiy B.A.,Technological Institute for Superhard and Novel Carbon Materials TISNCM
Journal of Physics and Chemistry of Solids | Year: 2013

Single-crystal Eu3+-doped wurtzite ZnO micro- and nanowires were synthesized by chemical vapor deposition. The nanostructures grew via a self-catalytic mechanism on the walls of an alumina boat. The structure and properties of the doped ZnO were characterized using X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning and transmission electron microscopy, and photoluminescence (PL) methods. A 10-min synthesis yielded vertically grown nanowires of 50-400 nm in diameter and several micrometers long. The nanowires grew along the ±[0001] direction. The Eu3+ concentration in the nanowires was 0.8 at.%. The crystal structure and microstructure of were compared for Eu3+-doped and undoped ZnO. PL spectra showed a red shift in emission for Eu3+-doped (2.02 eV) compared to undoped ZnO nanowires (2.37 eV) due to Eu3+ intraionic transitions. Diffuse reflectance spectra revealed widening of the optical bandgap by 0.12 eV for Eu3+-doped compared to undoped ZnO to yield a value of 3.31 eV. Fourier-transform infrared spectra confirmed the presence of europium in the ZnO nanowires. © 2013 Elsevier Ltd.


Ginkin V.P.,RAS Institute of Physics and Power Engineering | Ganina S.M.,RAS Institute of Physics and Power Engineering | Kartavykh A.V.,Technological Institute for Superhard and Novel Carbon Materials TISNCM
Advances in Applied Mechanics Research, Conference Proceedings - 7th Australasian Congress on Applied Mechanics, ACAM 2012 | Year: 2012

A non-equilibrium model of multicomponent melt solidification has been developed in which a Stefan problem with two boundaries is solved numerically, the boundaries being between the solid phase and the two-phase transition zone and between the two-phase transition zone and the liquid phase. The two-phase zone is represented as a porous medium with variable porosity. Account is taken of the additional force resisting the melt flow due to porosity and introduced by analogy with Darcys law. Computer simulation has been performed of the experiment on Sn-20 wt.%Pb binary alloy solidification by the method of downward-directed crystallization along the gravity vector. Shown in the paper are the results of a quasi two-dimensional benchmark experiment on horizontal (i.e., at the right angle to the gravity vector) directional solidification of a binary Sn-3 wt.%Pb alloy. The calculations were done using two crystallization models: the equilibrium model and the non-equilibrium one. It is shown that the non-equilibrium model gives a better description of the thermal field evolution and solute distribution caused by natural convection.

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