The radial thermal expansion coefficient α r of pure and Xe-saturated bundles of singlewalled carbon nanotubes has been measured in the interval 2.2-120 K. The coefficient is positive above T = 5.5 K and negative at lower temperatures. The experiment was made using a low temperature capacitance dilatometer with a sensitivity of 2·10 -9 cm and the sample was prepared by compacting a CNT powder such that the pressure applied oriented the nanotube axes perpendicular to the axis of the cylindrical sample. The data show that individual nanotubes have a negative thermal expansion while the solid compacted material has a positive expansion coefficient due to expansion of the intertube volume in the bundles. Doping the nanotubes with Xe caused a sharp increase in the magnitude of α r in the whole range of temperatures used, and a peak in the dependence α r (T) in the interval 50-65 K. A subsequent decrease in the Xe concentration lowered the peak considerably but had little effect on the thermal expansion coefficient of the sample outside the region of the peak. The features revealed have been explained qualitatively.

620.178.152:669.265.295 É. P. Pechkovskii, N. I. Danilenko, and M. V. KarpetsA β-titanium alloy, obtained by cooling a melt at a rate of~800°C/s, has been studied by the methods of scanning and transmission electron microscopy, short-duration and long-duration macroindentation, as well as uniaxial compression in a temperature range of 20-1000°C. The alloy in the solid state contains ultrafine dendritic crystals, in the interstices between which are nanosized particles of minor phases. The alloy may be regarded as heat-resistant alloy: it possesses a high thermal stability of mechanical properties, higher values of high-temperature strength and creep resistance.Keywords: multicomponent β-titanium alloy, high melt cooling rate, thermal stability, increased high-temperature strength.Introduction. When fabricating cast β-titanium alloys with structure ensuring a definite combination of mechanical characteristics, one usually proceeds from two basic principles: alloying of titanium with a large number of β-stabilizing and other elements and cooling of the melt at high rate [1-4]. As a result, when multicomponent titanium alloy solidifies, its microstructure acquires the appearance of dendritic crystals, which are a β-titanium based solid solution and are distributed in a matrix. The matrix contains a β-titanium based solid solution of different composition and chemical compounds of titanium with alloying elements (in most cases, intermetallics). In this case, primary dendritic crystals (which are usually large and branched) contribute ductility to alloy, and chemical compounds of titanium are in the fine-grained state, due to which high values of strength characteristics are achieved. By changing the composition and concentration of alloying elements and the melt cooling rate, one can change the ratio of the volume fractions of dendritic crystals and fine particles and their size and hence control the combination of the strength and ductility characteristics of β-titanium alloy in the solid state.In recent 5-10 years, a thermodynamic approach to the design of multicomponent alloys has received a large development effort [5][6][7]. Its essence is that multicomponent alloy can be obtained in the state of single-phase substitutional solid solution, which can be highly strong and thermodynamically stable. This is primarily achieved by selecting the appropriate number of components and their concentration ratio in the alloy. These factors can ensure in the calculated (charged) composition a higher mixing entropy value (and hence a lower free energy value of the alloy in accordance with the Gibbs equation) and maintain the alloy in molten state and under special cooling conditions in solid state as well. In this case, the larger the number of elements, the higher the value of mixing entropy, and its maximum value for the given number of elements is achieved for alloy of equiatomic composition. Because of the difference of the atomic radii of the substitutional elements, the crystal lattice (as a rule only bcc lattice or in ...

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