M.V. Gorshenkov

Resistance of alloy Zr – 2.5% Nb with ultrafine-grain structure to stress corrosion cracking

The effect of severe plastic deformation of commercial alloy Zr – 2.5% Nb by the method of equal-channel angular pressing on the mechanisms and kinetics of stress corrosion cracking in a 1% “iodine – methanol” medium is studied. Quantitative comparative data on corrosion resistance of the alloy with ultrafine-grain structure after equal-channel angular pressing and with coarse-grain structure after the traditional treatment are obtained.

Rapid preparation of InxCo4Sb12 with a record-breaking ZT = 1.5: the role of the In overfilling fraction limit and Sb overstoichiometry

Samples of indium-filled InxCo4Sb12 skutterudite were successfully synthesized by conventional induction melting without the use of evacuated quartz ampoules. Addition of In above the filling fraction limit (x ≈ 0.22) and adjustment of Sb excess in the induction-melted InxCo4Sb12 ingots allowed us to suppress formation of the unwanted CoSb2 phase in the sintered samples and effectively control the amount of the InSb impurity phase which precipitated in nanometer-sized regions along the grain boundaries of the main skutterudite phase. Measurements of the Seebeck coefficient, electrical conductivity and thermal conductivity of the InxCo4Sb12 samples with nominal In contents x = 0.2, 0.6, and 1.0 revealed a simultaneous increase in the electrical conductivity and decrease in the thermal conductivity. This results in the record value of the thermoelectric figure of merit ZT ≈ 1.5 for single-filled skutterudites which was attained in the In1Co4Sb12 sample at 725 K.

Ti–Ag–Pd alloy with good mechanical properties and high potential for biological applications

Ti-based alloys containing Ag were produced by tilt-casting method and their properties were studied. Even in its as-cast state, Ti94Ag3Pd3 showed relatively high tensile properties, good electrochemical behavior, and good biocompatibility. The relatively good mechanical properties of the as-cast α-Ti-type Ti94Ag3Pd3 alloy (tensile strength up to 850u2009MPa and elongation of ~10%) can be explained by its severely deformed, fine crystalline structure. The high biocompatibility of Ti94Ag3Pd3 can be explained by the Ag–Pd interaction, which inhibits the release of Ag ions from the surface. Ag, in combination with Pd has no toxic effects and demonstrates useful antimicrobial properties. The Ti94Ag3Pd3 alloy shows a good potential to be applied as a biomedical implant alloy.

Influence of Sodium Fluoride Doping on Thermoelectric Properties of BiCuSeO

We examined the effect of NaF doping on the thermoelectric properties of p-type Bi1−xNaxCuSeO1−xFx (xxa0=xa00, 0.05, 0.10, 0.15) synthesized by a facile method combining a solid-state reaction and spark plasma sintering. The substitution of Bi3+ by Na+ and O2− by F− led to an enhancement of electrical conductivity and a slight increase in thermal conductivity, while the Seebeck coefficient was slightly affected by the doping. The power factor (2.12xa0μWxa0cm−1xa0K−2 at 923xa0K) and the low thermal conductivity resulted in the dimensionless figure␣of merit ZT 0.42 for Bi0.95Na0.05CuSeO0.95F0.05 at 923xa0K. The obtained results indicated that ZT was not improved by the double substitution at the bismuth and oxygen sites.

Negative Electrode Comprised of Nanostructured CuO for Advanced Lithium Ion Batteries

Negative electrode comprised of CuO nanoparticles (CuO-NPs), with an average particle size of 50xa0nm have been successfully synthesized by simple and convenient chemical precipitation method. XRD, SEM, FTIR and TEM have been employed for physical characterization. The electrochemical performances have been evaluated by galvanostatic charge–discharge and cyclic voltammetry. During the cycling test at 200xa0mAxa0g−1, the CuO-NPs exhibited a stable discharge capacity of 516xa0mAxa0hxa0g−1, with 84% capacity retention. This superior electrochemical performance of CuO-NPs is mainly attributed to the nano-dimension of the particles, which benefit electron and Li ion transportation, with large electrode–electrolyte contact area.

The Effect of the Rate of Cooling from High-Temperature Single-Phase Region on the Microstructure and Magnetic Properties of AlNi Alloys

AbstractThe microstructure of as-cast and melt spun AlNi alloys was studied by transmission (TEM) and scanning electron microscopy as well as atomic force microscopy (AFM). The magnetic properties of the alloys were measured using a vibrating sample magnetometer. The water quenched and melt spun AlNi samples were characterized by zone microstructure formed as a result of solid solution decomposition into β- and β2 phases within the miscibility gap. Therefore, the subsequent aging of as-quenched alloy leads to the development of the zone microstructure instead of the decomposition of single-phase solid solution. The absence of preferential precipitations and discontinuous precipitation (DP) reaction was observed at grain boundaries (GB) of as-cast AlNi alloy after aging. The antiphase domains (APD) have been observed for the first time in the AlNi ribbons prepared by melt spinning. The effects of GB and APD boundaries on the decomposition of a solid solution in the AlNi ribbons were investigated. At first, a thin β-phase layer is formed along GB and APD boundaries. Then the decomposition leads to the formation of β2-phase layers on the both sides of β-phase layer. The GB and APD boundaries, which are decorated by precipitates of β- and β2 layers, become visible in the TEM and AFM micrographs. A DP reaction at GBs has been observed for the first time in the AlNi ribbons after supplementary aging. The cellular microstructure at GBs consisting of alternating lamellas of β′- and β′2 phases was formed after aging the ribbons at 773xa0K (500xa0°C) for 10xa0minutes.n

Microstructure and Magnetic Properties of Melt-Spun Nd-Rich Nd-Fe Alloys

The effect of composition on the magnetic properties and microstructure of Nd-rich Nd-Fe alloys prepared by melt-spinning were investigated. Several magnetic phases with ordering temperatures at about 10, 37, 48, and 420-480 K were detected from the temperature dependence of magnetization. The first transition is due to the presence of the double-hexagonal-close-packed Nd phase. The magnetic transitions at 37 and 48 K may be related to the face-centered-cubic Nd-based phase and the Nd-rich nanocrystals. The high-temperature ferromagnetic-paramagnetic transitions at 420-480 K may be connected with the amorphous-like Fe-Nd phase enriched in Fe, which is observed by transmission electron microscopy in the intergranular regions. At temperatures below 100 K, the magnetization of the Nd-Fe ribbons did not saturate in a magnetic field as high as 7200 kA/m. The correlations between the microstructure and coercivity of the Nd-rich Nd-Fe ribbons are discussed.

Multilayer “Steel/Vanadium Alloy/Steel” Hybrid Material Obtained by High-Pressure Torsion at Different Temperatures

The severe plastic deformation (SPD) method for joining dissimilar metal materials to obtain a multilayer hybrid material having an ultrafine or nanoscale structure was proposed. A nanostructured multilayer “0.08C-18Cr-0.5Ti steel/V-10Ti-5Cr alloy/0.08C-18Cr-0.5Ti steel” hybrid material was obtained by high-pressure torsion (HPT) at different temperatures. The analysis of the structure of the hybrid material and its components was carried out by the methods of transmission and scanning electron microscopies. The distribution of chemical elements in the cross section of the hybrid material was studied by X-ray microanalysis. The microhardness was measured to estimate the hybrid material hardening after HPT. Tight joint zones between the layers of the hybrid material were formed during HPT. The fragmentation of the steel and vanadium alloy layers was observed, and the “mixing” of the layers occurred after HPT at 293xa0K and 473xa0K (20xa0°C and 200xa0°C). A smoother interface between the layers was observed after HPT at 673xa0K (400xa0°C). The significant hardening (2.0 to 3.5×) of each layer of the hybrid material was observed as a result of HPT.

CHARGE SPECTRUM OF HEAVY AND SUPERHEAVY COMPONENTS OF GALACTIC COSMIC RAYS: RESULTS OF THE OLIMPIYA EXPERIMENT

The aim of the OLIMPIYA experiment is to search for and identify traces of heavy and superheavy nuclei of galactic cosmic rays (GCR) in olivine crystals from stony–iron meteorites serving as nuclear track detectors. The method is based on layer-by-layer grinding and etching of particle tracks in these crystals. Unlike the techniques of other authors, this annealing-free method uses two parameters: the etching rate along the track (V etch) and the total track length (L), to identify charge Z of a projectile. A series of irradiations with different swift heavy ions at the accelerator facilities of GSI (Darmstadt) and IMP (Lanzhou) were performed in order to determine and calibrate the dependence of projectile charge on V etch and L. To date, one of the most essential results of the experiment is the obtained charge spectrum of GCR nuclei within the range of Z > 40, based on about 11.6 thousand processed tracks. As the result of data processing, 384 nuclei with charges Z ≥ 75 have been identified, including 10 nuclei identified as actinides (90 < Z < 103). Three tracks were identified to be produced by nuclei with charges 113 < Z < 129. Such nuclei may be part of the Island of Stability of transfermium elements.

Thermoelectric Properties of n-Type Si0,8Ge0,2-FeSi2 Multiphase Nanostructures

We report on thermoelectric properties of n-type nanostructured bulk Si0.8Ge0.2 with the addition of FeSi2 prepared via two sintering routes: the conventional spark plasma sintering method and a direct current pressing technique. The thermal conductivity, the electrical conductivity, and the Seebeck coefficient have been determined over the temperature range from 25°C to 900°C in a helium atmosphere. The highest ZT value for the multiphase nanostructured composite was reached at ∼0.6 at 900°C. Embedding of 10xa0at.% FeSi2 phase had a positive impact on thermal properties but dramatically affected the power factor, which eventually resulted in a drop of the thermoelectric efficiency. It was also shown that the orthorhombic β-FeSi2 phase transforms to a tetragonal α-FeSi2 phase during high temperature sintering.