Structural and magnetic anisotropy of directionally-crystallized ferromagnetic microwires

Amorphous ferromagnetic microwires have drawn attention primarily due to their excellent soft magnetic properties as the elements of sensors. In this work, semi-hard magnetic microwires of composition Fe4.3Co67.7Si11B14Cr3 were obtained after a process of directional crystallization from amorphous state. The XRD analysis of crushed and whole wires identified the formation of the face-centered Co-modification as the main phase of directionally crystallized core alloy, which explains a large increase in anisotropy and coercivity. The application of a magnetic field during crystallization may orient the easy anisotropy axis of crystallites along the wire. This is confirmed by the investigation of crystallite orientation with respect to the wire axis and X-rays direction in diffractometer. The obtained results revealed that the formation of crystallites in amorphous Co-rich microwires occurs with the predominant orientation of the crystallographic direction [111] along the wire axis and the direction of a magnetic field during the directional crystallization process.

Transport Properties of Topological Insulator Bi0.83Sb0.17 Nanowires

ABSTRACTWe have investigated the transport properties of topological insulator based on single-crystal Bi0.83Sb0.17 nanowires. The single-crystal nanowire samples in the diameter range 200 nm – 1.1 μm were prepared by the high frequency liquid phase casting in a glass capillary using an improved Ulitovsky technique; they were cylindrical single-crystals with (1011) orientation along the wire axis. In this orientation, the wire axis makes an angle of 19.5o with the bisector axis C1 in the bisector-trigonal plane. Bi0.83Sb0.17 is a narrow gap semiconductor with energy gap at L point of Brillouin zone ΔE= 21 meV. In accordance with the measurements of the temperature dependence of the resistivity of the samples resistance increases with decreasing temperature, but at low temperatures decrease in the resistance is observed. This effect, decrease in the resistance, is a clear manifestation of the interesting properties of topological insulators - the presence on its surface of a highly conducting zone. The Arrhenius plot of resistance R in samples with diameter d=1.1 µm and d=200 nm indicates a thermal activation behavior with an activation gap ΔE= 21 and 35 meV, respectively, which proves the presence of the quantum size effect in these samples. We found that in the range of diameter 1100 nm - 200 nm when the diameter decreases the energy gap is growing as 1/d. We have investigated magnetoresistance of Bi0.83Sb0.17 nanowires at various magnetic field orientations. From the temperature dependences of Shubnikov de Haas oscillation amplitude for different orientation of magnetic field we have calculated the cyclotron mass mc and Dingle temperature TD for longitudinal and transverse (B||C3 and B||C2) directions of magnetic fields, which equal 1.96*10-2m0, 9.8 K, 8.5*10-3m0 , 9.4 K and 1.5*10-1m0 , 2.8 K respectively. The observed effects are discussed.

The Influence the Temperature of Drawing Process on the Transformation Retained Austenite into Martensite for TRIP Steel Wires

For the numerical analysis of TRIP steel wire drawing process, the Drawing 2d programme based of finite element method, has been used. The process was run following two variants, with small and large partial drafts for two drawing speeds: 1.11; 0.23 m/s. The investigations carried out allowed a relationship between temperature of drawing wires and the amount of retained austenite for wire surface and for wire axis.

Two Alternatives for Mathematical Expression of Triangular Strands in Six Strand Ropes

The creation of computer model of triangular rope strand needs mathematical interpretation of individual wires. It can be based on different assumptions in its derivation. The paper presents two options. In the first case, it is known the number of wires and the size of their diameters in the first layer of the strand, in the second case it is known number of wires and the diameter wires forming the core of strand. The parametric equations of wire axis are derived for both cases. The geometrical models of the strands are generated on the base of these equations.

Fabrication and Characterization of Single-segmented CoNiP and Multi-segment CoNiP/Au Nanowires

This paper represents the fabrication of CoNiP single segment and CoNiP/Au multisegment nanowires. We have fabricated these nanowires by electrodeposition method into polycarbonate templates with a nominal pore diameter about 100 nm. The hystersis loops were measured with the applied magnetic field parallel and perpendicular to the wire axis using a vibrating sample magnetometry (VSM). The structure morphology was observed by Scanning Electron Miroscopy (SEM) and the element composition of CoNiP/Au multisegment nanowires were analyzed by EDS. The results show that these nanowires are very uniform with the diameter of 100 nm. The observed coercivity (HC) and squareness (Mr/Ms) of CoNiP single nanowires are larger than the CoNiP/Au multisegment nanowires.

Angular dependence of giant magneto impedance and magnetic characteristic of Co-based wire in different magnetic field ranges

Angular dependence of the giant magneto impedance (GMI), hysteresis loops and magnetization curves have been investigated in amorphous wires with respect to direction and amplitude of the magnetic field in room temperature. The measurements were performed at different orientation angles of the applied magnetic field relative to the wire axis and various magnetic field strengths in moderate (0–200 Oe) and high (0–5000 Oe) ranges. The highest GMI response (500%) and magnetization (100 emu/gr) were found for angles close to the wire axis in high magnetic field range. By increasing the angle from 0°, in moderate external magnetic fields the GMI and magnetization decrease without reaching the saturation. However, in high magnetic fields (~ 5000 Oe) these parameters are nearly constant and almost saturated for all angles. In both magnetic field ranges, increasing the angle of applied field widens the impedance curves.

Geometrical Modeling of Steel Ropes

The paper deals with the mathematical geometric modeling of the ropes of circular cross- section. Such rope can be formed from strands of different shapes. There is considered steel rope made up of six strands, whose crosssection has oval, triangular or circular profil in this paper. The wires of these types of the strands are presented by parametric equations of the wire axis. The equations are implemented in the Pro/Engineer Wildfire V5 software for creating the geometrical model of the strand.

Research on Droplet Transfer of MIG Welding with Alternating Longitudinal Magnetic Field

The stress and motion state of droplet in MIG welding with alternating longitudinal magnetic field were analyzed, and the impact of alternating longitudinal magnetic field on the droplet transfer were studied by high-speed video camera. The results show that the droplet is spherical approximately and transfer to molten pool along the welding wire axis without external longitudinal magnetic field. When alternating longitudinal magnetic field was introduced into welding process, the droplet rotate around the welding wire clockwise and counter-clockwise alternately. Shape of droplet became flat and direction of transfer deviated from the welding wire axis under the action of magnetic field. As the exciting current increased, extent of deviation from the wire axis increases. When the exciting current is too large (I >20A), extent of deviation is too large and droplet are disintegrated into several small droplet during the transition. So droplet can not transfer into molten pool successfully and the bead can’t be formed.

Direct simulation of turbulent swept flow over a wire in a channel

Turbulent swept flow over a cylindrical wire placed on a wall of a channel is investigated using direct numerical simulations. This geometry is a model of the flow through the wire-wrapped fuel pins, the heat exchanger, typical of many nuclear reactor designs. Mean flow along and across the wire axis is imposed, leading to the formation of separated flow regions. The Reynolds number based on the bulk velocity along the wire axis direction and the channel half height is 5400 and four cases are simulated with different flowrates across the wire. This configuration is topologically similar to backward-facing steps or slots with swept flow, except that the dominant flow is along the obstacle axis in the present study and the crossflow is smaller than the axial flow, i.e. the sweep angle is large. Mean velocities, turbulence statistics, wall shear stress and instantaneous flow structures are investigated. Particular attention is devoted to the statistics of the shear stress on the walls of the channel and the wire in the recirculation zone. The flow around the mean reattachment region, at the termination of the recirculating bubble, does not exhibit the typical decay of the mean shear stress observed in classical backward-facing step flows owing to the presence of a strong axial flow. The evolution of the mean wall shear stress angle after reattachment indicates that the flow recovers towards equilibrium at a rather slow rate, which decreases with sweep angle. Finally, the database is analysed to estimate resolution requirements, in particular around the recirculation zones, for large-eddy simulations. This has implications in more complete geometrical models of a wire-wrapped assembly, involving hundreds of fuel pins, where only turbulence modelling can be afforded computationally.

Single-crystal Wires Based on Doped Bi for Anisotropic Thermoelectric Microgenerators

In this work, we have studied the possibility to use a microwire of BiSn to design an anisotropic thermoelectric generator. The glass-coated microwire of pure and Sn-doped bismuth was obtained by the Ulitovsky method; it was a cylindrical single-crystal with orientation (1011) along the wire axis; the C3 axis was deflected at an angle of 70° to the microwire axis. It is found that doping of bismuth wires with tin increases the thermopower anisotropy in comparison with Bi by a factor of 2 – 3 in the temperature range of 200 – 300 K. According to the preliminary results, for a Bi microwire with a diameter of 10 μm with a glass coating of 35 μm, the transverse thermopower is ∼ 150 μV/(K*cm); for BiSn, 300 μV/(K*cm).The design of an anisotropic thermogenerator based on BiSn microwire is proposed. The miniature thermogenerator will be efficient for power supply of devices with low useful current.In addition to the considerable thermopower anisotropy of BiSn wires in a glass coating, they exhibit stable thermoelectric properties, high mechanical strength and flexibility, which allows designing thermoelectric devices of various configurations on their basis.