Vol 118, No 5 (2017)

Microobjects (strips) were formed by contact photolithography using Та/Ni₈₀Fe₂₀/Co₉₀Fe₁₀/Cu/Co₉₀Fe₁₀/Ru/Co₉₀Fe₁₀/Fe₅₀Mn₅₀/Ta spin-valves prepared by magnetron sputtering. A mutually perpendicular arrangement of uniaxial and unidirectional anisotropy axes in microobjects has been formed using two different thermomagnetic treatment regimes. The magnetoresistive sensitivity of spin valve and spin-valve-based microobject has been found to depend on the mutual arrangement of the easy magnetization axis and direction of magnetic field applied upon thermomagnetic treatment. The obtained data have been interpreted taking into account changes in the induced anisotropy and anisotropy due to the shape of the microobject.

An experimental study of the mechanical and magnetic properties of Co–8 at % Al–X at % W (where Х = 4.6; 6.8; 8.5; 10; 12) polycrystalline alloys has been carried out depending on the tungsten content. It has been shown that an increase in the tungsten content induces the following changes: Young’s modulus changes from 240 to 259 GPa and the microhardness HV changes from 290 to 413 MPa. The Curie temperature of the intermetallic γ' phase (L1₂) grows from 1025 to 1049 K, and the saturation magnetization of the alloys decreases. The value of the coercive force also increases, from 1 to 500 Oe. The calculations of the specific heat of the γ' (L1₂)–γ (dcc) phase transition has shown that the highest amount of heat (304 J/g) is absorbed upon the phase transition in the sample containing the largest amount of tungsten (12.6 at %). The results obtained indicate the diffusion character of the transition, the rate of which is controlled by the diffusion of the slowest component of the alloy (in this case, tungsten). It has been found that the solvus temperature of the γ' phase increases from 1009 to 1044°С with an increase in the tungsten content from 4.6 to 12.6 at %.

Effect of mechanical activation of TiO2 and Cr2O3 oxides as starting materials was investigated for direct synthesis of TiCr₂. Differential thermal analysis (DTA) indicated that increasing the ball milling time resulted in lower exothermic reaction temperatures between molten Ca–Cr2O3 and molten Ca–TiO2. A model-free Kissinger type method was applied to DTA data to evaluate the reaction kinetics. The results reveal that the activation energy of the exothermic reactions decreased with increasing the milling time. The structure, oxygen content, and average particle sizes of the obtained TiCr₂ product were affected by the ball milling time of the starting materials. Increasing the milling time from 10 to 40 h decreased the average particle size and oxygen content of the obtained TiCr₂ from 10 to 2 μm and from 1690 to 1290 ppm, respectively. The X-ray diffraction (XRD) results showed that TiCr₂ compounds with metastable bcc phase can be produced using nano-sized starting materials, while only a slight amount of bcc phase can be obtained in the TiCr₂ compounds, using micron-sized starting materials. The TiCr₂ obtained by this method had a hydrogen absorption capability of 0.63 wt % and the kinetics of the hydrogen absorption increased for the 40 h milled sample.

Transmission electron microscopy, selected-area electron diffraction, and high-resolution transmission electron microscopy (HRTEM) have been used to determine the morphological and phase features of silver nanoparticles synthesized by a physical method of electric explosion of silver wires. In the nanoparticles obtained, the presence of a hexagonal phase was detected besides the cubic phase and the size dependence of the phase composition of the nanoparticles has been revealed; all particles smaller than 25 nm only had a hexagonal structure, particles with sizes of 25–30 nm contained both the hexagonal and cubic phases, and particles larger than 30 nm had only a cubic structure. Based on an analysis of the conditions of synthesis of silver nanoparticles, an attempt to explain the mechanism of the stabilization of the hexagonal phase depending on the particle size was undertaken.

The influence of the structural state of a copper–beryllium alloy on its resistance to friction fracture under adhesion interaction and abrasive wear has been investigated. It has been shown that the elastic interphase deformations that cause the tension of the crystal lattice of the particles of precipitated phase brings about a decrease in the wear resistance of the alloy at a retained high hardness. The relaxation of interphase deformations during the aging process leads to a significant increase in the wear resistance of the alloy, despite the reduction its hardness.

The results of an investigation of the influence of the parameters of high-frequency acoustic wave on the structure and properties of the zone of joint of homogeneous metals bonded by explosive welding under the action of ultrasound have been presented. The influence of the frequency and amplitude of ultrasonic vibrations on the structure and properties of the explosively welded joints compared with the samples welded without the application of ultrasound has been established. The action of high-frequency acoustic waves on the metal leads to a reduction in the dynamic yield stress, which changes the properties of the surface layers of the metal and the conditions of the formation of the joint of the colliding plates upon the explosive welding. It has been shown that the changes in the length and amplitude of waves that arise in the weld joint upon the explosive welding with the simultaneous action of ultrasonic vibrations are connected with a decrease in the magnitude of the deforming pulse and time of action of the compressive stresses that exceed the dynamic yield stress beyond the point of contact.

Complex investigations have been carried out of the radiation damage of nickel alloys microalloyed with interstitial carbon and boron impurities under cascadeless electron and cascade neutron irradiation. Boron’s contribution to the resistivity has been found and the binding energy of a vacancy with boron atom has been determined to be 0.2 eV. The main mechanisms of radiation-induced structural and phase changes have been revealed.