A Study of Chromite Dunites

Results of a study of chromite dunites with different concentrations of chromite — from 10 to 20% Cr₂O₃ — are reported. Thermomechanical properties of control specimens are determined. Chromite dunites require precalcination for their use in the manufacture of forsterite-chromite components for thermal power units of ferrous and, especially, nonferrous metallurgy.     

Spinodal decomposition of the nonstoichiometric YBa2Cu3O7−δ compound at room temperature

Electron and polarized-light optical microscopy have been used to study the spinodal decomposition of the YBa₂Cu₃O_7?δ compound depending on the oxygen content. Experimental data reported indicate that whatever the state —initial or preliminarily aged at a high temperature—of the YBa₂Cu₃O_7?δ (δ ≈ 0.2 and 0.4) nonstoichiometric oxide, it undergoes natural aging typical of metallic alloys.     

Effect of ultrasonic vibration on the dechromisation corrosion of a CuCr alloy in HCl solution

The effect of ultrasonic vibration on the dechromisation corrosion of a CuCr alloy in HC1 solution was studied and the corrosion mechanisms were analyzed. It is found that ultlasonic vibration reduces the dechromisation incubation time, accelerates the dechromisafion corrosion rate, decreases the temperature and concentration of HC1 solution, and when the dechromisation occurs it seriously weakens the microstmcture of dechromisation layer. It is concluded that ultrasonic vibration can accelerate destruction of the passivation film on the Cr surface and increase the activities of Cl^- and Cr.     

Phenomenon of structural recovery in nonstoichiometric compounds YBa2Cu3O7−δ and EuBa2Cu3O6.8

Experimental results are presented on the phenomenon of recovery (characteristic of aging metallic alloys) in single crystals of nonstoichiometric oxides YBa₂Cu₃O_～6.6 and EuBa₂Cu₃O_～6.8. After single low-temperature and high-temperature annealings (200 and 300°C), all signs of spinodal decomposition in these single crystals were found; after double heat treatment (200°C + 300°C), the restoration of structure inherent in the initial state (antiphase domains of twin orientation) occurred.     

Effects of atomic relaxation and the electronic structure of niobium (100) and (110) surfaces

A comparative analysis of the atomic relaxation and electronic structure of niobium (100) and (110) surfaces has been carried out using the VASP-PAW method. The relaxation-induced changes in interlayer spacings of surface layers demonstrate an oscillating behavior but they substantially differ for the two analyzed surfaces; namely for the (110) surface with the closest atomic packing two outermost surface layers are contracted by 4.3% and the relaxation becomes noticeable for three outer layers, while for the more “open” (100) surface these quantities equal 13.1 and six layers, respectively. An analysis of the layer-by-layer distribution of the densities of states, spatial distribution of the charge density, and densities of states at the Fermi level indicates that the most considerable changes near Fermi level take place for (100) surface.     

Enhancement of magnetic texture and functional characteristics of iron-based soft magnetic alloys

It has been shown that the formation of nitride-oxide magnetically active electrically insulating coatings on ribbons of iron-based soft magnetic alloys using the method of ion-plasma deposition and subsequent magnetic annealing in an ac magnetic field leads to a substantial improvement of their static and dynamic magnetic properties.     

Mechanical properties and fracture upon static tension of the high-carbon steel with different types of pearlite structure

The hardness and mechanical properties of the U10 steel (1.03 wt % C) with pearlite structures that were formed by isothermal decomposition at temperatures of 650°C (coarse-lamellar pearlite) and 500°C (fine-lamellar pearlite) as well as upon subsequent annealing of fine-lamellar pearlite at a temperature of 650°C for 10–300 min have been studied upon tensile tests. Fractures of the steel with different types of pearlite structure have been examined using scanning electron microscopy. The interrelation between the mechanical properties and the structural features and character of fracture has been analyzed for this steel with pearlite structures differing in the dispersity, morphology, and defect structure of cementite, and in the levels of solid-solution strengthening and microdistortions of the ferrite-constituent lattice.     

Recrystallization of the ultradispersed structure of pure iron formed at different stages of the deformation-induced strain hardening

Grain growth has been investigated during heating of pure single-phase iron with an ultra-dispersed structure of different types under conditions which exclude retardation by impurity atoms or by dispersed particles. The rate of growth mainly depends on the type of boundaries formed in this structure during a preliminary treatment, which determines the different kinetics of primary recrystallization. The thermal stability of submicrocrystalline (SMC) structure increases with increasing degree of deformation. In contrast to the materials with an impurity and carbide retardation, in pure iron an intermediate annealing of the SMC structure, which usually leads during low-temperature recrystallization to the formation of a honeycomb structure, does not influence thermal stability. The formation of thermally activated centers of recrystallization has been found to occur during heating of iron with a uniform isotropic SMC structure at the temperature of the onset of the recrystallization of moderately deformed iron. The formation of a honeycomb structure does not lead to a considerable reduction in the accumulated strain energy, and, during further heating, thermally activated nuclei of recrystallization are formed.     

Solving the dynamic traveling salesman game problem

A game problem of the successive capture of a team of evaders by a single pursuer under conditions of “simple motions” of the players is analyzed. The performance criterion is the total time all the evaders are captured. It is assumed that the pursuer is guided by the parallel pursuit law. In such a case, the optimal response of the evaders is the straightforward motion with maximum speed. The original infinite-dimensional problem can therefore be reduced to two finite-dimensional problems.