Vol 119, No 8 (2018)

Results of numerical calculations of the electronic structure of nonstoichiometric aluminum oxide with a concentration of oxygen vacancies of 6% have been presented. The calculations have been performed within the scope of the density-functional theory of the coherent-potential approximation with a disordered location of vacancies. It has been established that the presence of oxygen vacancies leads to the appearance of a peak in the density of states inside the energy gap and additional electronic states at the bottom of the conduction band, which gives a decrease in the energy gap to 2 eV. The simulation of the aluminum oxide of composition Al₂[O_0.98]₃\({\text{O}}_{{{\text{0}}{\text{.06}}}}^{{{\text{int}}\,{\text{erstitial}}}}\) with vacancies in the oxygen sublattice and oxygen atoms in interstices leads to a semiconducting character of the energy spectrum with a band gap of ~1 eV, which is formed between the p states of the impurity interstitial oxygen atoms and the s states of the vacancies.

The asymmetric pinning of a vortex-domain wall in regions with enhanced values of saturation magnetization and the anisotropy constant (defects) has been studied by a three-dimensional micromagnetic simulation at different geometric parameters of these regions. The dependences of the geometry of shifted hysteresis loops on a spacing between two defects and their size in a 100-nm-wide uniaxial magnetic film have been obtained.

Based on the example of analyzing the Rayleigh equations for ascending and descending branches of the magnetic hysteresis loop, the dimensionless hysteresis quantities B_r/B_max, W_h/W_max, H_c/H_max, and B_rH_c/W_h, which have the same functional dependence on the external magnetic field H_max, have been found. Hysteresis quantities proportional to the permeability μ or hysteresis loss W_h have been obtained. An analysis of the magnetically soft amorphous alloy Co₆₆Fe₃Cr₃Si₁₅B₁₃ with very high initial permeability showed that the similarity of dimensionless hysteresis quantities takes place not only in the Rayleigh region, but also in a wider region of the magnetic field.

Since their early development, High-Entropy Alloys have fueled the investigation of exotic metal combinations. Here, we present a strategy for the rational design of a library for multi-component alloys based on six hcp-structured metals. Seven five- and six-component equimolar alloys based on Co, Gd, Y, Sc, Ti and Zr were prepared via induction melting and characterized by PXRD, SEM–EDX and Vickers hardness. They all present ternary hexagonal phases (ScTiZr or GdScY) co-existing with one or more cubic phases and intermetallic compounds. Both ScTiZr and GdScY appear promising as the starting point for new single-phase High-Entropy Alloys families.

The effect of high pulsed magnetic fields on the martensitic γ → α transformation in Fe–Ni and Fe–Ni–Mn alloys characterized by dual kinetics has been analyzed. It has been shown that the higher the iron content and the lower the martensitic transformation temperature, the more substantial the effect of pulsed magnetic field on the athermal martensitic transformation (MT) in the Fe–Ni alloys. The possibility of athermal martensite nucleation at magnetic inhomogenities of austenite, which is characterized by disordered magnetic moments (antiferromagnetic contribution) within a local area that assumes coherent conjugation at the interface, has been discussed. It has been suggested that athermal MT in Invar Fe–Ni alloys characterized by dual kinetics occurs in a pulsed magnetic field via a first-order magnetic phase transformation.

The possibility of increasing the reversible deformation to 1.9% of corrosion-resistant steels 0.30C–14Cr–15Mn–4Si–3Ni–1V and 0.30C–14Cr–15Mn–4Si–3Ni,which exhibits the shape-memory effect has been shown. The increase has been achieved at the expense of a decrease in the chromium and carbon contents in an austenite matrix, which results from the decrease in the quenching temperature and increase in the time of destabilizing carbide aging.

Transmission electron microscopy, X-ray diffraction analysis, durometry, and mechanical tensile and impact toughness tests were used to study changes in the structure, phase composition, and mechanical properties in a high-strength VT22I titanium alloy (Ti–3Al–5Mo–5V–1Cr–1Fe) upon isothermal and thermomechanical treatments, including warm rolling and aging. It has been found that the decomposition of the β solid solution in an alloy preliminarily heated in the β region (Т_pt + 50°C) after isothermal treatment at 650°C for 1 and 4 min is accompanied by the formation of an intermediate α'' phase; upon holding for 20 min, an equilibrium α phase precipitates. The А₇В-type ordering processes, where β stabilizers and aluminum can serve as a B element, are possible and, upon final cooling, in water, the formation of an athermal ω phase can take place at the initial stages of decomposition. It has been shown that the warm rolling of the alloy at 650°C accelerates the processes of the decomposition of the metastable β solid solution, contributes to the refinement of the arising α precipitates, and suppresses the formation of the athermal ω phase upon cooling compared to the similar isothermal treatment without deformation. A regime of a thermomechanical treatment that provides the high mechanical properties required to fabricate elastic structural components has been proposed for this alloy.

Transmission electron microscopy and microindentation have been used to study the changes in the structure, phase composition, microhardness, and elastic modulus of the Ti–24.3Al–24.8Nb–1.0Zr–1.4V–0.6Mo–0.3Si (at %) alloy based on the orthorhombic titanium aluminide Ti₂AlNb alloyed with hydrogen to 8.5 at % upon aging in the temperature range of 600–700°C after quenching from 900°C. It has been detected that the alloying with hydrogen leads to a change in the morphology of precipitated orthorhombic (O) plates upon aging from a zigzag-shaped to packet morphology and at the aging temperature of 700˚С initiates the transformation of the substructure of the O plates into a polydomain one with the formation of the so-called “polysynthetic twin.” The relationship between the structural characteristics, the amounts of the arising phases, and the values of the microhardness and elastic modulus of the investigated alloys with and without hydrogen after quenching and aging has been established.

Structures of the massive MgB₂ samples deformed in Bridgman anvils that were initially in different structural states, namely, as-synthesized and post-four-stage-treated (via deformation + annealing), have been studied by methods of the X-ray diffraction, scanning and transmission electron microscopy, and measurements of microhardness. The process of the deformation of brittle ceramic samples of MgB₂ under high pressure has been discussed. An analysis of the obtained data has shown that the plastic deformation of the superconductor MgB₂ preliminarily compacted by a four-stage treatment has been implemented in the main through the mutual rotation of crystallites (grains) and by grain-boundary sliding without a noticeable refinement of the grain structure.