Vol 81, No 11 (2017)

The results are presented from experimental studies of the formation of martensitic twin structures in Ni_2.16Mn_0.84Ga Heusler alloy under the effect of magnetic fields of up to 14 T using a specially developed optical microscope under isothermal and adiabatic conditions. A qualitative model is proposed that explains the differences between the progress magnetoinduced magnetostructural first-order phase transitions under different thermodynamic conditions.

Spatial distributions of the residual elastic strains in layers of step-graded metamorphic buffers of two different designs, grown via molecular beam epitaxy on the basis of In_xAl_{1 − x}As ternary solutions, are obtained by means of reciprocal space mapping. It is shown that with allowance for work hardening, which affects strain relief in buffer layers and increases the strain in dislocation-free layers, the mechanism of strain relief in the final buffer steps, and the residual elastic strain in a buffer dislocation-free layer, are governed by the same phenomenological law as in a single-layer heterostructure.

Variations in the magnetic characteristics (specific saturation magnetization and coercive force) of Co–Fe–Cr–Si–B amorphous alloy (AA) are studied after high-pressure torsion (HPT) and heat treatment. The behavior of AA magnetic properties is analyzed with respect to structural transformations caused by external actions. The corrosion resistance of AA upon transitioning from an amorphous to a crystalline state is investigated. The established optimum annealing and HPT conditions yield a satisfactory combination of the magnetic properties and corrosion resistance of the investigated alloy.

The conditions for the existence of discrete breathers (DBs) in biatomic crystals of AB and A₃B composition are established, and their properties are studied by means of molecular mechanics using the examples of CuAu and Pt₃Al, respectively. The phonon spectra of the crystals are analyzed, and a gap in the phonon spectrum of CuAu is obtained via considerable homogeneous elastic strain. There is a gap in the phonon spectrum of the Pt₃Al crystal at zero strain, due to the considerable difference between the atomic weights of its components. The frequencies at which discrete breathers can exist in the considered crystals are determined. The energy localized on different types of DBs is estimated. The propagation of a current pulse through Pt₃Al resulting in the excitation of DBs with mild nonlinearity is simulated.

The effect deuterium has on phase transformations is studied for amorphous and crystalline fullerenes C₆₀ and C₇₀ at high temperatures of up to 1300°C and high pressures (2–8 GPa). Amorphous fullerene phases are obtained via long grinding in a planetary mill. Structure is studied by means of neutron diffraction. In all cases, amorphous graphite (nanographite) forms in the temperature range of 800–1100°C. This material has different diffraction spectra distinguished by the heights of the halos observed on the graphite diffraction maxima and their relative intensities. These spectra (the structure of nanographite) are affected by preliminary amorphization, the number of carbon atoms in the fullerenes (C60 or C70), and the introduction of deuterium atoms. The different spectra of amorphous (disordered) graphite testify to its varying structure.

Ti–Nb alloy with 40 wt % of Nb is obtained from a composite Ti–Nb powder by means of selective laser melting. The Ti–Nb alloy has a two-phase microstructure. The main β-phase of the solid titanium–niobium solution forms grains ranging in size from ~2 to 20 μm. A nonequilibrium α″-phase is found in the forms of lamellar, globular, and packet martensite inside the grains of the β-phase and along their boundaries.

State-of-the-art means of physical materials science are used to study the structure, phase composition, defect substructure, and tribological properties of a coating formed on low-carbon Hardox 450 martensite steel via the electrocontact deposition of an Fe–C–Ni–B wire and modified through subsequent irradiation with high-intensity pulsed electron beams. It is shown that electron-beam treatment results in the formation of a modified 50-μm thick surface layer, the main phases of which are the α-phase, iron boride FeB, and boron carbide B₄C. In the layer modified by electron-beam treatment, the transverse size of batch martensite crystals is reduced by a factor of 3, relative to the initial Hardox 450 steel, and ranges from 50 to 70 nm. It is established that the wear resistance of the deposited layer after electron-beam treatment grows by more than 20 times with respect to the wear resistance of Hardox 450 steel, and the friction coefficient is reduced by a factor of 3.5. The microhardness of a deposited layer ~7 mm thick is more than double that of the base metal.

X-ray diffraction line profile analysis is adapted to investigate the microstructure of alumina. The structure of electrocorundum and corundum powders produced from pseudoboehmite with submicronic and nanometer-sized particles is analyzed. The lognormal size distribution parameters and their dependence on the conditions of corundum synthesis are determined. The structure of dislocations in corundum with different synthesis prehistories is analyzed, and structural features of the studied material are revealed.

The elastocaloric effect (ECE) in fast-quenched Ti₂NiCu ribbon under the periodic action of tensile force is studied experimentally. The ECE is measured as a function of relative elongation and the frequency of cycles in the range of 0.2 to 4 Hz. The maximum measured ECE in the alloy is 9.4 K under a mechanical load of 300 MPa at a relative deformation of 1%, frequencies of 0.2 to 0.5 Hz, and a temperature of 67°C. The specific power of the ribbon is estimated; it reaches its maximum at a frequency of f = 4 Hz, corresponding to W = 10 W g⁻¹. The possible practical use of Ti₂NiCu alloy for elastocaloric cooling is discussed.