Vol 82, No 9 (2018)

The electroplastic effect is studied on mechanically loaded single crystals of nickel-based CMSX-4 superalloy and pure aluminum bicrystals. Both objects of study exhibit elevated plasticity under electrical pulses. Traces of the electroplastic deformation that occurs in CMSX-4 single crystals at current densities J higher than 3 kA mm⁻² and aluminum bicrystals at J exceeding 1.6 kA mm⁻² are analyzed using a scanning electron microscope.

Phase transitions in two types of amorphous fullerene phases (C₆₀–C₇₀ (50/50) mixtures and an amorpous C₇₀ fullerene phase) are studied via neutron diffraction at pressures of 2–8 GPa and temperatures of 200–1100°C. Fullerenes are amorphized by grinding in a ball mill and sintered under quasi-hydrostatic pressure in a toroidal-type chamber. Diffraction studies are performed ex situ. It is shown that the amorphous phase of fullerenes retains its structure at temperatures of 200–500°C, and amorphous graphite is formed at 800–1100°C with a subsequent transition to crystalline graphite. This process is slow in a mixture of fullerenes, compared to C₇₀ fullerene. According to neutron diffraction data, the amorphous graphite formed from amorphous fullerene phases has anisotropy that is much weaker in a fullerene mixture.

Amorphous TiNiCu alloys with copper contents of 28 to 38 at % are fabricated via melt spinning. The isothermal crystallization of alloys is conducted at 500°C with variable durations of the heat treatment (100 to 300 s). It is shown that shortening the duration of crystallization prevents the formation of brittle phases of the Ti–Cu system and contributes to the martensitic B2 ↔ B19 transformation, with the temperature intervals of transformation shifting to higher values and a marked increase in the enthalpy of the martensitic transitions and the magnitude of the shape memory effect.

The Bollman and King models are tested by means of molecular dynamics simulation for the formation of geometrically necessary disclinations in triple junctions of grain boundaries in metals. It is shown that the stresses arising in a triple junction due to the non-multiple lengths of low-angle tilt boundaries to the distance between grain boundary dislocations is not compensated for mainly by the formation of an additional disclination in the junction (the King model) but by the bending of one or several grain boundaries, accompanied by the displacement of grain boundary dislocations. A triple junction of the Bollman U-type (containing a geometrically necessary disclination) is not formed at the conjugation of tilt boundaries with common misorientation along the junction or at the conjugation of mixed-type boundaries.

Using an original approach, a pronounced two-way shape memory effect is created for the first time in rapidly quenched alloys of the quasibinary TiNi–TiCu system with copper contents of up to 38 at %. The technique includes the combined effect of the dynamic crystallization of the amorphous state by application of a single pulse of electric current of 10 ms duration and pulsed laser radiation (λ = 248 nm, τ = 20 ns). The obtained composite structure materials can be used to create different micromechanical devices, especially microswitches and microtweezers for gripping micro-objects.

A theoretical approach is developed for determining the parameters of nanoscale crystal structures using diffraction spectra of Auger electron energy losses. The approach is based on modeling the radial distribution functions of atoms while allowing for the sizes of atomic structures, and on the geometry of surfaces of three-dimensional, surface, and linear objects intersecting with a sphere. Using the example of allotropic carbon phases, it is shown that the proposed technique allows assessment of a studied object’s thickness and the depth of the analyzed signal output with an accuracy of one atom’s diameter.

The results are presented from experimental studies of the microstructure and phase composition of AK7ch Al–Si alloy with an iron content of 0.4 wt % before and after introducing a modifying mixture based on ultradisperse powders of metal oxides and cryolite into the melt. The formation of three-component phases α-Al₂FeSi and β-Al₅FeSi is established experimentally. The effect iron has on the crystallization of eutectic mixtures is considered using the phase diagram of the Al–Fe–Si system.

The effect low-amplitude oscillations have on the mechanical properties of Al and W in nanocontacts is studied by means of continuous stiffness measurements (CSM). It is established that the additional superpositioning of oscillations until a critical amplitude is reached has no effect on the mechanisms, kinetics, or plastic deformation of a material. The threshold amplitudes and frequencies of such oscillations are determined for Al (2.5 nm) and W (3.5 nm).

A number of advanced nondestructive thermographic tools are described that are based on the video recording of surfaces using thermal imaging cameras in which infrared radiation is induced by shortterm heating with an electric current or a stream of hot air. The tools allow the detection of cracks, delaminations, gaps, and other types of defects both inside and outside the shell of a structure that cannot be reached for direct inspection.

Structural mutual transformations of graphites and diamond-like phases are studied theoretically using the density functional theory. It is established that the phase transitions of hexagonal graphene to diamond- like phases should occur at uniaxial stresses of ~66–71 GPa, while some diamond-like phases can be obtained from tetragonal graphene at much lower pressures of ~40–52 GPa.

The results are presented from complex phase structural and magnetic studies for uncoated and hybrid nanopowders based on iron oxide of the core–shell type (Fe_3−xO₄@SiO₂). Their phase and structural characteristics are determined along with their and morphologies. It is shown that the nanopowders are nonstoichiometric magnetite Fe³⁺[Fe_{1-3 x}²⁺Fe_{1+2 x}³⁺V_x]О₄ in which there are volume and surface regions that differ by the electronic state of their iron ions. The results from magnetic measurements reveal a relationship between the dispersity and magnetic properties of nanopowders. The change in the thickness of a defect surface layer and its specific magnetization is analyzed quantitatively as a function of the mean size of magnetite nanoparticles and the presence of a coating. The resulting dependences are constructed and analyzed.