M. A. Zheltov

Morphology diagram of nonequilibrium patterns of ice crystals growing in supercooled water

The morphology diagram of ice crystal patterns, which grow freely in a supercooled water is obtained experimentally in a “supercooling-tip velocity” phase space. This diagram classifies eight nonequilibrium macroscopic structures growing in the supercooling temperature region of heterogeneous nucleation of ice in pure water at atmospheric pressure. We found different kinds of morphology transitions between structures such as the first order, continuous, and the fork-like bifurcation transitions. It was shown that the nonequilibrium patterns exhibit various growing behaviours such as tip-splitting, tip-oscillating, and tip-stable modes. Supercoolings as large as 30°C can be achieved allowing ready access to both the diffusive and kinetic growth regimes. We found the supercooling ranges that correspond to kinetic regime of solidification in which under controlled conditions, for a given supercooling levels both fractal and nonfractal nonequilibrium growth patterns are reproducibly observed. The possible reasons for the competition between fractal and nonfractal structures growing in highly supercooled water are discussed.

In situ monitoring of growth of ice from supercooled water by a new electromagnetic method

Abstract The electromagnetic emission (EME) accompanying freezing of distilled water and dilute aqueous NaCl solutions is revealed and investigated. The EME signal is a sequence of discrete pulses of the electric field potential in the vicinity of the outward surface of ice–water system during the crystallization process. We found correlation between parameters of emission and kinetics and morphology of growing ice and propagation of the growing-induced cracks. It is shown that measurements of an EME signal during the freezing of dilute aqueous solutions allow mapping of the mesoscopic-level patterning to the time series. The relationship between phenomenon of the EME and the Workman–Reynolds effect is discussed.

Kinetics and morphology of nonequilibrium growth of ice in supercooled water

The kinetics of free growth of ice in a distilled-water film supercooled to −30°C was studied by the video recording technique in the polarized light. In the supercooling range 12 < ΔT < 16 K, a first-order kinetic morphological transition was observed between the structure formed by needlelike crystals of ice and the quasiadiabatic “structure” of single grains having the shape of planar platelets with the thickness proportional to the thickness of the water film and relative supercooling. It was found that this transition is accompanied by jumplike changes in the main crystallization parameters such as the growth rate of grains, their size and number, their kinetic behavior, and the fractal dimension of the structure.

Acoustic precursor of unstable plastic deformation in the aluminum-magnesium alloy AMg6

A relation between the acoustic signal and the dynamics of the first deformation bands at the initial stage of development of the plastic deformation jump in the artificially aged AMg6 alloy has been established using the high-speed video recording and simultaneous measurement of the acoustic emission signal. It has been demonstrated that a sharp increase in the potential of a piezoelectric transducer in the first approximately 10 ms of the development of the deformation jump is the most informative characteristic of the acoustic signal. The mechanisms of propagation of deformation bands and generation of acoustic signals, as well as the possible use of acoustic precursors of plastic deformation jumps, have been discussed.

Nucleation mechanisms of macrolocalized deformation bands

For the first time, a phenomenological classification of the nucleation mechanisms of bands of macrolocalized deformation is formulated that is based on data from the high speed optical monitoring of a surface of aluminum-magnezium alloy deformed with a uniformly growing rate of applied stress,

Plastic deformation macrolocalization during serrated creep of an aluminum-magnesium Al-6 wt % Mg alloy

\dot \sigma _0 = const

Electromagnetic emission in the development of macroscopically unstable plastic deformation of a metal

. The classification includes eight nucleation mechanisms that depend on the applied stress: from the initial stage of formation of the Lüders band to the periodical nucleation of the conjugative bands in the structure of a neck prior to sample rupturing. The role of different mechanisms of band nucleation in the general picture of the jerky deformation of a metal is discussed.

Serrated creep and spatio-temporal structures of macrolocalized plastic deformation

Discrete electromagnetic emission caused by a jump of plastic deformation and fracture of single-crystal and polycrystalline ice is revealed and investigated. An album of electromagnetic signals is compiled, which makes it possible, on the basis of the electromagnetic-signal shape, to identify and study the kinetics of mesoscopic events of structural relaxation that are related to the dynamics of dislocation pile-ups and cracks.