Yu. I. Golovin

Serrated plastic flow during nanoindentation of a bulk metallic glass

The results of nanoindentation tests of bulk glassy Pd40Cu30Ni10P20 using a specially designed instrument with high time and spatial resolution are presented. Pronounced serrations of the indenter penetration depth are observed. The parameters of serrated flow (the number of serrations, their amplitude and duration) are dependent on the duration of the loading force pulse.

Nanoindentation and mechanical properties of solids in submicrovolumes, thin near-surface layers, and films: A Review

This paper presents a review devoted to the specific mechanical behavior of thin near-surface layers of various solids, materials, films, and multilayer coatings under local loading. Analysis is made of the principles, techniques, and instruments used for testing and determining mechanical properties of materials on a nanoscale, which, in recent years, have found a wide application under the general name “nanoindentation.” Information capabilities of this large and multifunctional family of methods employed for mechanical tests are discussed. Different aspects and specific features of the behavior of solids under severely constrained deformation caused by the local application of a microload to the surface of the test object are considered. Special attention is focused on the physical mechanisms of deformation and fracture under these conditions.

Magnetoplastic effects in solids

This paper is an overview of the studies into the effect of weak magnetic fields on the structure and mechanical properties of nonmagnetic solids of various nature (ionic, covalent, molecular, and metallic crystals, polymers, etc.). The various effects and aftereffects initiated by static, pulsed, and microwave magnetic fields that have been discovered over the past 15 years are classified and critically analyzed. The thermodynamic and kinetic aspects of the magnetic-field sensitivity of real solids with structural defects containing paramagnetic centers (electrons, holes, radicals, excitons, etc.) are discussed. Possible mechanisms for the effect of a weak magnetic field on the defect structure of crystals are considered. Special attention is given to the most developed chemical-physical theory of spin-dependent reactions between mobile particles and unpaired electrons. Interpretation of magnetoplastic effects is proposed in terms of the spin, electron, molecular, and dislocation dynamics of the complex multistage processes initiated by a magnetic field in a system of metastable structural defects.

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.

Electron paramagnetic resonance in a subsystem of structural defects as a factor in the plasticization of NaCl crystals

A change in the macroplastic deformation rate and an increase in the travel distances of edge dislocations are observed in NaCl single crystals placed in crossed dc and rf magnetic fields. The magnetic-field frequencies at which softening maxima are observed correspond to the resonance frequencies of transitions between Zeeman sublevels in paramagnetic complexes of structural defects.

Time-dependent characteristics of materials and micromechanisms of plastic deformation on a submicron scale by a new pulse indentation technique

Abstract A high-resolution dynamic nanoindentation technique has been developed (spatial resolution, about 1 nm; time resolution, about 50 μs). In addition we were able to record the electrical polarization of the indentation zone with a time resolution of about 100ns. It has been established that the process of the indenter penetration under step-like loading conditions can be described as consisting of several distinct stages (as many as four in some cases) that differ in kinetics and activation parameters. Relative contributions of non-equilibrium point defects and dislocations in each stage 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.

Softening of ionic crystals as a result of a change in the spin states of structural defects under paramagnetic resonance conditions

The purpose of this work was to investigate the plastic properties of Ca-or Eu-doped NaCl and KCl single crystals in crossed constant and microwave magnetic waves under paramagnetic resonance conditions. It was found that when the photon energy of the microwave field equals the Zeeman splitting of the electronic spin sublevels, resonance softening of the crystals, manifested as an increase in the free path of individual dislocations and the macroplastic flow velocity as well as a decrease of the microhardness of the crystals, is observed. It was established that metastable Ca-and Eu-impurity complexes, which are also sensitive to the constant magnetic field in the absence of the microwave field, as well as complexes formed by dislocations and point defects are responsible for resonance softening.

Micro- and nano-indentation approach to strength and deformation characteristics of minerals

In focus are methodology and effect of micro- and nano-indentation method in studying local deformation and failure of rocks. By micro- and nano-indentation, numerical values of Young’s modulus, and hardness of rocks and minerals have been obtained. The values of fracture toughness are obtained for separate minerals and at grain boundary. The authors highlight the use perspectiveness of the described method in estimating strength and deformation characteristics of rocks.

Nanostructure of optical fluoride ceramics

The real structure of samples of optical fluoride ceramics is studied by atomic force, scanning electron, and transmission electron microscopy. It is shown that the optical ceramic samples based on CaF2 have a lamellar structure, and the distance between lamellae is 25–50 nm. Most likely, lamellae have a twin nature. For BaF2 ceramic, lamellae are not typical, and they are concentrated near grain boundaries.