Impact fracture of ZnSe ceramics

Structurally different ZnSe ceramics prepared by various techniques were subjected to fallingweight impact fracture. Mechanoluminescence (ML) pulses generated during the motion and multiplication of dislocations were detected, as well as acoustic emission (AE) pulses produced predominantly during the growth of macroscopic (on the specimen scale) cracks. The luminescence began immediately at the moment of contact of a striker with the surface of the specimen, whereas the emission of sound occurred within 50–100 μs after the impact. The emission maxima in the ML and AE time series coincided with each other. The signal series were used to construct energy distributions upon the emission of light and the generation of sound. It was established that the ML amplitude (the number of emitted photons) is proportional to the energy released due to dislocation rearrangements, and the intensity (the square of the amplitude) of AE pulses is proportional to the energy released due to discontinuities of the material. It was found that the ML energy distribution follows a power law, which indicates the self-organization of an ensemble of dislocations during rapid plastic deformation. The AE energy distribution, on the contrary, was found to be random, i.e., typical of the growth of non-interacting cracks. It was shown that the efficiency of the interaction of dislocations depends, to a certain extent, on the technological prehistory of ZnSe ceramics.     

Dependence of the magnetic properties of an amorphous metal alloy on its nanoporosity

Magnetic and structural properties of an amorphous alloy based on iron are investigated. The properties and state of the alloy are changed under hydrostatic pressure of up to 1.3 GPa. An increase in the pressure leads to a linear increase in the maximum magnetic induction and a linear decrease in the remanence. Two nanopore fractions with average sizes of ～20 and 150 nm are revealed in the alloy with the use of small-angle x-ray diffraction. The application of the pressure decreases the size of nanopores and increases the average distance between their boundaries, i.e., increases the average sizes of continuity regions in the alloy. It is established that the relative change in the magnetic characteristics is linearly related to the change in the size of the continuity regions in the alloy. Upon extrapolation to zero nanoporosity, the remanence reduces to zero. The inference is made that the nanopores play a dominant role (as compared to other structural defects) in the magnetic properties of the alloy.     

Nanoporosity of fine-crystalline aluminum and an aluminum-based alloy

The presence of nanopores formed during the equal-channel angular pressing of aluminum is revealed using small-angle x-ray scattering. The parameters of nanopores are determined, and a correlation between the level of nanoporosity and the fraction of high-angle grain boundaries is found. The data obtained indicate that the level of nanoporosity can affect the tensile durability of fine-crystalline aluminum in the creep mode. The data on the regularities in the development of nanopores under deformation of the fine-crystalline aluminum-based alloy in the superplasticity mode are obtained.     

Evolution of microscopic cracks and pores in solids under loading

Experimental data on the development and partial healing of microscopic cracks and pores in loaded crystalline materials are considered. An analysis of the data indicates that fracture development has a number of specific features depending on the state of the materials and the testing conditions and is a kinetic thermal fluctuation process occurring virtually throughout the entire time of loading.     

Certain questions of Lobachevskii geometry,connected with physics

An historical survey of the development of Lobachevskii geometry as a typical representative of a geometry of negative curvature, Friedman cosmology, Lobachevskii geometry, and an interpretation of the velocity space in the special theory of relativity as a Lobachevskii space are presented.Translated from Itogi Nauki i Tekhniki, Seriya Problemy Geometrii, Vol. 13, pp. 157–188, 1982.     

Possible manifestations of quantum effects in the boron microindentation kinetics

The kinetics of indentation of a solid (viz., the dependence of the indenter intrusion depth on the time, force, and temperature), is analyzed theoretically taking into account quantum effects in the atomic dynamics of solids. The experimental study of the temperature dependence of the boron microhardness reveals qualitative and quantitative agreement with calculated dependences. A possible manifestation of quantum (tunnel) effects in the boron microindentation kinetics is predicted.     

Elastoplastic properties of a low-modulus titanium-based β alloy

The elastoplastic properties (elastic modulus, amplitude-independent damping ratio, microplastic flow stress) of a Ti-26Nb-7Mo-12Zr titanium β alloy are determined using an acoustic resonance method. The effect of the strain during thermomechanical treatment on the structural features of the micro-crystalline alloy and, hence, its elastoplastic properties is analyzed.     

Semiclassical theory of the radiative-collisional cascade in a Rydberg atom

We have developed a two-dimensional semiclassical model of the radiative-collisional cascade for hydrogen-like systems. We describe the collisions with electrons and ions by classical diffusion in the space of principal and orbital quantum numbers and use an iterative procedure that consistently takes into account the quantum nature of the radiative cascade for radiative transitions. The model establishes the correspondence between the quantum and classical approaches and indicates that the latter cannot be directly used to calculate the population kinetics of highly excited atomic states. Our calculations of the two-dimensional populations of highly excited atomic hydrogen states for selective, three-body, and photorecombination sources of population allow the data of one-dimensional kinetic models to be refined. The calculated intensities of recombination lines demonstrate the degree of nonequilibrium of the Rydberg state populations under typical astrophysical plasma conditions.     

Evolution of a Defect Structure during Creep Tests of Ultrafine-Grained Metals and Alloys Produced by Severe Plastic Deformation

Physics of the Solid State - The structural factors that lead to a decrease in the mechanostability of ultrafine-grained (UFG) metals and alloys during creep tests at increased temperatures have...