Remanenz und Ummagnetisierungsbeginn in Nickeleinkristallen

The hysteresis, especially the remanence, and the magnetostriction of nickel single crystal rods of 〈110〉, 〈111〉, 〈100〉 and medium orientation are measured at room temperature in a magnetic joke and their dependence on plastic deformation is investigated. In undeformed crystals the nucleation of reverse domains needs a negativeH-field several times the coercivity, thus causing an “overshooting” of the hysteresis. Very small plastic deformations initiate the formation of the reverse domains and destroy the overshooting. Similar to polycrystals, the remanence of the single crystals — except those with 〈100〉 as axis — falls steeply at the beginning of plastic deformation to about 40% of its initial value. The magnetization reversal and the role of nucleation processes are discussed for the different orientations.     

Relation between the Hurst Exponent and the Efficiency of Self-organization of a Deformable System

We have established the degree of self-organization of a system under plastic deformation at different scale levels. Using fractal analysis, we have determined the Hurst exponent and correlation lengths in the region of formation of a corrugated (wrinkled) structure in [111] nickel single crystals under compression. This has made it possible to single out two (micro-and meso-) levels of self-organization in the deformable system. A qualitative relation between the values of the Hurst exponent and the stages of the stress–strain curve has been established.     

The effect of temperature on laws of minor hysteresis loops in nickel single crystals with compressive deformation

The temperature dependence of minor hysteresis loops of compressively deformed nickel single crystals has been investigated in a wide temperature range below the Curie temperature of 628 K. There exist power-law relations between the field-dependent parameters of minor-loops, and their exponents are independent of both temperature and strain after the compressive deformation. These observations indicate the presence of universal power laws in minor hysteresis loops. The minor-loop coefficients of the power laws show a similar temperature dependence of the coercive force, which is quantitatively related to the dislocation density. These properties of minor hysteresis loops are useful for the accurate and quantitative nondestructive evaluation of age degradation in ferromagnetic materials.     

Paramagnetic resonance of nickel doped ZnS and CdS crystals

EPR measurements were carried out on nickel doped ZnS and CdS crystals at 4.2°K and 9.3 Gc/sec. In ZnS crystals the isotropic line corresponding to the naturally occuring nickel isotopes ⁵⁸Ni and ⁶⁰Ni is significantly narrower than previously reported. The single line attributed to natural nickel has been observed in CdS crystals. The hyperfine structure has been studied on samples enriched in ⁶¹Ni. The angular dependence has been thoroughly investigated.     

The effect of bloch-wall motion on the flow stress of nickel single crystals

Experimental evidence is presented that moving Bloch-walls decrease the flow stress of nickel single crystals. Via their strain fields, Block-walls interact with dislocations.     

Reversible change of shape in mabtensitic transformations

The thermal stability of the reversible changes in shape of opposite sign, obtained after preliminary plastic deformation of TiNi above and below M_d, is investigated. It is shown that the stability of the dislocational structure responsible for reversible changes in shape in martensitic transformations is determined by the phase state of the material in the course of its formation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 95–101, May, 1977.     

A study of the structure and scattering mechanisms of subterahertz phonons in lithium fluoride single crystals and optical ceramics

The methods of optical, electron, and atomic force microscopy (AFM) are applied to the study of the real structure of optical lithium fluoride ceramic obtained by hot deformation of single crystals. A comparative analysis is carried out of the scattering mechanisms of weakly nonequilibrium thermal phonons at liquid helium temperatures in LiF single crystals and ceramics. It is demonstrated that the phonon scattering in the original single crystals is determined by the forced vibrations of dislocations in the stress field of an elastic plane wave (a phonon), i.e., by the flutter mechanism. As the degree of deformation of the original material increases, the ceramics exhibit a change in the plastic deformation mechanisms, which leads to a decrease in the average size of grains and to an ordered structure. In this case, the dominant scattering is that by intergrain boundaries. The thickness and the acoustic impedance of these boundaries are evaluated.     

Sharp increase in mobility of spiral dislocations by a pulsed electric field

An investigation is made of the change in expansion rate V of spiral dislocational half-loops in NaCl crystals after brief application of an electric field. It is established that, after the application of a field pulse at fixed shear stress, V rises sharply at first and then, with time, falls exponentially to its initial value. The initial increase in V depends on the amplitude of the electric pulse, and the relaxation time of its subsequent fall on the temperature. The activation energy of the process is determined from the temperature dependence of the relaxation time.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 71–74, March, 1979.     

Plastic Strain of Nickel [001] Single Crystals: Simulation and Experiment

Technical Physics - Mathematical simulation and experiments are used to study plastic strain in nickel [001] single crystals. It is shown that the crystal exhibits self-organization of plastic...     

Extended topological defects as sources and outlets of dislocations in spherical hexagonal crystals

Extended topological defects (ETDs) arising in spherical hexagonal crystals due to their curvature are considered. These prevalent defects carry a unit total topological charge and are surrounded by scalene pentagonal boundaries. Topological peculiarities of reactions between ETDs and dislocations are considered. Similarly to boundaries of the usual planar crystalline order the ETDs emit and absorb the dislocations without preservation of their dislocational charge. Dislocations located inside the ETD area lose it and the enforced ETD decay can proceed in different ways without conservation of the total Burgers vector of the dislocations emitted.     

Study of creep and features of the dislocation structure in single crystals of Ni3Ge alloy

Data from investigating the dislocation structure of Ni₃Ge alloy single crystals formed during creep are presented. The creep of the Ni₃Ge single crystals with the [001] orientation of the deformation axis was studied. It was found that a fragmented substructure with varying degrees of disorientation occurs in the areas of macrolocalized deformation. A polycrystalline substructure consisting of fragments with a low dislocation density is formed in the local areas.     

Shear localization in dynamic deformation of copper single crystals

Dynamic deformation of copper single crystals, especially of fatigued copper single crystals with different orientations, was conducted on a split-Hopkinson pressure bar apparatus. The strain rates were in the range 2???9?×?10³?s^?1. After dynamic deformation, the adiabatic shear bands (ASBs) were examined in a light microscope and SEM. The width and spacing of ASBs formed under different strain rates in a fatigued copper single crystal were measured and the spacing of ASBs is one-order of magnitude smaller than the theoretical predictions. The possible reasons for the discrepancy were discussed. The critical strains for the ASB formation in four different orientated single crystals at stain rate of about 4?×?10³?s^?1 were determined by examining the post-deformation specimens and dynamic stress–strain curves. It is clearly indicated that the critical strains for the ASB formation are orientation-dependent in copper single crystals. A simple microscopic mechanism for ASB formation in fatigued single crystals was proposed.     

Mechanical twinning of yttrium oxide single crystals

The deformation structure of an yttrium oxide single crystal under point load was studied by microhardness and electron microscopy. It was concluded that mechanical twinning is the main mechanism of plastic deformation of these single crystals. A twin was simulated by rotating the structure around the three-fold axis. It was shown that the average change of the distance between anions was about 5% and that between cations was 15%. The comparison with the structure of the regions of the fluorite single crystals and optical ceramics deformed in the analogous manner was performed.     

Kinetics of structural relaxation and regularities of plastic flow of metallic glasses

On the basis of a calculation of the structural relaxation rate and an experimental acoustical-emission determination of the temperature of the transition from localized to uniform flow it is argued that the type of plastic deformation of metallic glasses is uniquely determined by the kinetic structure of the relaxation. In the case of a kinetically hindered structural relaxation, which is characteristic for tests of initial samples at temperatures T<380–420 K, a localized dislocational deformation is realized. At higher temperatures, “memory” of the thermal prehistory of the samples is lost (aging at room temperature), the structural relaxation rate grows abruptly and plastic flow becomes uniform viscoplastic flow. Fiz. Tverd. Tela (St. Petersburg) 41, 2167–2173 (December 1999)     

Dislocational kinetics in the intense deformation of fcc single crystals

The stability of the dislocational subsystem of fcc single crystals deformed in dynamic conditions is investigated. It is shown that, depending on the deformational conditions, the system may have one or two steady states, one of which is ρ _s ⁽¹⁾ . When the system has one trivial steady state, it may be stable or unstable. In some conditions, a second unstable point ρ _s ⁽²⁾ appears; in this case, ρ _s ⁽¹⁾ is stable. Tomsk State Architectural and Building Academy. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 43–48, August, 1997.     

Strain Avalanches in Microsized Single Crystals:Avalanche Size Predicted by a Continuum Crystal Plasticity Model

Plastic deformation of small crystals occurs by power-law distributed strain avalanches whose universality is still debated.In this work we introduce a continuum crystal plasticity model for the deformation of microsized single crystals,which is able to reproduce the main experimental observations such as Row intermittency and statistics of strain avalanches.We report exact predictions for scaling exponents and scaling functions associated with random distribution of avalanche sizes.In this way,the developed model provides a routine for a quantitative characterization of the statistical aspects of strain avalanches in microsized single crystals.     

The effect of aluminum alloying on strength properties and deformation mechanisms of the 〈123〉 Hadfield steel single crystals

The role of aluminum alloying on strength properties and deformation mechanisms (slip, twinning) of 〈123〉 single crystals of Hadfield steel under tensile loading at T = 300 K is demonstrated. It is found out that aluminum alloying suppresses twinning deformation in the 〈123〉 single crystals and, during slip, results in a dislocation structure change from a uniform dislocation distribution to a planar dislocation structure. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 3–7, October, 2007.     

Structure and mechanical properties of Ni<Subscript>3</Subscript>Ge single crystals under severe plastic deformation and heating

Mechanical tests are performed for Ni₃Ge alloy single crystals in the intense plastic shear deformation scheme under quasi-hydrostatic pressure at different test temperatures. Dependences of resistance to shear deformation on the Bridgman anvils’ angle of rotation are obtained. The microrelief of the surface damage of Ni₃Ge single crystals fractured by plane bending after specimens were withdrawn from the Bridgman anvils is studied. X-ray diffraction patterns of deformed Ni₃Ge single crystals are obtained.