Deformation of Nickel Titanium Single Crystal under Compressive Pulse

Russian Physics Journal - Nickel titanium single crystal is used to show the importance of the volume compressibility anisotropy in analyzing the elastoplastic deformation processes in metal single...     

Excess Atomic Volume and its Role in Fracture of Nickel Single Crystals

Russian Physics Journal - The paper studies the crack propagation in the nickel single crystal under uniaxial tension along the [010] crystallographic direction using the molecular dynamics...     

Kinetics of Plastic Deformation in CuBr Single Crystals at Low Temperatures

Single crystals of CuBr with zincblende structure, deformed in compression at a strain rate 2×10^-4 s^-1 between room and liquid-nitrogen temperatures, exhibit two well-defined regions in the critical resolved shear stress (CRSS) versus temperature relationship. At rather low temperatures in the range from 78 to 150 K, the slope d ln /dT of the straight line fitted to the data points plotted in log-linear coordinates is found to be 2.9 times greater than that at temperatures between 150 and 300 K. Similar behaviour is also observed in the case of temperature dependence of activation volume associated with the CRSS. Data analysis in terms of the kink-pair nucleation model of plastic flow shows that stress-assisted thermally-activated escape of screw dislocations trapped in Peierls troughs induces slip below about 150 K. At temperatures above 150 K, CRSS is determined by the unpinning of edge-dislocation segments from groups of randomly dispersed point defects, e.g. residual gaseous and metallic impurities, deformation-induced defects formed during the pre-yield stage etc.     

Evolution of Distribution of Dislocations in Ni3Ge Single Crystals During Deformation

The evolution of the distribution of dislocations in Ni₃Ge single crystals subjected to deformation in uniaxial compression is studied. The dislocation ensemble in the material under review is found to be of a chaotic homogeneous type. Contact interactions between dislocations prevail, and a linear relation of the spacing between dislocations to the length of dislocation segments is observed for stoppers of an arbitrary type. An equation is derived for the probability density function of the fraction of mobile dislocation segments. The solution to the equation is the normal distribution law. This solution can be extended to parameters that are functions of the dislocation density or spacing between dislocations. The experimental histograms of the spacing between dislocations and of that between arbitrary stoppers with a high significance level obey the lognormal law for all degrees of reduction studied.     

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...     

Patterns of the Deformation Relief in Ni3fe Alloy Single Crystals with Long-Range Atomic Order

Russian Physics Journal - Patterns of evolution of plastic deformation macrofragmentation and localization in [1.8.12] Ni3Fe ordered alloy single crystals under compression are investigated. A...     

Morphology and Growth of Single Crystals of Isotactic Polypropylene from the Melt

Isolated single crystals of isotactic polypropylene (iPP) grown from the melt were studied by optical microscopy and atomic force microscopy (AFM). The single crystals had a well-known rectangular shape when crystallized at high temperatures (T_c) above 155°C. The width increased with decreasing T_c, and the shape became hexagonal below 130°C. The single crystals were sectored with thickness difference between them. The growth rate along the a*-axis, G_a*, agreed well with the growth rate of spherulites, as expected. G_a* had two inflection points on the plots against (TΔT)^?1. The lower temperature inflection corresponds to the regime II-III transition, and the higher temperature one is accompanied by an inflection of the growth rate in the b-axis direction, G_b, which has been measured for the first time. The inflection of G_b at the lower inflection temperature of G_a* was much smaller than that of G_a* and may not exist. The crystals are basically surrounded with flat surfaces and no indications of kinetic roughening in the regime III were recognized in the AFM images. The inflections of G_a* and G_b caused a complicated shape change of the aspect ratio, having a minimum at around 135°C.     

On the Geometry of Diffusion Processes in Continuized Dislocated Crystals

Nonequilibrium diffusion processes of point defects in continuized dislocated crystals are considered. A generalized, stochastically motivated gauge procedure to introduce the geometry of a material space describing the influence of dislocations on the free diffusion process, is used. The dependence of diffusing processes and their steady states on the curvature of the material space of edge dislocations, on the scalar density of these dislocations, and on the interaction energy between dislocations and a diffusing atom, is analysed. An equation defining the interaction energy is deduced, using statistical arguments, from the material space geometry.     

Absorption Related to Electrochromism in Cubic Boron Nitride Single Crystals

A unusual electrochromism is observed in amber cubic boron nitride （cBN） single crystals when breakdown possibly related to impurities and defects occurs. The electrochromism induces an abrupt increase in the absorption coefficient of the cBN crystals within the visible and infrared region. The change of the absorption coefficient of cBN crystal can be increased linearly by raising the current after the electrochromism occurs, whereas it is irrelevant to the polarization of the incident light. The absorption related to the electrochromism in the cBN single crystal has potential applications in designing and manufacturing electro-optical modulators, optical switches, and other optoelectric devices.     

Temperature-Programmed Growth of Quasi-Free-Standing N-Doped Graphene Single Crystals from Acetonitrile Molecules

JETP Letters - This paper presents an original technique for temperature-programmed growth of N-doped substrate-sized graphene single crystals on Ni(111). The process includes acetonitrile...     

X-Ray Luminescence of Defects in Spinel Single Crystals

The flareup of x-ray luminescence in spinel single crystals (MgAl₂O₄) depending on the time of x-ray irradiation and the decay of fluorescence depending on the time elapsed after the termination of irradiation have been investigated. These dependences were measured at different powers of the irradiation dose (power of the x-ray tube) and at different temperatures of the samples. The experimental results suggest the existence of large-size complexes of defects, which include antisite defects and impurity ions, the exchange of charge carriers between which during and after irradiation leads to luminescence of the impurity ions. Transfer of charge carriers between isolated elements of the pairs of antisite defects (not interacting with the impurity ions) leads to the formation of a competing channel of recombination luminescence in the UV region of the spectra. The decay of fluorescence attributable to transitions in the Mn²⁺ and Cr³⁺ ions depending on the time elapsed after the termination of x-ray irradiation points to the existence of various combinations of antisite defects in the surroundings of these ions.     

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.     

Simulation of the Dynamic Breakdown of Ammonium-Perchlorate Single Crystals

Technical Physics - Dynamic breakdown of ammonium perchlorate single crystals is numerically simulated. A system of differential equations that describe processes in an equivalent circuit of a...     

A New Method for the Measurement of Thickness in Single Crystals

A new method for thickness determination of single-crystal thin samples at exact zone axis orientation, based on pattern recognition in convergent beam electron diffraction (CBED), is presented. The method is especially well suited to materials with a large unit cell in zone axis directions where the reciprocal lattice is uniformly dense with diffraction points. The new method is based on comparison of a measured CBED zone axis pattern with a set of calculated ones. Its accuracy was estimated to be around 10% in the 5–100 nm thickness range as checked for garnets at the [111] zone orientation.     

Energetic Substantiation of the Formation of Ytterbium Dimers in Single Forsterite Crystals

Physics of the Solid State - A structural computer simulation of ytterbium-containing forsterite crystals has been carried out. Atomistic simulation is performed using the GULP 4.1 software package...     

An Unitarized Model of Quasi-Two-Body Contributions to Single Pion Production by Mesons

A general formulation is presented of resonant final state interactions (isobars) in single pion production by mesons with particular reference to the N* case. An essential use is made of the separation of the process into the quasi-two-body production and the decay steps. This allows the insertion of the isobar hypothesis into a scheme capable of dealing correctly with the spin-angular momentum aspects. A general scheme is developed for the exploitment of the two-channel unitarity conditions in a partial wave analysis of the isobar production amplitudes. The method for computing normalized distributions is finally outlined.