Plastic flow macrolocalization in aluminum and the Hall-Petch relation

The parameters of plastic deformation macrolocalization are compared to the parameters of the Hall-Petch relation for the flow stress in polycrystalline aluminum samples with a grain size of 0.008–5.000 mm. Two types of the dependence of the localized plastic deformation autowave length on the grain size and two versions of hardening according to the Hall-Petch relation are found in the grain size range under study. The boundary between these versions is shown to correspond to d ≈ 0.1 mm for both cases. A relation between localized plastic flow patterns and the Hall-Petch relation is revealed.     

The nature of large-scale correlations in plastic flow

The nature of large-scale correlations in the locations of the centers of plastic flow during the deformation of crystalline solids is discussed. It is shown that regularities in the generation and development of such centers can be described as various types of autowaves arising from processes of self-organization. Examples are presented of the excitation-wave and phase-wave types of autowave processes experimentally observed during the deformation of single-crystal and polycrystalline metals and alloys. Some numerical parameters of the autowave processes are estimated. Fiz. Tverd. Tela (St. Petersburg) 39, 1399–1403 (August 1996)     

Deformation autowaves in nitrogen-doped γ-Fe single crystals

Experimental data on the evolution of macrodeformation fields of single-crystal samples of austenitic chromium-nickel steel with a superequilibrium nitrogen content under tension are analyzed on the basis of a model of autowave plastic flow. The conditions for the appearance and observation of different types of autowave deformation structures are established; such structures include a solitary front, a traveling autowave, and a stationary dissipative structure and are determined by the crystal-geometry of deformation and by the nitrogen concentration in the material. It is shown that a one-to-one correspondence exists between the type of deformation autowave and the stage of the plastic flow curve of the material. Zh. Tekh. Fiz. 69, 56–62 (October 1999)     

Instability of the crystal lattice of CuPd alloy

The results of structural investigations (x-ray structural analysis, small-angle scattering and electron microscopy) of the B2→Al deformation phase transition and the kinetics of the recovery processes of deformed CuPd alloy are presented. It is established that the phase transition occurs in regions of local plastic deformation and the B2→Al deformation transition helps to enrich these regions with palladium. Tomsk State Architecture-Construction Academy. V. D. Kuznetsov Siberian Physico-Technical Institute, Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 93–102, March, 1997.     

Kinetics of periodic processes during plastic flow

This paper establishes the dependence of the velocity of the self-consistent motion of the foci of inhomogeneous plastic deformation on the strain-hardening coefficient during the stretching of single-crystal γ Fe. It is shown that the relationship between the velocity and the indicated quantity is inversely proportional at the linear-hardening stage. An interpretation of the observed regularities is proposed on the basis of the concept of the autowave character of the plastic flow of solids and of self-organization in a deformed medium. The dispersion law of the plastic-deformation autowaves is established. Fiz. Tverd. Tela (St. Petersburg) 41, 1222–1224 (July 1999)     

Peculiar behavior of structure rearrangement in nanofiber of intermetallic Ni<Subscript>3</Subscript>Al,containing long-period paired thermal anti-phase boundaries,under high-rate tensile uniaxial loading along <001>

Using molecular dynamics simulations, peculiarities of structure rearrangement in nanofiber of intermetallic Ni₃Al containing long-period, paired, thermal (nonconservative) anti-phase boundarties (APBs is investigated in the course of high-rate, tensile uniaxial loading along <001>. Four main deformation stages are determined (quasi-elastic, plastic, material flow and rupture), with each stage revealing particular features of structure transformations and energy transfer. The presence of periodic thermal planar defects in the long-period nanostructure (combined thermal anti-phase boundaries) significantly affects the onset of plastic deformation. A change in the type of thermal APBs in the long-period structure in turn affects the time to total rupture of nanofiber under plastic deformation condition. For the thermal AA 1/2 < 110 > {001}APBs, the time to total nanofiber rupture is slightly decreased, while that for the thermal AB 1/2 < 110 > {001} APBs is considerably increased.     

Relation of the Lattice and Deformation Characteristics at Plastic Flow of Metals

Russian Physics Journal - A new approach is suggested for explanation of autowave processes during plastic deformation of metals. It is based on the postulate that a quasiparticle corresponds to a...     

Autowave Plasticity: Principles and Possibilities

Technical Physics - Basic concepts of the autowave model of development of a localized plastic flow of solids of different natures are considered. It is shown that plastic deformation develops in a...     

Origin of Elastic–Plastic Deformation Invariant

We consider the autowave mechanism of evolution of a localized plastic deformation of crystalline solids of different origins. It is found that localization of the plastic flow is determined by the relation between elastic and plastic phenomena in deforming materials. It is shown that the main parameter of deformation processes is the elastic–plastic deformation invariant, viz., a dimensionless quantity connecting quantitatively the parameters of elastic waves and self-sustained waves (autowaves) of localized plastic deformation. The correctness of this statement is verified for metals, alkali-halide crystals, and rocks. The physical origin of the invariant is explained on the basis of thermodynamic considerations.     

Possibility of the appearance of spin autowaves in a model of a ferromagnet with nonuniform dissipation

A model of a ferromagnet with nonuniform dissipation is introduced for the Landau-Lifshitz equations. It is shown that in this model a ferromagnet can be regarded as an oscillating active medium where the formation of autowave structures — spin autowaves, pacemakers, and spiral waves — is possible. Their wave characteristics, expressed in terms of the parameters of the medium, are found for a special case. Fiz. Tverd. Tela (St. Petersburg) 39, 513–515 (March 1997)     

Superelasticity and the propagation of shock waves in crystals

The separation of a shock wave into an elastic precursor and a plastic wave is a characteristic phenomenon occurring only in solid media. The existence of the elastic shock wave at pressures p ≈ 10 GPa, which is one or two orders of magnitude higher than the dynamic elastic limit, has been detected in recent numerical calculations and a femtosecond laser experiment. The plastic shock wave has no time to be formed in these ultrashort waves at p ≈ 10 GPa. The processes of the formation and propagation of the elastic and plastic waves in aluminum at higher pressures obtained by means of femtosecond lasers have been analyzed in this work. It has been found that the elastic precursor survives even under the conditions when the pressure behind the plastic front reaches a giant value p ∼ 1 Mbar at which the melting of the metal begins. It has been shown that superelasticity should be taken into account to correctly interpret the preceding laser experiments.     

Autowave model of localized plastic flow of solids

The features of plastic flow localization at all stages of strain hardening and at the prefracture stage were analyzed. It was shown that macroscopic localization of plastic flow at these stages can be considered as a self-organization process. At the linear hardening stage, an autowave process of flow localization occurs in the sample, which is characterized by the wavelength and propagation velocity. At the prefracture stage, the autowave process collapses with macroneck formation followed by the nucleation of a ductile crack.     

Superstructure phase transitions in Ge on Si (111) at the initial stage of epitaxial growth

The surface phase transitions 7 × 7 → 5 × 5 for two-dimensional and c2 × 8 →7 × 7 and 7 × 7 → c2 × 8 for three-dimensional Ge islands epitaxially grown on Si(111) were found experimentally using scan- ning tunneling microscopy. The first two transitions are associated with an increase in the level of misfit strains, while the last is related to a decrease in the stress level during plastic relaxation.     

Structural features of martensitic transformations upon the low-temperature deformation of metastable austenitic Fe-Cr-Ni alloy single crystals

The features of martensitic transformations upon the low-temperature (1.8–300 K) deformation of metastable Fe-18Cr-10Ni and Fe-18Cr-15Ni alloy single crystals with low stacking-fault energies were studied. It was shown that the γ → ɛ and γ → α martensitic transformations play the main role in increasing strength and plasticity when the deformation temperature is reduced to 4.2 K.     

Dispersion of autowaves in a localized plastic flow

The dispersion relation for localized plastic deformation autowaves emerging at the easy glide and strain-hardening stages in metals and alloys is established experimentally and analyzed. The quadratic form of this relation and the form of the wavenumber dependence of the phase and group velocities of autowaves are explained, as well as the quantitative interrelation between the characteristics of autowave processes of plastic flow localization and crystal lattice parameters of strained solids.     

Excitation of the Roper resonance in single- and double-pion production in nucleon-nucleon collisions⋆

In most investigations the Roper resonance is sensed only very indirectly via complex partial-wave analyses. We find indications for its excitation in the invariant nπ⁺ mass spectrum of the pp → npπ⁺ reaction at M ≈ 1360 MeV with a width of ≈ 150 MeV . The values fit very favorably to the most recent phase shift results as well as to the observations at BES. In the near-threshold two-pion production pp → ppπ⁰π⁰ , where the Roper excitation and its subsequent decays via the routes N ^* → Δπ → Nππ and N ^* → Nσ are the only dominant processes, we find its direct decay into the Nσ channel to be the by far dominating decay process --in favor of a monopole excitation of the Roper resonance.     

Prospects for the measurement of the structure of the coupling of a Higgs boson to weak gauge bosons in weak boson fusion with the ATLAS detector

The prospects for the measurement of the tensor structure of the vertex between a standard model Higgs boson and two weak gauge bosons using the distribution of the azimuthal angles between the two tagging jets in the weak boson fusion channel are studied in a Monte Carlo analysis using the fast simulation of the ATLAS detector. The decay channels H→τ⁺τ^-→ll+4ν, H→τ⁺τ^-→lh+3ν at m_H=120 GeV and H→W⁺W^-→llνν at m_H=160 GeV are used in the analysis. For a standard model Higgs boson it is found that purely anomalous couplings are expected to be excluded at a confidence level corresponding to 2σ or more at m_H=120 GeV and more than 5σ at m_H=160 GeV from 30 fb^-1 of data. With a value of 1 roughly reproducing the standard model cross section for a purely anomalous coupling, the standard deviation in a measurement of a contribution of a CP even anomalous coupling in addition to the standard model coupling is estimated to be 0.20 at m_H=120 GeV and 0.09 at m_H=160 GeV.     

Stress-induced martensitic transformations in [001] crystals of titanium nickelide and its relation to mechanical twinning in the <Emphasis Type="Italic">В</Emphasis>2-phase

Methods of transmission electron microscopy were used to investigate the mechanisms of plastic deformation of TiNi(Fe, Mo) [001] crystals on compression in the interval of stress-induced martensitic transformations. It has been revealed that the formation of {113} and {114} twins of the В2-phase by the В19′→В2 reverse martensitic transformation over another path is, alongside with mechanical (100) twinning of В19′ martensite, an important deformation mechanism in this interval.     

Electromagnetic polarizabilities of the nucleon and properties of the σ-meson pole contribution

The t-channel contribution to the difference of electromagnetic polarizabilities of the nucleon, (α - β)^t, can be quantitatively understood in terms of a σ-meson pole in the complex t-plane of the invariant scattering amplitude A ₁(s, t) with properties of the σ-meson as given by the quark-level Nambu-Jona-Lasinio model (NJL). Equivalently, this quantity may be understood in terms of a cut in the complex t-plane where the properties of the σ-meson are taken from the ππ → σ → ππ, γγ → σ → ππ and Nˉ → σ → ππ reactions. This equivalence may be understood as a sum rule where the properties of the σ-meson as predicted by the NJL model are related to the f ₀(600) particle observed in the three reactions. In the following, we describe details of the derivation of (α - β)^t making use of predictions of the quark-level NJL model for the σ-meson mass. An erratum to this article is available at .     

Study of the atomic structure of bcc and fcc crystals upon instantaneous plastic deformation

The evolution of the atomic structure of face-centered cubic (fcc) and body-centered cubic (bcc) crystals under the conditions of pulsed external loads and large plastic strains is investigated on the basis of computer experiments. The crystals are strained in steps to 32%. After each deformation step (2%), the system is relaxed by molecular dynamics to a new equilibrium state at 300 K. The results of the computer experiments show that plastic deformation can take place under instantaneous external loads either as a result of the motion of partial dislocations, twinning, or the turning and displacement of atomic planes, depending on the stage of the process. The laws governing the variation of the potential energy of the system and the rotation angle of the atomic planes as functions of the degree of plastic strain of the crystal are found. Zh. Tekh. Fiz. 67, 100–102 (December 1997)