Influence of the superconducting state on the thermal instability of low-temperature plastic deformation in crystals

The influence of the superconducting transition on the unstable, discontinuous nature of plastic deformation in crystals at low temperatures (<10 K) is discussed theoretically. It is established, within the mechanism of the thermal instability of low-temperature plastic deformation, that the superconducting state promotes the stabilization of deformation in a superconductor because of the positive sign of the temperature sensitivity coefficient of the flow stresses below the superconducting-transition temperature and the reduced level of energy dissipated by moving dislocations in comparison to the normal metal. The temperature-rate regions for stable and unstable deformation of a superconductor and the dependence of the stress-jump amplitudes on temperature and deforming stress are determined. Fiz. Tverd. Tela (St. Petersburg) 40, 1778–1784 (October 1998)     

Substructural phase transitions during intense plastic deformation of low-carbon ferrite-perlite steel

We have studied the evolution of the defect structure and phase composition of low-carbon ferrite-perlite steel subjected to intense plastic deformation using diffraction electron microscopy. It has been shown that a high degree of deformation is accompanied by disruption of the perlite columns. We have found and described two perlite decay mechanisms: decay of the carbide plates by a path of their granulation due to dislocation slip and dissolution of cementite arising from the outflow of carbon atoms from the carbide phase into ferrite crystal lattice defects. We have described the phenomenon of morphological reconstruction of the cementite-phase particles (a transition from layers to spheres) under plastic deformation conditions. Tomsk State Architectural and Construction University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 63–71, March, 1998.     

Residual stress field in steel samples during plastic deformation and recovery processes

An X-ray diffraction method was applied to measure residual stresses and stored elastic energy in deformed and annealed polycrystalline ferritic and austenitic steel samples. The orientation distribution of plastic incompatibility second-order stresses created during elastoplastic deformation was determined and presented in Euler space. Using deformation models, these stresses were correlated with different types of intergranular interactions occurring in the studied materials. An important decrease of the first- and the second-order residual stresses was observed during recovery and recrystallisation processes. Diffraction peak widths, related to dislocation density, were studied and correlated with stress variation during annealing process. Differences in stress relaxation between ferritic and austenitic samples were explained by different values of the stacking fault energy, which influences dislocation climb and cross-slip.     

Substructural and carbide transformations during plastic deformation in tempered chromium-nickel martensitic steel

The evolution of the defect and carbide subsystems has been studied during the plastic deformation of chromium nickel steel with the structure of tempered martensite. A correlation has been established between the substructural transformation and the change during plastic deformation. The nondislocation shear resistance has been estimated.Tomsk Civil Engineering Institute. Translated from Izvestlya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 25–32, December, 1992.     

Laws of substructural and phase transformations in the plastic deformation of martensitic steel

Substructural and phase transformations in the course of plastic deformation in tempered 34KhN3MFA steel are considered. A relation is established between the type of substructure and the phase state of carbon. A direct relation is established between the carbon content in the solid solution and the crystal-lattice distortion. The carbon concentration at dislocations and fragment boundaries is determined.Tomsk State Architectural and Building Academy. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 76–82, April, 1994.     

Dynamics of plastic deformation: Waves of localized plastic deformation in solids

Conclusions It has been shown here that a localized plastic deformation in structurally inhomogeneous media can be of a wave nature and can propagate in the form of nonlinear plastic waves, not only at the microscopic level but also at the mesoscopic level. It has been established that there is an interrelationship between this new effect and grain-boundary slippage (an effect which has been under study for a long time) and also with certain types of quasiviscous fracture in plastically deformable materials.We have discussed certain specific practical problems in the mechanics of plastic deformation, and for certain types of fracture. In the future, these problems will be discussed at a more profound level and in greater detail, because of experimental studies which are presently being carried out on the dynamics of deformation for various types of loading and fracture [17, 18, 31]. We hope that the approach proposed here for a theoretical study of the localization of deformation and fracture can be taken to study such effects as splitting off [31], the influence of defect fluxes on grain-boundary slippage [22], superplasticity [23], the behavior of tectonic faults and boundaries of various types [32], electroplastic and magnetoplastic effects, and high-temperature localization of deformation [25].The general nature of the approach proposed here results from the circumstance that a localization of deformation is present explicitly or implicitly during plastic deformation, and the behavior of this deformation plays a role of fundamental importance in the propagation of plastic deformation through a material.The author wishes to thank V. E. Panin for a constant discussion of this problem and I. O. Nedavnii for carrying out the numerical calculations.V. V. Kuibyshev Tomsk State University. Institute of Strength Physics and Materials Science. Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 19–41, April, 1992.     

Influence of current pulses in plastic deformation on the macrostructure of austenitic chromomanganese steel

Experimental data on the evolution of the microstructure of a 17GKhAF steel wire subjected to ordinary and electrically stimulated (by a pulsed current) drawing with a total constriction of up to 35% ate outlined. The change in scalar dislocational density, volume fraction of regions with strong lattice rotation, excess dislocational density in these regions, density of twins, and azimuthal disorientation of adjacent regions of microstructure are analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 84–90, September, 1991.     

Fractal characteristics of the surface of tungsten carbide-manganese steel composite after plastic deformation

The structure evolution in WC-80G4 steel composite heavily loaded by compression is studied. The fractal properties of the deformation relief appearing on the surface are determined. The fractal dimension of the deformed surface profile is shown to depend on the mean spacing between bands of localized deformation and on the parameters of the material fine crystal structure.     

Anomalous plastic deformation in nichrome

The temperature dependences of the properties of Kh20N80 Nichrome under tension have been found. Decarbonization of the alloy showed that there are two regions of anomalous strengthening, at 400–450 and 600–700 °C. The first region is attributed to order in the binary system, while the second is attributed to carbide aging. Correlation analysis of the oscillograms of the tension diagrams showed no local relationship between the load discontinuities and the intervals between them. The inadequacies of existing models for discontinuous flow are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 12–17, November, 1970.     

Relaxation waves in plastic deformation

Conclusion Experimental study of distortion fields of plastically deformed solids performed on a wide range of materials including fine- and coarse-grain body- and face-centered polycrystals, as well as amorphous alloys reveals that in these materials plastic deformation develops in the form of waves having translational and rotational components. This fact is in accordance with the currently developed theory of a turbulent mechanical field, which also has translational and rotational components.The plastic deformation waves are observable at a macroscopic structural level, and their spatial period (wavelength) is determined by the dimensions of the deformed object and dimensions of the basic structural elements (for a polycrystal, the grain size). The propagation rate of these waves is significantly less than the characteristic propagation rate of an elastic excitation and the velocity of previously described plastic waves which are produced by shock deformation, which latter speed is determined by the hardening coefficient.The character of plasticity waves depends on the form of the material's deformation curve, and on the stage of the hardening curve. The distribution of plastic distortion components changes especially significantly in prefailure regions, which allows detection of the latter long before formation of a macroscopic crack. The role of rotations in forming the failure process has been established.A synergetic interpretation of plasticity wave formation has been proposed, based on synchronization of relaxation acts occurring at stress concentrators during the deformation process.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 19–35, February, 1990.     

Interaction of the structural and magnetic subsystems in crystals upon severe plastic deformation by torsion

Interaction between the structural and magnetic subsystems of a crystal has been studied near phase transition lines. The consideration has been performed in terms of the Landau phenomenological theory. It has been shown that severe plastic deformation by torsion leads to a forced formation of a heterogeneous distribution in the magnetic subsystem. A nonsine space modulation of the magnitudes of the magnetic and structural parameters appears near the lines of the magnetic and structural phase transitions. An analysis of the obtained dependences has demonstrated a possibility of designing various distributions of the ferromagnetic vector in crystals under action of severe plastic deformation by torsion.     

Mechanism of strain hardening and dislocation-structure formation in metals subjected to severe plastic deformation

The equations of dislocation kinetics are used to theoretically analyze the mechanism of strain hardening and the formation of fragmented dislocation structures in metals at large plastic strains. A quantitative analysis of the available data on aluminum and an aluminum-magnesium alloy shows that strain hardening at large plastic strains and the formation of fragmented dislocation structures are related to the interaction and self-organization of geometrically necessary dislocations (GNDs). On the microscale, the source of the GNDs is a locally nonuniform plastic deformation induced by a dislocation-density gradient in dislocation-cell boundaries.     

Mechanism of the formation of shear microbands under plastic deformation of nanocrystalline materials

The mechanism of deformation localization and formation of shear microbands under plastic deformation of submicrocrystalline and nanocrystalline materials is theoretically discussed in the framework of the dislocation-kinetic approach. An equation of evolution of the density and self-organization of dislocations in these materials is formulated taking into account that the grain boundaries are the main sources, sinks, and barriers to moving dislocations. By solving this equation, it is found that the width of microbands and the distance between them depend on the nanograin size and the degree of plastic deformation. It is also demonstrated that there exists a critical grain size (350 nm in the case of α-Fe) above which no microbands are formed in the nanomaterial. The theoretical results are compared with the data available in the literature.     

Laws of electrical stimulation of plastic deformation of metals and alloys at various structural levels

The laws governing the electrical stimulation of plastic deformation at various structural levels are reviewed. The following topics are covered: the hierarchy of external current stimuli affecting plastic deformation; the variation of the mobility of individual dislocations in zones of thermally activated and quasiviscous motion associated with mechanical, electrical, and combined stimuli over a wide range of temperatures (microlevel); the evolution of defect structure in materials of various structural classes subjected to electrical stimulation over a wide range of strains (mesolevel); the ordered character of plastic deformation inhomogeneities; models of the stress — strain state in the presence of current stimulation (macrolevel) and their interpretation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 66–96, March, 1996.     

The inhomogeneity of plastic deformation

Considerable local strain differences occur in single crystals as a consequence of slip bands. A significant contribution to this phenomenon is the effect of the deformation rate on the inhomogeneity of its distribution. In polycrystalline materials the plastic deformation is affected by grain boundaries and their vicinity as well as by various orientations of single grains in onephase metals and alloys, and by various component properties in multiphase materials. In some cases it has been possible to describe these phenomena by means of micromechanics. Valuable information has also been acquired by means of three-dimensional stereology.     

Nondestructive indication of plastic deformation of cold-rolled stainless steel by magnetic minor hysteresis loops measurement

Cold-rolled austenitics stainless steel samples were non-destructively characterized by means of sets of magnetic minor hysteresis loops. The flat samples were magnetized by an attached yoke, and reliable parameters were obtained from the series of minor loops, without magnetic saturation of the samples. It was found, that some magnetic quantities, well known to be closely connected to the samples’ structure variation, especially relative coercivity and remanent induction, could be distinguished even more sensitively from minor loops, than from the major one.     

The influence of plastic deformation on the magnetoelastic properties of the CSN12021 grade steel

Magnetoelastic properties of materials are strongly influenced by changes of the dislocation structure that take place during the process of plastic deformation. Such changes can be used as a basis for a method of nondestructive evaluation (NDE) of the deformation level. So far, various methods, based on magnetic hysteresis loop properties as well as on the Barkhausen effect (BE), have been proposed. In the paper, the results obtained with the help of the abovementioned methods are compared with the results of the magnetoacoustic emission (MAE) signal measurements. The MAE signal is relatively easy to implement as a nondestructive method and unlike the BE effect signal gives information about the whole magnetized volume.