V. I. Danilov

Pattern formation in the work hardening process of single alloyed γ-Fe crystals

Abstract Experimental evidences on the evolution of macrodeformation fields of extended single Cr-Ni austenitic steel crystals having superequilibrium nitrogen content are interpreted in the framework of the autowave model of plastic flow. A prerequisite to the realization of the different types of deformation structure (autowave), i.e. a solitary moving front, a moving (waves) and a stationary periodical dissipative structure, and the best observing conditions are defined. It is shown that the propagation rate of deformation nuclei is found to be inversely proportional to the work hardening coefficient in the linear work hardening stage of the plastic flow.

The self-excited wave nature of the instability and localisation of plastic deformation

The nature of the localisation of plastic flow observed during deformation of crystalline solids is discussed. The nucleation and evolution of the zones of strain localisation have been shown to reveal certain trends which could be described as autowaves of different kinds initiated by the processes of self-organization. Examples of self-excited wave processes, e.g., phase and excitement waves, that were observed experimentally by the deformation of mono- and polycrystalline metals and alloys are cited. Some of the numerical parameters of self-excited wave processes have been evaluated.

Localized strain autowaves at the initial stage of plastic flow in single crystals

Plastic strain localization in single crystals of pure metals and alloys is studied on the yield plateau and at the easy glide stage with a zero or small strain hardening coefficient. The difference between localization patterns in the two cases is explained, and strain localization mechanisms are suggested. At these stages of plastic deformation, various types of autowaves are observed.

Plastic flow instability: Chernov–Lüders bands and the Portevin—Le Chatelier effect

We have studied the regularities in the evolution of macroscopic nonuniformities in the plastic flow of metals in the form of the Chernov–Lüders bands and the Portevin—Le Chatelier effect. The regularities in the evolution of strain inhomogeneity in these two cases have been established, and the kinetics of motion of the Chernov–Lüders fronts and abrupt deformation in the Portevin–Le Chatelier effect has been analyzed. It has been shown that the Chernov–Lüders fronts and Portevin–Le Chatelier jumpwise straining can be treated as macroscopic autowave processes of switching and excitation, respectively, in deformed media of various origins.

Kinetics of localized plasticity macrodomains at the prefracture stage in metals

The behavior of localized plasticity macrodomains is experimentally studied at the final stage of the plastic flow in going to necking and ductile fracture in fcc, bcc, and hcp materials. General features of the localization process at the stage of prefracture are found. They are a constant velocity of domains and their tendency to consistently move toward the focus of a bundle of straight lines in space-time diagrams. A correlation between the type of fracture and the kinetics of localized plasticity domains is established.

Plastic strain localization in Fe-3%Si single crystals and polycrystals under tension

Plastic flow localization in siliceous iron single crystals and polycrystals under identical stretching conditions is considered. The localization patterns are analyzed at the stages of linear and parabolic deformation hardening, as well as at the stages of necking and plastic fracture. The localization patterns observed in the alloy in the single-crystalline and polycrystalline states are compared.

Character of variation in the microhardness of the (0001) plane of Zn single crystals under the action of electrostatic field and the possible reason for this effect

The influence of electric potential on the microhardness of the crystallographic plane (0001) of zinc single crystals has been studied. It has been established that the microhardness decreases with an increase in the supplied potential and, at the value of 0.05 V, reaches saturation. The total decrease in the microhardness is 8%. It has been shown that the variation of the microhardness is statistically significant. The observed effect has been explained by a reduction in the surface energy density due to electrization of the surface. The reduction in the surface energy with allowance for the existing single layer of adsorbed water has been estimated.

Crystallographic aspects of macroinhomogeneous plastic flow in single crystals of metals

Various crystallographic aspects of the distribution of strain-localization zones have been studied in single crystals of metals subjected to tensile stresses at different orientations of the tension axes and characterized by different mechanisms of plastic flow (slip of dislocations and martensite transformations). It is shown that the crystallographic orientations of the strain-localization zones (interpreted as the patterns of plastic-flow self-organization) are preserved within the whole deformation process. Some characteristic features of the dynamics of the strain sites are considered.

Autowave model of crystal plasticity: Macro- and microdefects

A new approach to the problem of the plastic flow of solid crystals is proposed. This approach is based on studying the macroscopic localization patterns of plastic deformation, which can be considered as different types of autowave processes of defect self-organization. An unambiguous correspondence between the localization patterns and stages of plastic flow in single crystals and polycrystals is established. The propagation velocity of localized plasticity autowaves is inversely proportional to the strain-hardening coefficient, and the dispersion relation is quadratic. A new model is proposed to describe the development of plastic flow localization.

Macroscopic localization of plastic flow in zinc single crystals oriented for basal slip

The patterns of plastic-flow localization in hcp Zn single crystals oriented for slip in the {0001} 〈2110〉 systems are investigated. The main spatial and temporal regularities of the flow localization are established for all portions of the three-stage curve of such crystals. The relationship between the type of localization patterns and the regularities of strain-hardening of single crystals is traced for each stage. The role of the kinking in the formation of the observed macroscopic-flow distributions is estimated.