S. A. Barannikova

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.

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.

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.

Tensile plastic strain localization in single crystals of austenite steel electrolytically saturated with hydrogen

The effect of interstitial hydrogen atoms on the mechanical properties and plastic strain localization patterns in tensile tested Fe-18Cr-12Ni-2Mo single crystals of austenite steel with low stacking-fault energy has been studied using a double-exposure speckle photography technique. The main parameters of plastic-flow localization at various stages of the deformation hardening of crystals have been determined in single crystals of steel electrolytically saturated with hydrogen in a three-electrode electrochemical cell at a controlled constant cathode potential.

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.

On the kinetics of localized plasticity domains emergent at the pre-failure stage of deformation process

The behavior of localized plasticity domains occurring at the final stage of the plastic flow process has been investigated. A series of runs was conducted on materials differing in the crystal lattice type which disclosed regular features exhibited by the flow process upon transition to macroscopic necking and viscous failure. It is found that the most distinctive regularity is the occurrence of flow domains that are moving in a concerted manner towards the pole of the bundle of domain trajectories plotted in the time-space coordinates. The deformation patterns are found to be related to the kinetics of nucleation and motion of localized plasticity fronts. The probable origin of the observed effects is considered.

Dispersion of the plastic strain localization waves

The main laws of the macroscopic localization of plastic straining in a bcc alloy Fe-3% Si on the stage of linear strain hardening are considered. It is established that the strain localization exhibits a wave character and the velocity of propagation of the strain localization wave is determined. The law of dispersion of the waves of localized plastic straining is found for polycrystalline aluminum and for iron-based alloys in both single crystal and polycrystalline states.

A new type of plastic deformation waves in solids

Abstract.The plastic flow of metals and alloys in a single-crystal and a polycrystalline state involves processes in which different types of wave are generated. In the easy-glide and linear work-hardening stages of flow, waves of new type are found to propagate. The motion velocity of these waves is found to be inversely proportional to the work-hardening coefficient. An attempt is made to relate the new wave type to the self-organisation phenomena observable in deforming crystals. The propagation rate of these waves is shown to depend on the energy flow through the specimen tested. The space period of the local strains region is proportional to the logarithm of the specimen length.

Changes in ultrasound velocity in the plastic deformation of high-chromium steel

The change in ultrasound velocity in the plastic deformation of high-chromium 40X13 stainless steel with ferrite–carbide structure (initially), martensite structure (after quenching), and sorbite structure (after high tempering) is investigated. The loading curve is different for each state. In the initial state, the loading curve is practically parabolic. In the martensitic state, linear strain hardening is the only stage. In the sorbitic state, a three-stage curve is observed. The structure of the steel after different types of heat treatment is studied by optical and scanning probe microscopy. In parallel with the recording of the loading curve, the change in properties of the ultrasonic surface waves (the Rayleigh waves) in the steel under tension is measured. To determine the speed of the Rayleigh waves, rectangular pulses (length 100 ns) are generated periodically at the input of the emitting piezoconverter and the wave is recorded after passage through the sample by the receiving piezoconverter, which is connected to a digital oscillograph. The resulting digital signal is used to measure the time from pulse generation to the appearance of a signal at the receiver output. The distance between the converters is constant. The changes in the ultrasound velocity during active loading are determined by the plastic flow—that is, by the stages in the corresponding loading diagram. The structure of the steel determines not only the type of deformation curve in uniaxial extension but also the dependence of the ultrasound velocity on the strain.

Laboratory observation of slow movements in rocks

It is established that the development of a localized plastic strain during compression of samples of rocks (sylvinite, marble, and sandstone) deformed by different micromechanisms has an autowave character. It is shown that the velocity of propagation of autowaves arising in the samples under compression is 10−5 to 10−4 m/s (0.3 to 3.0 km/g) and is close to the velocity of slow waves observed in the Earth’s crust after earthquakes or rockbursts.