The paper investigates the macrolocalization of plastic strain due to uniaxial loading of low carbon/austenitic stainless steel produced by electron-beam additive manufacturing followed by annealing at different temperatures. The stress-strain curve of the bimetallic composite is described by the parabolic law. Due to annealing in the range of 350 to 650°C, the yield strength reduces, while strain-to-failure grows as compared to the as-built composite. Localized plastic strain follows the stress-strain curve in all composite states and layers. At the parabolic hardening stage, the formation of a stationary dissipative system of localized plasticity occurs at strain hardening of 0.5. When strain hardening is ≤0.5, a high-amplitude deformation zone appears in the transition layer, which coincides with the site of eventual fracture.

At room temperature, the deformation of most bcc metals, which contain a small amount of interstitial elements, is accompanied by the formation of a Lüders band and its monotonic propagation over the tensile yield area. Within the framework of the autowave concept, front of the Lüders band is a switching autowave, which realizes the transition from a metastable elastically deformable state to a stable plastically deformable state. However, in the temperature range of blue brittleness of mild steels of 423 – 510 K, when the interaction of atoms of the dissolved substance with mobile dislocations takes place, propagation of the Lüders band is accompanied by a discrete flow. The patterns of propagation of the Chernov-Lüders fronts in ARMCO iron in the temperature range from 296 to 503 K and strain rates from 6.67·10 –6 to 3.7·10 –2 s –1 are considered in this paper. It was established that under these conditions both monotonic and discrete kinetics of front movement can be realized. Regardless of the movement nature, the Lüders deformation and width of the front remain unchanged throughout the entire process. The local strain rate at the front depends on magnitude of the effective stress, and with monotonic kinetics it increases with stress according to an exponential law, and with discrete kinetics it increases according to a linear law. This difference is due to different autowave modes that are formed in this case. The autowave of localized plasticity switching corresponds to monotonic kinetics, and the autowave of excitation – to discrete kinetics.

The structure and mechanical properties of a bimetallic joint obtained by electric arc surfacing of high-alloy stainless steel onto carbon steel were investigated. Metallographic studies and microhardness measurements have shown that a decarburized layer is formed on the carbon steel side, a high-strength white martensitic area on the stainless-steel side, and a layer with a large proportion of the carbide component is observed directly at the fusion boundary. Subsequent heating to 950°C with a holding time of 1 hour leads to an improvement in the stress-strain state of the deposited metal, but an increase in microhardness is observed in the martensitic region near the fusion boundary. To obtain optimal characteristics, it is necessary to reduce the annealing temperature and increase its duration.

The subject of the study is a metal composite obtained by electric arc surfacing in argon of corrosion–resistant steel on low-carbon steel. Powdered chromium-nickel steel was deposited with an increased content of silicon and molybdenum relative to the traditional composition. In this work, we studied the elemental and structural-phase compositions, as well as the mechanical properties of both components of the material and the composite as a whole in the initial state and after annealing at 680 °C for 3 h. The main part of the corrosion-resistant component is a two-phase auste­nitic-ferritic mixture with a ratio of 65 % HCC phase and 30 % BCC phase. The material has high microhardness (more than 4000 MPa). The highest microhardness (4550 MPa) is observed in a narrow strip of deposited metal with a width of 25 μm, where the phase composition is represented by martensite (BCC), and austenite is absent. The transition across the boundary into carbon steel is accompanied by a decrease in microhardness to 1225 MPa. Here, a decarbonized zone with a width of 180 μm was formed near the fusion line. The resulting non-equilibrium stress-strain state of the composite led to low strength, low plasticity and brittle fracture of the deposited layer during tensile testing. After annealing, microstructure of the corrosion-resistant component became more uniform in size of both austenitic and ferritic structural elements. As a result of these transformations, internal stresses decreased and microhardness decreased to 3100 MPa. At the same time, the width of the decarbonized zone in the base metal increased. All these changes led to the fact that, although the tensile stress of the annealed material increased by 8 %, and the deformation to rupture – by 27 %, however, nature of the fracture remained brittle and rupture still occurs along the deposited layer. This is determined by the austenitic-ferritic phase composition of the stainless component, which, in turn, is determined by chemical composition of the deposited material.

Luders deformation in an aluminum-magnesium alloy was studied in a wide range of loading rates. It was found that the deformation is always accompanied by the propagation of deformation fronts, which move either continuously or intermittently depending on the strain rate. The kinetics of fronts is determined by the reaction of active deformable media to an external mechanical action and is determined by the autowave nature of plastic deformation.

The authors studied the nature of mobile fronts of localized deformation that generate and propagate during deformation of metastable austenitic-martensitic TRIP steel VNS9-Sh along the entire length of the loading curve from the yield point to fracture. A joint research of the nature of the deformation fronts movement and kinetics of the magnetic phase accumulation made it possible to establish that the fronts under consideration are the fronts of the thermoelastic phase transformation of metastable austenite into martensite. This transformation is realized firstly by formation of the Chernov–Lüders bands and then the Portevin–Le Chatelier bands. Both processes are consistent with staging of the deformation curve, which contains a pseudo-plateau, a section with an increasing hardening coefficient, and a section with a decreasing hardening coefficient. It is shown that the deformation-induced phase transformation corresponds to the fronts propagating on the pseudo-plateau and on the section of loading curve with an increasing hardening coefficient. The Portevin–Le Chatelier bands, which are formed in the section of the loading diagram with a decreasing hardening coefficient, are not associated with “austenite-martensite” transformation and have a twin nature. The kinetics of thermoelastic transformation fronts, as well as deformation fronts in materials with a shear mechanism of shaping, can be described in terms of the autowave concept. On the yield plateaus, the phase transformation occurs through generation and propagation of localized plasticity switching autowaves. In the section with an increasing hardening coefficient, it continues through generation and movement of excitation autowaves. The propagation regions of excitation autowaves are limited in the sample space. They are set by the zones of origin and annihilation of primary switching autowaves which were formed on the yield plateau.

The kinetics of localized deformation has been studied in a low-carbon steel/austenitic stainless steel composite produced by electron beam additive manufacturing. It is shown that the stress-strain curve of the bimetal is described by a parabolic law. Plastic deformation in all composite layers is localized according to the curve stages. First, a stationary dissipative system of localized plasticity foci is formed at the parabolic hardening stage with n = 0.5. At n ≤ 0.5, a high-amplitude deformation zone is observed in the transition layer, where a fracture eventually occurs in the specimen.

The kinetics of Chernov–Lüders and Portevin–Le Chatelier deformation processes at the yield plateau in an aluminum-magnesium alloy is analyzed. It is established that the deformation is localized in moving deformation fronts. In general, the movement of the fronts proceeds discretely and only in the phase of abrupt unloading of the sample. Continuous movement of deformation fronts is possible if the rate of recovery of the operating stresses applied by test device is greater than or equal to the rate of stress decline controlled by internal processes at a lower structural-scale level. The kinetics of the motion of deformation fronts, both in the Chernov–Lüders and Portevin–Le Chatelier processes, can be described within the autowave concept of plastic flow, and the fronts themselves represent excitation autowaves.

The paper analyzes the elastoplastic transition in Fe–0.025 wt. % C at a temperature of 296–503 K and strain rate of 6.67·10−6–3.33·10−3 s−1. The analysis shows that the lower yield stress increases by a power law with increasing the strain rate, and that its rate sensitivity decreases linearly with increasing the test temperature. At temperatures lower than 393 K, the rate sensitivity of the lower yield stress is normal, and at 393–503 K, it is zero. In the range 393–503 K, the kinetics of the Lüders bands is changed from steady to discrete, and the higher the strain rate, the higher the temperature of this transition. Using the available data on the dynamics of dislocations and diffusion of interstitial impurities in the test alloy, it is demonstrated that the kinetics of Lüders bands are controlled by the effect of dynamic strain aging. If the arrest time of mobile dislocations tw at barriers which are overcome via thermal activation is comparable with the precipitation time of interstitial atoms ta at these dislocations, the motion of a Lüders band is discrete, and the band represents an excitation wave of localized plasticity; its refractory period is determined by the time of dynamic strain aging. If ta >> tw, the band moves monotonically and represents a switching autowave. The results of the analysis suggest that the effect of serrated yielding at the lower temperature boundary of blue brittleness can be suppressed by increasing the strain rate. When the arrest time of dislocations tw decreases, the comparability of tw and ta is broken, and no excitation autowave is formed. The data reported in the paper can be used to develop warm rolling technologies for materials with a sharp elastoplastic transition.

Plastic deformation and fracture of Zr–1% Nb alloys exposed to quasi-static tensile testing have been studied via a joint analysis of stress-strain curves, ultrasound velocity and double-exposure speckle photographs. The possibilities of ductility evaluation through the εxx strain distribution in thin-walled parts of zirconium alloys are shown in this paper. The stress-strain state of zirconium alloys in a cold rolling site is investigated considering the development of localized deformation bands and changes in ultrasound velocity. It is established that the transition from the upsetting to the reduction region is accompanied by the significant exhaustion of the plasticity margin of the material; therefore, the latter is more prone to fracture in this zone exactly. It is shown that traditional methods estimating the plasticity margin from the mechanical properties cannot reveal this region, requiring a comprehensive study of macroscopically localized plastic strain in combination with acoustic measurements. In particular, the multi-pass cold rolling of Zr alloys includes various localized deformation processes that can result in the formation of localized plasticity autowaves. Recommendations for strain distribution division over the deformation zone length in the alloy in the pilger roll grooves are provided as well.

In this work we report the kinetics of plasticity of St3 low-carbon steel-based composite alloy prepared via vacuum electron beam cladding of 09G2S steel wire. The digital image correlation method revealed the existence of macroscopic localization of plastic flow at the yield plateau and parabolic hardening stage. The kinetic characteristics of localized plasticity domains were measured in various composite layers, as well.

In this work the kinetics of localized plastic deformation in polycrystalline aluminum under creep was investigated. It was found a similarity in the behaviour of autowave processes at the stages of steady-state and accelerated creep compared with that observed at the linear stage and the stage of pre-fracture under active loading. At the stage of steady-state creep in aluminum sample, a system of equidistant localized plasticity sites propagates at a constant wave velocity. At the tertiary creep a stationary high-amplitude zone of localized plasticity is formed and the other localization zones moving synchronously at different rates. Using experimental data on the evolution of the sites of localized plastic deformation at the tertiary creep, the space-time coordinates of failure can be predicted for the object under load.

The kinetics of macroscopic strain localization in a bimetal formed by electron-beam cladding of a 09G2S low-carbon steel wire on a St.3 substrate is studied. The mechanical uniaxial-tension tests of flat samples are carried out at a constant rate at room temperature. The mechanical properties and plastic flow stages in the bimetal are compared with those of the starting materials. The kinetics of the plastic strain localization zones in different bimetal layers is studied by digital speckle photography.

The paper presents the study of the process of deformation-induced γ → α-transformation in TRIP-steel and its effect on the strain-hardening coefficient at the macroscopic level. It is shown that a phase transformation starts with the propagation of Luders bands during the pseudo-plateau, when the strain-hardening coefficient is constant. The boundaries of Luders bands are switching autowaves of localized plasticity. After the annihilation of switching autowaves in the samples in the austenitized state, the phase transformation continues with the movement of deformation fronts of the Portevin–Le Chatelier bands, which are excitation autowaves. In this case, the strain-hardening coefficient increases to a maximum value and then decreases up to fracture. The nucleation and propagation of phase transformation fronts is confirmed by magnetic measurements. After the transition to the stage where the hardening coefficient decreases, the γ → α' phase transformation decays and is no longer the predominant mechanism of plastic flow.

Investigations of the kinetics of localized plastic deformation fronts in aluminum alloy 1550 have been made. It has been established that in this alloy fronts of Chernov–Lüders bands (CLB) and Portevin–Le Chatelier bands (PLC) are observed. A distinctive feature of CLB fronts in this material is their discrete movement only in the phase of specimen unloading. Continuous movement of the fronts is possible here if the rate of effective stress restoration through the testing machine is greater than or equal to the rate of stress relaxation controlled by internal processes at a lower structural scale level. After the yield plateau, discontinuous yielding is realized. Nucleation sites of localized deformation fronts at this stage are predefined by CLB fronts. These fronts pass 2–3 times through the entire gauge length of the specimen. Then, at low strain rates, the load curve has a monotonic hardening section, where PLC fronts are not formed. At deformation rates ≥3.33 × 10−4 s−1 such section does not exist. In both cases, fracture occurs in the discontinuous yielding mode. The movement of localized deformation fronts is discussed within the concept of autowaves.

The paper studies the transformation-induced plasticity of steel chromium-nickel-molybdenum structure depending on the reduction ratio during warm rolling. Optical and atomic force microscopies provide the surface profiling information. The parameters of the main structural elements such as the austenite grain size and martensite laths, width and height of twins are determined in this paper. It is shown that the reduction ratio has no significant effect on the volume fraction of the martensite phase, but changes martensite into lath martensite with high dispersity. The austenite strain hardening during rolling causes a four-fold increase in the yield point and a two-fold increase in the microhardness as compared to the initial state of the austenite steel.

We consider the regularities of a plastic flow in materials with strain-induced phase transformation in titanium nickelide and trip steel as examples. The experimental analysis of plastic deformation processes has been carried out using the technique of digital correction of speckle images, which makes it possible to describe quantitatively the behavior of plasticity fronts associated with phase transformation in the given materials. The mechanisms of formation of the Lüders fronts as well as the Portevin–Le Chatelier fronts at different stages of the plastic flow are considered.

The regularities of plastic flow in materials with deformation-induced phase transformations on the example of titanium nickelide and TRIP steel are studied. For experimental analysis of plastic deformation processes, the method of digital image correlation has been used, which allows us to quantitatively describe the behavior of plasticity fronts associated with the course of phase transformations in the materials under study. The mechanisms of formation of Lüders bands and Portevin-Le Chatelier bands at different stages of plastic flow are considered.