Abstract—The effect of severe plastic deformation performed in a Bridgman anvils at 77 K on the saturation magnetization, the phase composition, and the crystal geometry characteristics of the phases of a metastable austenitic–martensitic Fe–18Cr–10Ni alloy is investigated. High-pressure (hydrostatic) torsion at a true strain e = 3.4–5.8 at 77 K is found to form two martensitic phases, namely, the ferromagnetic α phase and the paramagnetic ε phase. Mechanisms explaining the nature of changing the saturation magnetization are proposed.

A study of the phase transformation in technically pure titanium under different types of deformation has been performed: upset under high pressure and high hydrostatic-pressure torsion (HPT). A set of modern methods of the study included microindentation, X-ray diffraction, transmission electron microscopy, as well as EXAFS-spectroscopy in synchrotron radiation for detailed studying a local atomic structure of phases. The correlation between the phase transformation course and the deformation method has been found. It has been shown that in contrast to pressure without a shear component, the shear deformation under high pressure at room temperature contributes to the occurrence of a high-temperature β-phase with a local atomic order different from that in the initial phase.

Исследованы механические характеристики композитных материалов на основе сплава Fe – 18 % Cr – 10 % Ni, состоящих из пластичных макроскопических областей аустенита, распределенных в высокопрочной мартенситной матрице. Получены кривые напряжение – деформация для образцов, в которых аустенитные области различаются по размерам и форме. На основе анализа построенных диаграмм определены формы аустенитных областей, оптимальные с точки зрения сочетания прочностных и пластических характеристик материала.

The possibility of the formation of a multi-metal composite from two dissimilar alloys, Ti50Ni25Cu25 and Fe50Ni33B17, upon high-pressure torsion (HPT) at room temperature has been studied. The consolidation of the dissimilar layers upon HPT has been established. It is revealed that the leading role in the consolidation of the dissimilar layers upon HPT belongs to the method of joining materials by their mutual severe plastic deformation.

Mechanical characteristics of composite materials based on Fe – 18% Cr – 10% Ni alloy and composed of plastic macroscopic austenite regions distributed in a high-strength martensite matrix are studied. Stress-strain curves are obtained for the specimens with austenite regions differing in size and in shape. The plotted curves are used to determine the shapes of the austenite regions optimal in terms of combining the strength and ductility parameters of the material.

The review describes a number of important recent studies in the field of physical fundamentals of severe plastic deformations (SPDs) in metals and alloys and their further systematization. Based on analyses of experimental data and theoretical approaches, we formulate for the first time three fundamental principles and seven characteristic features inherent in SPD processes. SPD physics is entirely based on the postulates of nonequilibrium thermodynamics. A solid under deformation is considered a mechanical dissipative system in which the total energy continuously decreases or dissipates, converting into other, nonmechanical, forms of energy. Within the framework of the proposed nonequilibrium evolutionary thermodynamics, it is possible to describe from a unified standpoint the evolution of the structure of defects for polycrystalline and amorphous metallic materials upon SPD. We note that the process of mechanical alloying of powders should not be completely identified with SPD processes.

A multi-metal composite was consolidated from the Ti50Ni25Cu25 and Fe50Ni33B17 alloys by room-temperature high-pressure torsion (HPT). The structural research methods used in this study were X-ray diffractometry, high-resolution transmission electron microscopy, scanning electron microscopy with an electron microprobe analyzer in the mode of backscattered electrons, and the measurement of indentation hardness and modulus of the composite constituents. The structural aspects of the bonding process have been examined. The method of joining materials using their coupled severe plastic deformation has been established to play a leading role in the consolidation of the dissimilar layers upon HPT.

Mechanical characteristics of composite materials based on Fe – 18

The results of surface hardening of tungsten carbide hard alloys carried out using concentrated energy flows are presented. A VK6OM alloy with a thickness of 20 μm is applied on a VK10KS hard alloy by electrospark machining. This results in a surface hardened layer consisting of W2C. The hardness of the resulting layer is 22 000 MPa, the friction factor is 0.23 (compared to the friction factor 0.41 of the original hard alloy), and a strong but low resistant base. In this work, a surface layer was obtained on the VK10KS hard alloy with a thickness of 40 μm, phase composition TiC, W2C, by single-component electroexplosive titanium doping. The nanohardness of this layer is 25 000 MPa, the friction factor is 0.14. A surface layer 3–4 μm thick with the phase composition TiB2, TiC, W2C was obtained on the VK10KS hard alloy by multicomponent electroexplosive titanium-boron doping. The nanohardness of the hardened layer is 27 500 MPa, the friction factor is 0.10. Using a separate cathode technique, an ion-plasma TiN + ZrN coating (50% Ti + 50% Zr) 20 μm thick was deposited on the VK10KS hard alloy surface. Nitrogen was used as the reaction gas. The nanohardness of the surface layer strengthened in this way is 38 500 MPa, the friction factor is 0.07. The ion-plasma TiN + ZrN coating has good adhesion to the substrate. The use of the proposed surface hardening of the VK10KS hard alloy makes it possible to choose one of the hardening methods based on the operating conditions of the hard-alloy tool, to extend its service life, save scarce materials (tungsten and cobalt).

The effect of cryogenic temperatures of deformation in a Bridgman chamber via severe plastic deformation by torsion under a high quasi-hydrostatic pressure at temperatures of 293 and 77 K on the structure and mechanical properties of commercial (low-alloy) titanium is studied. Transmission electron microscopy is used to perform a detailed statistical analysis of the structure of titanium with different contents of microalloying elements.

The data on the effect of carbon and nitrogen on the stacking fault energy (SFE) of austenitic steels are summarized. Threshold values of SFE characterizing the stability of austenite are given. The effective value of SFE for high-nitrogen austenitic steels is found to be 20–25 mJ/m2. At this value, these steels have the best combination of strength, ductility, and impact strength at a retained high stability of austenite to the γ–ε–α transformation during cooling and plastic deformation.

The structure–phase state of the tread surface and the fillet of differentially quenched 100-m rails after long-term operation (tonnage of 1770 mln t). The transformation of the pearlite structure on the tread surface is found to be slower in comparison with the fillet surface. The distribution of carbon atoms in rail structure has been estimated.

The structural-phase state and the fracture surfaces of low-carbon alloy steel coatings formed by arc surfacing are studied by scanning and transmission electron microscopy. A quantitative analysis of the structure and dislocation substructure parameters of the coatings is performed. The contributions of the scalar and excess dislocation densities to the hardening of the coatings are estimated.

The effect of heat treatment on the structure and mechanical properties of Co-Fe-Cr-Si-B/Fe-Cr-B/Fe-Ni-B amorphous alloys has been studied systematically. Melt-quenching (spinning method) was used for production of investigated amorphous alloys. The transmission electron microscopy (TEM) was used to study the structure transformations. The effect of temperature on deformation behavior (plasticity, microhardness, crack resistance, and the density and average length of shear bands) of the amorphous alloys was studied by bending and microindentation. It is shown that the ductile–brittle transition, which occurs at the stage of structure relaxation in amorphous alloys, is caused by two factors: a decrease in the susceptibility of the amorphous matrix to plastic flow and an abrupt decrease in the resistance to the development of quasibrittle cracks. It is established that the transition to a two-phase amorphous–nanocrystalline state upon annealing leads to substantial strengthening of the alloys and a partial recovery of their plasticity. It is proved that the strengthening of amorphous alloys at the initial stages of crystallization can be initiated by the difference in the elastic moduli of the amorphous matrix and the precipitated nanocrystals, as well as by the specific features of the interaction between nanocrystalline phase particles and shear bands propagating under external actions. It is established that the phenomenon of plasticization in amorphous alloys (the crack resistance can increase after annealing in a certain temperature range) is due to the effective retardation of cracks on nanoparticles.

The influence of severe plastic (megaplastic) deformation in a Bridgman anvils on the structure, hardness, and spontaneous magnetization of a metastable Fe–18Cr–10Ni alloy in two initial states, namely, austenitic state after hot plastic deformation and martensitic state after subsequent cold plastic deformation, is investigated. High-pressure (quasi-hydrostatic) torsion at a true strain e = 4.7–5.8 is found to form two martensitic phases, namely, the ferromagnetic α phase with a high specific saturation magnetization and the paramagnetic ε phase. Two dispersed phases, which differ significantly in magnetic respect, largely explain the complex nature of changing the saturation magnetization with the strain and the high hardness of the alloy.

The crystallization mechanisms and kinetics in amorphous Ti50Ni25Cu25 alloy produced by different methods of amorphization have been studied by X-ray diffraction at room temperature and in situ synchrotron diffraction upon heating up to 823 K. One of the amorphous states was obtained by melt quenching (MQ) at a cooling rate of approximate to 10(6) K/s. The other amorphous state was realized in a polycrystalline alloy of the same composition by high pressure torsion by four revolutions of the movable anvil (HPT4). Differential scanning calorimetry was used to determine the temperatures of crystallization and glass transition, as well as a change of the thermal effect as a function temperature. It is shown that the amorphous states under consideration substantially differ in the mechanisms and temperature parameters of crystallization. The amorphous phase produced by HPT4 was found to be less stable with respect to heating than the amorphous phase obtained by MQ. The origins of the difference in the crystallization kinetics of the amorphous phases obtained by MQ and HPT4 are discussed.

The excess internal energies ΔUQ and excess entropies $$\Delta {{S}_{Q}}$$ of ten metallic glasses with respect to their parent crystalline states are determined from calorimetric studies. The elastic energy ΔUel of the subsystem of interstitial defects responsible for relaxation phenomena in metallic glasses according to interstitialcy theory is calculated within this theory using the measured high-frequency shear modulus. It is established that the quantities ΔUQ and ΔUel coincide with each other within an accuracy of no less than 10–15%. It is concluded that the excess internal energy and excess entropy of metallic glasses are due primarily to the elastic energy of the subsystem of interstitial defects. The dissipation of this energy into heat under heating reduces ΔUQ and ΔSQ to zero because of the complete crystallization. The entropy per defect is estimated from calorimetric data as Sd ≈ (20–30)kB, which is characteristic of interstitial defects.

By the methods of transmission electron microscopy (TEM) at micro- and nanoscale levels the quantitative transformations of structure at a depth of 0, 2, 5, 10 mm along central axis and symmetry axis of fillet head of lengthy differentially quenched rails after severe plastic deformation (passed tonnage of 1770 mln. gross tons) are revealed. At a microscale level the transformation of cementite plates by newly formed grain boundaries absorption of carbon atoms from bulk carbides is established. At a nanoscale level the subgrain structure, being formed in surface layers, contains cementite nanodimensional particles, localized in junctions and along subgrain boundaries. This type of structure was formed as a result of dynamic recrystallization under megaplastic deformation being realized in a process of extremely long-term service of rails. The formation of so-called ‘channels of deformation’ is determined. It is shown that scalar and excess dislocation density in ferrite constituent of steel structure increases as the rail head surface is approached.