The effect of pre-recrystallization annealing on the features of structural-phase transformation and microhardness of 3Ni-Al powder mixture after high-energy ball milling (HEBM) was studied. Immediately after HEBM, the formation of highly defective nanostructured states was detected in the nickel component of the precursor. These structural states were found to be characterized by nonzero bending–torsion tensor components and high levels of local internal stresses and their gradients. It is hypothesized that the formation of such states provides the necessary conditions for mass transfer and the synthesis of the ordered Ni3Al compound at a temperature significantly lower than the formation temperature of this compound, according to the equilibrium phase diagram. It has been shown that a slight change in annealing temperature (tens of degrees) favors the dominance of one of the competing structural-phase transformation processes that determine hardening and softening. Moreover, the hardening effects of ordered submicron- and nanoscale phases either partially or completely offset the softening due to the relaxation of highly defective structural states after annealing.

A comparative study of the low-temperature fracture characteristics of V-Cr-W-Zr and V-Cr-Ta-Zr vanadium alloys under impact and tension conditions was performed. The impact toughness characteristics, yield strength and ductility values were determined in the temperature range from 83 to 293 K. Scanning electron microscopy methods were used to reveal the main fracture types depending on the deformation method and temperature. It was established that the temperature range of the brittle-ductile transition of V-Cr-W-Zr alloy under impact conditions is in the range from 173 to 223 K, while for V-Cr-Ta-Zr alloy this range shifts to the cryogenic temperature region from 83 to 173 K. It was shown that the strength of the studied alloys at cryogenic temperatures is not determined by their structural-phase state, at the same time, a structural dependence of ductility is observed. The ductility of V-Cr-Ta-Zr alloy is almost twice as high as that of V-Cr-W-Zr alloy, as a consequence of the greater extent of grain boundaries. It has been established that the Tabor relation is not satisfied for V-Cr-Ta-Zr and V-Cr-W-Zr heterophase alloys.

A study of fractographic features of fracture surfaces, patterns of structural-phase transformations, and mechanisms of plastic deformation and fracture of low-activation vanadium alloy V–Cr–W–ZrC in the process of toughness tests was carried out. The appearance of a qualitatively new (non-dislocation) mechanism of plastic deformation was revealed—the mechanism of bcc → hcp → bcc transformation with a change in the systems of reverse transformations and (or) the participation of quasi-viscous mass transfer in the fields of high local pressure gradients. An important feature of this mechanism is its activation at the nanoscale level with the formation of nanovolumes several nanometers in size—new carriers of homogeneous transformation deformation of the Bain type. A significant feature of these carriers is the absence of any effective obstacles such as dislocations or disorientation boundaries for both homogeneous tensile/compressive deformation and quasi-viscous mass transfer. The activation of bcc → hcp → bcc transformations as a new non-dislocation deformation mode is based on the phenomenon of phase instability of the bcc crystal in fields of high local stresses and high local gradients of the nanoscale level. The above transformations (both direct and reverse) can be carried out under conditions of thermodynamic gain with a local (in the transformation zone) decrease in energy in the transformation region. This leads to intense softening of the material and high deformation and relaxation rates of highly defective substructures of deformation and deforming and local internal stresses.

The results of a study of the features of the structural-phase state of the surfacing formed by remelting of a multicomponent precursor with an electric arc with a non-consumable tungsten electrode in a protective argon environment on a steel substrate are presented. A non-equiatomic mixture of refractory metal powders W-Ta-Mo-Nb-Cr-Zr-Ti after high-energy ball milling was used. It has been established that the resulting structural state is represented by several multicomponent phases that differ in elemental composition, type of crystal lattice, morphology and defect structure and can be described as a complex structural-phase composite. A smooth nature of the change in microhardness values was discovered as one moved from the lower part of the substrate to the upper boundary of the surfacing, which indicates the gradient nature of the structural-phase state. It is assumed that a decrease in the size of structural elements of dendrites in areas with a high density of high-strength phases is a consequence of the formation of a high density of nuclei during phase formation, the competing growth of which limits the size of these structural elements.

The thermal stability of the internally oxidized V-Cr-Zr alloy was studied depending on the concentration of oxygen introduced during chemical-heat treatment. It was found that an increase in the oxygen concentration from 0.65 to 1.34 at.% promotes an increase in the temperature of the primary recrystallization start from 0.7Tmelt to 0.85Tmelt. It was shown that as the value of the stoichiometric ratio coefficient increases, not only does the activation temperature of primary and secondary recrystallization shift to the region of higher temperatures, but also, in contrast to classical concepts, a tendency toward almost simultaneous implementation of these processes is observed. Thus, the use of chemical-heat treatment to increase the thermal stability of the V-Cr-Zr alloy by 300 degrees or more is experimentally substantiated.

The effect of high-energy ball milling duration on the morphology and microhardness of Cu-Al powder mixture, characterized by high relaxation capacity of the components, is studied. It is shown that as early as in the primary processing stage the initial powder particles are combined into plate-shaped conglomerates. A longer ball milling duration promotes the consolidation and compaction of the conglomerates. It is found out that these processes are accompanied by the formation of a solid solution of aluminum in copper with a subsequent formation of ordered phases. A transformation of the structural-phase state of the powder mixture causes a significant increase in its microhardness.

A study of the influence of annealing in the range from 700 to 1600°С on the microstructure features and microhardness values of the V–Cr–W–Zr alloy after thermomechanical treatment was carried out. It was found that, as a result of rolling in the V–Cr–W–Zr alloy, texture fibers α, γ, θ are formed. It has been established that the structural state after thermomechanical treatment is stable up to 800°С. At 900°С, primary recrystallization is activated, which at 1000°С covers the entire volume of the material. Collective recrystallization processes occur in the temperature range of 1100–1400°С. Secondary recrystallization is activated at 1500°С. Under conditions of primary, collective, and secondary recrystallization, against the background of orientational grain growth, the disappearance of the texture components of the θ-fiber is observed. It was established that, in the temperature range of 1500–1600°С, a partial redistribution of W occurs. The influence of the average grain size on the microhardness values of the alloy was analyzed. The main mechanisms of material strengthening are discussed.

The article presents the results of investigation of the morphology and elemental composition of refractory metals multioxide particles synthesized under conditions of laser ablation of a high-entropy alloy. The alloy was obtained by spark plasma sintering of an equiatomic mixture of powders (W–Ta–Mo–Nb–V–Zr–Cr–Ti) after preliminary high-energy ball milling. It was found that the multioxide particles formed under conditions of laser ablation with sizes from 20 to 80 nm have a spherical or quasi-spherical shape and are characterized by an almost uniform volume distribution of oxygen and refractory elements. The results of transmission electron microscopy and X-ray diffraction analysis indicate an amorphous-crystalline structural state of the multioxide particles. After annealing at a temperature of 700 °C, the particles, while maintaining nanoscale sizes, acquire a nonequiaxed shape with partial faceting. With the complex use of structural investigation methods, it was found that almost the entire volume of the powder mixture transforms into a crystalline phase characterized by a tetragonal lattice. Low-angle fragmentation boundaries and areas with high crystal lattice curvature were found inside the particles. It is assumed that residual local stresses are a consequence of local imperfection of the crystal lattice (dilations and distortions due to differences in the sizes of atoms), which can be represented as partial disclinations and their configurations.

The features of the microstructure evolution of Mo-47 %Re alloys under severe plastic deformation by highpressure torsion were studied. Using the dark-field analysis of discrete and continuous misorientations, depending on the plastic deformation degree, a quantitative certification of the parameters of highly defective structural states was carried out. The main mechanisms of formation of ultrafine-grained and nanocrystalline structural states were revealed. By measuring at different distances from the torsion axis in sections perpendicular to the anvil plane, the microhardness values of the studied alloys were determined, the maximum values of which reach more than 12 GPa. It was established that a decrease in microhardness in the peripheral part at maximum realized deformation values is associated with the formation of cracks along grain boundaries. An analysis of the microstructure transformation features of the studied alloys in a "high-strength state" formed during high-pressure torsion was carried out. It is assumed that under these conditions the dislocationdisclination mechanism and the mechanism of lattice reorientation by quasi-viscous flows of nonequilibrium point defects are the main mechanisms of structural transformation of Mo-47 %Re alloys at the submicrocrystalline and nanoscale levels, respectively.

The influence of high-energy ball milling duration on the microhardness values of the precursors from the Nb–Al powder mixture is studied. The main stages of microhardness increase, characterized by the specificity of its values change relative to the HEBM duration, are identified. As the microhardness values increase, an increase in the spread of its values is observed, which indicates the heterogeneity of the structural-phase state. Structural investigation methods have established that after 3.5 min HEBM an ordered AlNb2 compound is formed, the volume fraction of which is about 4

The effect of high-temperature annealing on the structural-phase state and microhardness of Ni3Al samples obtained by spark plasma sintering after high-energy ball milling has been studied. Using X-ray diffraction analysis, scanning and transmission electron microscopy, a comparative study of the features of the structural-phase state of Ni3Al samples depending on the duration of preliminary high-energy ball milling and annealing temperature was carried out. Temperatures have been identified that ensure simultaneous grain growth at a high density of nuclei, which contributes to the formation of a fine-grained structural state. Depending on the state of the material, the corresponding microhardness values have been determined. The influence of the annealing temperature on the strengthening mechanisms has been analyzed.

The characteristics of the relaxation and recrystallization processes in pure tantalum deformed by rolling at room temperature are studied. It is established that at 800°C the recovery processes are activated and nuclei of recrystallization grains appear. After 1000°C, an activation of primary recrystallization is observed, which, after annealing at 1200°C, involves the entire material volume. It is shown that the processes of structural relaxation beginning at 800°C are accompanied by a dramatic decrease in microhardness.

The results of investigations of the effect of thermomechanical treatment (TMT) regimes on the regularities of phase transformations, microstructure, and mechanical properties of low-activation alloys of the V–4Ti–4Cr–(C, O, N) system are summarized. The mechanisms of these transformations and the relationship between the microstructure and the level of strength and plasticity are established. The TMT regimes are presented that provide a uniform bulk distribution of nanosized particles of stable oxycarbonitride, a significant increase in their density (dispersion), and an increase in the thermal stability of the microstructure. It is shown that these regimes lead to a significant (by 30–60

Using the methods of transmission and scanning electron microscopy, the microstructure of a V–W–Cr–Zr alloy is studied as a function of its plastic deformation value under the condition of high-pressure torsion in the Bridgman anvils. The main stages of structure transformation and the respective mechanisms are identified. It is found out that the grain and defect structure transformation up to e ≈ 1.1 is provided by the dislocation and dislocation-disclination mechanisms, which when combined activate the processes of submicrocrystalline structure formation. The deformation impact in the strain interval from e ≈ 1.1 to e ≈ 3 is characterized by a significant increase in the grain-boundary length. A high strength state is achieved in the course of this deformation, where the dislocation modes of plastic deformation are suppressed. This is accompanied by the activated processes of formation of two-level nanostructured states, wherein the principal mechanism is a quasi-viscous re-orientation by the flows of non-equilibrium point defects. A further increase in the deformation to e ≈ 5.3 gives rise to refinement of the submicrocrystalline grains and formation of two-level nanostructured states in the entire material volume. The main contribution to the grain- and subgrain transformations comes from the disclination and quasi-viscous modes of plastic deformation. At higher strain degrees (e > 5.3), the size of submicrocrystalline grains does not virtually change, and the transformation of two-level nanostructured states makes itself evident in the rotations of some of the fragments of this structure with respect to the other by small angles from tens of fractions of a degree to several degrees. The formation of the submicrocrystalline state is followed by a multiple increase in the microhardness; its values are observed to saturate at e ≈ 3.3.

A comparative study of the features of the microstructure of bimetallic composites of the Me-Al (Cu, Ni, Nb) type, obtained by ball milling of powder mixtures and consolidation by torsion under pressure in Bridgman anvils, was carried out. In all systems studied in this work, the formation of a nanoband structural state is observed, the elements of which are elongated predominantly along the direction parallel to the anvil plane. It has been established that in local areas characterized by the absence of the aluminum component, an SMC state without a nanolaminate structure is formed. An analysis of the features of structure formation was carried out taking into account the comparison of the characteristics of powder systems components (melting point, shear modulus and stacking-fault energy). It was shown that low shear modulus of aluminum, compared to other components, in combination with a higher homologous temperature, provides it high accommodative ability. It has been suggested that under conditions of torsion under pressure, the aluminum component, being a kind of solid lubricant, ensures slipping and flattening of stronger layers of the second component, which contributes to the formation of a nanolaminate structure in the metal-aluminum systems under consideration.

Using regression analysis through a component-wise search for regressors, a computational approach is proposed for estimating the oriented curvature of vortex-like atomic structures. The studied discrete vector fields of atomic displacements of such structural states are obtained based on the results of molecular dynamics simulations of a deformable defect-free crystallite. Within the given approach, a continuous representation of the desired discrete vector field is obtained. The redistribution of the free volume and reorientation of the crystal lattice are analyzed. It is found that the value of oriented curvature outside specific regions (vortex centers and regions of compensation of atomic displacements) is about |K| ≈ 0.286 nm-1. The relationship is shown between vortex-like structures and model concepts of a continuous disclination-type defect.

The results of experimental and theoretical investigations of the thermal stability of heterophase structure of low-activated vanadium alloys with various types of nonmetallic phases (TiC, ZrC, and ZrO2) in the temperature‒time intervals of their technological treatment and operation in the core of nuclear and thermonuclear reactors are presented. It is shown that the thermal stability of these phases is determined by their thermodynamic stability and coagulation rates, which are responsible for the thermal stability of the nanosized heterophase structure. An important factor controlling these rates is the ratio between the standard thermodynamic potentials of their formation and the corresponding potentials of vanadium carbides and oxides. An assumption is made about the possibility of increasing the thermal stability of the heterophase structure of V–ZrC alloys by 100–200 K compared to V–TiC alloys and by 200–300 K in V–ZrO2 compositions.

The paper investigates the influence of dispersion hardening of the V–Cr–W–ZrC alloy on the temperature dependence of its yield strength at different tendency to non-dislocation homogenous distortion enabling BCC → HCP → BCC transformation by the Bain deformation mechanism. The discussion concerns the homogenous deformation mode and dislocation mechanisms in plastic deformation during the formation of strength properties (heat resistance) and low-temperature plasticity of vanadium alloys.

A comparative study of the features of the structure and characteristics of the mechanical properties of the V–Cr–W–Zr alloy depending on the modes of thermomechanical treatment has been carried out. It has been established that, compared with the standard mode of thermomechanical treatment, the use of the modified mode leads to a more than twofold decrease in the average grain size. The influence of the temperature of homogenizing annealing on the grain sizes after thermomechanical treatment has been revealed. Such a transformation of the structural-phase state when using a modified mode of thermomechanical treatment contributes to an increase in the short-term strength by ≈12 and ≈21

The study of the influence of the duration of preliminary high-energy ball milling on the features of the structural-phase state and the level of microhardness of consolidated Ni3Al samples obtained by the method of spark plasma sintering has been carried out. It was found that the inhomogeneous state of the precursor from the 3Ni-Al powder mixture in the case of preliminary ball milling of a short duration (1 min) is a cause of the formation of an inhomogeneous structural-phase state of the consolidated Ni3Al sample. An increase in the duration of high-energy ball milling provides a homogeneous phase compo-sition, promotes the refinement of the grain structure and an increase in the microhardness values of the obtained Ni3Al samples. The main factors determining the processes of structural-phase transforma-tion during the formation of Ni3Al under the conditions of spark plasma sintering, depending on the pre-liminary high-energy ball milling, are revealed. It is shown that grain boundary strengthening is the one of the effective mechanisms for increasing the strength of the material under study.(c) 2022 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.