Alexander N. Tyumentsev

Effect of thermomechanical treatment modes on the features of heterophase and grain structure, and mechanical properties of V–Cr–Zr–Ta alloy

A comparative study into the influence of thermomechanical treatment mode on the structural-phase state and physical and mechanical properties of low activation vanadium alloys (V–Cr–Zr–Ta system) has been conducted. It is found that a modified thermomechanical treatment of this alloy increases the short-term strength at 20 and 800°C. It is shown that an increase in the stabilizing temperature of V–Cr–Zr–Ta alloy up to 1100°C provides the same mechanical properties as the properties of V–Ti–Cr system alloys after similar treatment and stabilizing at 1000°C.

Stress fields and energy of disclination-type defects in zones of localized elastic distortions

This paper studies theoretically the elastically deformed state and analyzes deformation mechanisms in nanocrystals in the zones of localized elastic distortions and related disclination-type defects, such as dipole, quadrupole and multipole of partial disclinations. Significant differences in the energies of quadrupole and multipole configurations in comparison with nanodipole are revealed. The mechanism of deformation localization in the field of elastic distortions is proposed, which is a quasi-periodic sequence of formation and relaxation of various disclination ensembles with a periodic change in the energy of the defect.

Influence of temperature on microstructure parameters and microhardness of dispersion-hardened V–Cr–Zr–W alloy after deformation by torsion under pressure

Study of microstructure transformation and microhardness changes of dispersion-hardened V–Cr–Zr–W alloy after severe plastic deformation by torsion on Bridgman anvils and subsequent heat treatments was conducted. Basic stages of relaxation processes were revealed: at 800°C recovery processes take place and primary recrystallization begins; at 900°C primary recrystallization intensifies; in range of 950–1050°C collective recrystallization processes activate; at 1200°C secondary recrystallization starts. Microhardness measurement and comparison of its values with structural states features were conducted. Strengthening mechanisms and their contribution at various stages of defect substructure relaxation are discussed. It is shown that increase of thermal stability of V–Cr–Zr–W alloy microstructure is a consequence of the formation of high density of thermally stable Zr (O–N–C)-based nanoparticles.

Evolution of microstructure and microhardness of dispersion-hardened V–Cr–Zr–W alloy during deformation by torsion under pressure

Results of the study of the microstructural evolution and microhardness changes of dispersion-hardened V–Cr–Zr–W alloy under severe deformation during torsion on Bridgman anvils are presented. Typical structural states and mechanisms of their formation are revealed for basic evolution stages as well as appropriate microhardness values are determined. It was shown that at true logarithmic strain values (e) in the range 0.7 ≤ e 2, the anisotropic submicrocrystalline structure is observed and the formation of two-level nanostructural states was found within grains. In the strain range (e) from 3 to 6.6, submicrocrystal sizes hardly change, but changes of two-level nanostructural state parameters are observed: the nanofragment size decreases and values of elastic curvature of the crystal lattice increases.

Microstructure and mechanical properties of vanadium alloys after thermomechanical treatments

The results of investigation of dispersion strengthening effect on parameters of structural-phase states and characteristics of short-term strength and ductility of vanadium alloys of V–4Ti–4Cr, V–2.4Zr–0.25C, V–1.2Zr–8.8Cr and V–1.7Zr–4.2Cr–7.6W systems with different concentration of interstitial elements after optimized thermomechanical treatment mode were summarized. It was shown that for effective realization of dispersion strengthening by Orowan-type mechanism at least 25–50% of the initial volume fraction of coarse particles should be transformed into fine-disperse state and redistributed over the volume of material.

Nanostructural states in Nb-Al mechanocomposite after combined deformation treatment

Nanostructural states were investigated, that were formed in Nb-Al system-based mechanocomposite after combined deformation treatment that includes mechanical activation in a planetary ball mill and subsequent consolidation by torsion under pressure on Bridgman anvils. The formation of the layered structure, consisting of Nb and Al nanobands with width from several to several tens of nanometers was revealed. The structural states with high elastic curvature of crystal lattice and high level of local internal stresses found in Nb and Al subgrains were investigated by transmission electron microscopy.

Features of plastic deformation and fracture of dispersion-strengthened V–Cr–Zr–W alloy depending on temperature of tension

Influence of tension temperature on features of plastic deformation and fracture of V–4.23Cr–1.69Zr–7.56W alloy was investigated by scanning and transmission electron microscopy. It is shown that temperature increase leads to activation of the recovery processes, which manifests in the coarsening of microstructure elements, reducing the dislocation density, relaxation of continuous misorientations.

Features of change of V–4Ti–4Cr alloy hardness during microstructure evolution under severe plastic deformation

Features of changes of microhardness and nanohardness of V–4Ti–4Cr alloy at different stages of microstructure transformation during severe plastic deformations by torsion under pressure are presented. Microstructure features and mechanisms of its transformation affecting the hardness of studied alloy are discussed. Local temperature increase and activization of relaxation processes of nonequilibrium nanostructure states with high (hundreds of degrees/µm) elastic curvature of the crystal lattice are considered as main factors that define nonmonotonic character of changes in the microhardness at the stage of formation and evolution of the two-level structural states. In alloy under study at a value of true logarithmic deformation e ≥ 6.6 the formation of areas consisting of nanocrystals several nanometers in size with a high density of large-angle boundaries and elastic curvature of the crystal lattice hundreds of degrees/µm was found. Hardness of the material (Hnano ≈ E/16) differs little from its theoret...

Microstructure and properties of pure and composite metal powders after mechanical activation in planetary ball mill

The effect of mechanical activation in planetary ball mill on microstructure parameters and microhardness of metal materials was shown on the example of pure metal powders (Cu, Ta, Nb) and composites (Nb Al, Cu Al and Ti Al systems). High-defect stuctural states formed under severe plastic deformation were revealed and quantitatively investigated. The analysis of the relationship between parameters of these states and microhardness level was carried out.