Papers by Author: Elena D. Tabachnikova

Abstract: The ultrafine-grained copper was obtained by 12 passes of equal-channel angular pressing method. The uniaxial tensile tests at room temperature and the subambient temperature of 77 K show that the yield stress increases from the value of 128 MPa to the value of 138 MPa, respectively. In addition, the lowering the test temperature tends to the increase of the deformation before the failure. The fractographic analysis shows the transcrystalline ductile failure for all samples. Due to the high plasticity of nanostructured copper no influence of the nanoporosity on the failure process was observed.

Abstract: In metallic glasses plastic deformation occurs via the creation and the propagation of a softened region in the shear bands. Some of the high strength metallic glasses (as Zr-based metallic alloys) exhibit complex shear band topography and the final failure respects the allocation of the shear bands. We studied the differences in the fracture surfaces of Zr-and Mg-based amorphous alloys. Ductile behaviour of the shear bands in Zr-based amorphous alloy tends to the dimple creation during the failure. On the fracture surfaces the vein pattern morphology manifestations were present. Conchoidal fracture was typical for Mg-based amorphous glass. Two different surface morphologies, plumes and rib marks ornament the fracture surfaces.

Abstract: Several structural states of the CoCrFeNiMnV_x (x=0, 0.25, 0.5, 0.75) high entropy alloys with different content of the intermetallic σ phase are studied in uniaxial compression in temperature range 4.2-300 K. Peculiarities of strain hardening stages and temperature dependences of the yield strength are registered and analyzed considering dislocation sliding as main deformation mechanism in matrix fcc phase. Influence of σ phase particles, deformation twins and stacking faults on the deformation behavior of the CoCrFeNiMnV_x alloy is discussed.

Abstract: The investigations of the failure characteristics of Fe76Ni2Si9B13 bulk amorphous alloys prepared by shock wave consolidation of powders were performed. The strength decreased with the lowering temperature from 300 to 4.2 K. For this temperature interval, the brittle failure prevails. The failure propagates across particles as well as along particle boundaries. The riverlike pattern with fine dimples was observed on the fracture surface. The apparent surface energy and the fracture toughness values estimated by means of the fractography were similar to these for typical brittle materials.

Abstract: Several structural states of nanostructured zirconium were achieved by high pressure torsion (HPT) at pressures of 2 and 4 GPa with and without subsequent low temperature annealing. The nanostructured Zr was studied by X-Ray Diffraction, Transmission Electron Microscopy and Differential Scanning Calorimetry to reveal the microstructure, phase composition and the thermal stability of this material. The fine grained structure being achieved by HPT had an average grain size of 100-200 nm. It was shown that HPT at 4 GPa leads to a phase transformation from α-Zr to ω-Zr, which has been demonstrated to be reversible by annealing at 300 °C without considerable change of the grain size. The evaluation of texture evolution in Zr during HPT exhibits activity of prismatic slip systems. DSC curves confirm the presence of HPT deformation induced lattice defects and the occurrence of the ω-α phase transition in Zr.

Abstract: The fracture surface morphology of Fe76Ni2Si9B13 bulk amorphous alloys failed in compression at temperatures from 4.2 to 300 K was investigated. The samples were prepared by the explosive compaction technique from amorphous powder. It has been found that fracture stress decreases with temperature from 300 to 4.2 K. In this temperature range, the brittle failure prevails. The failure propagates across particles and along particle boundaries too. The fracture micromorphology is riverlike pattern with fine dimples.

Abstract: Plasticity of ultra-fine grained (UFG) zirconium (grain size ~ 0.4 µm), produced by intensive plastic deformation (IPD) - a combination of extrusion, annealing, and drawing, have been studied within the temperature range 300 – 4.2 K in uniaxial compression. It was found that decrease of grain sizes in the result of IPD leads to considerable increase of strength characteristics for the UFG zirconium in comparison with coarse-grained (CG) zirconium (in 6 times at 300 K and 4 times at 77 K); and plasticity of the UFG zirconium keeps rather large (strain > 0.15). Two stages of the strain-hardening and decrease of the activation volume for plastic flow with deformation have been registered. A conclusion was made about the identity of basic deformation mechanisms in the UFG and CG zirconium: simultaneous action and mutual influence of intragrain dislocation gliding and twinning.

Abstract: Low temperature mechanical characteristics under quasistatic uniaxial tension and compression have been studied of ultra fine-grained structural state of polycrystalline titanium – nanostructured titanium, processed by the equal channel angular pressing (ECAP). Values of the yield stress and the uniform plasticity at 300, 77, and 4.2 K for nanostructured (NS) and polycrystalline coarse-grained (CG) titanium of different commercial purity have been compared.