Vol 2017, No 10 (2017)

The change in the energy of a crystal induced by subgrain boundary formation during plastic deformation is studied by computer simulation. The crystal is shown to react to the changes caused by the appearance of plastic misfits: it changes its defect structure to minimize an increase in its elastic energy.

The shapes and the relative position of martensitic inelasticity and forward transformation diagrams are experimentally studied. The strain dependences of the stress in loading under martensitic inelasticity conditions after an experiment on the accumulation of the forward transformation–induced strain at a constant or variable stress are investigated on titanium nickelide samples. It is found that the hardening of the martensite part of the representative volume of a shape memory alloy (titanium nickelide) after forward transformation under a nonmonotonically changing stress can be nonuniform. The cross hardening phenomenon is theoretically described in terms of the model of nonlinear deformation of a shape memory alloy during phase and structural transformations.

The morphology of the electrolytic copper single crystals formed under the mechanical activation of a cathode is described. Pentagonal pyramids and conical microcrystals with high growth steps are shown to form during electrocrystallization under these conditions. It is experimentally found that microcrystals grow on disclination defects, in particular, at the sites of termination of twin growth boundaries, and mechanical activation causes the formation of such defects.

The structural and thermomechanical properties of rapidly quenched layered amorphous–crystalline Ti₅₀Ni₂₅Cu₂₅ composite materials with various ratios of amorphous and crystalline phases are studied. These layered composite materials are shown to exhibit the two-way shape memory effect accompanied by bending deformation without additional thermomechanical treatment. The ratio of amorphous and crystalline phases is found to affect the reversible change in the shape of the composite material.

The effect of the wet milling time on the magnetic properties of powder compositions consisting of the hard magnetic Sm₂Fe₁₇N_x (x = 2.9–3.0) nitride and a rapidly quenched Nd_9.6Fe_76.3Co_4.3Zr_3.4B_6.4 (at %) alloy, which are taken in different mass proportions, is studied. The compositions containing no more than 20 wt % alloy are found to exhibit a substantial increase in the magnetic characteristics as compared to those of the nitride. It is shown that the determining effect on the coercivity is related to the degree of structural imperfection of Nd–Fe–B powders, whereas the specific remanent magnetization and the specific magnetization in a field of 2 T are determined by the corresponding characteristics of the alloy. The optimum composition and efficient treatment conditions for powder mixtures are determined.

The specific features of the existing methods of quantitative texture analysis of semiproducts and products made of titanium and zirconium alloys are analyzed. A technique is proposed to determine the Kearns coefficients (f parameters) for sheets made of hcp-metal-based alloys with allowance for the weighting factor of each reflection in the standard stereographic triangle. The f parameters calculated for sheets made of a zirconium alloy and various titanium alloys using different techniques are compared. The accuracy of measuring the Kearns coefficients by the inverse pole figure method is estimated.

The formation of the anisotropy of the mechanical properties, the texture, and the phase composition of thin-sheet Al–4.3Cu–1.4Li–0.4Mg and Al–1.8Li–1.8Cu–0.9 Mg alloys have been studied by X-ray diffraction and tensile tests. Various types of anisotropy of the strength properties of the alloys have been revealed: normal anisotropy (strength in the longitudinal direction is higher than that in the transverse direction) in the Al–4.3Cu–1.4Li–0.4Mg alloy and inverse anisotropy in the Al–1.8Li–1.8Cu–0.9Mg alloy. It is shown that the anisotropy of the strength properties is dependent not only on the texture of a solid solution, but also on the content and the texture of the δ' (Al₃Li) and T1 (Al₂CuLi) phases and their coherency and compatibility of deformation with the matrix.

Effect of structure and texture on the anisotropy of the mechanical properties of the MA2-1pch magnesium alloy subjected to equal-channel angular pressing and subsequent annealing has been studied in two mutually perpendicular planes Y and X (along and across the pressing direction). The anisotropy of the mechanical properties is shown to be due to various orientations of shear bands and various types of texture inside the bands and outside them in planes X and Y.

The evolution of the structure and the hardness of single-phase Ni–Cr alloys with 2–12.5 at % Cr is studied during high-pressure torsion. It is established that the hardness of the alloys, unlike pure nickel, continuously increases in the entire true strain range 0.2–12. Alloying with chromium is shown to substantially inhibit the formation of a submicrocrystalline structure and to enhance the refinement of microcrystallites.

The notch sensitivity of sheet corrosion-resistant 08Kh17T steel is estimated in the states before and after high-temperature (1000–1100°C) internal nitriding during tensile tests accompanied by the measurement of acoustic emission signals. A crack in the steel is shown to propagate according to a ductile mechanism is all states. As the nitrogen content increases from 0.60 to 0.85%, the ultimate tensile strength of the steel decreases by 15% in the presence of a stress concentrator and remains substantially higher than the yield strength of the sheet steel without a stress concentrator.

The evolution of the phase composition and the imperfect substructure of the 30Kh2N2MFA bainitic structural steel subjected to compressive deformation by 36% is quantitatively analyzed. It is shown that deformation is accompanied by an increase in the scalar dislocation density, a decrease in the longitudinal fragment sizes, an increase in the number of stress concentrators, the dissolution of cementite particles, and the transformation of retained austenite.

The structure of coronal teenage dentin and the development of cracks in it are studied on microand nanolevels. The material is found to fail according to a ductile mechanism on a microlelvel and according to a ductile–brittle mechanism on a nanoscale. This behavior is similar to the failure of a polyethylene film and rubber, when significant elastic and irreversible deformation precedes crack growth. The viscoelastic behavior can be considered as the reaction of dentin to an applied mechanical load.

The influence of various thermomechanical treatment schemes, which include rotary forging and severe plastic deformation by equal-channel angular pressing, on the structure and the mechanical and functional properties of TiNi alloys is studied. Treatment according to these schemes is shown to result in the formation of a mixed nano- and submicrocrystalline structure with a high dislocation density, which ensures high mechanical (σ_0.2 = 760–954 MPa, σ_u = 917–1097 MPa, δ = 21–51%) and functional (maximum completely recoverable strain of 6.8–8%) properties.

A joint analysis of acoustic emission pulse amplitudes, deformation diagrams, and fracture surfaces is used to study the fracture kinetics and mechanisms of 20GL steel specimens having different hardnesses and cut from the upper fragment of a freight bogie solebar. The fracture of the steel specimens subjected to normalizing and having a uniform strength and ductility over the entire cross section proceeds continuously. The crack that nucleated in the specimens with a gradient strength distribution over the cross section after volume–surface quenching slows down in a layer of a variable strength and ductility and stops in a ductile core. The crack sizes are determined from the measured peak amplitudes of acoustic emission.