Vol 60, No 3-4 (2018)

Problems arising due to abnormal grain growth, the main of which concerns determination of the start and end of this process in materials with various initial microstructures and the behavior of disperse particles, are considered. Grain growth is studied by the method of numerical simulation. A pioneer diagram presenting the conditions of development and suppression of abnormal grain growth at a fixed rate of dissolution of particles is plotted in the “initial grain size – initial retarding force” coordinates. The causes of abnormal grain growth in nanocrystalline materials are analyzed, of which the principal one is supposed to be the presence of submicroscopic pores. The results obtained are used to develop novel methods for controlling the grain structure in various structural and functional materials.

Structural changes developing under tempering of low-carbon martensitic steel are studied by the method of electron backscatter diffraction. The evolution of the crystal lattice curvature reflecting the softening process and the packet-block structure of the martensite are analyzed. The dependence of the self-accommodation of packets on the combination of variants of the interphase orientation relation is determined. The growth of new martensite laths under tempering, which is related to this dependence, is considered.

Three variants of behavior of austenitic chromium-nickel steels with different degrees of austenite stability under cold compressive plastic deformation are considered. The susceptibility of the steels to formation of the first portions of ferromagnetic α′-martensite and paramagnetic ε-martensite is shown to differ depending on the composition of the steel and on the degree of the deformation. The possibility of nucleation and transformation of an intermediate paramagnetic ε-phase and ferromagnetic α′-martensite in the chromium-nickel steels with moderately unstable martensite under plastic deformation is demonstrated.

The kinetics of discontinuous precipitation of Ag₂Al intermetallic in alloy Al – 10% Ag is studied after 10-h holding in vacuum at 530°C and subsequent water quenching. The DSC and dilatometric curves are plotted for heating rates ranging from 5 to 20 K/min. The activation energy of formation of the Ag₂Al γ-phase is computed from the DSC data with the help of the Boswell equation and by the Kissinger method.

Ways for advancing the processes of production of heat-removing and emitting compositions based on W and Pd for creating articles for semiconductor and vacuum electronics are considered. It is shown that the widely demanded W – Cu pseudoalloys may exhibit advanced parameters if they are synthesized with the use of the special features of their formation determined in the work by analyzing the structure of the porous refractory skeletons and the infiltration technique. The experimental processes of fabrication of emitting compositions from sintered powders of palladium and Pd5Ba intermetallic are still far from the stage of commercial production due to the absence of expedient modes of thermal deformation treatment for sintered articles of type PdB2, which follows from the data of the studies of their microstructure.

The conditions of formation of turbulent structures in metallic hybrid materials under pressure torsional deformation are considered. The structures formed in compositions of “steel 08Kh17T/copper/steel 08Kh17T”, “steel 08Kh17T/alloy É125/steel 08Kh17T”, and “alloy V – 10% Ti – 5% Cr/alloy É125/ alloy V – 10% Ti – 5% Cr” under pressure torsion are studied in order to investigate metal-base layered hybrids with different capacities for hardening under high strain. Different kinds of interfaces between the layers are described as a function of the composition of the hybrid.

Comparative analysis of the morphology of ductile fractures for a wide spectrum of products from structural steels (profiles, forgings, sheets), testing modes (tension, impact) and variants of cutting of specimens (longitudinal, tangential, and third-direction (over the thickness of the sheet) ones) is performed using the results of measurements. Informative components of ductile fractures connected with the observed differences in the toughness and in the ductility are determined. It is shown that the ductile fractures may be ranged objectively, which is required for solving problems of certification and control of the quality of metals.

The structure and properties of magnesium alloy WE43 are studied after homogenizing and rotary swaging deformation conducted in several stages with step lowering of the temperature from 400 to 325°C and increasing the extrusion ratio to 2.56 – 2.78. The deformation yields an ultrafine-grained (UFG) structure with a mean size of the structural components about 500 – 800 nm and particles of aMg₄₁Nd₅ phase with a mean size of about 300 – 400 nm. The formation of the UFG structure raises the strength of the alloy. The best combination of mechanical properties is provided by swaging with the final temperature 325°C. It is shown that the rotary swaging deformation does not affect the corrosion rate of the alloy measured by the methods of potentiodynamic polarization, loss in the mass and emission of hydrogen.

The applicability of various criteria for evaluation of the fracture toughness of a discretely reinforced carbon–carbon composite material for friction purposes is considered. The values of the K_1c, J_1c, J_c and COD criteria of fracture toughness are calculated. The distribution of the fields of displacements and deformations on the surface of specimens is determined by the method of numerical correlation of digital images with the use of a VIC-3D system. The stress fields are calculated.

The mechanical properties of newly developed austenitic nitrogen corrosion-resistant Cr – Ni – Mn steels with copper additive are studied in the temperature range of hot and warm deformation. The results of the hot and warm compressive tests are used to determine the specific levels of strain resistance at different temperatures of pressure treatment, which may be used for designing processes for making hot-deformed products from the experimental steels. It is shown that warm deformation and tempering are suitable for hardening nitrogen steels with the aim to apply them as nonmagnetic corrosion-resistant heat-resistant materials. The materials for cryogenic purposes should be subjected to a high-temperature thermomechanical treatment and quenching (solid solution treatment).

Alloying of aluminum alloys with scandium, which provides a unique combination of properties, is considered. However, scandium is very expensive, and its presence raises considerably the cost of the alloys. It is shown that the content of scandium may be reduced without lowering the level of the properties.

The possibility of the use of the effect of magnetic impedance as a criterion for estimating the homogeneity of potentially amorphous melt-quenched alloys and for optimizing of the heat treatment mode of nanocrystalline soft magnetic alloy 5BDSR is considered. The measurements of the effect of magnetic impedance on small-section specimens cut from amorphous ribbons show the possibility of getting additional information on the variation of magnetic properties under nanocrystallization. The magnetic characteristics of alloy 5BDSR are shown to be unsteady after single-stage annealing by the modes standardized for this material. It is shown that double-stage heat treatment stabilizes the magnetic properties of the alloy and elevates these properties.

Joint analysis of acoustic emission (AE), strain diagrams, structures and fractures is used to study the kinetics and mechanisms of fracture of specimens, fragments and unit-cast railroad car solebars from steel 20GL in different strength states. A system of AE monitoring of damage of solebars during motion of the train is developed and applied. The crack sizes are determined by measuring peak amplitudes of acoustic emission.

The third author’s name should read P. Gebara.