Vol 61, No 3-4 (2019)

Results of a study proving formation of long-period stacking ordered (LPSO) phases in the structure of magnesium alloy VMD16 of the Mg – Zn – Zr-system are presented. It is shown that the LPSO-phases have the form of plates from 1.5 to 25 nm thick. After a homogenizing annealing, the content of Zn and Y in the LPSO-phases changes. Special features of the morphology of these phases are considered.

Oxide layers deposited on magnesium by microarc oxidizing with introduction of different silicon-containing components, i.e., nanoparticles of SiO₂ and Na₂SiO₃ sodium metasilicate, into the electrolyte are studied. The effects due to individual and joint use of these substances as components of the electrolyte are compared. It is shown that the best wear resistance of the oxide layers is provided after addition of SiO₂ nanoparticles into the electrolyte, and the best corrosion resistance is obtained due to joint introduction of SiO₂ nanoparticles and sodium metasilicate. The mechanisms of interaction between SiO₂ nanoparticles and the forming oxide layer are suggested.

Results of a study of magnetic properties and structure of specimens of magnets obtained from heat-treated cast alloy Fe₂NiAl milled in a planetary mill together with CuAl₂ and Al addition alloys, pressed in a magnetic field, and sintered in vacuum or by spark plasma sintering (SPS) are presented. The suggested method for fabrication of sintered permanent magnets gives solid hard magnetic materials with high coercivity and relatively high saturation magnetization.

Methods and processes of surface hardening of parts from iron-carbon alloys are analyzed. It is shown that each of the known methods has advantages and disadvantages. A complex process for hardening of parts from iron-carbon alloys is suggested for obtaining the specified combination of properties. In the first stage of the complex treatment the part is subjected to vacuum-plasma sputtering and then to a thermochemical saturation in superheated vapor of aqueous solutions of salts. The coating is formed layer-after-layer, which raises its tribotechnical properties and prolongs the service life of the coated material by a factor of 3 – 4.

The effect of the temperature-and-rate conditions of straining on the structural characteristics of pressed alloy 45% Ti – 45% Ni – 10% Nb is studied. The microstructure and the content of elements in the alloy are determined. The phases are analyzed using a MIRA//LMU scanning electron microscope. The data obtained are analyzed statistically with the help of the STADIA 7.0 software. Scanning electron microscopy is used to show that the content of elements in the alloy does not depend on the straining conditions, i.e., the temperature, the strain rate, and the strain. The results of the tests are processed statistically and used to develop technologies for the nuclear power industry.

The microstructure and mechanical properties of alloys of the Al – Si system modified with nanosize tungsten powder in an amount of 0.01 – 0.5 wt.% during casting are studied. The phase composition, the sizes, and the localization of phases in the microstructure of the initial and modified Al – Si alloys are investigated by the methods of optical, scanning, and transmission electron microscopy. The ultimate strength, the elongation, and the impact toughness of the Al – Si alloys are determined before and after modification with nanosize tungsten powder.

Special features of the structural and mechanical behavior of aluminum alloy D16 under equal-channel angular pressing (ECAP) and subsequent cooling to cryogenic temperatures are studied. The mean grain size, the conventional yield strength, and the elongation are determined. It is shown that the ECAP refines the grains and raises the strength properties of the alloy.

Influence of molybdenum additions on the microstructure and corrosion resistance of powder alloys based on the TaCr₂ Laves phase is studied. The phase composition of the alloys in different conditions is determined. Growth in the mass of the alloys is determined after 100-h oxidation at 900°C. The effect of the molybdenum additions on the structure and properties of the TaCr₂ -base alloys is shown to be positive. An optimum composition is suggested.

Magnetic hysteresis properties (residual induction B_r, coercivity H_c and maximum energy product (BH )_max) of Fe – 27% Cr – 10% Co (27Kh10KA) hard magnetic powder alloy are assessed after different heat treatments. Optimum modes of heat treatment are determined using TRM251 programmed derivative-proportional-integral controllers. The magnetic characteristics of the specimens exceed those of the widely used alloy 25Kh15KYuBF with a higher cobalt content. The prospects of the Fe – 27% Cr – 10% Co (27Kh10KA) powder alloy for commercial production are considered.

Precision nickel alloy 40KhNYu-VI used for fabricating nonmagnetic precision bearings is studied after nitriding in glow discharge in an experimental facility at a high temperature (730 and 900°C) and in commercial equipment at 540°C. The effect of the temperature and duration of nitriding and of the mode of heat treatment on the structure and hardness of the surface layer obtained is determined.

Scanning electron microscopy and confocal laser scanning microscopy are used to study a fracture surface of hydrogen-charged low-carbon steel, which has been deformed in air at room temperature to 12% residual strain and then crushed in liquid nitrogen. It is shown that the quasi-cleavage facets formed during the room-temperature deformation have a strongly curved surface in contrast to the flat cleavage facets formed under the loading in liquid nitrogen. It is inferred that the quasi-cleavage facets in the hydrogen-charged steel do not form by the mechanism of cleavage in the deformed structure.

Results of a study of white iron cementite in binary Fe – C and ternary Fe – C – Si compositions and in castings of unalloyed white iron with traditional composition are presented. It is shown that the hardness and the corrosion strength of the cementite may vary in a wide range depending on the rate of cooling of the iron after crystallization. Optimum processes for casting and heat treatment of members of tilling machines from chilled cast iron are developed for raising their strength and wear resistance.

Two principles of alloying are suggested for creation of aluminum alloys sparingly alloyed with scandium, which intensify the metastability of the process of crystallization in continuous casting of ingots. The first principle consists in keeping a one-to-one scandium-to-zirconium proportion, for example, 0.11% Sc and 0.11% Zr. The second principle consists in multicomponent alloying with transition and rare-earth metals, which intensifies the metastability of crystallization.

The methods of optical and scanning electron microscopy, microhardness measurement, differential scanning calorimetry (DSC), dilatometry, dynamic mechanical analysis, and hydrostatic weighing are used to study the structure and the physical and mechanical properties (density, microhardness, modulus of elasticity, coefficient of linear thermal expansion) of cold-deformed brass LS59-1 in the initial condition and after heating to 800°C. The DSC heating curve exhibits exo- and endothermic effects due to stress relaxation and retrogression (the exothermic effect at 115 – 235°C), melting of lead segregations (the endothermic effect at about 328°C), transition of the β′-phase into a disordered β -condition (the endothermic effect with minimum at 458°C), and transition of the brass into a single-phase β -condition (the endothermic effect at 642 – 747°C with minimum at 721°C).