No 3 (2023)

An attempt is presented to determine the influence of the spray direction on the particles movement in a plasma flow in order to assess the influence of gravity. Three spray directions are selected: down, up and horizontal. Titanium powder PTM-1 TU 14-22-57-92 was considered. For each of the spraying directions under consideration, the movement of titanium powder particles of different dispersion in the plasma flow was calculated using the finite element method with using the SolidWorks software package. Particles with sizes of 1, 50 and 90 microns were selected as the sprayed powder material. The change in the temperature of powder particles when moving in a plasma flow depending on the direction of spraying has been studied. A comparative analysis was carried out for the spraying directions under consideration, based on the results of which the advantages and disadvantages were described and recommendations were given for conducting the processes of obtaining powder and applying coatings. The presented data can be useful when choosing the position of the substrate for applying functional coatings. The influence of gravity on the separation of the resulting powders and on the temperature distribution of the plasma flow in the studied area is demonstrated. To verify the calculation results, a full-scale experiment was carried out in a plasma installation assembled at the IMET Ural Branch of the Russian Academy of Sciences, which is used for producing powder and applying coatings, taking into account its design features. The results have practical benefits for developers and consumers of technological equipment.

The possibility of increasing the wear resistance of steel 45 surfaces by 19.9 times and titanium alloy VT6 by 3.6 times after cathodic electrolytic plasma nitriding in a solution of ammonium chloride and ammonia and subsequent anodic electrolyte-plasma polishing in a solution of ammonium sulfate. A positive effect on wear resistance was revealed reducing surface roughness and removing the outer part of the oxide layer using anodic electrolytic plasma polishing and increasing the hardness of the surface layer as a result of cathodic nitriding. The wear mechanism is defined as fatigue upon plastic contact and boundary friction.

A review of literature data on the interaction of hydrogen with metallic materials is presented. The main damage processes such as high-temperature hydrogen corrosion and hydrogen embrittlement (HE) are reviewed. The most common mechanisms of HE are described. The well-known regularities and issues of the influence of the chemical composition, structure, hydrogen concentration, temperature and strain rate on the development of HE are generalized, and the results of our own studies of the effect of hydrogen on the mechanical properties of pipe steels are presented.

The destruction mechanism during static stretching of flat samples of structural steel 09G2S in a defect-free state and with an artificial defect in the form of a fatigue crack are studied using the method of acoustic emission and fractographic analysis of surface violations. 

The kinetic patterns of nitride formation have been established and the sequence of structural transformations characterizing high-temperature (at 1900 °C) nitridation of Zr-U alloys containing 2 and 5 wt.% U in the range from 3.5 to 60 minutes is presented. During high-temperature saturation with nitrogen for each composition, the solid solution (Zr,U) decomposes with the formation of composite structures ZrN-(ZrN1-n/UxEy/U)-ZrN (where E is O, N; n, x, y are stoichiometric coefficients ). During the decomposition of the solid solution, zirconium nitride is formed and a phase of metallic uranium is released, which accumulates impurities contained in the initial solid solution in the central part of the sample. Kinetic curves for a temperature of 1900 °C are approximated by an exponential law and correspond to the nitridation of zirconium. The nitridation rate of the (Zr,U) solid solution increases with increasing uranium content. To complete the formation process of a compact nitride solid solution of (Zr,U)N of stoichiometric composition, it is necessary to increase the temperature and increase the reaction duration.

In this work, the effect of rotary swaging (RS) with a deformation degree (ε) equal to 1.28 and 2.31 on the microstructure, corrosion resistance and mechanical properties of a potential medical alloy Mg-1.1%Zn-1.7%Dy was studied. It was shown that RS at ε = 1.28 leads to a grain refinement of the studied alloy by 10 times (from ~300–400 µm to ~30–40 µm). An increase in the deformation degree up to ε = 2.31 leads to the formation of an inhomogeneous microstructure with regions containing both grains ~30–40 µm in size and zones with grains ~5–10 µm in size. Grain refinement after Rs leads to an increase in resistance to electrochemical corrosion (corrosion potential increases from -1550 ± 9 mV in the quenched state to -1442 ± 23 and -1454 ± 35 mV after RS at ε = 1.28 and ε = 2.31, respectively), but does not cause a change in the current density. But the degradation rate of the alloy increases with an increase in the deformation degree up to 3.46 ± 1.06 mm/y. The structure refinement after RS at ε = 1.28 leads to a significant increase in the strength of the alloy in comparison with the quenched state (ultimate tensile strength (UTS) increases from 70 ± 13 to 273 ± 7 MPa) with a drop in ductility from 23.1 ± 5.1 to 14.0 ± 2.9%. An increase in the deformation degree up to ε = 2.31 does not lead to an increase in the strength of the alloy (UTS = 267 ± 4 MPa), but causes an increase in ductility (δ = 21.1 ± 1.6%), apparently due to texturechanges, occurring in the alloy.