Problems of materials science

The effect of the homogenization annealing duration on the critical brittle temperature of 15Kh2MFA-A vessel reactor steel has been studied. The criterion for calculating the duration of the annealing is determined – this is the total duration of heating of the ingot and forging before the first and second removals. It is shown that in order to achieve Тк0 not less than minus 50°С, a total specific exposure at a temperature of 1220±20°С of not less than 2.5 min/mm of section is required. 

The effect of calcium consumption during out-of-furnace processing and its content in the finished metal on the quality of sheet steel grade 10KhSND, obtained from continuously cast slabs, has been studied. The research is based on the results of evaluating the macrostructure of slabs obtained from a continuously cast billet, as well as after testing the finished metal to determine impact strength, contamination with non-metallic inclusions, and ductile-brittle transition temperature. The paper analyzes the effect of consumption and calcium content in the metal. 

The effect of heat treatment on the structure and properties of a new weldable heat-resistant alloy based on Ni–Fe–Co–Nb–Ti–Тa with a low coefficient of thermal expansion for parts of gas turbine engines was studied. The stability of the intermetallic globular phase, the features of precipitation of lamellar particles during annealing after quenching were studied. It is shown that the structure formed during heat treatment with nanosized cuboid and rounded particles of the γ′-phase, as well as with a small amount of lamellar η-phase precipitates along the grain boundaries, provides a high set of properties and excellence heat-resistance in comparison with iron-nickel commercial alloys of a similar purpose. With uniform precipitation of the γ′-phase higher tensile strength are achieved. 

The paper studies structural transformations of the brazing seam and fillet of the T-joints formed during the diffusion brazing of the titanium alloy VT6S with filler alloy of the Ti–Cu–Ni–Zr system. The soaking time during brazing under the designed temperature is regarded as one of the most important processing terms. It is shown that the satisfactory level of the mechanical properties of the joints could be achieved at the proper technological parameters that provide removal of any alloying additions from the brazing seam as well as the minimum fillet size. The lamellar structure of the base titanium alloy could be recommended as the most desirable for the diffusion of brazed joints.

The results of optimizing the technological modes of deposition of titanium coatings by the microplasma method are presented in order to identify the most productive one. Variable values of the current strength of the electric arc, the flow rates of the plasma-forming and transporting gases were used as variable parameters. The sputtering material was PTOM-1 grade titanium powder of various fractional compositions: 20–32, 32–40, and 40–71 µm. A series of experiments was carried out on a combination of a number of factors. The following factors were considered: a coating thickness of at least 200 μm, the exclusion of sintering of the sprayed powder in the channels of the plasma torch, low porosity of the coating (no more than 5%), a tight fit of the coating to the substrate, and the exclusion of delamination of the coating during mechanical processing. As a result, the most optimal modes of coating deposition were identified. For coatings with the lowest porosity (from 1.0 to 1.9%), when all the above indicators were achieved, the morphology and microhardness were studied. According to the SEM microimages of transverse sections, it was determined that the coatings adhere tightly to the substrate material, there are no areas with delamination of the coating, and the microhardness of the coatings is in the range of 685–744 HV. 

A mathematical model has been developed for the crystallization of aluminum alloy granules under cooling conditions in an aqueous and water-steam media. The practical significance of the mathematical model lies in predicting the average value of the dendritic parameter of the obtained granules depending on the granulation method, the characteristics of the granulation process and the size of the obtained granules. The average value of the dendritic parameter makes it possible to predict the fineness of the granule structure and, consequently, the mechanical properties of the granular material. The mathematical model makes it possible to determine the speed of a melt drop in an aqueous media and takes into account the presence of a steam jacket effect, i.e., a vapor layer that appears between a crystallizing drop and an aqueous media, which significantly reduces the intensity of heat removal and the rate of crystallization. The application of the mathematical model was tested on the obtaining of granules of high-alloyed aluminum alloys (alloys D1 and D16 of the Al–Cu–Mg system, alloys V95 and V96Ts of the Al–Zn–Mg–Cu system), made by centrifugal spraying of the melt from a perforated rotating crucible and drip method during cooling in an aqueous media. The cooling rate and the crystallization rate of the granules obtained in real experiments were determined by measuring the dendritic parameter of the material structure. The mathematical model showed a high convergence of the simulation results and of real experiments of aluminum alloy granulation.

The method of manufacturing high-strength structural carbon fiber from toupreg based on PPS-214 grade polyphenylene sulfide (Fortron, Germany) and AS4 high-strength carbon fiber (Hexcel, USA) using a promising ATL-technology (Automated Tape Laying) with laser heating is considered. The technology was adapted for the material under study, laboratory models in the form of plates were made, physical and mechanical tests of laboratory samples were carried out. The quality of the binder distribution and the presence of defects were assessed by raster electron microscopy. The influence of the reinforcement, pressing and vacuum heat treatment schemes on improving the mechanical properties of the studied carbon fiber was investigated. It has been found that the samples subjected to vacuum heat treatment have higher mechanical properties due to an increase in the adhesion of the toupreg tapes to each other and the removal of discontinuities formed during the calculation. The value of the ultimate strength at interlayer shear of samples made using a parallel-diagonal scheme increases by 108%, at bending by 370% and by 65% at compression.

By processing the toupregs by the ATL with laser heating and subsequent thermal treatment of the products, it is possible to obtain high-strength structural materials with improved physical and mechanical properties, as well as high repeatability and equality of properties throughout the area of the products, even using complex reinforcement schemes.

A method has been proposed for calculating fatigue damage under cyclic loading, in which the loading in half-cycles is not simple, i.e., the stress components in a half-cycle do not change proportionally to one parameter. In addition, the proposed method takes into account the situation when the strain rate in a half-cycle affects the degree of damage to the material (for example, in the case of material deformation under conditions of creep or exposure to a corrosive environment) and this rate can change in different loading half-cycles.

The article contains the results of potentiodynamic and thermogravimetric research of anode behavior and oxidation of Zn22Al alloy, doped with scandium, in various media. The anode, kinetic and energy characteristics of alloys in isothermal conditions have been established. Doping of the Zn22Al alloy with scandium in an amount of 0.1 to 1.0 wt. % contributes to the increase of its anodic resistance to oxidation. The rate of oxidation and corrosion of alloys doped (0.01–0.1%) with scandium is 1.5–3 times lower than that of the Zn22Al alloy. Alloy oxidation products consist of a mixture of protective films ZnO, Sc2O3, ZnAl2O4 and Al2O3·Sc2O3. 

Steels and alloys of various structural classes are considered from the point of view of the required level of service characteristics necessary for the safe operation and manufacture of a sodium-cooled reactor plant steam generator. After the analysis, it was found that the optimal structural material for the steam generator of a high-power reactor plant with a sodium coolant is martensitic stainless steel with a chromium content of 12 wt.%.

The paper considers phenomena of formation of color centers due to intrinsic and impurity defects in fluorite crystals activated by rare-earth ions Pr3+, Nd3+, Yb3+ under γ- and UV-radiation. Using CaF2 activated with Yb3+ and Pr3+ ions as an example, the work shows the effect of the photodynamic process on the photochemical resistance to formation of color centers of a Yb-containing crystal. It also demonstrates the effect of heating on the restoration of the original color of a Pr-containing crystal after γ-radiation as a result of change in the electronic state of praseodymium ions. The features of the formation of ions in the R2+ state in CaF2:R3+ (R3+ = Pr, Nd, Yb) crystals after γ-irradiation are investigated and explained, and quantitative estimates of the R3+→R2+ conversion processes are given.