Bulletin PNRPU. Mechanical engineering, materials science

The features of chemical, structural and phase composition of the diamond-metal interphase zone, formed in the process of thermal diffusion metallization of diamond by chromium, titanium, iron, nickel and cobalt powders at the same temperature-time mode, that corresponds to the sintering of diamond-containing WC-Co-matrices with self dozed copper impregnation, were studied. It was shown that a metallized coating is formed on the surface of the diamond, consisting of a mixture of carbides, metals and graphite phases in process of thermal diffusion metallization by chromium and titanium using scanning electron microscopy, X-ray spectral, X-ray phase analysis and Raman spectroscopy. The insignificant content of graphite formations and their intermittent nature of the diamond-metal interfacial zone ensures a strong adhesion of the metallized coating to the diamond through the carbides of the corresponding metals. The formation of an intermediate layer strongly adhered to the diamond also occurs at the diamond-metal interphase zone at thermal diffusion metallization of diamond by iron. The intermediate layer has a complex structural phase composition comprising a mixture of iron, a solid solution of carbon in iron and graphite phases. It was suggested that an intermediate layer on the surface of diamond can be formed by solidification of the liquid phase with the eutectic composition resulting from the melting of the diamond-iron contact pairs. Samples of diamond-nickel and diamond-cobalt under the heating conditions specified in the experiment cause intense catalytic graphitization of diamond with the formation of numerous traces of erosion on its surface. The observed weak adhesive interaction of these metals with diamond is probably due to the high melting temperatures of the Ni-C and Co-C eutectics, which does not allow the metals to react with diamond under given experimental conditions.

As the object of study in this work, we used the two-phase (α + β)-titanium alloy VT23 in the delivery state. A preliminary heat treatment of the samples was carried out at different temperatures, including annealing, quenching at various temperatures, and subsequent cooling in water in order to obtain different stability of the β-phase. Using the methods of optical microscopy, X-ray phase analysis and mechanical tests, microstructure, phase composition and mechanical properties of samples of the VT23 two-phase titanium alloy with different β-phase stability were studied. The parameters of the cubic lattice of the β phase after various heat treatment modes are determined, the dependence of the lattice period on the quenching temperature due to the change in alloying system is established. The results of uniaxial tensile and impact bending tests of samples of this alloy at room temperature showed that an increase in quenching temperature from 800 to 860 °C gives a rise in strength, ductility, impact strength and crack propagation characteristics. Methods of instrumental impact tests revealed the effect of quenching temperature increasing on the type of loading diagram and characteristics of impact strength. A fractographic study of the fracture surface of VT23 alloy specimens after impact tests showed that the observed change in the type of loading diagrams is in good agreement with the change in the fracture mechanism and, in particular, with the elimination of intergranular structure on impact specimens fracture surface after increasing the quenching temperature to 860 °C, which contributes to the destabilization of the β phase in relation to stress-induced martensitic transformation. It was found that crack growth in samples with a metastable β-phase occurs along the boundaries of martensitic plates and their packs.

The article describes the technological features of the machining of polymer composite materials on the example of a common and popular manufacturing process operation - drilling. Technological features consist in the difficulty of obtaining high quality machined surfaces of polymer composite materials (lack of fluffiness, delamination at the tool inlet and outlet, the required roughness parameters), low productivity, as well as low durability of the cutting tool. Ways of increasing the efficiency of drilling polymer composites due to artificially superimposed vibrations of various ranges: low-frequency, high-frequency and ultrasonic are considered. An overview of the possible effects of the combined ultrasonic drilling of polymer composites is given, when vibrations in the ultrasonic range are superimposed on the traditional drilling scheme. The most significant effect observed with ultrasonic drilling is the reduction of force factors, that is, a significant reduction (up to 80%) of cutting forces, which leads to high quality processing of polymer composite materials. The nature of this reduction in cutting forces has not yet been disclosed in the literature; it lies in the vibration mechanics and variable contacts of the cutting tool and the workpiece. The laws of ultrasonic oscillations are written in the form of harmonic oscillations equations. For drilling polymer composites, amplitudes from 15 μm to 30 μm were chosen, depending on the hole diameters being processed, and frequencies for applying are recommended: 20 kHz and 50 kHz. The article created the prerequisites for a joint research project on the basis of two universities: Perm National Research Polytechnic University and Institute for Machine Tools (IfW) University of Stuttgart, for the study of ultrasonic drilling.

A modified technique was applied to obtain an internal oxidation zone to reveal the actual grain after high-temperature heating and various exposure times. The need to modify the method for identifying the boundaries of the actual austenite grain lies in the fact that the application of methods for identifying austenite grains according to GOST 5639 does not always bring a positive result, especially chemical etching methods. The analysis of the grain structure of steels with the Kh2G2S2MF alloying system after heating at temperatures from 900 to 1200 °C is carried out. The influence of the exposure time (15, 30 and 60 minutes) on the growth of austenitic grain at each austenitization temperature is analyzed. The average sizes of austenitic grains were calculated and austenite recrystallization temperatures were determined for each steel, which is an integral part for setting the heat treatment regimes associated with continuous cooling or isothermal processing of metal products under production conditions. After various exposures at each austenitization temperature, a comparative analysis of two methods for determining the average grain size was carried out: the method for determining grain size using the Olympus Stream Motion 1.8 software and using the SIAMS 700 solids microstructure fragment analyzer. SIAMS 700 is currently quite common and popular program designed for various quantitative analysis of the structures of metallic materials. The analyzer of fragments of the microstructure of solids is installed in the laboratory on the basis of various enterprises and universities. Olympus Stream Motion 1.8 software is bundled with an Olympus GX-51 light microscope and can also be used to calculate the average real austenite grain size. It has been shown that economically-alloyed medium-carbon structural steels of the Kh2G2S2MF alloying system are hereditarily fine-grained. It was determined that only when heating above 1150 °С a sharp grain growth begins, however, the average size of the actual austenite grain is in the range of 50-60 microns.

The dynamics of the circulation sub used to strengthen the walls of the well during drilling is studied. The design and functioning principle of the sub in the process of their operation is considered. The main stages of the work of the sub are highlighted. The description of each stage is given and the corresponding design schemes are presented, which take into account the geometric, power and operational parameters of the system. Taking into account the accepted assumptions the mathematical models presented in the form of a set of relations characterizing mechanical and hydrodynamic processes of functioning of the translator are constructed. The conditions that impose operational, technological and structural restrictions on the modes of each of the stages of its operation are introduced in the calculation. Under the accepted assumptions, the value of the critical pressure required to push the ball through the seat of the bushing structure is determined. Relations are established between this pressure and the geometric characteristics of the ball. The procedure for calculating the circulation mode of the plugging fluid or drilling fluid when opening the side holes is given. The method of obtaining ratios for determining the pressure on the riser required to ensure the required flow rate of the drilling pump is presented. For each stage of the circulation sub, the characteristic of the algorithms and the order of numerical simulation of the dynamics of the considered design are given. A software module has been formed to implement the solution of the obtained equations. According to the results of mathematical modeling the features of dynamic phenomena in the process of circulating sub are revealed. Numerical values of the system characteristics that affect its dynamics by varying the design and technological parameters of the sub are obtained. The calculation results are formed in the form of tables and graphs. A number of them are presented in the article in the form of corresponding diagrams.

The paper describes experimental studies of multiple-layer electron beam surfacing by wire material. An experimental selection of electron-beam surfacing modes for wire material was carried out. The evaluation of the regimes was carried out by visual control of the process and the result of surfacing. Regimes of electron beam surfacing with the following technological methods were studied: ring oscillation of the electron beam and various focusing modes in the static position of the electron beam, feeding the filler wire into the molten pool, feeding the filler wire above the surfacing zone. By changing the focusing modes, several characteristic electron beam focusing positions were investigated: below the substrate surface; on the surface of the substrate; between the level of the filler wire on the substrate surface; at the filler wire level; above the level of the filler wire. In addition, the influence of the filler wire positioning on the quality of the deposited roller was investigated. The wire feed into the surfacing zone at an angle of 45-60° to the surface and a horizontal feed of the wire over the surfacing zone were studied. During the experiment, various variants of horizontal wire feeding were used: front, side, rear. In the final part of the experimental studies, multiple-layer surfacing was performed using an ER308LSi filler wire 0.8 mm in diameter to a plate of the stainless steel with a thickness of 13 mm. A specimen of an annular surfacing was obtained, consisting of four layers, 3 mm high. Two layers were obtained with the exact positioning of the filler wire, one layer with offset of the wire relative to the axis of the deposited roller in one direction and one layer with offset in the other direction.