No 12 (162) (2024)
Materials science in mechanical engineering
METHODOLOGICAL FOUNDATIONS OF THE MATERIALS SCIENCE ASSESSMENT OF THE QUALITY OF LUBRICANTS FOR LOADED INTEGRATIONS OF MACHINES AND MECHANISMS. MESSAGE 2. THE INFLUENCE OF THE COMPOSITION OF LUBRICANTS ON THE STRUCTURAL AND PHASE STATE OF THE DEFORMATION ZONE OF METAL TRIBOUNITS AND THEIR ANTIFRICTION PROPERTIES
Abstract
The results of experimental studies of deformation and diffusion in the surface layers of metallic frictional couples, which form the experimental and theoretical basis of the materials science approach to the quality evaluation of lubricants, are presented. The concepts of the component’s role for the lubricating medium in the implementation of the plasticizing and strengthening triboeffect are formulated. Structural condition characteristics for the surface layers of copper alloys during friction on steel in the mode of boundary lubrication in surface-active lubricants, are described. The conditions for achieving minimum power losses of such tribosystems for friction and wear have been found. The greatest service life of tribounit in a lubricating medium containing surfactants is resulted from wear resistance increase of a copper alloy with a relative decrease in hardness and increased plasticity of its surface layer. At the same time, a decrease in hardness due to the plasticizing effect of surfactants occurs only in the near-surface deformed layer of tribomaterial, while in its deeper layers with no plasticization resulted from a lubricating medium effect, the mechanical characteristics of the antifriction alloy remain at the required high level. It is demonstrated that alloys with a single-phase structure of an α-solid solution and a wide concentration range of solubility of the alloying element in the solid state meet these requirements. It is found that such boundary conditions are provided by the presence of stationary macroscopic diffusion flows of alloying elements in the zone of contact deformation of a polycomponent tribomaterial. The role of local diffusion phenomena in quasispinodal phase transitions is indicated. Examples of the selective transfer phenomenon during friction in industrial lubricants, are given.
Science intensive technologies in mechanical engineering. 2024;(12 (162)):3-14
3-14
IN ADDITION TO TENSION STRESS HAVING AN EFFECT ON THE INTENSITY OF PITTING CORROSION OF LOW-CARBON TUBULAR STEELS
Abstract
A significant part of accidents on trunk lines are ensured by metal corrosion. The most dangerous form of corrosion of trunk lines is location-action (pitting) corrosion of the inner wall of the pipe. An important factor in the corrosion process of the inner wall of a trunk line is the stress-strain state of the pipe metal, which impact on the intensity of pitting corrosion has been underexplored. This article presents the results of a study of the effect of tensile stresses on the intensity of pitting corrosion of low-carbon tube steels St3 and 08sk grades. As part of the study, corrosion tests of steel samples in stressed and non-stressed states were carried out, followed by determination of the depth of formed corrosion pits using a photometric technique. It is shown that for steel samples in a stressed state at a stress level of 0,7 with flow limit σT of the analyzed steels, the rate of pit depths increased 2,3 times for steel St3 and 1,2 times for steel 08sk compared with non-stressed samples, which significantly exceeds the value of a similar factor for the rate of general corrosion.At the same time, the obtained values of the mechanochemical coefficients also turned out to be higher than in case of a general corrosion – 0,0059 and 0,0014 MPa-1 compared to 0,0011. The authors explain the more intense effect of the stress state on the rate of pitting corrosion by the occurrence of stresses in the metal of the bottom part of the corrosion pits, which are significantly greater than the stresses occurring in the rest of the metal of the subsurface layer of the sample subjected to general corrosion.
Science intensive technologies in mechanical engineering. 2024;(12 (162)):15-24
15-24
PRODUCTION OF CERMET IN A COMBUSTION MODE BY MEANS OF INFILTRATION OF CU + TI MELT INTO POROUS TITANIUM CARBIDE
Abstract
Results for the interaction of a hot porous titanium carbide frame obtained in the mode of self-propagating high-temperature synthesis with a copper-titanium melt, are presented. The studies were carried out using two types of samples: without and with preheating up to 300 ºC before synthesis in a furnace. The samples were flat compressed tabs of stock material consisting of two layers with different composition. The lower layer was Ti and C stock, and the upper layer was a mixture of Ti and Cu. The process of sample synthesis was carried out in air. After the reaction took place in the lower layer of the samples and the formation of a porous titanium carbide frame, in both samples the upper layer melted and was absorbed into the lower layer unreservedly. X-ray phase analysis of the central part of the sample showed the presence of three phases – Ti, Cu and Cu3Ti. It was found that the resulting composite was a porous TiC frame impregnated with an alloy of copper and titanium. Titanium carbide grains had a largely non-stoichiometric composition and were polyhedral particles of an average size of 20 microns, as well as particles of stoichiometric composition with a size of no more than 10 microns. An intermetallic compound was found in some areas on the surface of TiC particles in the form of a thin film. In addition, it was found that preheating the initial sample in a furnace to 300 ºC before synthesis increases the content of stoichiometric titanium carbide in the obtained cermet.
Science intensive technologies in mechanical engineering. 2024;(12 (162)):25-30
25-30
Surface layer quality, contact interaction, friction and wear of machine parts
WEAR SIMULATION FOR ROLLING FRICTION WITH SLIDING MOVEMENT
Abstract
The paper views mathematical and numerical models of wear of elastomeric materials developed by the authors in dead rolling with sliding movement. When developing a mathematical model, classical ideas about the kinematic characteristics of a massive elastomeric tire rolling along the abrasive surface of the disc were used. To describe the intensity of wear, the model uses the concepts of wear formulated by D. Archard and modified in relation to the studied objects - rubber-based resin elastics SRI-3 and SRS-30–ARKM-15 rubbers reinforced with carbon nanostructures. The numerical implementation of the mathematical model is performed in the Matlab software package. In order to simplify the numerical calculation, it was decided to switch the rolling slip model to the pure sliding model. The choice of the integration step in time allowed to stabilize the instability of the solution. Thus, the numerical model examined sliding of an elastomeric cylinder along the abrasive surface of the disk at a speed equal to the sliding speed and varying the normal load. The finite element method (FEM) was used as a numerical calculation method. At a fixed depth of indentation, the verification of the developed model was carried out. According to the simulation results, the dependences of the wear intensity of an elastomeric material on the magnitude of specific pressures are obtained. A comparative analysis of the simulation results and the data obtained experimentally make it possible to determine the difference at the level of 20 percent, which may be due to the limitations of the model when thermal characteristics of the materials are not taken into consideration. Thus, the developed model has demonstrated its viability and will be further refined upon taking into account the identified limitations.
Science intensive technologies in mechanical engineering. 2024;(12 (162)):31-38
31-38
Technological support of operational properties of machine parts and their connections
THE EFFECT OF FINISHING ON THE WEAR RATE IN THE INITIAL PERIOD OF OPERA-TION OF CYLINDRICAL TRIBOSURFACES
Abstract
Increasing the durability of sliding friction pairs parts cannot be possible on a regular basis using more expensive structural materials or, moreover, applying special coatings which are obtained due to using plasma energy or vacuum technologies. It is known that shortening running-in period can significantly increase the surface area and, in addition, provide a more stable operation mode at the stage of the main service life of the product, due to specific conditions and operating modes.
Numerous attempts to access surface roughness parameters corresponding to the roughness parameters formed during normal wear-out period often did not lead to the desired results. As further research in this direction has shown, the time of the run-in period is spent on the formation of the surface layer structure under the influence of specified loads, slippage speeds, initial loads, grades of lubricants, etc. And the steady-state roughness parameters are stabilized only on the substructure characteristic of this pair. In the presented article, an attempt is made to use only the grain size of steel surfaces from the available variety of descriptions of the structural parameters of the parts surface layer. This decision is supported by the fact that the parameter is regulated by GOST 5639-82 (State Standard), and there is a proven method for determining it by using the appropriate hardware. Focusing on the grain size of the tribosurface, it became possible to show the potential of reducing the period of running-in through the conditions of technological influencing factors on the tribosurface.
Science intensive technologies in mechanical engineering. 2024;(12 (162)):39-45
39-45