Bulletin PNRPU. Mechanical engineering, materials science

The issues of reliability and durability of the API thin-walled sucker rod pumps new for Russian Federation are considered. Here were reviewed real failures caused by corrosion fatigue of pump valve rod operating under cyclic loading in aggressive environment. A high set of mechanical properties as a satisfactory metallurgical quality cannot prevent fatigue failure, but only postpone it in time. Fatigue and its particular, even more dangerous form, corrosion fatigue, destroy structures in the most dangerous constructional places. Even in simple parts, the stresses in concentrators such as threads exceed more than five times the nominal stress level, which is away from the concentrator. The stress value is calculated both by the classical analytical method according to modified Inglis formula, and by modern methods of finite element analysis. At paper is presented a graphical diagram of the stress distribution. The maximum loaded microvolumes of the material are a tiny fraction of the total volume of parts. Corrosion fatigue, based on its corrosion nature, does not have an “dry” endurance limit due to growing corrosion damage in the form of pitting corrosion. Even small pits significantly increase the stress level at stress concentrators. The maximum stress of investigated pumps valve rods after corrosion increase for 29 % due to the formation of a simplified hemispherical pit at the root of thread. In reality, corrosion damage is irregular and appears to increase stress even more. Recommendations for the prevention of corrosion fatigue are given in the form of a list. They are actions of various levels of complexity, from practically not requiring additional costs to those requiring organizational development and subsequent maintenance.

One-component TiN and TiAlN coatings obtained by the PVD method have been studied. Microstructural analysis of coatings was carried out using an Ultra 55 microscope, structural analysis was carried out on a DRON-4 diffractometer, functional properties were studied on a Micro-combi tester and an AE-5 tribological setup according to the “finger-disk” scheme. Ion etching and microstructural analysis of the multilayer TiAlN - TiN - TiAlN coating was carried out on a Hitachi IM4000 setup. The physicomechanical and tribological properties of one-component coatings are determined depending on their phase composition and structural characteristics. The optimal phase composition of the TiAlN layer and the TiN layer, at which a high microhardness, resistance of the coating to deformations, and a low coefficient of friction are formed, have been revealed. So for the TiAlN layer, the optimal composition is to achieve the maximum volume fraction of the h-Ti3Al2N2 phase, and for the TiN layer, the optimal composition is to achieve the largest volume fraction of the c-TiN phase. The established dependences of the functional properties of TiN and TiAlN coatings on their phase composition, microstructure parameters served as the basis for designing a multilayer TiAlN - TiN - TiAlN coating. The alternating layers of TiAlN and TiN have optimal phase and structural characteristics and a set of high performance characteristics. Industrial tests of valves rods reinforced with multilayer TiAlN - TiN - TiAlN coatings were carried out under conditions of contact load, temperature and exposure to reagents of the working medium. The test results showed an increase in the service life of rods hardened by a multilayer TiAlN - TiN - TiAlN coating in comparison with unhardened ones by 3 ... 3.5 times.

Abstract In the article, based on the analysis of the results of experimental studies of the dependence of the cutting temperature and transverse shrinkage of the chips on the cutting speed, a method is given for assigning the cutting speed during rough turning and boring of large-sized parts of rocket technology from titanium alloy VT6, taking into account the provision of safe processing conditions based on regulating the amount of shrinkage of the chips. Unlike most structural materials, chip shrinkage in titanium alloys can be “negative”. That is, thinning of the shavings can occur. In some cases, this can be dangerous, since the formation of fine chips and, moreover, dust in the process of chip formation leads to its ignition with intense combustion. One of the main factors affecting the productivity of machining is the cutting speed, the higher the speed, the higher the productivity. However, when processing large-sized parts of rocket technology, the enterprise currently uses metal-cutting equipment that does not have a cooling system. Thus, in order to avoid the formation of "negative" chips and their ignition, it is necessary to carefully select the cutting conditions. As a result of the research, it was found that, depending on the assigned cutting speed, it is necessary to select the feed of the cutting tool in such a way that the thickness of the resulting chips, taking into account the amount of shrinkage of the chips, would be greater than 0.07 mm. To achieve the required roughness of the machined surface, in the case of an increase in the feed of the cutting tool, it is necessary to geometrically select the value of the rounding radius at the tip of the cutter.

The paper investigates a polarization-maintaining single-mode optical Panda type fiber with a quartz diameter of 80 microns, covered with a two-layer polymer protective coating (PC) with a diameter of 167 microns, which is used to manufacture the sensitive loop of a fiber-optic gyroscope. An intermediate test of the waveguide after fabrication is simulated: a fiber with a tension force of 0.2 N is wound in one row on an aluminum coil and subjected to thermal cycling according to a given law in the operating temperature range °C. Within the framework of the work, 7 variants of the ratios of the internal and external PC were considered while maintaining the total fiber diameter, taking into account the heterogeneous properties of structural elements, the viscoelastic properties of the PC materials and the contact interaction of the fiber with the coil without taking into account the friction on the mating surfaces. The considered temperature range partially includes relaxation transitions in both PC layers, which leads to the appearance of creep deformation and changes in many physical and mechanical characteristics of the material. The behavior of the PC materials is described by the theory of linear viscoelasticity by means of the Prony model; to take into account the effect of temperature on the properties of the PC materials, the temperature-time analogy described by the Williams-Landell-Ferry equation is used. As a result of numerical experiments, dependences are obtained that describe the evolution of the stress-strain state in the fiber, the maximum contact pressure at the interface, and the change in the refractive index in the light-conducting core. A change in temperature during a thermal cycle affects the stress-strain state (SSS) of the entire fiber and the light-conducting core for all the considered ratios of the PC. With an increase in the percentage of the inner layer, a more non-linear character of deformation behavior is observed. Relaxation transitions in materials affect not only the stress-strain state of the system, but also the contact pressure, which is associated with a continuous change in the contact interaction area under the influence of temperature. It has been found that the optimal thickness of the internal memory is in the range from 30 to 70% of the total thickness of the memory. An additional study of the effect of the thickness on the waveguide near the standard ratio of the thicknesses of the PC is required.

This paper presents the results of a study of the main regularities in the formation of the structure and properties of the heat-resistant titanium alloy VT-20 of the Ti-Al-V-Mo-Zr system in the repair technologies of argon-arc and laser powder surfacing. A significant disadvantage of recovery surfacing technologies is some structural features of the formation of the deposited material, in particular, the likelihood of non-fusion both along the border with the base metal and between the deposited layers, unfavorable structure, anisotropy, and, as a result, a decrease in mechanical properties. Laser powder surfacing was carried out on an MLS FL 040 installation based on a fiber-optic diode laser. Argon-arc surfacing was carried out on standard equipment. Structural studies of the deposited material, fusion zones between layers were carried out using light microscopy, quantitative metallographic analysis and tests of strength properties were carried out. The deposited metal microstructure consists of a lamellar α-phase, which is typical for pseudo-α-alloys with very low β-stabilization coefficients, which include the VT-20 alloy. The level of defectiveness of the deposited material, the morphology of the structure of the deposited layers have been studied. It has been established that the structure of the material deposited by laser technology has a significantly lower level of defectiveness of surfacings: no pores and cracks have been identified, and non-fusion areas are insignificant in length. It is shown that laser powder surfacing contributes to the refinement of the structure of the deposited titanium alloy, increasing the fineness of the α-phase plates, which is accompanied by an increase in microhardness to an average level of 250 HV. The technology of laser powder surfacing is proposed as the main repair technology for selected products made of titanium alloys.