Bulletin PNRPU. Mechanical engineering, materials science

The article presents the results of completed research and practical application of products with welded seams and protective coatings obtained by electron-beam welding, hardening and powder electron-beam surfacing in vacuum at the enterprises of the military-industrial complex. As a result of the complex analysis by the team of authors in the Problem laboratory of welding processes and creation of protective coatings of I. I. Polzunov AltSTU on the basis of more than 25 years of experience in the field of electron-beam technologies, the technology of electron-beam hardening of the most technologically complex piston aluminum alloys of the hypereutectic composition of the brand AK21M2,5H2,5 has been developed. The authors developed and successfully tested the technology of production of composite piston from high-silicon aluminum alloy AK21M2,5H2,5, made of two parts with their subsequent electron beam welding. Hardening with the melting of the working edges of the diesel for hot deformation of spray of diesel fuel allowed at JSC "Altaidizel" increasing of heat resistance surface 2 times. Actual is the practical use of the technology of electron-beam surfacing of high-alloy powder alloys based on the Ni-Cr-B-Si system for repair and restoration of worn surfaces of heavily loaded parts: crankshafts and camshafts of internal combustion engines, crosspieces, ball bearings, camshaft pushers, wheel hubs V-belt drives, propellers, etc. To create protective coatings on the sealing surfaces of the shut-off steam boiler and pipeline valves - saddles, plates and spheres the technology of direct electron-beam powder deposition in vacuum was proposed. The developed technologies can be recommended for implementation at the enterprises of the Altai region, specializing in the field of engine building, in the production of new or restoration and repair of worn parts and components for internal combustion engines.

The High Velocity Air Fuel (HVAF) thermal spraying process has been used to deposit cermet coatings, represented by WC-CoCr and WC-NiCr, onto a steel 40 substrate. The major objective of this study is to make a comparison between these two coatings to indicate their performance to resist the cavitation erosion-corrosion when tested using ultrasonic vibratory method. Scanning Electron Microscope (SEM) was used to characterize these two coatings. In addition, the profilometry of the substrate and the coated surfaces was conducted to indicate the initial state of the surfaces. The obtained results from the cavitation test showed that the coating by WC-NiCr has exhibited a better performance than that of WC-CoCr coating according to the test conditions. In this regard, total weight loss of WC-NiCr coating reached to 0.66% of the original specimen weight whilst it was about 0.82% for the WC-CoCr coating. SEM micrographs of the eroded surfaces of these three materials, substrate and two coatings, have evidenced that the surface of the WC-CoCr was more damaged than the surface of the WC-NiCr coating. The HVAF thermal spraying process can be effectively used in deposition the two coatings such that improvement of steel 40 up to 2.3 and 1.8 times has been obtained by applying the WC-NiCr and WC-CoCr coatings, respectively.

The methods of the theory of optimal control (Pontryagin's maximum principle, the method of moments) make it possible to set and solve problems of optimal control of technical and technological processes with constraints on control. This makes it possible to apply the methods of optimal control theory to optimize welding processes with restrictions on concentrated welding sources. Modeling of welding sources in a wider class of piecewise-continuous and piecewise-constant functions allows to describe with greater accuracy a whole range of high-concentrated sources that are generated by modern welding equipment and are used in welding technologies. In the modern theory of welding processes and technology of welding production, such heat sources are used for which the parameters can change without inertia. For example, in many welding sources (laser radiation, electron beam, electric arc), the power in a pulsed mode changes instantaneous, almost inertialess. And the heat sources generated by the electron beam are inertialess in controlling their movement, power, and focus. Therefore, taking into account the property of inertialess changes in the basic parameters (shape of the heating spot, power, power density distribution over the spot, etc.), the source model must be built in the class of discontinuous functions. This, in turn, allows us to formulate and solve problems of determination of optimal welding modes using the latest methods of the theory of optimal control. One of the main technological methods of forming welding sources with the required shape of the heating spot and the corresponding power density distribution is the oscillatory movement of a normal-circular source according to the line scan. In the case of line scanning, a normal-line source most accurately describes the uniform distribution of power density along the length of the heating spot and cross section. Discontinuity of the first kind at the boundary of the heating spot can be provided with an admissible error.

The significant problem in production of special hull structures is welding of high-strength and ultra-strength steels by a tensile strength of 800 MPa and more. High-strength alloy steels require a specific approach to the manufacture of welded structures in comparison with conventional low-carbon and low-alloy. The fundamental difficulty in this steel's type welding is the tendency to appearance of as cold and hot (crystallization) cracks, in addition to the formation of structural phases reducing the resistance to brittle fracture of weld-metal and HAZ metal. Another significant problem in high-strength steels welding is to obtain mechanical properties of welded joints comparable to the level of the base metal in the absence of welded structures heat treatment. Recently in body structures welding of high-strength steels is carried out using ferrite-perlite or austenitic types electrode metal. The general disadvantages of currently used special equipment welding technologies are the low mechanical characteristics of weld joints. The high-strength steel's weldability problem decision as well as the weld metal and HAZ metal mechanical properties improvement may be achieved by the optimal welding thermal cycles and the faithful determination of welding electrode materials. The present paper describes the main ways of high-strength steel weldability problem resolving, provided by the development of flux-cored wire. Moreover, article indicates the ways to improving the mechanical properties of the weld metal and HAZ. It was offered welding technology, taking into account the above peculiarities of plant's production. Listed measures allow cancel costly heat treatment process and obtain a defect free weld joints. It was established that defects in the form of cracks on the fusion line and in the HAZ during the metallographic examination of microsections were not detected. Developed cored wire with Fe-Cr-Mn-Mo-N doping system, containing up to 0.3 wt. % nitrogen, allows to obtain an austenitic structure in the weld metal with improved mechanical properties.

Features of structure formation of heat-resistant weld metal based on Ni3Al, deposited with different arc welding speeds with composite wire, were investigated. It was deduced from experiments, that the high-quality formation of weld metal under the condition of arc surfacing heat cycle is provided with range of its rate of energy input q = 8,5-33 kJ/cm. The energy component of value q is limited by the range of welding current I = 280-300 A and arc voltage U = 25-27 V, which provides close to the homogeneous melting of the components of composite wire contained the low-melting and refractory components and the largest values of their recovery effervesces in the weld metal. It was shown that under the conditions of surfacing heat cycle its speed should be limited to 16-18 m/h in order to prevent the formation of in excess t.d.p. phases. The weld metal structure is characterized by high enough dispersion of its two base components - γ+γ' the solid solutions, forming with eutectic and peritectic reaction participation. It was identified that the enhanced heat resistance of weld metal alloyed by ultrafine particles of carbide WC is reached due to its less tendency to the particle coarsening of γ' eutectic phase. Estimation of the heat resistance index K (proportion between sample weight after test and original specimen weight) showed, that investigated weld metal type more efficiently resists to chemical destruction of the surface during high temperature heating compared with alloys containing large amount of chromium (20 and more % w.t).

The performance characteristics of gearing are determined by the quality of the manufacturing surfaces of the mating gear wheels. With the help of a globoid diamond-abrasive worm, аmethod of tooth-honing of working surfaces of teeth has been developed. The profiling of the globoid worm is performed according to the technique used in the theory of gearing. For a given end profile of the part, the profile of the globoid worm with the given kinematics of coupling and the parameters of the globoid tool are calculated using the formulas for coordinates transformation and the equations of tangency (equation of geering). To create the treatment effort, the globoid tool must be embedded in the surface. In this case, the nature of the change in the profile of the part is determined by the new position of the globoid abrasive hone, determined by the deviations of the parameters of the installation of the globoid tool. The nature of the deviation of the profile of the part is determined theoretically from the perpendicular to the theoretical profile in the solving of the inverse problem of profiling The derived analytical dependences allow calculating the deviations of the actual profile from the theoretical one depending on the parameters of the globoid chon installation and determining the influence of each parameter individually or the complex effect of all parameters simultaneously. In the future, these dependencies can be used to determine the cutting forces in the contact zone of the globoid worm and the rotor of the positive displacement motor and then proceed to calculate the amount of material removal and roughness of the resulting working surfaces of the part, depending on the characteristics of the abrasive layer of the globoid worm. The considerable length of the contact line in the case of globoid gearing presupposes the development of a technique for determining the deviations between the real and theoretical profiles at different points of the contact line

The paper studies the problem of increasing the durability of wear of the feed and bending rollers of spring-coiling machines. The contact of the rollers with spring wire is considered as the frictional interaction of the “alloy steel - carbon steel” pair, in which, due to the nature of the work, the structure and chemical composition of the contact layers significantly change to form secondary structures with abrasive properties. Experimental modeling of the frictional interaction of samples of two grades of high-alloyed steels with carbon spring steel showed that the wear of alloyed steel can be significantly reduced by preliminary treatment with a magnetic field. It is assumed that the wear of alloyed steel is carried out by particularly hard secondary structures that arise during contact on conjugated carbon-steel. Special experiments on friction pairs "alloyed steel - carbon steel" with the measurement of the microhardness of friction traces showed that such structures are formed, and the magnetic treatment prevents this. According to the results of statistical analysis of a wide array of measurements, the manifestation in frictional contact of strengthening mechanisms not only of deformation nature, but also of mechanisms associated with chemical transformations and the formation of strong covalent bonds, which determine the abrasive properties of secondary structures, has been established. A series of tribotechnical experiments with spectral analysis and assessment of the chemical composition of friction traces on carbon steel revealed the crucial role of carbon mass transfer and carbide forming elements from conjugated alloyed steel, due to which solid secondary structures are formed on the surface of carbon steel. It is shown that additional carburization of the outer layers of its crystal lattice takes place, which, apart from traditional hardening due to its distortion, has a catalytic effect on the realization of chemical nature mechanisms in the form of formation of doped cementite, carbide phase and intermetallic compounds, despite the short duration of frictional contact. It is concluded that the effect of magnetic treatment consists in increasing the structural stability of the contact layers of the alloyed steel grating under frictional interaction with carbon steel due to the formation of an energy barrier for diffusional mass transfer of carbon and alloying elements inside the grating.