VT6 Alloy Research Articles

Исследование стойкости пластин из сплава ВТ6 с линейно изменяющейся градиентной структурой к направленному высокоскоростному воздействию

The study results of the protective (barrier) properties of oxide and nitride coatings against the penetration of hydrogen during the thermal hydrogen treatment (THT) are summarized and the formation regularities of the linearly changing gradient structure of the VT6 titanium alloy are established. It has been found out that the finely dispersed (α + β) — structure on the surface formed as a result of THT provides increased strength properties, and the large-lamellar structure in the center provides high impact strength. It is shown that plates made of VT6 alloy of 12.5 mm thick with the linearly varying gradient structure demonstrate good dynamic resistance when fired with 5.45 mm and 7.62 mm jacketed bullets with a steel core.

Composition of surface layers of titanium VT6 alloy after implantation of tantalum ions

The paper presents the results of the investigation of the surface layer composition of titanium alloy VT6 obtained after ion implantation with tantalum ions. It is shown that tantalum ion implantation can lead to a significant reduction in surface roughness, as well as a beneficial effect on the corrosion properties of the titanium alloy.

Microstructure and Mechanical Properties of Titanium Alloy VT6 and VT20L Diffusion Joints

Microstructure and Mechanical Properties of Titanium Alloy VT6 and VT20L Diffusion Joints

Влияние состава электролита на процесс электролитно-плазменного полирования титановых сплавов

Electrolyte-plasma polishing (EPP), also known as electrolyte-plasma treatment (EPT) has become widespread in industry as an alternative to traditional chemical, electrochemical and mechanical methods of improving the surface quality of products made of metallic materials. EPP is an innovative technology used to obtain metal surfaces with low roughness and a high gloss. Electrolyte-plasma polishing is widely used in aerospace, biomedical, precision instrumentation and other. This work is devoted to the study of the effect of the electrolyte composition on achieving the effect of polishing titanium alloys during the implementation of the EPP process. The studies were carried out on the example of polishing a titanium alloy VT6 (Ti – 6 Al – 4 V) in a three-component aqueous electrolyte containing NaF, NH2OH·HCl and KCl. It was shown that, depending on the concentration ratio of NaF and NH2OH·HCl protolyte salts, either the formation of oxide films or their anodic dissolution in the presence of a ligand can be observed on the treated surface, with the production of a clean, non-anodized metal surface, accompanied by a decrease in roughness (polishing effect). It is established that the polishing effect is achieved at a certain ratio of NaF and NH2OH·HCl, which ensures the formation of hydrogen fluoride in it in an amount sufficient to dissolve the oxide films formed on the treated surface.

Горячий обжим крупногабаритных трубных заготовок

The generalized results of breaking-down modeling process of large-format pipe stocks made of titanium alloy VT6 are presented. Based on the simulation results of this operation, a static study has been undertaken, according to its results regression dependencies have been obtained, which contribute to assess the impact of a various parameter complex of this technology on the efficacy of the process.

Determining rational process parameters for selective laser melting of powder titanium alloy VT6

The current pace of development seen by the aerospace industry requires manufacturing techniques that would enable to make parts in the shortest possible timeframe and at minimum cost. Additive manufacturing technology, which is applied in blanking operations, should be described as an innovative area that ensures reduced labour intensity and manufacturing costs. Additive manufacturing technology allows to obtain blanks that are close to the geometry of the final part, i.e. near net shape parts. Additive technology makes it possible to produce unique hollow parts with sophisticated cooling channels of any shape, as well as mesh filter elements with the cell size determined by the size of the powder granules. Thus, printing of parts using metal powders would be of special interest for the aerospace industry. Selective laser melting (SLM) as one of the additive manufacturing areas is of relevance for the aerospace industry as it enables to obtain parts with a more sophisticated geometry in comparison with conventional technology. One of the key stages in the SLM process design that defines the mechanical properties of the synthesized material includes identifying rational parameters of scanning. This paper describes the results of a study that attempted to determine rational scanning parameters for powder titanium alloy VT6. Rational parameters of scanning were established through statistical processing of experimental data. Thus, they include the laser power of 275 W, the scanning pitch of 0.12 mm, the scanning speed of 805 mm/sec, with the layer thickness of 50 μm. The paper describes the results of a uniaxial tensile test carried out with cylindrical specimens produced at 0o, 45o and 90o to the dosing unit and at 0o, 45o, 60o, 90o to the base platform.The research work described in this paper was carried out by the staff of the Shared Knowledge Centre on its equipment using CAM technology; Agreement No. RFMEFI59314X0003.

Study of the destruction of the chassis main cross member made of VT22 alloy

The reasons for the destruction of the chassis main cross member made of alloy VT22 are considered and analyzed in bench test conditions. The chemical composition, mechanical properties, as well as macro- and microstructure of the material were studied. The tests of the cross-arm material for crack resistance and low-cycle fatigue (LCF) with the determination of the durability were carried out. The results of analysis proved that material meets the declared performance characteristics. A fractographic study of the traverse fracture showed that the fracture occurred from several foci according to the fatigue mechanism. The length of the longest fatigue crack was 1.7 mm and the critical stress intensity factor KIc was thus attained. Proceeding from the dimensions of the part at the site of fracture, the maximum crack length and the value of the critical stress intensity factor obtained experimentally KIc = 56.5 MPa • m1/2, we have calculated the nominal tensile stress at the moment of fracture. The calculated value of the nominal stresses is 1022 MPa, which is comparable to the yield strength of the material (1100 MPa). A high level of tensile stresses in the loading cycle is considered the most probable reason for the destruction of the chassis main cross member in the conditions of bench tests.

Protective properties of diffused chrome-calorizing coatings with TiN and Ti2AlN barrier layers on VT6 alloy

The results of the research of phase and chemical composition, structure and micro hardness of diffusion coatings, obtained by chrome-calorizing of VT6 structural titanium alloy, are presented. Chrome-calorizing was carried out at a temperature of 1050 °C for 4 h in powder mixtures of chromium, aluminum, inert additive and activator. As a result of saturation, multilayered coatings with the participation of nitrides TiN, Ti2AlN and intermetallic Al3 (Ti, Cr), Al2Ti, AlTi3 are formed. The micro hardness of TiN, Ti2AlN surface layers is 16.0–14.0 GPa, which increases the wear resistance of the VT6 alloy by 3.7 times. Moreover, it has been established that the presence of Ti2AlN and Al3 (Ti, Cr) phases increase the heat resistance of the VT6 alloy in the air atmosphere to a temperature of 700 °C.

TECHNOLOGY FOR RESTORATION AND REPAIR OF AIRCRAFT ENGINE PARTS

Problems of increasing the service life of compressor blades of aircraft gas turbine engines using detonation spraying technology are considered. The simulation of the parameters of the velocity and temperature of the particles of the sprayed material in the barrel of the detonation unit and in the flooded space to the substrate was carried out, followed by the choice of the optimal technological parameters of the spraying process. The control system of the detonation unit has been modernized. An experiment was carried out on the deposition of the Al2O3 coatings on the samples of a substrate made of titanium alloy VT3-1. Based on the results of the experiment, technological recommendations were developed concerning both the parameters of the spraying process and the parameters of the preparation of the substrate surface before spraying. The equipment for brazing the blades of the guide vanes is described and a device for spraying coatings on the end surfaces of the compressor blades is proposed. Thus, a complex technology has been developed for restoring the end surfaces of titanium alloy compressor blades by deposition of Al2O3 coatings.

Ускоренная оценка влияния технологических факторов на прочностные характеристики Ti-6Al-4V И Al-Cu-Mg

Introduction. The strength of construction materials when used under cyclic loads is of great importance in design engineering. A significant number of factors that affect the fatigue resistance have predetermined the creation of numerous methods that consider such influence. Nondestructive methods that are based on the connection of the physical degradation of material with strain properties enable evaluating experimentally the fatigue properties of materials. Purpose of study: the analysis of the processes of energy dissipation and strain accumulation during the inelastic cyclic strain of samples, using the VT6 (Ti-6Al-4V) titanium alloy and the D16 (Al-Cu-Mg) aluminum alloy before and after the technological impact. The work experimentally investigates the physical processes of degradation of the VT6 and D16 alloy samples that accompany the process of fatigue failure in materials with homogeneous and inhomogeneous stress-strain states in the concentrator (in the form of a hole and a weld). Typical modes are used to reach the fatigue testing that determine the critical stress in a material sample – the stress at which physical properties (temperature, strain) change without reaching the fatigue failure of samples. Critical stress amplitudes in the cycle, based on the data obtained during the experiment and the results of mathematical simulation, are compared. The effect of stress concentrators on critical loads that a detail can withstand after a unit operation is estimated by the finite-element method (FEM). As a result, the effect of the operational and technological factors on critical stress determined by strain and temperature is estimated. Comparative tests of the VT6 and D16 alloy samples with and without stress concentrators showed that the amplitudes of critical stress decrease by more than 30% in comparison with the ones that are without stress concentrators. The low-cycle fatigue tests of the D16 alloy samples are carried out. Mathematical simulation of the cyclic strain of the samples is carried out using MSC.Marc package. The results of the cyclic loading tests, which show that the characteristics of the technological process reduce the amplitudes of the critical stress of the VT6 and D16 alloys and affect the fatigue properties of the D16 aluminum alloy, are discussed. Mathematical simulation corresponded positively to the experimental data. Such correspondence indicates the possibility of conducting qualitative numerical assessments of the beginning of the inelastic strain accumulation process in structures with stress concentrators under the cyclic stress and the increasing stress amplitude, using the typical sample made of hardening elastoplastic material.

Influence of the Sintering Conditions on the Structure, Phase Composition, and Porosity of Titanium Alloy VT6 Parts Formed by Powder–Polymer Injection Molding

Influence of the Sintering Conditions on the Structure, Phase Composition, and Porosity of Titanium Alloy VT6 Parts Formed by Powder–Polymer Injection Molding

Microstructure and Mechanical Properties of Materials Formed by Diffusion Bonding of VT6 Alloy Parts Produced by Rolling and Selective Laser Melting

Nowadays, the rapid development of the new methods of assembling large-scale parts consisting of several materials elaborated by different manufacturing methods is observed. These materials are unique in terms of the mechanical and physical properties of the part. Diffusion welding is one of the most promising multipurpose assembling techniques allowing the formation of lowporous high-quality welding joints with stable mechanical properties and absence of oxide inclusions. This method is widely applied for assembling titanium alloy parts requiring the welding in a vacuum due to the high chemical activity of titanium in the normal atmosphere containing oxygen, nitrogen and hydrogen. In this work, the structure and properties of parts produced from Ti6Al4V titanium alloy by the combination of laser powder bed fusion, hot rolling and diffusion welding were studied. The diffusion welding was performed in an autoclave (at temperature T = 920 оC, pressure 4 MPa, holding time of 4 h) and hot isostatic pressing (at temperature T = 930 оC, pressure 100 MPa, holding time of 2 h). It was shown that the microstructure of the weld joint depended on the welding method (autoclave or HIP). No defects in the zone of diffusion joints were observed in both cases. The impact toughness of samples obtained during hot isostatic pressing is higher than for the samples obtained in an autoclave. Both types of welded samples had high mechanical properties and met the requirements of GOST 23755–79 standard for bulk titanium samples.The authors would like to thank V. V. Cheverikin, Candidate of Technical Sciences, MISiS, and P. V. Petrovskiy, Candidate of Technical Sciences, MISiS, for conducting metallography studies and discussing the results. This research was funded by the Ministry of Science and Higher Education of the Russian Federation. Within the framenork of the Government Resolution No. 218 based on the Agreement on subvention assignment No. 075-11-2019-058 dated 25.11.2019 “Establishing a production line for locally reinforced titanium alloy components designed to operate under high loads and temperatures as a part of innovative gas turbine engines“.

Influence of the beam oscillation parameters on the porosity of electron beam freeform fabricated titanium alloy SPT-2

The effect of electron beam oscillation on the formation of metal during electron beam freeform fabrication has received practically no attention. Nevertheless, it is a variable technological tool that allows to significantly influence the formation of metal during EBFFF process, including the probability of defects formation. The effect of the focus current, the form, and the frequency of the beam oscillation on the formation of pores in single beads by method of electron beam freeform fabrication of the titanium alloy SPT-2 on the substrate of the alloy VT6 was investigated. The porosity of the obtained beads was studied using x-ray images. It was found that too deep an arrangement of the focal plane relative to the substrate surface leads to excessive pore formation. Reducing the oscillation frequency from 1000 Hz to 100 Hz made it possible to completely get rid of the pores in the metal. The use of a spiral-shaped oscillation made it possible to reduce the probability of pore formation in comparison with an oscillation in the form of concentric circles.

Effect of Metal-Powder Composition Fraction and Layer Thickness on Structure and Mechanical Properties of Alloy VT6 Synthesized Material Prepared by Selective Laser Melting

Effect of Metal-Powder Composition Fraction and Layer Thickness on Structure and Mechanical Properties of Alloy VT6 Synthesized Material Prepared by Selective Laser Melting

Features of the hydrogen distribution in a weld seam made by electron beam welding of titanium alloys

ABSTRACT This paper presents the research results of the hydrogen distribution in welded joints made by electron beam welding of titanium alloys VT20 and VT23. The distribution of hydrogen in the cross-section of welded joints is measured in the following zones: the weld seam, the heat-affected zone and the base metal by means of through the use of spectral analysis through the use of a low-voltage pulse discharge on an ISP-51 spectrograph. It was found that hydrogen peaks in permanent joints made by electron beam welding, in contrast to argon arc welding, are located not only in the heat-affected zone, but mainly in the central part of the welded joint. Chemical analysis of the permanent joints fractures, investigated through the use of a electron-scan microscope HitachiS-3400N, established that pores in welded joints made by electron beam welding arise as a result of desorption into the melt of capillary-condensed contaminants located in defects at the ends of the edges, due to the occurrence a solid-phase compound in front of a molten bath. It is found that the changes in the hydrogen content with the formation of defects render next influence: temperature conditions for heating of the welded edges, the welding speed and the thickness of the welded blanks.

Пути повышения свойств заготовок деталей ГТД из жаропрочных титановых сплавов, полученных методом прямого лазерного выращивания

Today, additive technologies for the production of billets from heat-resistant titanium alloys are used in aircraft engine building and the aerospace industry. However, the mechanisms of structure formation and the level of mechanical properties in such blanks are poorly understood and are of interest. Currently, available data are not sufficient for the confident application of additive technologies in the production of aircraft engines. This paper evaluates the microstructure and substantiates the possibility of improving the mechanical properties of workpieces of GTE parts made of VT20 titanium alloy, obtained by laser-powder additive surfacing. For research, workpieces with a size of 215x120x4 mm 120x85x14 mm were grown. As a "building" material, a powder of spherical shape of particles was used, the chemical composition of which corresponds to the alloy VT20. The research results showed that during laser-powder growth in the VT20 alloy, the formation of "hardening" structures is observed, due to the accelerated heat removal into the previously formed layer of cast metal. In this regard, the strength of the alloy sharply increases, and its impact toughness and relative narrowing decrease. Note that stress relief annealing after growing (T = 750 ± 10 ° C, holding time - 1.5 ... 2.0 h.) does not significantly affect the level of mechanical properties. When the annealing temperatures rise to critical levels, significant structural changes are observed in the VT20 alloy, which in turn affects its mechanical properties. Based on the analysis of microstructures and the results of mechanical tests after distinct types of heat treatment (800 ° C, 850 ° C, 920 ° C, holding time - 60...75 min.), it was found that an increase in the plastic properties of the VT20 alloy is observed when the samples are heated to temperatures close to the temperature of the polymorphic transformation (960...1000 ° C). Annealing of workpieces after surfacing according to mode T = 920 ± 10 ° C, holding time - 60...75 min. allows to somewhat reduce the strength characteristics of the VT20 alloy, while increasing its impact strength and relative narrowing.

Мікроструктура сплаву ВТ8 після випробувань на малоциклову втому

Specimens of titanium alloy VT8, which is used for the manufacture of gas turbine engine elements, were investigated in the initial state and after fracture toughness testing by methods of transmission electron microscopy and diffraction analysis. The features of the microstructure, structure morphology, the nature of phase distribution and structural components were established. Defects in the crystal structure, the formations of dislocation inhomogeneities and local concentrators of internal stresses were identified using JEM-200CX transmission electron microscope. The scalar dislocation density is determined by the secant method. The study of VT8 titanium alloy samples before and after destruction, which is used for the manufacture of GTE elements, using the methods of transmission electron microscopy and diffraction analysis was made. Microstructural investigations for a detailed analysis of the structure features, morphology and phase formations distribution, as well as their components establishment, the nature of crystal lattice defects, the formation of dislocation inhomogeneities and local concentrators of internal stresses were performed on a JEM-200CX transmission electron microscope. The scalar dislocation density was measured by the secant method. It is shown that the studied samples of VT8 titanium alloy are characterized by a two-phase (α + β) microstructure in the form of large -phase plates, 0.15 ... 0.76 μm in size, interspersed with an insignificant amount of thin-plate β-phase, with a size of 0.04 ... 0.21 μm. Based on scalar dislocation densities, the level of local internal stresses in the places of dislocation accumulations, which are sources of crack formation, was analytically estimated. Dispersed particles of secondary phases characterized by different sizes and different structure morphologies were identified. The calculated dislocation densities and an estimate of the average distance over which they move in the process of deformation are used as the basis for creating a statistical map of localized deformation level indicators in the alloy structural components and on the fracture surface. It is shown that as a result of fracture after testing for low-cycle fatigue, the dislocation density increases, the level of local internal stresses increases, and the formation of a cellular structure in the α- and β-phases and deformation grain-boundary defects occurs. Keywords: VT8 alloy, dislocation structure, microstructure, transmission electron microscopy, local internal stresses.

Increasing the efficiency of technological preparation for the production of the manufacture components equipment for the mineral resource complex

An increase of components production for the equipment intended for oil and gas production is a key factor for analyzing existing technological processes and searching for new technological solutions to improve the efficiency of the production process and the quality of components. The article presents a simulation model designed to determine the rational technological processing parameters for the production of the “Centralizer shell” part. The basis for optimizing the working cycle of a production line is synchronization based on the principle of proportionality, which involves equalizing the duration of all technological operations with the rhythm of the production line. Synchronization of technological operations on the production line is carried out by choosing rational cutting parameters for each technological transition (cutting speed, feedrate, number of working passes). The “Centralizer shell” part is made of titanium alloy VT16, which has high strength, corrosion resistance and ductility. For the part under consideration, the permissible values ​​of the cutting parameters were determined based on the calculation of the total processing error, as well as the frequency of replacement of the worn cutting tool. The simulation model described in the article made it possible to increase the efficiency of the production process due to the synchronization of technological operations and the search for rational technological parameters, as well as to improve the manufacturing quality of the “Centralizer shell” part by analyzing the processing error at various parameters of the technological process.

Оксидный поверхностный слой и твердофазная свариваемость титановых сплавов

It is known that the ultrafine-grained (UFG) structure in alloys is thermally unstable. An important task for the modern aviation engineering is to preserve the UFG structure in parts for responsible purposes after their production in order to maintain the high level of their mechanical properties. In particular, the solution to this task necessitates the reduction of the temperature of solid-phase bonding while ensuring the necessary quality of the permanent joint. It is known that along with the average grain size, the oxide surface layer can also significantly affect the solid-phase weldability of titanium alloys at low temperatures, but the latter has been extremely poorly studied. In this regard, the influence of an oxide film is considered for domestic two-phase titanium alloys VT6 (Ti-Al-V system) and VT8 (Ti-Al-Mo system), which differ in the main alloying element for the stabilization of the β-phase. As a result of the experiments, the absence of an oxide layer in the zone of solid-phase connection of the ultrafine-grained (UFG) VT6 alloy after welding in vacuum at a reduced temperature of 600°C was metallographically revealed. This has a positive effect on the quality of welded samples according to the conducted mechanical tests. A continuous oxide layer was found in the solid-phase joint zone after welding at a temperature of 600°C for the UFG alloy VT8. The experimental results indicate that the UFG titanium alloy VT6, doped with relatively “mobile” vanadium, has the potential to reduce the lower temperature of solid-phase welding in vacuum by 50°C in comparison with the titanium alloy VT8.

Structure and Properties of TiN–Pb Magnetron Coatings on VT6 and 12Kh18N10T Alloys

Structure and Properties of TiN–Pb Magnetron Coatings on VT6 and 12Kh18N10T Alloys