VT6 Titanium Alloy Research Articles

Development of a method for assessing the degree of hydrogenation of titanium alloy VT1-0 by acoustic method

In this paper, the possibilities of using a non-destructive acoustic method to determine the degree of hydrogenation of titanium alloy VT1-0 are investigated. The features of the use of various acoustic parameters for the construction of engineering techniques for determining the structural state of a titanium alloy at various stages of its hydrogenation are analyzed. A number of computational and experimental methods for determining the mass fraction of hydrogen in a titanium alloy are proposed, based on the use of its acoustic characteristics, which increase the accuracy and stability of the algorithms underlying the calculation part of the methods. The sources of errors of the proposed methods, the limits of their applicability, as well as the requirements for hardware and software for their implementation are analyzed. The results of acoustic measurements carried out on samples from the VT1-0 alloy are compared with the ideas about the patterns of its structural changes during its hydrogenation. The possibility of creating engineering algorithms for assessing the state of the material of products subjected to hydrogenation on the basis of experimental data obtained in order to prevent dangerous degradation of its operational properties is shown.

NEW METHODOLOGIES FOR ASSESSING CAVITATION LOAD AND RESISTANCE OF STRUCTURAL MATERIALS AND PROTECTIVE COATINGS IN NUCLEAR POWER INDUSTRY. PART I. MONOFRACTIONAL APPROACH

The paper presents a new method for assessing the cavitation load and durability of structural materials and protective coatings. To determine the cavitation load on a rotating disk or other test rig, a new method for extracting erosion loads based on tests of reference materials on a reference cavitation rig is proposed. Direct measurements of the cavitation load in a cavitation tunnel with a slot cavitator, performed using piezoelectric sensors, made it possible to obtain information on the spatial distribution of the impact load. As an analytical function for modeling cumulative erosion curves in the monofractional approach, the logarithmic formula of L. Sitnik is used, assuming that cavitation erosion is a stochastic process described using fatigue theory. Armco iron is chosen as a reference material, in view of the weak dependence of its erosion rate on cavitation qualitative features. Therefore the local load value could have been extracted from the eroded surface profile of the Armco iron sample. Using the example of TiN coating analysis on stainless steel and VT3-1 titanium alloy, the time dependencies and threshold characteristics of their resistance were determined depending on the parameter of the density of the supplied energy.

Горячее деформирование корпусных заготовок в изотермических условиях

Core operations with hollow products, having a periodically changing internal profile, consists in the final machining of press forgings. However, at the same time, metal rejects are high, and despite the high quality of the products obtained, their mechanical characteristics do not always meet the requirements of functioning. For the equipment units, when subjected to heavy loads, the parts are usually made of high-strength materials. Due to the complexity of the work on a workpieces made of high-strength alloys, operations are carried out with heating of the deformed zone of the in-process part or with a total heating. The use of slow deformation in the hot state under certain speed conditions is promising. The process of the internal pattern formation for hollow shells made of titanium alloy VT6 is viewed. These products are mainly used as various airframes and are made using special methods of mechanical engineering. Due to the use of high-strength billet materials, there are difficulties with the mechanization of the production methods. The article evaluates force conditions for generation of geometry on the shells based on CAE modeling. The simulation was performed in the deform complex. The focus of the research was on the assessment of deformation forces and stress intensities. The influence of deformation ratio, strain rates, punch geometry on the strength of the process and stress intensity has been revealed. A regression equation to estimate the forces of the process is deduced. Recommendations on the design of fillets forming operations have been obtained. Deformation modes aimed at achieving rational power modes, respectively, loads on the tool, which indirectly affects its durability, as well as the stress condition in the product, have been found.

INFLUENCE OF WELDING PARAMETERS ON THE PERFORMANCE CHARACTERISTICS OF THE THERMOCATODES

Methods of controlling welding parameters, physical and physico-chemical transformations that occur during welding are considered in the work. The physico-chemical mechanism of welding is considered - the deformation of the crystal lattice, the transfer of metal on the contacting surfaces, the mixing of deformation products, diffusion, phase transformations, the appearance of new chemical compounds - intermetallics, oxides, carbides. Studies of the influence of the main parameters of friction welding on the formation of the structure of the welded joints of the investigated alloys have been carried out. The microstructures of welded joints OT4 + VN-2AE and VT6 + VN-2AE are given. The obtained dependence of the relative strength of the OT 4 + VN-2AE connection on the parameters of the welding process. The given microstructures were obtained by SEM from the surface of OT 4 + VN-2AE and VT6 samples, based on which it was determined that the destruction begins with the formation of microcracks in the contact zone on the side of the VN-2AE niobium alloy. It was determined that a layer saturated with oxygen is formed in the diffusion zone due to which the β-modification of Ni2O5 with a significant specific volume is formed, which causes high internal stresses and the formation of microcracks. The reason for the decrease in the mechanical properties of the welded joint OT 4 + ВН-2АЕ was established - the formation of a phase (Ti-Nb) with an orthorhombic lattice, the degree of curvature of which determines the degree of strengthening of the layer and depends on the niobium content. These data are confirmed by X-ray structural analysis. The analysis of the concentration curves of niobium and titanium shows that titanium does not diffuse into the narrow contact zone of the niobium alloy, and niobium forms a wide diffusion zone in the contact zone of the OT 4 alloy. It was established that niobium contributes to the increase in the solubility of aluminum in λ-titanium, which leads to increase in weldability plasticity and corrosion resistance. It was determined that the low mechanical properties of the welded joints of the VN-2AE alloy with the OT-4 and VT-6 titanium alloys are due to the same nature - the oxidation of the niobium alloy at the welding temperature. It was established that the weak link of the welded joint is the surface of the niobium alloy.

Влияние технологических параметров процесса прямого лазерного выращивания на качество формируемого объекта из титанового сплава ВТ23

Introduction. Laser engineered net shaping (LENS) or Direct metal deposition (DMD) is considered as a promising method for manufacturing products of complex configurations from titanium-based alloys, as it allows minimizing the use of machining and loss of material to waste. Currently, neither the LENS technological process of titanium alloy VT23 has not been developed, nor the structural features of the alloy after LENS have not been studied, which will make it possible to determine the scope of application of the material after LENS. The purpose of this study is to determine optimal modes of the LENS process for manufacturing of quality parts from titanium alloy VT23. Methodology. The alloy specimens obtained with laser power 700÷1300 W in increments of 100 W and scanning speed 600÷1,000 mm/min in increments of 200 mm/min and distance between adjacent laser tracks 0.5–0.9L (L — track width) in increments of 0.2L were analyzed in the study. The elemental composition of the powder material was studied by X-ray fluorescence analysis and reducing combustion in a gas analyzer, the structure of the objects obtained by LENS was analyzed by metallographic and X-ray phase analysis methods as well as microhardness was determined. Results and discussion. It is established that high-quality objects without cracks, with low porosity can be synthesized from VT23 alloy by LENS method using the following modes: laser power 700÷1100 W, scanning speed 800–1,000 mm/min, track spacing 0.5–0.7 of the individual track width L. It is shown that after all investigated LENS modes, the VT23 alloy had a dispersed (α+β) structure of the “basket weave” type. It is revealed that regardless of LENS mode the amount of β-phase in the alloy structure is about 30 %. It is shown that the microhardness of the deposited material does not depend on LENS modes and is 460 HV.

Effect of Structural-Phase State on the Deformation Behavior and Mechanical Properties of Near β Titanium Alloy VT22 in the Temperature Range 293–823 K

Effect of Structural-Phase State on the Deformation Behavior and Mechanical Properties of Near β Titanium Alloy VT22 in the Temperature Range 293–823 K

Effect of Hydrogen on the Development of Deformation and Fracture in Titanium Alloy VT22 in the Temperature Range of 293–823 K

Effect of Hydrogen on the Development of Deformation and Fracture in Titanium Alloy VT22 in the Temperature Range of 293–823 K

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ РАСПРЕДЕЛЕНИЯ НАПРЯЖЕНИЙ В СТЕНКАХ КОНУСНЫХ ИМПЛАНТАТОВ ИЗ СПЛАВА ВТ6

Today, an interdisciplinary approach to solving the problems of implantology is the key to the effective use of intraosseous dental implants. The possibilities of preclinical modeling of the state of bone tissue and the future implantation and prosthetic beds allow us to assess the possible risks of implant rejection, calculate the necessary tightening force of screws in implantation systems and predict the points of application and stress distribution of dental implantation materials, taking into account the latter, the desire to improve modeling will allow us to obtain a predictable treatment result. In this study, a mathematical model of the stress distribution on the walls of a conical implant was investigated, taking into account the physical properties of the VT 6 material, an assessment was carried out using the example of computer models with embedded alloy characteristics, and the Mises distribution indicators were calculated. It is worth noting that the VT6 alloy has a very high quality, thanks to alloying additives. This titanium alloy includes aluminum, which has a beneficial effect on the strength of implants, as well as vanadium, which can increase the strength of the metal and make it more ductile. Titanium alloy VT6 has characteristics that are comparable to those of stainless steel, due to which it is considered as an inert metal for use in the oral cavity. The novelty of the proposed model lies in the fact that it operates with the minimum possible set of input data and provides adequate estimates of the most significant output parameters that are necessary for practical application. The obtained analytical results are illustrated by examples of calculating equivalent stresses in implants and peri-implant tissue for real structures of the future orthopedic prosthesis.

Effects of ion-plasma treatment temperature of the aluminium coating on the structure and phase composition of the VT6 titanium alloy

In this study, we studied the effects of aluminum coating treatment temperature on the microstructure and phase composition when applied to a VT6 titanium alloy substrate within a low-pressure arc discharge plasma environment. The ion-plasma treatment was conducted at 450 and 500 °C, employing argon shielding, while the aluminum coating was deposited using the vacuum-arc process, resulting in a coating thickness of ~3 μm. Microstructural analysis was performed using a scanning electron microscope, and the structural and phase composition were examined using X-ray diffraction (XRD) imaging in symmetric imaging mode with CuKα radiation. Our findings demonstrate that the application of the aluminum coating initiates the formation of a near-surface α-stabilized layer, extending up to 2.5 μm in thickness due to the heat generated during the ion cleaning process. Subsequent ion-plasma treatment further results in the development of a TiAl3 intermetallide site, reaching thicknesses of up to 1.5 μm, while the α-stabilized region expands to 5.5 μm. Higher temperatures during the treatment process contribute to an increase in the thickness of these aforementioned layers and also lead to the emergence of an intermediate TiAl intermetallic layer.

Experimental and theoretical study on high-temperature creep of VT6 titanium alloy under multi-axial loading conditions

In the framework of damage mechanics, we discuss a new mathematical model that describes the kinetics of the stress–strain state and damage accumulation during material degradation by the mechanism of long-term strength under complex multiaxial stress state. An experimental and theoretical technique is proposed for determination of material parameters and scalar constitutive functions for damaged media based on specially set experiments on laboratory specimens. The results of experimental studies and numerical simulations of short-term high-temperature creep of VT6 titanium alloy under uniaxial and multiaxial loading are presented. Numerical results are compared with the data obtained through experiments. Particular attention is paid to simulating the process of unsteady creep for complex deformation modes, accompanied by rotation of main areas of stress, strain and creep strain tensors. It is shown that the developed version of the constitutive relations of the damaged media enables us to describe the processes of unsteady creep and long-term strength of structural alloys under multiaxial stress with the accuracy sufficient for engineering calculations.

Electrospark Deposition of Ti – Al – Cr – B Coatings on Titanium Alloy VT3-1

Electrospark Deposition of Ti – Al – Cr – B Coatings on Titanium Alloy VT3-1

A study of cavitation erosion resistance of an ion nitrided titanium alloy by means of the vibration and rotating disk methods

In this work, a comparative analysis of the cavitation erosion resistance of the Ti–6.7Al–2.5Mo–1.8Cr–0.5Fe–0.25Si alloy (known as brand VT3-1) before and after low-temperature ion nitriding is carried out. Two test methods were applied, using vibrative (ASTM G-32) and rotating disk rigs, respectively. The kinetic dependences of the erosive destruction of samples of titanium alloy VT3-1 in the initial state, after ion nitriding and stainless steel AISI 321 were obtained. A study of the microstructure, hardness and surface morphology was carried out. The samples were examined using optical and scanning electron microscopy. The relationship between mass loss and cavitation erosion duration was experimentally determined and analyzed. The erosion rate on a rotating disk stand is much higher than during vibration tests. A large cavitation load gradient provides additional opportunities for analyzing the durability of materials and coatings using this method.

CREEP OF VT1-0 TITANIUM ALLOY IN DIFFERENT STRUCTURE STATES AFTER IRRADIATION WITH HELIUM IONS

The effect of irradiation with helium ions at T = 350°C with an energy of 20 keV and a dose of 1.5·1018 Не/cm2 on the structure and properties of VT1-0 titanium alloy in the initial and nanostructural states was studied. It has been shown that irradiation of VT1-0 samples in the initial state leads to a decrease in mechanical properties when tested under creep conditions at T = 350 °C, which may be due to dynamic recovery. A material in a nanostructured state is characterized by an increase in strength and creep rate at a test temperature of T = 350°C, while maintaining a plasticity reserve. The effect is associated with the structure rearrangement, grain growth and the development of strain hardening processes as the effective stress increases.

Влияние концентрационно-временных условий наводороживающего отжига на насыщение водородом титанового сплава ВТ23

Kinetics of the processes of volumetric and surface unidirectional absorption of hydrogen by two-phase (α+β) — titanium alloy VT23 (Ti—Al—Mo—V—Fe—Cr) at a temperature of 800 °C in the concentration range from 0.2 to 0.8% (wt.) has been studied. It is established that by varying the concentration of introduced hydrogen during volumetric hydrogenation annealing, it is possible to form structures in the volume from three-phase (α+α′′+β) to single-phase β. It is shown that by changing the conditions of hydrogenation and using barrier coatings, it is possible to control the depth of hydrogen penetration and, consequently, the completeness of the α→β transformation, forming a unidirectional gradient structure changing from (α′′+β) at the side of the «entrance» of hydrogen to (α+β) at the opposite one. It is noted that the absorption of 0.6% (wt.) hydrogen during unidirectional surface hydrogenation proceeds 20 times slower than during volumetric hydrogenation. It was established that with unidirectional surface hydrogenation, the hydrogen content in the near-surface layers was 0.2% (wt.) higher than the introduced hydrogen concentration calculated for the sample volume.

ESTIMATION OF FATIGUE CURVES USING ORTHOGONAL POLYNOMIALS

The article proposes a methodology for processing fatigue tests carried out to assess the fatigue curve of materials and structural elements, the most important design characteristic of the endurance, service life and reliability of aircraft products, transport engineering and other structures operating under conditions of both regular and irregular loading. The task of estimating the parameters of the fatigue curve is often complicated by the limited scope of fatigue tests, significant scattering of cyclic durability, uneven duplication of experiments at a given level of alternating stress amplitudes, the presence of censoring, especially at low levels, and other factors. which necessitates the use of the weighted least squares method. These circumstances lead to the violation of the conditions for using standard methods of regression analysis and the least squares method. This is especially true for the confidence assessment of the fatigue curve, the accuracy of which significantly depends on these factors. For this purpose, the article proposes to apply the procedure of orthogonalization of factor characteristics to estimate the parameters of the fatigue curve, which reduces the errors arising from standard approaches and makes it possible to obtain accurate confidence intervals for durability. A special feature of the technique is the use of orthogonal polynomials in statistical procedures, which makes it possible to modify the covariance matrix of estimates by converting it to a diagonal form, regardless of the spread of the weight parameters of the original data. These transformations make it possible to perform statistical procedures for point and confidence estimation when processing the results of fatigue tests. To test the methodology, a statistical analysis of a large volume (about 200 samples) of fatigue tests of samples with varying degrees of stress concentration from titanium alloy VT3-1 and aluminum alloy V-95 was performed, algorithms and computer programs were developed in the public domain.

EFFECT OF STRUCTURAL-PHASE STATE ON THE DEFORMATION BEHAVIOR AND MECHANICAL PROPERTIES OF NEAR β TITANIUM ALLOY VT22 IN THE TEMPERATURE RANGE 293-823 K

This paper investigates the effect of thermomechanical treatments, including deformation by radial shear rolling or severe plastic deformation by abc pressing with subsequent aging at 773 K, on the structural-phase state, deformation behavior and mechanical properties of commercial near β titanium alloy VT22 (Ti-5Al-5Mo-5V-1Cr-1Fe). The structure of the alloy after radial shear rolling and subsequent aging consists of transformed β grains with a lamellar α + β structure and primary α-phase particles. Severe plastic deformation of the alloy followed by aging causes the formation of a grain-subgrain α + β structure with an average characteristic size of 0.23 µm. It is found that after the thermomechanical treatments, the strength characteristics of the alloy at room temperature increase by ~40% compared to the as-received alloy. The alloy after radial shear rolling and aging retains a 40-20% higher strength in the temperature range of 293-823 K. The strength of the alloy after severe plastic deformation and aging becomes lower than that of the as-received alloy already at a temperature of 773 K. Analysis of creep parameters at 743 K shows that the creep deformation of the alloy in the state after radial shear rolling and aging occurs by the motion of dislocations (glide + climb). The creep deformation of the alloy in the state after severe plastic deformation and subsequent aging is largely contributed to by grain boundary sliding.

RELATIONSHIP BETWEEN STRESSES FOR THE BOUNDARIES OF SCALE LEVELS OF FATIGUE DIAGRAM AND THE DIFFERENCE OF THE MESOAND MACROSCALE FRACTURE MECHANISMS

Statistical data analysis was performed based on the results of standard tests with metallic materials. The relationship was found between the so-called fatigue limit, which is considered as the transition boundary between microand mesoscale fatigue fracture processes, and mechanical characteristics under monotonic tension. Using heat-resistant alloy EI698 and titanium alloy VT22 as examples, it was shown that the mechanisms of fatigue crack initiation and growth in materials with different ratios of fatigue strength to yield strength are different. The mechanism of slip band formation determines the fatigue crack initiation and its early growth stage for materials with a σ-1/σ0.2 ratio close to 1 and higher, as was shown for EI698. For materials with a σ-1/σ0.2 ratio below 1, the fatigue crack initiation is associated with mechanisms other than slipping, as demonstrated for VT22.

Формирование градиентных структур в титановом сплаве при обратимом легировании водородом

The possibility of transforming a large-plate structure and creating a gradient structure in samples of titanium alloy VT23 during thermal hydrogen treatment has been studied. It is shown that by varying the concentration-time parameters of hydrogenation annealing, it is possible to regulate the depth of hydrogen penetration and purposefully form the structure of near-surface layers. Subsequent low-temperature vacuum annealing makes it possible to transform the coarse-plate structure into a finely dispersed one with a hardness of up to 40 HRC. It was established that the thickness of a layer with a finely dispersed structure during unidirectional hydrogenation with a barrier coating is twice as large as during volumetric nonequilibrium hydrogenation in the absence of a coating.

Electrolic plasma polishing of complex parts in magnetic field

The article discusses a new technology of electrolyte-plasma polishing (EPP) of turbomachine parts with the imposition of an external magnetic field, which improves the quality of the surface layer. The results of experimental studies of the effect of electrolytic-plasma polishing of blades made of titanium alloy VT6 with the imposition of an external magnetic field are presented, indicating the prospects of using the proposed EPP method for processing parts of complex configuration, as well as the possibility of increasing the stability of the EPP process with the introduction of a magnetic field as an additional technological factor.

Demin K.A. Role of pulsed electron beam treatment in forming of operational properties of working surfaces of biomedical titanium alloy products

The article presents the study of the effect of pulsed electron beam treatment on the surface roughness of samples made of titanium alloy VT-6, obtained by two methods: mechanical processing and additive manufacturing. It has been established that electron beam treatment allows reducing the roughness of titanium alloys in both cases, which can be extremely important for polishing small-sized products, particularly those with low mechanical strength or unique microrelief surface.