VT6 Alloy Research Articles

Fatigue Resistance of the Sheets of Heat-Resistant Titanium Alloys

The results of a study of the resistance to fatigue fracture of sheets made of heat-resistant titanium alloys VT18U (Ti–6.5Al–4.3Zr–2.4Sn–0.8Nb–0.7Mo–0.1Si, wt.%), VT8 (Ti–6.4Al–3.4Mo–0.3Si, wt.%), and VT25U (Ti–6.51Al–3.76Zr–1.71Sn–3.94Mo–0.5W–0.13Si, wt.%) has been presented. Fatigue curves have been obtained in the initial state and in the oxidized one after isothermal annealing at a temperature of 560 °C for 1000 h in air. It has been established that after annealing, the fatigue resistance of all oxidized alloys in the low-cycle region decreases by an order of magnitude. The fatigue limit of the oxidized alloys VT18U and VT25U does not change and is about 320 MPa. The high-cycle fatigue limit of the VT8 alloy decreases from 300 MPa in the initial state to 230 MPa in the oxidized state. It has been established that after annealing, the phase composition of an oxide of 250 nm in thickness on the surface of the alloys is different and contains the phases of anatase and rutile for the VT18U and VT25U alloys and contains predominantly rutile for the VT8 alloys, which is why the fatigue limit of the oxidized alloys differs.

Synthesis of (Ti, Cr)xCy Carbides in VT6 Alloy by Direct Laser Deposition

Synthesis of (Ti, Cr)xCy Carbides in VT6 Alloy by Direct Laser Deposition

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.

Особенности обрабатываемости резанием новых высокопрочных титановых сплавов с ультрамелкозернистой структурой для деталей авиационной техники

The results of experimental studies of the cutting parameters effect (cutting speed, feed, depth-of-cut) on the roughness of Ra, the microstructure of the surface layer of Ti-6Al-4V alloy samples with a conventional coarse-grained (CG) and ultrafine-grained (UFG) structure obtained by equal-channel angular pressing are presented. In framework of solving the problem connected with studying the machinability of a new VT6 alloy having an UFG structure, the development of a methodology for experimental research under turning was carried out. Physical parameters such as vibrations and noise under cutting, power consumption, numerical parameters of roughness, the magnitude and the pattern of residual stresses distribution and others are determined according to cutting modes and the tool used for the operation. It is shown that when turning at a low cutting speed, the roughness of CG sample is better than UFG of the alloy. With an increase in the cutting speed by 1,5 times, on the contrary, a sample with an UFG structure has a lower roughness Ra compared to a CG sample. Differences in the morphology and microstructure of the chips formed within comparative machining are discussed, taking into account types of microstructure of the alloy being treated, namely, presence of plastic flow lines in the chip microstructure after turning an UFG sample, the formation of large shifts, chips and tiny fractures in the chips after turning a CG alloy. It is found that new titanium alloys under turning obtain better cutting machinability in terms of such parameters as surface roughness, noise and vibration under cutting, and a more favorable character of residual stresses and riveting in the surface layer. Studying these factors, it is possible to predict a significant reduction of tool wear and stabilization of its durability compared to conventional coarse-grained titanium treatment.

The Effect of Thermal Action on the Change in the Chemical Composition of the Surface Layers of a Titanium Alloy, with a Sprayed Carbon Film, after Irradiation with N<sup>+</sup> Ions

The effect of thermal exposure under high vacuum conditions on the chemical composition of the surface layers of the VT6 alloy with mixed implantation of N+ ions by a carbon film is investigated. It is shown that under the conditions of thermal exposure, the change in the concentration profiles of the distribution of elements is determined by the processes of chemical interaction, in which the diffusion of carbon and nitrogen into deeper layers does not occur. On the contrary, their concentration decreases and this is due to the formation of volatile compounds CO, CO2 or (CH)2 under thermal exposure. Titanium in the surface analyzed layer is in an oxidized state with various degrees of oxidation. Up to a depth of about 10 nm, the oxidation state of titanium is Ti4+ and Ti3+, and in the transition region of the film/substrate is Ti2+.

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.

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.

К ВОПРОСУ О ПРЕИМУЩЕСТВЕННОМ МАССОПЕРЕНОСЕ НА ГРАНИЦЕ СВАРЕННЫХ ВЗРЫВОМ КОМПОЗИЦИЙ ТИТАНОВЫЙ СПЛАВ+НИХРОМ

The results of studies of preferential mass transfer at the boundary of explosion-welded compositions X20N80+VT1-0, X20N80+OT4 and X20N80+VT20 are presented. It has been established that the structure of the interphase boundary is practically independent of the time parameters of the stabilizing heat treatment and is determined by its temperature. The main influence on the phase and chemical composition of the diffusion interaction zone formed during heating at the Ti-NiCr boundary is the degree of alloying of the titanium alloy. In this case, the diffusion gradient is predominantly directed towards titanium VT1-0 and its alloys OT4 and VT20.

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.

Statistical investigation of mechanical properties of VT6 alloy bars with globular-lamellar structure

Statistical investigation of mechanical properties of VT6 alloy bars with globular-lamellar structure

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.

Электроискровое модифицирование поверхности аддитивного сплава ВТ6 высокоэнтропийным и аморфным электродами

Unsatisfactory quality of the surface layer of additive products, in particular increased surface roughness, prevents the widespread use of electron beam powder bed fusion (EBPBF). Electrospark treatment (EST) is one of the methods for smoothing and hardening the surface layer. The work shows the possibility of modifying the surface of additive VT6 alloy samples by reactive EST with multicomponent electrodes. For this purpose, the authors used electrodes made of the Fe48Cr15Mo14Y2C15B6 bulk metallic glass forming alloy and the FeCoCrNi2 high-entropy alloy. Based on the results of scanning electron microscopy, it was identified that after EST, both modified layers have a thickness of about 16 μm. X-ray diffraction phase analysis showed that in the case of treatment with an amorphous electrode they contain carboborides of the Ti(B,C) type, and in the case of treatment with a high-entropy electrode – intermetallic of the Ti2(Fe,Ni) type. The modified layers have average hardness values of 19 and 10 GPa and elastic modulus of 234 and 157 GPa, respectively, which significantly exceeds the values of these parameters for the EBPBF-grown VT6 alloy. Electric discharge modification of the surface with multicomponent electrodes led to a decrease in roughness by 8...11 times due to the melting of the protrusions and filling of the dimples with the melt to a depth of more than 50 μm. A comparative analysis of the results of tribological tests showed a change in the wear mechanism as a result of EST of the additive VT6 alloy. Wear resistance increased by 4 and 3 orders of magnitude when using electrodes made of a bulk metallic glass and high-entropy alloy, respectively.

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.

Electric spark alloying of steel, titanium and niobium alloys using rotating electrode method

The article presents the results of a study of electrospark coatings on metals and alloys using the rotating electrode method. The influence of various parameters on the formation of an electrospark coating on steel 20, titanium VT1-0, niobium and niobium alloy 5VMTs, on titanium VT1-0, niobium and niobium alloy 5VMTs with subsequent siliconization has been studied. The dependences of the growth of the thickness of the electrospark coating with increasing doping time, current in the circuit, and electrode rotation speed were obtained. It has been established that with increasing thickness of the electrospark coating, the thickness of the silicide layer increases. Electric spark alloying leads to an increase in the heat resistance of steel 20 with an aluminum coating by 1.5—3.0 times, of titanium by 2—9 times, and of titanium with a nichrome coating by 2 times. The heat resistance of titanium with a copper electrospark coating after siliconization increases up to 2—10 times, depending on the thickness of the electrospark layer and the siliconization temperature.

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.

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.

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.