VT6 Alloy Research Articles

Модифицирование поверхности быстрорежущего инструмента совместным насыщением вольфрамом и азотом

Research significance is contingent on the requirement strengthening for high-speed cutting tools performance and wide-spread introduction of automatic lines and NC-machines. An increase of the tool service life is also necessary for the reduc-tion of putting expensive alloying elements to use, primarily, tungsten. The solution of these problems requires the use of technologies for hardening cutting surfaces. Combined processes of thermochemical treatment processes, uniting diffusive surface alloying with nitrogen saturation have shown their effectiveness in the surface hardening of various steels. Now the aim is to study the process of combined surface tungsten and nitrogen saturation of high-speed steel for increasing small-sized tool durability. Experimental studies were carried out on samples and small-diameter drills made of P6M5 steel. For laboratory experiments connected with combined process of thermochemical treatment an installation for nitriding in multi-component media was used. Metallization with tungsten was carried out by the slip method with parallel nitriding of the tool in a glow discharge. To determine the regime that provides the necessary temperatures for oxygen and nitrogen saturation, the temperatures of the control steel samples were measured on the surface and in the core at different durations of the cur-rent pulse in the heating phase. Metallographic analysis proved that thermochemical treatment resulted in a modified sur-face layer with a thickness of 10…15 microns, formed in P6M5 steel. The structure of the layer is an internal nitriding zone, which consists of a solid tungsten and nitrogen solution in iron and dispersed inclusions of tungsten nitrides. Dispersion and solid solution hardening provide a two-fold increase in the microhardness of the modified W-N layer compared to the alloy base. A transitional diffusion zone of nitrogenous martensite has been revealed under the hardened layer, creating a smooth microhardness gradient from the layer to the core, protecting it from embrittlement, peeling and staining. Using a metallophysical simulated test in predeveloped methodology, the calculation of the hardening index of the modified layer (yield point increase) was made. It showed that with increase in the concentration of tungsten in the layer, the proportion of the component of the dispersion hardening by W2N particles also increases. Full-scale tests in production conditions showed that the tool with a hardened layer had increased resistance. The durability of drills, determined by the number of drilled holes made before its dropping-out, increases by 2,2 times when drilling on 30XGSA steel and by more than 7,0 times when drilling a titanium alloy VT-23.

Технологические режимы раздачи и обжима при локальном нагреве

The processes of spread and reduction of a heated rough piece under visco-plasticity conditions are viewed. The ratio for force stress calculating in operations, damage to the material of the rough pieces is obtained. In the branches of special en-gineering, high-strength alloys based on titanium and aluminum are used. In the branches of special engineering, high-strength alloys based on titanium and aluminum are used. These alloys have mechanical properties anisotropy. Processing of these alloys is difficult. For this reason, the pressure treatment operation is performed with heating of the deformation zone. The material in the deformation zone exhibits viscous properties. Deformation hardening and softening (stress relaxa-tion) of the material take place simultaneously. Besides, the lower the deformation rate, the greater the softening. In this regard, a constitutive equation representing these processes is found. The factor of hardening and softening creates condi-tions for reducing the power mode of pressure treatment operations and increasing the degree of primary part forming. Stress relaxation calculation with the help of analytical dependencies is necessary at the stage of expansion and pressing development. The calculated ratios are recorded as a function of the speed of these operations. In this case, the specified deformation (the change in the degree of forming) is taken into account, adjusted depending on the speed and mechanical characteristics of the bearing alloy anisotropy. The calculated ratios are obtained under conditions of a flat voltage scheme, which corresponds to expansion and pressing. Stress equilibrium equation and yield condition of anisotropic material are used. The joint solutions of this equation and yield conditions determine values of the meridional and circumferential stress-es arising in the piece part material. The values of the stresses allow calculating the forces of operations. It is shown that the speed of expansion and pressing and mechanical properties anisotropy affect the damage to the material of the «green body». Dependences for the calculation of damage are obtained on the basis of energy and deformation strength criteria. These dependencies allow predicting the quality of products. It is also shown that anisotropy affects the technological modes of expansion and pressing. As the anisotropy coefficient increases, the stresses and forces of operations decrease. Calculations of stresses, forces and material damage in the process of expansion of anisotropic titanium alloy VT14 at 875 ℃ are made.

Features of Plasma Coating Formation from Silicon Carbide on Titanium Alloy VT6

Features of Plasma Coating Formation from Silicon Carbide on Titanium Alloy VT6

Structure and Distribution of Chemical Elements in the Transition Zone in Deposited VT20 and VT1-0 Alloy Samples

Structure and Distribution of Chemical Elements in the Transition Zone in Deposited VT20 and VT1-0 Alloy Samples

Plasma Electrolytic Oxidation for Dental Implant Surface Treatment.

50 IRIS dental implants (Scientific Production Company LICOSTOM, Russia), 10-mm long and 4 mm in diameter, were manufactured from the VT1-0 alloy. The implant surface was treated by two PEO methods: 1) in the aqueous solution of alkaline electrolyte without any additional modifiers (PEO-Ti); 2) in the aqueous solution of orthophosphoric acid-based electrolyte containing calcium carbonate (PEO-Ca). Implants made of VT1-0 alloy after milling and without additional treatment served as control samples. The implant surfaces were studied by electron microscopy and energy dispersive X-ray spectrometry. Some of the implants were installed in sheep, samples were obtained at 2, 4, and 8 weeks and studied by microcomputer tomography. Regardless of the electrolyte composition, a highly developed porous surface was formed in the samples with PEO-modified surfaces. The surface of the PEO-Ti samples in a simple unmodified electrolyte was characterized by a large number of open pores with a wide range of size distribution from 200 nm to 3 μm. The pore size distribution was of a monomodal character, with a maximum near 0.23 μm. The PEO samples in the Ca-containing electrolyte had pores also in a wide range from ~80 nm to ~7 μm. The pore distribution, in contrast to PEO-Ti, was bimodal in nature, with the main maximum in the region of 1.05 μm and the concomitant maximum near 2.45 μm.The obtained surfaces of both types (PEO with Ca and Ti) possessed high purity and optimal microroughness for osseointegration. Both types of PEO treatment (PEO with Ca and Ti) have demonstrated a similar osseointegrative potential, nevertheless, the surface of the PEO-Ca showed a better contact with the implant surface (49.8%) than PEO-Ti (42.4%) obviously due to the presence of calcium in its composition. The PEO-formed implant surfaces demonstrate high osseointegrative properties after any variants of treatment and show the potential for application in osteoporosis.

PLASMA-ELECTROLYTIC MODIFICATION OF STEEL AND TITANIUM SURFACES BY COMBINING CATHODIC NI-TRIDING AND ANODIC POLISHING

The possibility of increasing the wear resistance of steel 45 surfaces by 19.9 times and titanium alloy VT6 by 3.6 times after cathodic electrolytic plasma nitriding in a solution of ammonium chloride and ammonia and subsequent anodic electrolyte-plasma polishing in a solution of ammonium sulfate. A positive effect on wear resistance was revealed reducing surface roughness and removing the outer part of the oxide layer using anodic electrolytic plasma polishing and increasing the hardness of the surface layer as a result of cathodic nitriding. The wear mechanism is defined as fatigue upon plastic contact and boundary friction.

Technological properties of sheet titanium alloys VT6

This paper presents a comprehensive study of the microstructure, mechanical and technological properties (formability and weldability in solid state) of sheet blanks made of titanium alloy VT6, developed specifically for superplastic forming and diffusion bonding (SPF / DB) in PJSC VSMPO-AVISMA Corporation using various technologies. The conducted studies have made it possible to establish that sheets of titanium alloy VT6 with different microstructure in the temperature range of 850 – 920°C exhibit good superplastic properties. Studies of the technological properties of experimental sheets show their good weldability and high formability under superplasticity conditions. The relative length of the pores in the zone of the solid-phase joints is from 5.3 to 1.8 %, the equivalent deformation during SPF is from 1500 to 2700 %. The technological properties of the VT6 alloy in different states are very similar. The results obtained allow us to recommend this experimental sheet alloy for the manufacture of hollow structures by the SPF / DB process under superplasticity.

Influence of VT6 Alloy Components on the Formation of Surface Layers by Ions Ar+ and N+ Alternating Irradiation

Influence of VT6 Alloy Components on the Formation of Surface Layers by Ions Ar+ and N+ Alternating Irradiation

Structure and Properties of Electroexplosion Molybdenum Coating Deposited on Titanium Alloy VT6

Structure and Properties of Electroexplosion Molybdenum Coating Deposited on Titanium Alloy VT6

Determining the influence of irradiation swelling on creep and damage in elements with orthotropic material properties

This paper reports a method that numerically models the deformation and accumulation of hidden damage in structural elements that are in an inhomogeneous thermal field and are exposed to radiation. Materials considered are those exhibiting orthotropy (transversal isotropy) of long-term properties. The problem is stated as an boundary – initial value one. To solve it, the finite element method and the initial-difference method of time integration are used. To simulate the anisotropy of the process of accumulation of hidden damage, a damage tensor is applied. The development of irradiation swelling strains is described using the equation for a limited temperature range and a specific fluence value. The results of numerical modeling of creep and damage in plates in tension with circular notches, which are in an inhomogeneous temperature field, are considered. The material of the plates is a titanium alloy VT1-0. It was found that the effect of irradiation significantly, up to 6‒7 %, increases the level of deformation in the plate. Radiation significantly, by almost 4 times, reduces the time until the completion of the hidden fracture of the plates. It was found that orthotropy of radiation swelling properties leads to redistribution of areas with significant strains and damage values. It has been established that the effect of irradiation swelling also qualitatively changes the nature of the distribution of maximum damage in the plate, which extends to a fairly large area. Such results are due to the additional effect of irradiation swelling strains on the rate of general irreversible deformation and redistribution of stresses

Creation and study of intermetallic coating of the Ni–Ti system reinforced with tungsten carbide to increase wear resistance of titanium alloy

The results of studying the intermetallic coating of the Ni–Ti system with the addition of tungsten carbide are presented. The coating was synthesized on the surface of titanium alloy VT6 using an integrated approach – preliminary deposition of a precursor coating from monometallic nickel by cold gas-dynamic spraying and subsequent laser processing. It is shown that the introduction of tungsten carbide into the intermetallic matrix provides an increase in hardness by a factor of three or more, as well as a decrease in wear intensity by a factor of 80 compared to the wear resistance of VT6 titanium alloy. A technology has been developed and a batch of steam turbine blades with a wear-resistant coating on the surface of shrouds has been manufactured.

Superplastic Behavior and Microstructural Features of the VT6 Titanium Alloy with an Ultrafine-Grained Structure during Upsetting

In this paper, the superplastic behavior of the two-phase titanium alloy VT6 with an ultrafine-grained (UFG) structure produced by equal-channel angular pressing is examined. The deformation of specimens with a UFG structure was performed by upsetting in a temperature range of 650-750 °C and strain rate range of 1 × 10-4-5 × 10-1 s-1. Under these conditions, an increased strain-rate sensitivity coefficient m was observed. The calculation of apparent activation energy showed values in a range of 160-200 kJ/mol while the superplastic flow of the VT6 alloy was occurring. When superplastic behavior (SPB) was impeded, the energy Q grew considerably, indicating a change in mechanism from grain-boundary sliding (GBS) to bulk diffusion. A change in temperature and strain rate influenced the development of superplastic flow and the balance of relaxation processes. Microstructural analysis shows that the UFG state is preserved at upsetting temperatures of 650 and 700 °C. A decrease in strain rate and/or an increase in upsetting temperature promoted a more active development of recrystallization and grain growth, as well as α2-phase formation. In a certain temperature and strain-rate range of the UFG VT6 alloy, α2-phase plates were found, the formation of which was controlled by diffusion. The effect of the α2-phase on the alloy's mechanical behavior is discussed.

Fracture of aircraft titanium alloys under high-frequency loading

The paper is devoted to the problem of fatigue failure of two-phase titanium alloy VT3-1 under the action of high-frequency cyclic loading. Samples for the tests were made from the compressor disk of aviation engine D30-Ku installed on Tupolev Tu-154 planes. Repeated alternating loading was carried out by displacements of small amplitude at 20 kHz, coinciding with the first harmonic of longitudinal elastic vibrations of the sample. Analysis of specimen fracture surfaces shows predominant subsurface fracture. Analysis of areas of fatigue nucleation allows identifying elements of microstructure associated with crack nucleation. The results of the study can be used in the interpretation of fracture scenarios of structural elements in operation. Increasing the resource of products under such loads is possible through the use of damping layers or tapes, where possible.

Influence of electron‑beam surfacing modes on thickness and uniformity of single‑layer coating when restoring parts made of titanium alloys

The influence of the beam current, the distance between the beads of the clad material and the wire feeding intensity during electron‑beam (EB) surfacing of titanium alloy VT9 on the thickness and uniformity of the resulting restoring coating was investigated. As the beam current strength increases, the width of the deposited layer increases and the height decreases. The optimal distance between the beads should be considered an offset that does not exceed the width of the bead. It is possible to control the height of the deposited layer in a wide range by precise dosing of the wire feed intensity. The uniformity of surfacing is ensured by a balanced energy impact. Chemical composition of the clad layer meets the requirements of normative documents on the content of impurity gases for products from medical materials, obtained by additive technologies. The results of the study are used in the restoration of the surface of the landing gear element of aviation equipment.

Monitoring of vacuum diffusion welding process of titanium alloy using mathematical modelling

The results of evaluation and analysis of technological modes of diffusion welding in vacuum of titanium alloy VT6 using mathematical modeling are presented. Within the framework of the general concept of mathematical modeling existing in the description of powder metallurgy processes, a mathematical model was used to solve planar problems of the plastic flow of metal, which allows us to study the stress-strain state of real materials in the process of their formation. To solve the flat problems of plastic metal flow, a developed technique was used, which allows calculating and having experimental rheological dependencies, as well as mechanical test data, to choose the deformation modes optimal from the point of view of the quality of joints when they are obtained by diffusion welding in vacuum. The results obtained made it possible to optimize the parameters of diffusion welding of titanium powder blanks.

The Study of the Fe and Ni Effect on the Temperature of the VT14 Alloy Superplastic Moulding

The Study of the Fe and Ni Effect on the Temperature of the VT14 Alloy Superplastic Moulding

Multicharged metal ions generation in a self-magnetically insulated ion diode

A self-magnetically insulated ion diode was used to produce a pulsed beam of metallic ions from explosion emission plasma. The ratio of integral transferred charge for the Al, Ti and Mo ions amounted to at least 63% to the total beam charge. The ion diode had design features, which consisted in a bladed cathode and a removable perforated anode overlay made of VT-8 alloy. Analysis of the charge to mass characteristics of beam ions and the ion current density waveforms by the time of flight methodic with use of a Faraday cup showed the content of aluminum and titanium ions in the third to fourth states of ionization. Keywords: ion diode, metal ions, magnetic spectrometer, track detector CR-39.

Генерация многозарядных ионов металлов в ионном диоде с магнитной самоизоляцией

A self-magnetically insulated ion diode was used to produce a pulsed beam of metallic ions from explosion emission plasma. The ratio of integral transferred charge for the Al, Ti and Mo ions amounted to at least 63% to the total beam charge. The ion diode had design features, which consisted in a bladed cathode and a removable perforated anode overlay made of VT-8 alloy. Analysis of the charge to mass characteristics of beam ions and the ion current density waveforms by the time of flight methodic with use of a Faraday cup showed the content of aluminum and titanium ions in the third to fourth states of ionization.

Research of the influence of the kinetics of a hydrogen-containing medium on the stress-strain state of a cylindrical shell made of titanium alloy

This paper considers a mathematical model of the stress-strain state of a circular cylindrical shell made of titanium alloy VT1-0, operating in an aggressive hydrogen-containing environment. The shell is under the action of an internal evenly distributed pressure. To formulate the problem and carry out calculations, a model with triple nonlinearity is used, formulated within the approach associated with normalized stress spaces. The resulting algorithm for solving the problem of studying the effect of an aggressive medium on titanium alloy shells effectively takes into account the substantially nonlinear change in the parameters of the stress-strain state depending on the time factor. In the study, a system of nonlinear resolving equations for calculating the shell was formulated, results were obtained for the key parameters of the effect of a hydrogen medium on the stress-strain state of a cylindrical shell, taking into account embrittlement.

Зносостійкість титанового сплаву ВТ1-0 з модифікованою поверхнею в умовах абразивного впливу

The cost of rebuilding machine parts as a result of wear is enormous and rising every year. At a US symposium on reducing wear in machinery, the general consensus was that wear management is central to solving national problems such as energy conservation, material reduction, and ensuring the reliability and safety of mechanical systems. Nitriding significantly increases the wear resistance of metals and alloys. The formation of chemical compounds in titanium alloys by introducing nitrogen or increasing its concentration limit changes the rate of chemical reactions and the kinetics of oxide film growth, and increases their adhesion to the substrate. This leads to a decrease in the intensity of adhesive node formation and improves the tribological characteristics of titanium alloys. Therefore, it is necessary to study a titanium alloy with a hardened nitrided layer to obtain experimental results to determine the regularity of the influence of diffusion saturation parameters on wear resistance under abrasive conditions. The universal installation "VIPA-1" was used for vacuum ion nitriding in the pulse mode and the formation of diffusion layers on the surface. Technological parameters of vacuum ion nitriding in the pulse mode: temperature - 550°C, pressure - 25-150 Pa, processing time - 10 hours, ratio of reaction gases - 80% Ag + 20% N2. For experimental studies, samples of VT1-0 titanium alloy with dimensions of 30x30 mm and a thickness of 5 mm were used. The surface hardening of the samples was carried out uniformly around the entire perimeter, which ensures a uniform thickness of the diffusion layer. The analysis of the operating conditions of the friction surfaces of most structural elements made it possible to use the installation for bench tests according to the scheme of wear with a free abrasive (Brinell method). Wear tests were carried out on an experimental setup in accordance with GOST 23.208-79 (Fig. 2). The friction process was modelled in the presence of a free, not rigidly fixed abrasive, which coincides with the American standard ASTM C 6568. The experiment was carried out at a sliding speed of 0.158 m/s, a load of 20 kg (with a shoulder of 272 mm) and a friction path of 50 m. Steel 45, hardened to a hardness of 480-500 HB, was used as a reference. The wear body was a disc made of VT1-0 titanium alloy with a diameter of 100 mm and a thickness of 3.5 mm. On the basis of experimental studies, it has been established that the main mechanisms for increasing the wear resistance of titanium alloys as a result of the process of diffusion saturation of the surface with nitrogen during vacuum ion nitriding in the pulse mode are strengthening of the surface layers; creation of a favourable residual stress pattern; change in the patterns of deformation of the surface layers; change in the chemical and adhesive properties of the surface; transfer of diffusing nitrogen atoms into the depth of the matrix during friction due to the tribodiffusion effect. Conclusions. 1. Maximum wear rate of titanium alloy VT1-0 without hardening. 2. The effect of thermocyclic nitriding increases the wear resistance of VT1-0 alloy: in sand - 3 times; in water + sand - 3.5 times; in salt + sand - 2.5 times. 3. The effect of isothermal nitriding increases the wear resistance of VT1-0 alloy: in sand - 4 times; in water + sand - 3.5 times; in salt + sand - 2.5 times.