VT6 Alloy Research Articles

STUDY OF THE INFLUENCE OF THE KINETICS OF HYDROGEN SATURATION ON THE STRESS-DEFORMED STATE OF A SPHERICAL SHELL MADE FROM TITANIUM ALLOY

In this paper, a mathematical model is considered that allows one to determine the stress-strain state of a spherical shell made of titanium alloy VT1-0, the external load is assumed to be transverse uniformly distributed, acting on the outer surface, the medium is assumed to act on the inner surface of the shell. For this, a nonlinear model was used, presented in normalized stress spaces. Fastening along the contour of the shell is rigid. Nonlinear resolving equations for calculating a spherical shell are obtained. An algorithm for solving the problem of hydrogenation of titanium alloy shells has been developed. A practical solution was made by a two-step method of sequential perturbations of parameters using the MatLab and Maple software packages. To solve the system of the obtained differential equations, the method of finite differences is applied. The calculation of the stress-strain state of the shell is obtained taking into account the diffusion process of an aggressive hydrogen-containing medium, and the obtained solution is compared with the results of the classical nonlinear theory without taking into account the aggressive medium. The results of comparing these solutions demonstrate quantitative differences in the parameters of the shell deformation process, which are explained by a more accurate account of the influence of the type of stress state. This approach has a rather flexible mechanism for considering the initial and induced differential resistance, demonstrates a high accuracy of matching the obtained theoretical results with empirical data on loading a wide range of materials under complex types of stress state.

The effect of ion‑plasma nitriding on the enduring quality and the nature of changes in the surface roughness of titanium alloys VT1‑0, VT6 and OT4‑1

The effect of the temperature of the ion‑plasma nitriding process on the enduring quality of the resulting hardened layers on titanium VT1‑0 and titanium alloys VT6 and OT4‑1 and the effect of ion‑plasma nitriding on the change in the Ra parameter of the surface roughness of titanium samples is investigated. It is defined that ion‑plasma nitriding leads to a significant increase in the enduring quality of the titanium alloys under study. The depth of the enduring quality groove in untreated samples of titanium VT1‑0, alloys VT6, OT4‑1 was 11, 7 and 10 microns, respectively, whereas in samples after ion‑plasma nitriding, the wear groove had a depth of 1.9, 0.9, 2.1 microns. It was revealed that when the initial roughness of the processed samples is more than Ra 0.1 microns after ion nitriding, the roughness index Ra, one of the key components of surface quality, decreases.

Surface Modification of Titanium VT6 Alloy Obtained by Additive Technologies Using Reactive Electrospark Treatment

Surface Modification of Titanium VT6 Alloy Obtained by Additive Technologies Using Reactive Electrospark Treatment

Inspection of ratcheting models for pathological error sensitivity and overparametrization

Accurate analysis of plastic strain accumulation under stress-controlled cyclic loading is vital for numerous engineering applications. Typically, models of plastic ratcheting are calibrated against available experimental data. Since actual experiments are not exactly accurate, one should check the identification protocols for pathological dependencies on experimental errors. In this paper, a step-by-step algorithm is presented to estimate the sensitivities of identified material parameters. As a part of the sensitivity analysis method, a new mechanics-based metric in the space of material parameters is proposed especially for ratcheting-related applications. The sensitivity of material parameters to experimental errors is estimated, based on this metric. Moreover, a relation between pathological error sensitivity and overparametrization is established. This relation gives rise to a new criterion of overparametrization. The advantages of the new overparametrization criterion are exposed and its plausibility is checked by alternative criteria, like the consideration of correlation matrices and validation of identified parameters on “unseen” data. For demonstration purposes, the accumulation of irreversible strain in the titanium alloy VT6 (Russian analog of Ti-6Al-4V) is analysed. Three types of phenomenological models of plastic ratcheting are considered. They are the Armstrong-Frederick model as well as the first and the second Ohno-Wang models. Based on real data, a new rule of isotropic hardening is proposed for greater accuracy of simulation. The ability of the sensitivity analysis to determine reliable and unreliable parameters is demonstrated.

Investigation of the properties of oxide coatings on titanium alloys obtained by plasma electrolytic oxidation

The use of structures made of titanium and its alloys, which have improved corrosion, physical and mechanical properties, are in demand in many industries. In this regard, the processes of modifying the surface of metals are of interest. One of the modern and promising methods of metal surface treatment is plasma electrolytic oxidation. Currently, there is a problem of widespread use of this process when DC modes are used in the implementation of the process. This is due to the large consumption of electricity. The purpose of this work is to study the morphological and corrosion properties of oxide coatings obtained in the pulsed anodecathode mode on titanium alloys VT1-0 and VT5 in various electrolyte solutions. Modification of the surface of titanium alloys was carried out at the duration of the anode current pulse of 250 ± 25 microseconds, the duration of the cathode current pulse of 5 ± 0.5 ms, the repetition frequency of the anode and cathode pulses of 50 ± 0.5 Hz. Alkaline solutions served as electrolytes. Oxide coatings obtained in various electrolytes are characterized by different porosity and coating thickness. Coatings with a finely porous structure, with an average pore diameter from 0.09 microns to 0.4 microns, and larger pore sizes of 0.6 – 0.7 microns were obtained. The porosity of the coatings ranges from 6.12% to 12.2%. According to the data of energy dispersion analysis, it was found that the structure of oxide coatings includes both components of the processed metal and components of the electrolyte solution. The main components, in this case, are oxygen and processed metal, as well as other elements such as boron, phosphorus, aluminium, fluorine, sodium, silicon and others. Corrosion tests according to GOST 9.308-85 under the influence of neutral salt mist at a temperature of (35 ± 2) °C with 1500 hours in the Ascott CC 450 chamber, it was shown that there was no corrosion damage to the coatings.

FIB-DIC Residual Stress Evaluation in Shot Peened VT6 Alloy Validated by X-ray Diffraction and Laser Speckle Interferometry.

Ga-ion micro-ring-core FIB-DIC evaluation of residual stresses in shot peened VT6 (Ti-6Al-4V) alloy was carried out and cross-validated against other non-destructive and semi-destructive residual stresses evaluation techniques, namely, the conventional X-ray diffraction and mechanical hole drilling. The Korsunsky FIB-DIC method of Ga-ion beam micro-ring-core milling within FIB-SEM with Digital Image Correlation (DIC) deformation analysis delivered spatial resolution down to a few micrometers, while the mechanical drilling of circular holes of ~2 mm diameter with laser speckle interferometry monitoring of strains gave a rough spatial resolution of a few millimeters. Good agreement was also found with the X-ray diffraction estimates of residual stress variation profiles as a function of depth. These results demonstrate that FIB-DIC provides rich information down to the micron scale, it also allows reliable estimation of macro-scale residual stresses.

Review of the author’s own results obtained from mechanical testing of titanium alloys

Experimental data obtained at different times by the author for various titanium alloys are collected in one place. The mechanical properties of the VT1-0 alloy at normal temperature, the creep and creep rupture of the VT5 and VT6 alloys at 650 °C, the secondary creep of the VT1-0 alloy under complex stress conditions at 550 °C are considered. The final values of strains observed either at the rupture time or at mechanical test termination are taken as a criterion for combining all these data.

Tribotechnical properties of experimental hard alloys with modified cobalt binder

Introduction. This paper discusses tribomechanical characteristics of experimental hard alloys with a modified cobalt binder under friction without lubrication on hard-to-cut materials – stainless steel and titanium alloy. The research objective is to evaluate the process of friction interaction for each friction pair according to a number of parameters, and to determine the optimal combinations of “experimental hard alloy – structural material” on the basis of the established tribological indicators.Materials and Methods. Tribological tests of hard alloys were carried out using a cylinder-to-disc friction scheme for different sliding speeds and temperatures under constant load without the use of lubricants. Comparison of the friction interaction process was carried out by the frictional force, volumetric wear and roughness of the friction tracks on the counterbody. Stainless steel 12H18N9Т and titanium alloy ВТ3-1 were used as counterbody materials. The resistance of experimental compositions to the abrasive type of wear was determined through measuring the surface dynamic microhardness on a scanning nanohardness tester by analyzing the thickness of the scratches caused by the indenter.Results. According to the results of surface microindentation, the experimental alloys 2.22 (binder 5.65% Co + l.8% Mo + 0.6% Ti) and 2.23 (binder 5.1% Co + 2.7% Mo + 0.61 % Ti) are characterized by the highest microhardness. For these materials, the average scratch width at various forces was minimal. During tribological tests, the best frictional characteristics were recorded for stainless steel in combination with experimental alloy 2.22, and for the friction pair “titanium alloy VT3-1 — hard alloy 2.23”. The friction of this combination of materials was characterized by low friction coefficients with a low level of fluctuations, minimal wear of samples, and changes in the initial microrelief of their surfaces.Discussion and Conclusions. As a result of the research, the optimal friction pairs from the point of view of tribological interaction were established, specifically “titanium alloy VT3-1 — hard alloy 2.23” and “stainless steel 12X18N9T – hard alloy 2.22”. The frictional interaction for these combinations of materials is characterized by minimal volumetric wear, which will contribute to increasing the wear resistance of the tool in the areas of elastic contact on the front and rear surfaces.

Features of manufacturing and clinical application of porous titanium implants for treatment of injuries and diseases of the spine

When treating injuries and diseases of the spine, it becomes necessary to replace the vertebral body or intervertebral disc with an implant. Such an implant should ensure the performance of the supporting function of the spine and facilitate the formation of a bone block (fusion). For this purpose, the most effective can be considered porous titanium that meets the requirements for biocompatibility, strength characteristics and rigidity. The possibility of obtaining such implants by diffusion welding of a specially twisted wire made of VT1-0 alloy and subsequent thermal hydrogen treatment, including thermal diffusion saturation of the implant blank with hydrogen and its subsequent removal during vacuum annealing, is considered. It is shown, that thermal hydrogen treatment makes it possible to transform the mechanical contacts of the wire after diffusion welding of the work piece into physicochemical ones. This makes it possible to increase the strength characteristics of the implant with a high volumetric porosity (up to 60–70 %) and bring its rigidity closer to the rigidity of the vertebrae. Optimization of the modes of diffusion welding and thermal hydrogen treatment was carried out to obtain a high complex of strength and plastic characteristics of implants. Clinical studies of the use of porous implants obtained by the proposed technology have shown their high efficiency in the treatment of injuries and diseases in the cervical, thoracic and lumbar spine. 247 clinical cases of the use of "cellular" porous implants (54 patients with injuries and 193 with degenerative-dystrophic diseases of the spine) were considered. In 214 cases, an improvement in the condition of patients was noted (86.6 %). Deterioration was observed in 4 patients (1.6 %), which was associated with contusion and edema of the spinal cord after the injury. It was found that in a relatively short period (up to 5–6 weeks), through the growth of bone tissue occurs through the implant. In this case, the formation of osteophytes on the lateral surface of the implant is not observed, which reduces the likelihood of injury.

STRUCTURE OF COMMERCIAL TITANIUM SUBJECTED TO LOW-TEMPERATURE ION NITRIDING

The structural-phase state of commercial titanium of grades ВТ1-00 (VT1-00) and ВТ1-0 (VT1-0) has been studied in the initial state and after various types of low-temperature ion nitriding. In the initial state, the VT1-00 and VT1-0 alloys have a single-phase α-Ti structure with a hexagonal close-packed crystal lattice. The hardness of titanium is 140–150 HV 10. It has been shown that ion-beam nitriding of VT1-00 alloy at low temperatures of 350 and 450 °С leads to the formation of thin (up to 5 μm) nitrogen-hardened layers with a hardness of 160–180 HV 0.05. As a result of ion implantation at temperatures of 500 and 550 °C, a nitrogen-modified layer with a microhardness of 190–220 HV 0.05 is formed in the surface layers of the VT1-00 titanium alloy, containing a solid solution of nitrogen in the α-Ti matrix phase. Nitrogen implantation of the VT1-00 alloy at a temperature of 620 °C leads to the formation of titanium nitrides TiN0.26, ε-Ti2N, η-Ti3N2-x in the surface layer of titanium alloy. The microhardness of VT1-00 titanium treated with nitrogen ions at 620 °C increases to 360 HV 0.05. In the case of ion-plasma nitriding (IPN) of VT1-0 titanium at 550 °C for 5 h, a nitrogen-modified layer up to 20 μm deep is recorded in its surface layer, containing isomorphic phases: α-Ti and titanium nitride TiN0.26. The microhardness of the VT1-0 titanium alloy subjected to IPN is 190 HV 0.01.

Research on end mill vibration in machining of VT9 titanium alloy

The reason for the failure of carbide end mills is the chipping of the cutting edges at the transition from the radius edges to the helix edges on the cylindrical part of the cutter. One of the reasons for the chipping of the cutting edges are the vibrations of the end mills which arise due to the intermittent cutting process and the variability of forces acting on the end mill. The principle of operation of a vibration measuring device is considered which allows vibration measurements to be carried out when milling with an end mill. The main measuring elements of the device are two eddy current sensors that allow measuring the vibration displacement of the milling cutter in two directions perpendicular and parallel to the movement of the longitudinal feed. The device has a compensation sensor that takes into account the influence of related factors, and a sensor for fixing the instantaneous rotation speed of the machine spindle. The milling cutter itself, fixed in a collet chuck, was used as an elastic element of the oscillating system. The data of measuring the amplitude of vibrations during milling of titanium alloy VT9 with a four-tooth and six-tooth end mill are presented. The study of vibrations of end mills included two stages. At the first stage, the influence of milling parameters and modes, as well as milling schemes (up and down milling) on the frequency and amplitude was investigated. At the second stage, measures were worked out to reduce the intensity of vibrations and increase the reliability and durability of the milling cutters. The research results showed lower amplitude values when working with a six-tooth cutter.

RESISTANCE OF TITANIUM ALLOYS TO CAVITATION WEAR

The wear rate of titanium alloys VT1-0, TC5, VT6, VT14, OT4 under the action of microshocks due to cavitation, which is created in distilled water under the surface of the ultrasonic wave emitter, were determined. It was found that the increase in hardness and improvement of cavitation wear resistancefor these alloys depends on the alloying elements, and is also increased after heat treatment and ion-plasma modification of the sample surface. Although no unambiguous correlation was found between the structural class of the alloys and their cavitation wear. Due to ion-plasma modification of alloys, the cavitation wear resistanceis increased by several times, in particular, the VT6 alloy by 3 times. The phase composition of the samples before and after ion-plasma modification was studied and it was found that alloy resistance to cavitation significantly depends on it.

CREEP OF VT1-0 ALLOY IN DIFFERENT STRUCTURAL STATES

The effect of electrons irradiation with an energy of E = 10 MeV and a dose of D = 5·1019 сm–2 on the structure evolution and creep of alloy VT1-0 in initial and nanostructured states obtained by the IPD method has been stud-ied. It is shown that, the deformation nanostructure of VT1-0 is resistant to subsequent deformation under creep conditions at T = 20 °C and is destroyed at T = 350 °C due to the development of recrystallization processes. Irradi-ation by electrons with an energy of E = 10 MeV and a dose of D = 5·1019 сm-2 has slightly effect on the mechanical characteristics of VT1-0, both in initial and nanostructured states, but leads to the conservation and stabilization of the nanostructure during creep at T = 20 °C and to the deceleration of the process of structure transformation at T = 350 °C as a result of a decrease in the level of internal stresses.

Исследование защитных свойств покрытий, полученных методом микродугового оксидирования в щелочных растворах электролитов

The article presents the results of a study of the corrosion properties of oxide coatings compacted with polymers and without compaction. Oxide coatings were obtained on VT1-0 and VT5 titanium alloys under the influence of fast pulsed actions of the micro-arc oxidation (MAO) process. To form MAO coatings, a pulsed mode of the process was used with an anodic current pulse duration of 250 ± 25 μs; the cathodic current pulse duration of 5 ± 0.5 ms; pause between anodic and cathodic current pulses 250 ± 25 μs; repetition rate of anodic and cathodic pulses 50 ± 0.5 Hz. Alkaline solutions were used as electrolytes. Fluoroplastic and epoxy resin solutions were used to seal the oxide coatings. The obtained MAO coatings have 4.4 – 7.5 % porosity on the VT1-0 alloy and 5.4 – 12.1 % on the VT5 alloy. The average diameter of oxide coating pores varies from 0.1 to 0,5 µm. X-ray phase analysis showed titanium dioxide in anatase and rutile modification in the oxide coatings composition. Tests performed in a 24 % solution of sulfuric acid at 40 and 75°C showed that the coatings on the VT1-0 alloy, both oxide and oxide-polymer, are more corrosion resistant than similar coatings on the VT5 alloy. All types of coatings produced on VT1-0 alloy are corrosion-resistant at a test temperature of 40 °C. Consolidation of MAO coatings with polymeric materials improves corrosion properties.

Review of experimental data on mechanical tests of titanium alloys

The experimental data obtained at different times for various titanium alloys are collected in one place. Mechanical properties of VT1–0 alloy at normal temperature, creep and creep rupture properties of VT5 and VT6 alloys at 650°C, secondary creep properties of VT1–0 alloy under complex stress at 550°C have considered. The criterion for combining all these data was the large strains.

Ударная вязкость титанового сплава ВТ6 с ультрамелкозернистой структурой, полученной методом равноканального углового прессования

The wide use of two-phase titanium alloys in aircraft engine building, as well as the intense development of this industry, stipulate more and more stringent requirements to structural materials and the enhancement of their reliability, strength and performance characteristics. The formation of an ultrafine-grained (UFG) state in metals and alloys using severe plastic deformation (SPD) processing enables achieving high strength properties. However, an important aspect of UFG materials is their structural and textural effects which may lead to a strong anisotropy of their properties. In this respect, the authors studied the effect of microstructural features on the mechanical properties and impact toughness of the VT6 alloy after equal-channel angular pressing (ECAP) and subsequent deformation by upsetting, imitating die forging. The study showed that the formation of a UFG structure in the VT6 titanium alloy with a grain size of about 0.4 µm allows increasing the ultimate tensile strength up to 1250 MPa. The additional upsetting of the UFG alloy at T=750 °C leads to grain growth up to 0.5–1 µm and a decline in strength to 1090 MPa as a result of the recovery and recrystallization processes. Impact toughness tests were conducted on specimens with a V-shaped stress raiser at room temperature, showing that the impact toughness of the UFG VT6 alloy was 0.41 MJ/m2. The tests revealed the anisotropy of impact toughness in the UFG VT6 alloy after equal-channel angular pressing and additional upsetting due to the metallographic and crystallographic texture formed as the result of deformation treatment. In test direction No. 1, the impact toughness value is the lowest and equals 0.31 MJ/m2.

Исследование структуры и коррозионной стойкости титановых сплавов, полученных методом электроимпульсного (искрового) плазменного спекания

The results of the structure and corrosion resistance researches of titanium alloys VT1-0, PT-3B and VT6 obtained by spark plasma sintering (SPS) are described. Microstructure, phase composition and microhardness have been investigated. It is shown that the alloy samples have a homogeneous high-density microstructure and high values of microhardness. The alloys samples showed high corrosion resistance in the electrochemical corrosion tests in acidic aqueous solution causing intergranular corrosion. The alloys also showed high resistance against hot salt corrosion. It has been suggested that the high hardness of the alloys as well as the differences in corrosion resistance of the central and lateral surfaces of the samples are due to the diffusion of carbon from the graphite mold into the sample surface.

ХАРАКТЕРИСТИКИ ПРОЧНОСТИ И ВЫНОСЛИВОСТИ ПРУТКОВ И ШТАМПОВОК ЛОПАТОК ИЗ СЕРИЙНЫХ ЖАРОПРОЧНЫХ ТИТАНОВЫХ СПЛАВОВ И НОВОГО ТИТАНОВОГО СПЛАВА ПСЕВДО-α-КЛАССА

Presents the microstructure and mechanical properties of bars and blade forgings made of new heat resistant titanium alloy. A typical microstructures of studied industrial alloys were demonstrated. The main clue of the article is noted to fatigue stability of bars and forgings material. The analysis of strength and impact toughness of bars and blade forgings made of industrial titanium alloys VT3-1, VT8, VT8M-1, VT9, VT20 were carried out in comparison with new heat-resistant titanium near- alloy.

ДОСЛІДЖЕННЯ ВПЛИВУ ТВЕРДОГО ЗМАЩУВАННЯ НА ПОКАЗНИКИ ПРОЦЕСУ АЛМАЗНОГО ШЛІФУВАННЯ ВІДПОВІДАЛЬНИХ ДЕТАЛЕЙ З ТИТАНОВИХ СПЛАВІВ

Titanium alloys are widely used in military equipment because of theirs excellent physical properties, such as corrosion resistance, heat resistance, fatigue resistance, and high specific strength. However, the hardness and strength of titanium alloy are high, and the coefficient of thermal conductivity is poor, so the cutting performance is poor. The influence of solid lubricant on the parameters of the process of diamond grinding of hard-to-cut material – titanium alloy VT22 was studied. The evaluation was carried out on the basis of the surface roughness parameter Ra and the postcontact temperature Tpc. It has been established that the use of a solid lubricant based on stearic acid (65%) and molybdenum disulfide (35%) reduces the post-contact temperature by 1.4 ... 2.1 times and the roughness by 1.3 ... 1, 6 times in comprising with results under dry grinding conditions. Solid lubricant has an ambiguous effect on the grinding performance of VT22 depending on transverse feed. It may be linked up to state transition of stearic acid and growth its surface activity. The best results on the surface quality with solid lubrication were achieved under grinding with cutting speed Vc = 25 m/s and transverse feed f = 0.005 mm/double pass.

Damage-failure transition in VT6 titanium alloy under consecutive dynamic and VHCF loads

The lifetime of VT6 (Ti-6Al-4V) titanium alloy under consecutive dynamic and very-high cycle fatigue loads is studied. The relevance of the problem is determined by the applications to the prediction of the endurance fatigue limit for materials and structural elements of aircraft gas turbine engines experiencing random dynamic effects under flight cycle conditions. The titanium alloy specimens were used to perform High Cycle Fatigue (HCF) and Very High Cycle Fatigue (VHCF) tests on the ultrasonic testing machine, which allows fatigue loading for 108-1010 cycles with amplitude up to several tens of micrometers and frequency of 20 kHz. It is shown that VT6 alloy specimens in the 108 cycle regime subject to dynamic preloading reduces the fatigue strength by 70%. Structural study of the fracture surface for the specimens after consecutive loading was conducted using the profilometry data to identify the roughness scale invariants induced by defects for corresponding areas responsible for the staging of fatigue damage-failure transition. The scale invariants and corresponding lengths were used to formulate the generalized Paris law governing the crack growth in damaged materials.