Heat-resistant Titanium Alloys Research Articles

Multi-scale dispersion strengthening for high-temperature titanium alloys: Strength preservation and softening mechanisms

The long-lasting expectation “the hotter the engine, the better” calls for the development of high-temperature metallic alloys. Although the high specific strengths of titanium alloys are compelling for such applications, their deleterious softening beyond 600 °C imposes serious limitations. Much has been known for decades regarding the phase metallurgy for precipitation strengthening design in titanium alloys, however, the other facile strength promotion mechanism, dispersion strengthening, remains comparatively less-explored and unutilized. The present research concerns the multi-scale dispersion strengthening in titanium alloys, with mechanistic emphases on the critical plasticity micro-events that affect strength preservation. Due to the simultaneous introduction of intragranular dispersoids and intergranular reinforcers, the current titanium alloys present superior engineering tensile strength of 519 MPa at 700 °C. Throughout the examined 25–800 °C temperature range, noticeable softening induced by the thermal activation occurs above 600 °C, accompanied by evident strength loss. The temperature-dependence transition of dominated softening mechanisms from dynamic recovery to dynamic recrystallization has been clarified by theoretical calculations. Furthermore, the strengthening effect of multi-scale architectures is underpinned as the enhanced dislocation strengthening owing to the introduction of thermally-stable heterointerfaces, which could generically guide the design of similar heat-resistant titanium alloys.

Effect of oxidation on mechanical properties and surface condition of heat-resistance titanium alloy VT41

The present article dedicated to influence of oxygen affected zone of VT41 heat-resistant titanium alloy's samples. The samples were made of 023 mm rods and 1 mm thick sheets and processed by short term heat treatment at 300 - 900°C in atmosphere furnace. Mechanical properties of samples were measured at room temperature by straining (rods) and bending (sheets) Surface of fractured samples were studied by means of ТЕМ. The results of the present work gave an opportunity to match the temper colors of the samples with the temperature of heat-treatment, mechanical properties and the depth of fragile oxygen affected zone. The dependencies of relative strain and reduction area versus heat-treatment temperatures were determined. It was defined that a critical changing of plasticity's characteristics appears at heattreatment temperature above 500°C. The appearance of bright temper colors leads to enlarging of dispersion of ultimate stress and critical bending angle. When temperature of annealing goes up to 800°C the bending angle of sheet-samples decrease significantly at room temperature. As accurate measuring of the depth of oxygen affected zone and thickness of Ti02 layer by means of optical metallography and fractography at low temperatures is seriously complicated than one could qualify a depth of oxygen affected zone on the spot by determining an annealing colors. The appearance of bright yellow annealing colors with metal shining didn't bring any critical changes of mechanical properties.

Determining the structure and properties of heat-resistant titanium alloys VT3-1 and VT9 obtained by electron-beam melting

This paper reports a comprehensive study that investigated the quality of heat-resistant titanium alloys VT3-1 and VT9 obtained by the method of electron beam melting (EBM). It is shown that EBM makes it possible to produce high-quality metal of ingots of heat-resistant titanium alloys VT9 and VT3-1. Semi-finished articles were made in the form of bars from ingots obtained by the EBM method. It was established that in the macrostructure of the deformed metal there are no cracks, delamination, cavities, metal and non-metallic inclusions. The macrostructure of the metal of the bars corresponds to 4 points for the alloy VT3-1 and 4–5 points for the alloy VT9 on the 10-point scale of microstructures of instruction 1054-76. It was shown that the metal microstructure of forged bars of VT9 alloy consists of primary β grains with a continuous or intermittent α-rim along the grain boundaries 3–4 μs thick. The structure of the metal in the volume of grain – lamellar type with partially globularized plates of the α phase, plates of α-phase of close orientation form α colonies measuring 10–40 μs. The thickness of the α plates is 1–5 μs, between the plates or globules of the α phase there is a layer of β phase with a thickness of 1–2 μs. The microstructure of the deformed metal of titanium alloy VT3-1 consists of primary β grains, the volume of which contains colonies of lamellar α phases measuring 10–100 μs. The thickness of α plates is 1.5–3 μs, the layer of β phase in the intervals between α-plates is mainly 0.3–0.5 μs. The microstructure of semi-finished articles in the form of deformed bars of alloys VT9 and VT3-1 corresponds to type 4–6 according to the 9-type scale of the microstructure of instruction 1054-76. Studies of the mechanical properties of the obtained semi-finished articles have shown that they meet all the requirements of regulatory standards that are put forward by industry to the quality of the metal of heat-resistant titanium alloys

Nanoindentation and micro-cantilever testing for understanding cold-dwell sensitivity of heat-resistant titanium alloys

The mechanism of cold-dwell fatigue of the Ti alloys Ti-6242S and IMI 834 was investigated by measuring their local strain-rate sensitivities using nanoindentation analysis, electron backscatter diffraction, and energy-dispersive X-ray spectroscopy. In addition, microcantilever bending tests involving a load-holding-induced change in plastic strain near grain boundaries were conducted to investigate the plastic behavior of the alloys. The difference in the strain-rate sensitivity exponent between soft and hard grains was large in Ti-6242S and small in IMI 834, although slips were generated in the hard grains of both IMI 834 and Ti-6242S by activated slips in the soft grains during the microcantilever bending tests. The hardness of IMI 834 varied with its Al concentration, whereas no Al-concentration-dependent changes in hardness were observed in Ti-6242S. These results suggest that the stress redistribution was caused by differences in the concentrations of solid elements and the crystal orientation of the hard and soft grains.

Laser Surface Strengthening of Heat-Resistant Titanium Alloy for Gas Turbine Engines

Laser Surface Strengthening of Heat-Resistant Titanium Alloy for Gas Turbine Engines

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.

Prospects for the Implementation of New Materials and Technologies in the Aerospace Industry

Abstract This article considers the main materials used to make aircraft, both fuselage and engines. First, the problems that force developers to introduce new materials in aircraft production are identified. We then present features of the introduction of heat-resistant titanium alloys, ways of improving the mechanical properties of parts made of titanium alloys, and methods of manufacturing complex details. Other promising materials for the aviation industry, such as high-entropy alloys, quasicrystals, carbon-carbon materials, and nickel foam, are also considered.

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

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

Study of the Effect of Rhenium on Heat-Resistant Titanium Alloy Mechanical Properties and Microstructure

Complexly alloyed heat-resistant titanium alloys of the composition Ti–5Al–5Mo–5V–3Cr–1Re are studied. High-temperature test mechanical properties of these alloys in compression and tension at 600°C are provided and compared with similar properties of alloy Ti–5Al–5Mo–5V–3Cr. It is established that addition of rhenium increases alloy high-temperature strength properties and plastic deformation processes occur mainly in the β -phase not affecting α -phase.

Machinability of Heat-Resistant Titanium Alloys during Turning

The article discusses the properties and features of heat-resistant titanium alloys. The microstructure of a new titanium alloy VT41, its mechanical and service properties after various processing modes are presented. The main problems in the machining of difficult-to-machine titanium alloys are considered. The developed mathematical model of the formation of errors in turning titanium alloys, taking into account thermal deformations and dimensional wear of the cutting tool, elastic deformations of the technological system, is described. The paper presents the results of experimental research on turning of heat-resistant titanium alloy VT41 on a multi-parameter stand.

The Effect of Coatings on the Oxidation Kinetics of Intermetallic Titanium Alloys of the Ti2AlNb and γ-TiAl Systems

The results of a study of the effect of aluminide coatings of the NiCrAlY and Al(Si) systems on intermetallic heat-resistant titanium alloys VIT1 based on Ti2NbAl orthophase or TNM-B1 based on γ-TiAl on the resistance to isothermal oxidation are presented. The structures, phase, and chemical composition of the coatings after annealing and after high-temperature oxidation at temperatures of 650 and 700°C are considered. The coating layer of the Al(Si) system consisting of TiAl3, TiSi2 and Ti5Si3 sets a barrier for inhibiting diffusion of titanium into the coating layer of the NiCrAlY system, which is based on high-temperature phases of β-NiAl and γ'-Ni3Al, which provide heat resistance.

Comparison of the Strength Properties of Heat-Resistant Titanium Alloys at Elevated Temperatures

The results of statistical studies of the strength properties of rods made of heat-resistant titanium alloys at test temperatures of 20-600 °C are represented. The initial data for the research were the results of experiments published in various sources from the 1960s to 2019.The chemical composition of the alloys has been compared by aluminum and molybdenum equivalents and tensile strength at various temperatures. With an increase in the degree of alloying with a-stabilizers and neutral hardeners, the heat-resistant properties of alloys increase and remain at higher temperatures. However, this may reduce the thermal stability of alloys with an aluminum equivalent of more than 9.0%. The highest strength properties while maintaining thermal stability have alloys with aluminum equivalents of 8.5-9.0% and molybdenum of 1.0-4.5%. Regression dependences of the average values of strength properties on the test temperature, silicon content, and aluminum and molybdenum equivalents of alloying elements and impurities have been determined.

Analysis of the Microstructure, Phase Composition, and Oxidation Kinetics of Heat-Resistant Titanium Alloys with Gadolinium

The structure, phase composition, and local chemical composition of half-finished products (rods) made from Ti–Al–Mo–Zr–Si- and Ti–Al–Mo–Zr–Sn–Si-based alloys additionally microalloyed with 0.4 wt % gadolinium have been studied in this work. The structure of the rod made from the Gd-alloyed Ti–Al–Mo–Zr–Si composition was found to be characterized by the presence of Gd2O3 gadolinium oxide particles. The structure of the rod made from the Gd-alloyed Ti–Al–Mo–Zr–Sn–Si composition, which contains tin as a low-melting element, is characterized by the presence of Gd–Sn–O complex oxide particles, whose cores and shells are Gd5Sn3 intermetallics and Gd2O3 gadolinium oxide, respectively. The formation of such particles in both alloys occurs at the stage of ingot solidification, and the particles remain in the materials at all stages of their subsequent treatment. The oxidation kinetics of the alloys upon isothermal holding in a temperature range of 600–800°С is studied depending on the structure of half-finished products. The oxidation processes of the Ti–Al–Mo–Zr–Sn–Si alloy are less intensive than those of the Ti–Al–Mo–Zr–Si alloy. The alloying with gadolinium up to 0.4 wt % leads to the accelerated oxidation of the tin-free alloy, which is due to the presence of Gd2O3 particles precipitated at grain boundaries and interfaces. The alloying of the tin-containing composition with gadolinium almost does not affect the oxidation kinetics at 600–700°С and slightly decelerates the oxidation at 750–800°С; this is related to the presence of the Gd–Sn–O oxide particles in the structure, which are uniformly distributed over the grain body. The laws of oxidation of both the compositions free from gadolinium and alloyed with gadolinium were determined. It was shown that the oxide film formed upon the oxidation of both alloys is multilayer and consists of alternating layers of aluminum and titanium oxides. In this case, the progressive growth of oxide film layers alters the film exfoliation owing to the high brittleness of aluminum oxides. The presence of gadolinium oxide particles in both alloys leads to the porosity of diffusion zone of the base metal upon oxidation.

The weldability investigation of the high-temperature titanium alloys with dissimilar combination using a linear friction

ABSTRACT The work is carried out on the study of weldability at the linear friction welding (LFW) of samples from heat-resistant titanium alloys VT8-1 with VT41. The work is relevant, since the technology of linear friction welding can be used in the manufacture of high pressure impellers (blisks) for modern promising gas turbine engines. It will improve the technical characteristics of the final product, reduce costs, and improve the control measuring machines (CMM). The received results showed that the LFW technology allows to obtain welded joints with strength at the level of the least durable of the welded materials.

Effect of morphology of primary a on fatigue crack propagation resistance in a near a heat resistant Titanium alloy

DAT54 is a new near a heat resistant Ti alloy developed for disk applications in the compressor part of jet engines. DTA54 with bimodal microstructure shows a good balance of fatigue strength and creep life, and performs better than Ti-6242s up to 873 K. However, the influence of microstructure on properties, especially the effect of the morphology of primary a on fatigue crack growth resistance is not understood. In this study, samples with different types of microstructure were prepared by applying different heat treatment temperatures, and the influence of microstructure on fatigue crack growth properties at ambient temperature and 823 K was investigated. Influence of environment was also investigated by testing in vacuum and in air condition. Acicular microstructure shows lower fatigue crack growth rates in Paris’ region than the bimodal microstructures at 823 K. For the bimodal structures, aspect ratio of primary a do not have apparent influence on fatigue crack growth rates in Paris’ region, whereas fatigue threshold (DKth) seems to be affected by the morphology of primary a.

Peculiarities of wear of nanostructured topocomposites on the hard-alloy basis

The article considers the wear resistance and wear peculiarities of nanostructured topocomposites with the clustered gradient architecture. The authors regard the specificity of the impact of the cluster morphology on the contact interaction under microcutting conditions. They study the causes of persistence of the high wear resistance for the given class of nanostructured topocomposites. The mechanisms of energy dissipation from the tribocontact zone due to their nanogeometry and the structural-phase structure are analyzed. The contribution of triboactivated diffusion and deformation processes to providing the increased wear resistance of topocomposites on the hard-alloy basis is differentiated. Their approbation in the conditions of edge cutting processing of heat-resistant titanium alloy is carried out.

Vacuum superplastic deformation behavior of a near-alpha titanium alloy TA32

TA32 is a heat-resistant titanium alloy developed for superplastic forming in fabrication of near-space supersonic aerocraft. Clarification of superplastic deformation behavior is important to the optimization of forming parameters. Superplastic tensile test was conducted in vacuum to eliminate the effect of surface oxidation on experimental data, the test temperature and strain rate varied from 900oC to 960oC and 5.32×10-4 to 2.08×10-2s-1, respectively. It was observed that the size of equiaxed α grains exhibited a trend of coarsening with the increase of temperature and decrease of strain rate. Textures of deformed specimens exhibited random distribution with a decreased texture intensity compared with the as-received materials. The superplastic deformation mechanism of TA32 alloy was dominated by grain boundary sliding, which is accommodated by grain rotation and dynamic recrystallization.

Сопоставление прочностных свойств жаропрочных титановых сплавов при повышенных температурах

Сопоставление прочностных свойств жаропрочных титановых сплавов при повышенных температурах

Effect of cluster-gradient architecture of nanostructured topocomposites on features of tribointeraction with heterophased material

The wear resistance and wear characteristics of cluster-gradient architecture (CGA) nanostructured topocomposites are studied. The specifics of tribocontact interaction under microcutting conditions is considered. The reasons for retention of high wear resistance of this class of nanostructured topocomposites are studied. The mechanisms of energy dissipation from the tribocontact zone, due to the nanogeometry and the structural-phase structure of CGA topocomposites are analyzed. The role of triboactivated deformation and diffusion processes in providing increased wear resistance of carbide-based topocomposites is shown. They are tested under the conditions of blade processing of heat-resistant titanium alloy.

Microstructure and properties of permanent joints of ultrafine-grained titanium alloys produced by linear friction welding

This paper presents the results of a study of the microstructure and mechanical properties of welded joints obtained by linear friction welding of samples from heat-resistant titanium alloys VT8M-1 (Ti-5.4Al-1Sn-1Zr-4Mo-0.15Si) and VT25U(Ti-6.5Al-1.8Sn-4Zr-4Mo-1W-0.2Si). In the VT8M-1 alloy, an ultrafine-grained (UFG) structure was formed prior to welding. The features of the phase and structural transformations in the areas of contact and thermomechanical effect of welding were shown, as well as the microhardness distribution across the width of the welded joints. The obtained values of strength characteristics of a welded joint during short-term and long-term tests at 400 °C indicate their correspondence to the level of the monolithic VT8M-1 alloy with a UFG structure.