High Temperature Titanium Alloy Research Articles

The Relationship between Microstructure and Fracture Behavior of TiAl/Ti2AlNb SPDB Joint with High Temperature Titanium Alloy Interlayers.

In this paper, spark plasma diffusion bonding technology was employed to join TiAl and Ti2AlNb with high temperature titanium alloy interlayer at 950 °C/10kN/60 min, then following furnace cooling at cooling rate up to 100 °C/min. After welding, the joint was aging heat-treated at 800 °C for 24 h. The microstructure and the elements diffusion of the TiAl/Ti2AlNb joint was analyzed by field emission scanning electron microscopy (FESEM) with EDS. Moreover, the tensile properties of the joint were tested at room temperature, 650 °C, and 750 °C. The results show that the spark plasma diffusion bonding formed a high quality TiAl/Ti2AlNb joint without microcracks or microvoids, while also effectively protecting the base metal. Significant differences in the microstructure of the joint appeared from TiAl side to Ti2AlNb side: TiAl BM (Base Metal) → DP(Duplex) and NG (Near-Gamma) → α2-phase matrix with needle-like α-phase → bulk α2-phase → needle-like α-phase → metastable β-phase → Ti2AlNb BM. After heat treatment at 800 °C for 24 h, the microstructure of the TiAl side and the interlayer region did not change, but the density and size of the needle-like α-phase in region 3 increased slightly. The microstructure of Ti2AlNb near the weld changed obviously, and a large number of fine O phases are precipitated from the metastable β phase matrix after heat treatment. Except for the Ti2AlN near-interface region, the effect of heat treatment on the microstructure of the joint is not significant. The microhardness of the joint is in the shape of a mountain peak. The maximum microhardness at the interface is above 500 HV, and it is significantly reduced to 400 HV after heat treatment. The fracture of the joint occurred at the interface at room temperature, 650 °C, and 750 °C. with the tensile strength 450 MPa, 540 MPa, and 471 Mpa, respectively, and mainly showing brittle fracture.

Argon-arc welding of high-temperature titanium alloy doped by silicon

The Paton Welding Journal, 2022, №05. International Scientific-Technical and Production Journal «The Paton Welding Journal» «The Paton Welding Journal» has been published monthly since 2000 in English, ISSN 0957-798X. «The Paton Welding Journal» is a cover-to-cover English translation of the «Avtomaticheskaya Svarka» (Automatic Welding) journal. The «Avtomaticheskaya Svarka» journal has been published monthly since 1948 in Russian, ISSN 005-111X.

Enhanced Erosion Resistance of an Ultrafine-Grained Ti Alloy with a PVD Coating

This paper presents the results of a comprehensive study of the erosive wear resistance, strength, and adhesive characteristics of the high-temperature structural titanium alloy Ti-5.7Al-3.8Mo-1.2Zr-1.3Sn (the Russian grade VT8M-1) with coarse-grained and ultrafine-grained (UFG) structures and a protective erosion-resistant TiVN coating produced by physical vapor deposition (PVD), deposited on the alloy surface. A microscopic analysis of the areas subjected to the action of abrasive particles was performed, and different characters of erosive wear were revealed depending on the structural state of the alloy. The obtained results convincingly demonstrate that by means of refining the grain structure of alloys and depositing a protective ion-plasma TiVN coating on the alloy surface, it is possible to significantly increase the erosion resistance of materials operating under high loads and in aggressive environments.

Development of Ti-Al-Ta-Nb-(Re) near-α high temperature titanium alloy: Microstructure, thermal stability and mechanical properties

• The Ta, Nb and/or Re elements were used to increase the microstructural stability of high temperature Ti alloy. • The Ta and Nb exhibited weak β-stabilizing ability, while the Re was a strong β-stabilizer and obviously increased the content of β phase. • A trace Re addition retarded the growth of ordered α 2 precipitates due to the increase of Ta and Nb concentrations in the α phase. Mechanical properties and microstructural stability under the service temperature are important to the high temperature titanium alloy. In order to evaluate the potential in increase the service temperature of Ti alloy, two near-α Ti alloys with high content of Al as α-stabilizer and Ta, Nb and/or Re as β-stabilizers were designed and prepared by ingot metallurgy and thermomechanical processing, and the microstructure and mechanical properties before and after thermal exposure at 650 °C for 100 h were characterized. The results indicated that due to the weak β-stabilizing ability of Ta and Nb elements, only a small amount of β phase was formed in Ti-10Al-4Ta-2Nb alloy. With a trace Re addition, the β phase was obviously increased in Ti-10Al-4Ta-2Nb-0.25Re, indicating that the Re was a strong β-stabilizer. Under the same thermomechanical conditions, the Re addition decreased the volume fraction of primary α (α p ) phase and refined the secondary α (α s ) phase evidently. The primary α phase presented an obvious core-shell structure in the Ti-10Al-4Ta-2Nb alloy, with higher Al concentration in the shell. While the core-shell structure was not obvious in the Re-containing alloy due to the Re decreases the diffusion of Al, Ta and Nb elements. A large number of ordered α 2 precipitates can be observed in the α p and α s phases of two alloys. The α 2 precipitates continuously grew up during thermal exposure, however, their growth rate in the α s phase of Re-containing alloy were lower than that of Ti-10Al-4Ta-2Nb alloy. Although plenty of ordered α 2 precipitates formed in the Ti-10Al-4Ta-2Nb alloy, the alloy had a certain plasticity at room temperature. The trace Re addition evidently increased the tensile strength but caused the decrease of the plasticity. After thermal exposure, the strength was further increased, while the plasticity was decreased for both of alloys.

Chemical Composition, Microstructure, Tensile and Creep Behavior of Ti60 Alloy Fabricated via Electron Beam Directed Energy Deposition.

Electron beam directed energy deposition (EB-DED) is a promising manufacturing process for the fabrication of large-scale, fully dense and near net shape metallic components. However, limited knowledge is available on the EB-DED process of titanium alloys. In this study, a near-α high-temperature titanium alloy Ti60 (Ti-5.8Al-4Sn-4Zr-0.7Nb-1.5Ta-0.4Si) was fabricated via EB-DED. The chemical composition, microstructure, tensile property (at room temperature and 600 °C), and creep behavior of the fabricated alloy were investigated and compared with those of the conventional wrought lamellar and bimodal counterparts. Results indicated that the average evaporation loss of Al and Sn was 10.28% and 5.01%, respectively. The microstructure of the as-built alloy was characterized by coarse columnar grains, lamellar α, and the precipitated elliptical silicides at the α/β interfaces. In terms of tensile properties, the vertical specimens exhibited lower strength but higher ductility than the horizontal specimens at both room temperature and 600 °C. Furthermore, the tensile creep strain of the EB-DED Ti60 alloy measured at 600 °C and 150 MPa for 100 h under as-built and post-deposition STA conditions was less than 0.15%, which meets the standard requirements for the wrought Ti60 alloy. The creep resistance of the EB-DED Ti60 alloy was superior to that of its wrought bimodal counterpart.

Research on entrance delamination characteristics and damage suppression strategy in drilling CFRP/Ti6Al4V stacks

Carbon Fiber Reinforced Polymer (CFRP) and CFRP/Ti6Al4V stacks are now commonly used in the aircraft industry. In the integrated drilling process of CFRP/Ti6Al4V stacks, the entrance delamination defects of CFRP is often more serious than that in drilling single CFRP. Considering the anisotropy of CFRP, this paper analyzed the entrance delamination defects caused by the CFRP drilling phase and the influence of titanium alloy drilling phase on the evolution of entrance delamination defects of CFRP. A series of drilling experiments were carried out on CFRP and CFRP/Ti6Al4V stacks respectively. The causes and differences of entrance delamination defects in the drilling process of CFRP and CFRP/Ti6Al4V stacks were compared from the aspects of drilling force, temperature and titanium alloy chip formation. In addition, the entrance delamination defects suppression strategy called high and low frequency vibration-assisted drilling method (CVAD) in drilling CFRP/Ti6Al4V stacks was investigated. The results indicate that in the single CFRP drilling process, the entrance near 135° cutting angle of CFRP fiber presents slight type I and type III delamination defects due to the tool structure and fiber anisotropy. However, in the CFRP/Ti6Al4V stacks drilling, the thermal-mechanical effect of high temperature titanium alloy chips leads to the evolution of more serious type I elliptical delamination defects at the entrance of CFRP. By using CVAD method to reduce the titanium alloy chip size and drilling temperature, the entrance delamination defects of CFRP/Ti6Al4V stacks can be effectively suppressed. The findings of this paper can contribute to identifying the formation of entrance delamination defects in CFRP and providing guidance for improving the processing quality of CFRP/Ti6Al4V stacks.

Excellent high-temperature strength and ductility of graphene oxide reinforced high-temperature titanium alloy matrix composite fabricated by hot isostatic pressing and heat treatment

GO reinforced high-temperature titanium alloy matrix composite with excellent high-temperature strength and ductility was successfully fabricated by hot isostatic pressing and heat treatment. After solution and aging treatment, the high-temperature strength of the composite was significantly improved because the increase of in-situ TiC at the interface enhanced interface bonding and the microstructure changed from equiaxed structure to bimodal structure. At the same time, the dissolution of silicides increased the high-temperature ductility. After solution at 1075 °C and aging at 700 °C, the tensile strength, yield strength and elongation at 600 °C of the high-temperature titanium alloy with 0.3 wt% GO reached 749 MPa, 571 MPa and 18.5%, respectively.

Study on Tensile Fracture Behavior of New Type High Temperature Titanium Alloy Ti-Al-Nb at Room Temperature

In this paper, in order to explore the development of a titanium-based superalloy with a working temperature of 700°C to 750°C and good ductility at room temperature, using Ti+Al+Ti2AlNb ternary powder as the raw material, the temperature is 1200°C to 1300°C, 30MPa, 1.5h Directly mixed and sintered under hot pressing conditions, a new type of titanium-based superalloy (TiAl+Ti2AlNb) samples were prepared. The fracture morphology of hot-pressed sintered samples and tensile samples used scanning electron microscope (Scanning electron microscope, referred to as SEM) and Electron backscattered diffraction (EBSD) for observation. Discuss the room temperature tensile fracture behavior of a new type of high temperature titanium alloy Ti-Al-Nb, and lay a technical foundation for the development of a new type of high temperature titanium-based alloy with low brittleness at room temperature.

Effects of W Addition on Microstructure and 650 °C Mechanical Properties of Ti-Al-Sn-Zr-Mo-Nb-W-Si Alloy

The influence of W addition on microstructure and mechanical properties of Ti-Al-Sn-Zr-Mo-Nb-W-Si high temperature titanium alloys are investigated by optical microscope (OM), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), tensile tests and large stress endurance tests at 650 °C. The results show that W is mainly solubilized in β phase. Microstructure observations indicate an obvious reduction in the size of transformed β structure (βt), primary α phase (αp) and the thickness of secondary lamellar α phase (αL), with the increase of W content. It is also observed that adding more W could improve the elongation, tensile strength and large stress rupture properties at 650 °C. However, combined with previous research, adding more β stabilizing elements could refine the size of each phase, which will be detrimental to the high temperature yield strength of the alloy. Therefore, in order to reasonably utilize the strengthening effect of W and make the alloy have high yield strength and tensile strength at 650 °C, its content should be controlled between 1 ~ 2 wt%

Structure and properties of near-a titanium products obtained by direct laser deposition and heat treatment

Advanced techniques of obtaining products require careful selection of materials for various industries. Titanium alloys are widely used in the aerospace, shipbuilding and mechanical engineering industries. The development of near-a titanium alloys should be considered a significant achievement in the field of metallurgy and heat treatment (HT) of titanium alloys. This article presents a study carried out with the aim of optimizing heat treatment modes for high-temperature titanium alloys obtained by direct laser deposition (DLD). Heat treatment was carried out in the temperature range (700-1000°C), covering three typical temperature ranges, i.e. the temperature range for the partial decomposition of martensite, the temperature range for the complete decomposition of martensite, and the phase transformation temperature were subsequently selected as the heat treatment temperatures. Based on metallographic analysis, the influence of heat treatment modes on the structure, as well as the tensile properties at room temperature, of TA15 titanium DLD-samples.

Dynamic Softening and Hardening Behavior and the Micro-Mechanism of a TC31 High Temperature Titanium Alloy Sheet within Hot Deformation.

TC31 is a new type of α+β dual phase high temperature titanium alloy, which has a high specific strength and creep resistance at temperatures from 650 °C to 700 °C. It has become one of the competitive candidates for the skin and air inlet components of hypersonic aircraft. However, it is very difficult to obtain the best forming windows for TC31 and to form the corresponding complex thin-walled components. In this paper, high temperature tensile tests were carried out at temperatures ranging from 850 °C to 1000 °C and strain rates ranging from 0.001 s−1 to 0.1 s−1, and the microstructures before and after deformation were characterized by an optical microscope, scanning electron microscope, and electron back-scatter diffraction. The dynamic softening and hardening behaviors and the corresponding micro-mechanisms of a TC31 titanium alloy sheet within hot deformation were systematically studied. The effects of deformation temperature, strain rate, and strain on microstructure evolution were revealed. The results show that the dynamic softening and hardening of the material depended on the deformation temperature and strain rate, and changed dynamically with the strain. Obvious softening occurred during hot tensile deformation at a temperature of 850 °C and a strain rate of 0.001 s−1~0.1 s−1, which was mainly caused by void damage, deformation heat, and dynamic recrystallization. Quasi-steady flowing was observed when it was deformed at a temperature of 950 °C~1000 °C and a strain rate of 0.001 s−1~0.01 s−1 due to the relative balance between the dynamic softening and hardening. Dynamic hardening occurred slightly with a strain rate of 0.001 s−1. Mechanisms of dynamic recrystallization transformed from continuous dynamic recrystallization to discontinuous dynamic recrystallization with the increase in strain when it was deformed at a temperature of 950 °C and a strain rate of 0.01 s−1. The grain size also decreased gradually due to the dynamic recrystallization, which provided an optimal forming condition for manufacturing thin-walled components with the desired microstructure and an excellent performance.

Rapid dynamic transformation in the initial stage of hot deformation of a near alpha titanium alloy

The peak flow stress of a near alpha high temperature titanium alloy exhibits a special rapid drop behavior at low strain during hot compression. The experimental result indicates that this rapid drop of peak flow stress is related to the rapid dynamic transformation from alpha phase into beta phase which is induced by the deformation at elevated temperature. Both peak flow stress and the dynamic transformation change with different hot deformation parameters, and the drop of peak flow stress keeps almost consistent variation with the evolution of dynamic transformation observed from the microstructural morphology. The higher deformation temperature and the lower strain rate with the small increase of strain are beneficial to accelerate the dynamic transformation and the drop of peak flow stress. The dynamic transformation is mainly controlled by the immigration of alpha/beta interface shrinking from edge to center of equiaxed alpha phase or the penetration of beta phase into alpha phase from edge to inside.

Recent advances in silicon containing high temperature titanium alloys

Silicon (Si), which exists in the form of solid solution and silicide, is an important component in high temperature titanium (Ti) alloys. The content of Si is often limited to less than 0.5wt.%, but powder metallurgy shows the potential for the preparation of titanium alloys with high Si content and high temperature. The addition of Si is beneficial to the improvement of strength, creep resistance and oxidation resistance of high temperature titanium alloy, but it will reduce the plasticity, especially the plasticity at room temperature. In this review, with particular stress on the influence of heat treatment and hot working process on the precipitation behavior of silicide, as well as on the effect of Si on the properties and strengthening mechanism of high temperature titanium alloys. The development direction of high temperature titanium alloy containing Si is to increase the content of Si and to control the precipitation behavior of silicide through reasonable process.

Constitutive Model and Microstructure Evolution of a Novel TG6 High-Temperature Titanium Alloy during Hot Deformation

Constitutive Model and Microstructure Evolution of a Novel TG6 High-Temperature Titanium Alloy during Hot Deformation

Effect of annealing temperature on microstructure, texture and tensile properties of TA32 sheet

The aim of this paper was to study effect of annealing temperature on microstructure, texture and tensile properties of a high temperature titanium alloy sheet. The as-received sheet exhibited an equiaxed structure consisting of primary α phase and few retained β phase. The α phase texture showed a typical B-type texture with <0001> inclined to normal direction. The intracrystalline substructure played an important role on tensile strength when the annealing temperature below 900 °C. Duplex microstructure with B + R-type texture was obtained when annealing temperature increased to α＋β region (900–990 °C). The intensity of B-type texture and R-type texture was found to be determined by the volume fraction of primary α phase and transformed β phase. Significant increase of tensile strength after α＋β region annealing was thought to result from the secondary α-β interfaces strengthening, and the formation of R-type texture lead to the anisotropy of tensile strength. Widmanstatten structure was obtained when the sheet suffered a β phase region annealing (1000–1020 °C) and the tensile strength decreased instantly.

Effect of pre-strain temperature on the subsequent dynamic recrystallization of parent β phase and transformed α-variant selection in a novel near α titanium alloy

The microstructure and micro-orientation evolution of a novel high-temperature titanium alloy were characterized during a two-step deformation process. In the first step, the specimens were deformed at temperatures of 800, 850, 900 and 950 °C, and subsequently deformed in the same β-phase region of 1050 °C. The specimens pre-strained at 800 °C and 950 °C were fully recrystallized during the β-phase deformation process. By contrast, the specimens pre-strained at 850 and 900 °C were not fully recrystallized during the β-phase deformation process. This indicates that the extent of dynamic recrystallization did not increased monotonically with the pre-strain temperature. The extent of dynamic recrystallization was related to the stored energy accumulated in the α and β-phase during the pre-strain deformation. The change in stored energy was based on the difference in microstructure morphology produced by different pre-deformation temperatures,and stored energy was quantitatively estimated based on the local misorientation distribution. Meanwhile, the generation of dynamically recrystallized grains was beneficial to decreasing the generation possibility of the macro-zone. This decrease was attributed to the refinement of β-grains and randomly distributed orientation, which was also related to the decrease in the typically distributed “two parallel wings” orientation between the α and β phase induced by uncrystallized deformation. Additionally, the two-step deformation process with the pre-strain at the (α + β) middle regime was an effective strategy to promote the dynamic recrystallization and decrease the generation probability of the macro-zone.

Microstructure Evolution of near α Titanium Alloy during Multi-Step Thermomechanical Deformation Process

A new type of near α high temperature titanium alloy of Ti-Al-Sn-Zr-Mo-Si-Er was studied. The samples with different primary α phase content were prepared by solid solution at 950 °C/1 h—1010 °C/1 h. The multi-step hot compression experiments were carried out by Gleeble-3500 in a sequence of upper region of α + β phase, then followed by lower region of α + β phase. The effects of primary α phase content and deformation temperature on the microstructure of the alloy were studied by means of true stress-strain curve and optical microscope. The results show that the content of primary α phase gradually decreases from 45.4% at 950°C to 0% at 1010°C. As the deformation temperature decreases from 940°C to 900°C, the content of α phase increases gradually from 65% to 94%, which is changed from dynamic recrystallization to deformed structure elongated along RD direction. It is found that the arrangement of α phase along RD direction is the longest at 920°C. With the increase of the deformation temperature in the multi-step high temperature region from 970°C to 990°C, the width of deformed α phase decreases from 3.64 μm at 970°C to 2.71 μm at 990°C. The optimized microstructure is composed of 20% primary α phase arranged along RD direction. This process has a certain potential in the process of hot deformation of the alloy. Key words: high temperature titanium alloy, primary α phase, multi-step hot deformation

Influences of Solution Temperatures on Microstructure and Mechanical Properties of near α Titanium Alloy

A new type of Ti-Al-Sn-Zr-Mo-Si series high temperature titanium alloy was prepared by a water-cooled copper crucible vacuum induction melting method, and its phase transition point was determined by differential thermal analysis to be Tβ = 1017 °C. The influences of solution temperature on the microstructures and mechanical properties of the as-forged high temperature titanium alloy were studied. XRD results illustrated that the phase composition of the alloy after different heat treatments was mainly α phase and β phase. The microstructures showed that with the increase of the solution temperature, the content of the primary α phase gradually reduced, the β transformation structure increased by degrees, then, the number and size of secondary α phase increased obviously. The tensile results at room temperature (RT) illustrated that as the solution temperature increased, the strength of the alloy gradually increased, and the plasticity decreased slightly. The results of tensile test at 650 °C illustrated that the strength of the alloy enhanced with the increase of solution temperature, the plasticity decreased first and then increased, when the solution temperature increased to 1000 °C, the alloy had the best comprehensive mechanical properties, the tensile strength reached 714.01 MPa and the elongation was 8.48 %. Based on the room temperature and high temperature properties of the alloy, the best heat treatment process is finally determined as: 1000 °C/1 h/AC+650 °C/6 h/AC.

Effect of Pulse Current on Mechanical Behavior of High Temperature Titanium Alloy Ti55

The effects of pulse current on the tensile properties of high temperature titanium alloy Ti55 were investigated by pulse current assisted uniaxial tensile test under different electrical parameters. It was found that with the increase of peak current and pulse width, the tensile properties of Ti55 are significantly improved. At the same time, the pulsation effect of current on the mechanical properties of Ti55 was investigated. The results show that the tensile displacement of low pulsation group was higher, while the elongation of high pulsation group was higher. In order to explore the mechanism of pulsation effect of current, EBSD was adopted. The results indicated that high pulse current can significantly promote the dislocation movement and recrystallization. In addition, some macrozones was found in low pulsation group, which indicated that high pulsation current was more suitable for material forming than low pulsation current.

Interaction between Al and other alloying atoms in α-Ti for designing high temperature titanium alloy

Increasing the solubility of Al and inhibiting the growth of Ti3Al precipitates in high temperature titanium alloy improve both the thermal strength and thermal stability of the alloy. In principle, this may be achieved by adding some other alloying atoms which attract Al so as to serve as traps for Al in the alloy. In the present work, the interaction energies between Al and alloying atoms X with X covering all the transition metal (TM) and noble metal (NM) elements in the Chemical Elemental Period Table (CEPT) are calculated by using a first principles method in order to screen the traps for Al. The effects of temperature (taking Mo-Al interaction as an example) as well as the newly found off-center site-occupation of alloying atoms (Acta Mater. 197, 2020, 91) on the interaction energies are considered. We show that the interactions between Al and the TM alloying atoms early in the CEPT are weak. The middle TM alloying atoms attract but the late TM and NM ones repel Al. At finite temperature, the lattice vibration enhances whereas the configurational entropy weakens the Mo-Al attraction. Both effects become stronger with increasing temperature. The physical origins underlying the X-Al interactions are revealed by analyzing the electronic density of states and bonding charge density. Alloying atoms such as Mo, Tc, Ru, W, Re, and Os are identified to benefit the strength and thermal stability of high temperature titanium alloys. This work is helpful to the rational design of high temperature titanium alloys.