High Temperature Titanium Alloy Research Articles

Improving thermal stability and creep resistance by Sc addition in near-α high-temperature titanium alloy

High-temperature titanium alloys’ thermal stability and creep resistance are significant during service in high temperatures. This study systematically investigated the thermal stability and mechanical properties of Ti-6.5A1–2.5Sn-9Zr-0.5Mo-1Nb-1W-0.3Si-xSc (x, 0–0.5 wt.%) at 650 °C. The lamellar secondary α phase is refined and the formation of Sc2O3 is increased with the increasing scandium (Sc) additions, which improves the strength of the alloy, while excessive Sc2O3 becomes the crack source and deteriorates the plasticity. The oxygen content in the matrix is reduced by the interaction between Sc and oxygen, inhibiting the growth of the Ti3Al phase and improving the thermal stability of the alloy. Meanwhile, Sc accelerates the dissolution of the residual β phase and precipitation of fine, diffusely distributed ellipsoidal silicides, which strongly prevents dislocation movement. The enhancement of creep resistance for the Sc-containing alloy is attributed to the refined lamellar secondary α phases, Sc2O3 particles, Ti3Al phase, and silicides, especially the precipitated silicides. Eventually, the 0.3Sc alloy shows optimal thermal stability (the plasticity loss rate 17.3%) and creep resistance (steady-state creep rate 4.4 × 10–7 s–1). The investigation results provide new insights into the mechanism and thermal stability improvement in high-temperature titanium alloys modified by rare earth (RE).

Effect of α+β phase rolling and aging treatment on laminated bimodal structure in high temperature titanium alloy

In this work, we have prepared a novel laminated bimodal structure with layer-by-layer distribution of αp and αs phase in high temperature titanium alloy by α+β phase rolling and aging treatment. The lamellar bimodal microstructure is comprised of long-primary αp and secondary αs phase in the Ti-6.0Al-3Sn-5Zr-0.5Mo-1.0Nb-1.0Ta-0.4Si-0.2Er alloy. During α+β phase rolling at 990 °C, the primary αp grain deformed to elongated layer structure, while the lamella secondary αs deformed to kinked and broken chaos morphology. After 800 °C for 1h stabilization and 700 °C for 5h aging treatment, the thickness of the elongated αp layer slightly grew, while the kinked and broken αs were recovered and partially recrystallized to form a layered fine grain structure. The lamellar bimodal microstructure, i.e., elongated primary αp with layered bimodal αs phase has enhanced strength and ductility of the high temperature titanium alloy. This enhanced strength and toughness is mainly attributed to the lamellae αp structure and layered fine αs grain formed by hot rolling and aging treatment.

Investigation on the Optimal Amount of Y and B Elements in High-Temperature Titanium Alloy Ti-5.9Al-4Sn-3.9Zr-3.8Mo-0.4Si-xY-yB

This article presents a novel and feasible approach for researching the quantity of the ceramic phase and component optimization in high-temperature titanium alloys with small trace amounts of ceramic phases. Different near-α titanium alloys with varying yttrium and boron contents were prepared through the utilization of a vacuum non-consumable arc furnace melting method. The alloy used was a Ti-5.9Al-4Sn-3.9Zr-3.8Mo-0.4Si base. Its microstructure, texture, mechanical properties, and fracture behavior were studied. The observation of the as-cast structure shows that the addition of different doses of trace Y and B elements significantly refines both the original β grains and α grains. Moreover, the addition of the B element transforms the Widmanstätten structure in the titanium alloy structure into a basketweave structure. The addition of Y can refine the grain structure, improve the uniformity of the matrix structure, and act as a strong deoxidizer, which will take away the oxygen in the matrix and purify it. The TiB whiskers generated with the addition of B promotes dynamic recrystallization behavior and leads to more equiaxed α grains being precipitated around them, resulting in a significant refinement of the microstructure of the as-cast alloy. After adding a small amount of B, the texture strength of the α phase is significantly reduced, indicating that TiB whiskers inhibit the formation of texture. After conducting performance screening and structure analysis, the study supplements the analysis of Y’s regulation of the titanium alloy structure. The regulation is primarily explained by combining the results of the analysis of boron content, phase diagram analysis, mechanical properties, and fracture analysis. The mechanical analysis introduces the unique load transfer strengthening of TiB whiskers combined with an analysis of high-temperature mechanical properties, as the threshold for addition. The optimal amounts of Y and B additions are 0.6 wt% and 0.8 wt%, respectively. The optimized alloy obtained under this condition can achieve a tensile strength of 950 Mpa at 500 °C without any plastic deformation or heat treatment.

Creep rupture life prediction of high-temperature titanium alloy using cross-material transfer learning

High-temperature titanium alloys are the key materials for the components in aerospace and their service life depends largely on creep deformation-induced failure. However, the prediction of creep rupture life remains a challenge due to the lack of available data with well-characterized target property. Here, we proposed two cross-materials transfer learning (TL) strategies to improve the prediction of creep rupture life of high-temperature titanium alloys. Both strategies effectively utilized the knowledge or information encoded in the large dataset (753 samples) of Fe-base, Ni-base, and Co-base superalloys to enhance the surrogate model for small dataset (88 samples) of high-temperature titanium alloys. The first strategy transferred the parameters of the convolutional neural network while the second strategy fused the two datasets. The performances of the TL models were demonstrated on different test datasets with varying sizes outside the training dataset. Our TL models improved the predictions greatly compared to the models obtained by straightly applying five commonly employed algorithms on high-temperature titanium alloys. This work may stimulate the use of TL-based models to accurately predict the service properties of structural materials where the available data is small and sparse.

Mechanism of graphene oxide promoting silicide precipitation in high-temperature titanium alloy

Graphene oxide (GO) can strongly promote the precipitation of silicide and improve the strength of high-temperature titanium alloys. However, it is difficult to control the precipitation location and size of silicide due to the unclear influence mechanism. In this paper, the mechanism of GO promoting silicide precipitation in high-temperature titanium alloy was studied by EPMA, SEM, TEM and theoretical analysis. With the increase of GO in the range of 0–0.50 wt%, the amount and size of silicide both increased significantly. The nanoscale silicide precipitated only at α/β phase boundaries in the high-temperature titanium alloy without GO, and microscale silicide precipitated simultaneously at α/β phase boundaries and in α phase when the amount of GO reached 0.30 wt%. The reason of GO promoting silicide precipitation was that the increase of α phase content by pinning phase boundaries and introducing C and O elements by GO led to the increase of Si concentrations in both α and β phases during hot isostatic pressing. Finally, the quantitative relationship between the maximum precipitation temperature of silicide and addition amount of GO was established to provide a basis for the composition and process design of GO reinforced high-temperature titanium matrix composites.

A Review of Additive Manufacturing Techniques and Post-Processing for High-Temperature Titanium Alloys

Owing to excellent high-temperature mechanical properties, i.e., high heat resistance, high strength, and high corrosion resistance, Ti alloys can be widely used as structural components, such as blades and wafers, in aero-engines. Due to the complex shapes, however, it is difficult to fabricate these components via traditional casting or plastic forming. It has been proved that additive manufacturing (AM) is an effective method of manufacturing such complex components. In this study, four main additive manufacturing processes for Ti alloy components were reviewed, including laser powder bed melting (SLM), electron beam powder bed melting (EBM), wire arc additive manufacturing (WAAM), and cold spraying additive manufacturing (CSAM). Meanwhile, the technological process and mechanical properties at high temperature were summarized. It is proposed that the additive manufacturing of titanium alloys follows a progressive path comprising four key developmental stages and research directions: investigating printing mechanisms, optimizing process parameters, in situ addition of trace elements, and layered material design. It is crucial to consider the development stage of each specific additive manufacturing process in order to select appropriate research directions. Moreover, the corresponding post-treatment was also analyzed to tailor the microstructure and high-temperature mechanical properties of AMed Ti alloys. Thereafter, to improve the mechanical properties of the product, it is necessary to match the post-treatment method with an appropriate additive manufacturing process. The additive manufacturing and the following post-treatment are expected to gradually meet the high-temperature mechanical requirements of all kinds of high-temperature structural components of Ti alloys.

Effect of hydrogen on hot deformation behavior and microstructure evolution of Ti65 alloy

Thermohydrogen processing (THP) is a potential method for enhancing the formability of titanium alloys. However, there has been no report on the deformation behavior and microstructure evolution of hydrogenated Ti65 alloys, which are new high-temperature titanium alloys used above 600 °C. In this study, we conducted a series of isothermal hot compression tests in the α+β and β phase field of Ti65 alloy specimens with varying hydrogen content to investigate the effect of hydrogen on high-temperature flow behavior and microstructure evolution. The results showed that after hydrogenation, the number of α phases in Ti65 alloy significantly decreased. δ hydride precipitates were observed in the specimen with 0.43 wt% hydrogen, resulting in an apparent refinement of its microstructure. Adding 0.25 wt% hydrogen reduced the deformation temperature by about 60 °C and increased deformation strain rate by nearly two orders of magnitude for Ti65 alloy. This improvement can be attributed to how hydrogen promotes dislocation movement, dynamic recrystallization (DRX), and dynamic recovery (DRV) during deformation. Similarly, as strain increases, the instability region on the hot processing map gradually decreases or even disappears due to broadening effects from added hydrogen; thus expanding its hot processing window further. This research deepens our understanding regarding deformation behavior while providing theoretical guidance for THP applications using Ti65 alloy.

Effect of Y Content on Precipitation Behavior, Oxidation and Mechanical Properties of As-Cast High-Temperature Titanium Alloys

To improve the heat resistance of titanium alloys, the effects of Y content on the precipitation behavior, oxidation resistance and high-temperature mechanical properties of as-cast Ti-5Al-2.75Sn-3Zr-1.5Mo-0.45Si-1W-2Nb-xY (x = 0.1, 0.2, 0.4) alloys were systematically investigated. The microstructures, phase evolution and oxidation scales were characterized by XRD, Laser Raman, XPS, SEM and TEM. The properties were studied by cyclic oxidation as well as room- and high-temperature tensile testing. The results show that the microstructures of the alloys are of the widmanstätten structure with typical basket weave features, and the prior β grain size and α lamellar spacing are refined with the increase of Y content. The precipitates in the alloys mainly include Y2O3 and (TiZr)6Si3 silicide phases. The Y2O3 phase has specific orientation relationships with the α-Ti phase: (002)Y2O3 // (1¯1¯20)α-Ti, [110]Y2O3 // [4¯401]α-Ti. (TiZr)6Si3 has an orientation relationship with the β-Ti phase: (022¯1¯)(TiZr)6Si3 // (011)β-Ti, [1¯21¯6](TiZr)6Si3 // [044¯]β-Ti. The 0.1 wt.% Y composition alloy has the best high-temperature oxidation resistance at different temperatures. The oxidation behaviors of the alloys follow the linear-parabolic law, and the oxidation products of the alloys are composed of rutile-TiO2, anatase-TiO2, Y2O3 and Al2O3. The room-temperature and 700 °C UTS of the alloys decreases first and then increases with the increase of Y content; the 0.1 wt.% Y composition alloy has the best room-temperature mechanical properties with a UTS of 1012 MPa and elongation of 1.0%. The 700 °C UTS and elongation of the alloy with 0.1 wt.% Y is 694 MPa and 9.8%, showing an optimal comprehensive performance. The UTS and elongation of the alloys at 750 °C increase first and then decrease with the increase of Y content. The optimal UTS and elongation of the alloy is 556 MPa and 10.1% obtained in 0.2 wt.% Y composition alloy. The cleavage and dimples fractures are the primary fracture mode for the room- and high-temperature tensile fracture, respectively.

Enhanced mechanical properties of a near-α titanium alloy by tailoring the silicide precipitation behavior through severe plastic deformation

The microstructure evolution, tensile properties, and strengthening mechanisms of a near-α high-temperature titanium alloy with high Zr and Si content during isothermal multi-dimensional forging (IMDF) at the β-phase region were systematically investigated. The results show that the alloys exhibit a basket-weave microstructure after IMDF, with the silicides diffusely distributed in the matrix. As the forging temperature decreased, the intragranular primary α laths became more refined and the volume fraction of silicides increased, while the average size of silicides gradually decreased. The dynamic spheroidization of α laths occurs preferentially at the prior β grain boundary and extends into the grains as the deformation temperature decreases. The IMDF-1100 alloy possesses excellent high-temperature tensile properties and moderate room-temperature tensile properties, with ultimate tensile strengths (UTS) of 738.4 MPa and 1124.8 MPa at 650 °C and room temperature, respectively, which makes the alloy have tremendous potential for aerospace applications. The strengthening of the alloy at room temperature is primarily attributed to microstructure refinement and the thermal mismatch between silicide and matrix. However, owing to the weakening of grain boundaries at 650 °C, grain refinement leads to a decrease in tensile strengths. When tensile at 650 °C, the fragmentation and decohesion of large-size silicides tend to cause premature fracture of the alloy, and the microstructure with small-size silicide distribution presents better ductility.

High temperature softening mechanism of powder metallurgy TA15 alloy

The understanding of softening mechanisms for high-temperature titanium alloys at service temperature is essential to guarantee their service stability and safety. High-temperature softening is mainly manifested as grain boundary softening for metallic materials. To clarify the softening mechanism and failure mode of high-temperature titanium alloy TA15 (Ti-6.5Al–2Zr–1Mo–1V, wt.%) at temperature around service temperatures, coarse prior β grains were obtained by spark plasma sintering at 1300 °C, other than 1000 °C which is the traditional power metallurgy (P/M) consolidation temperature for TA15. Meanwhile, the effect of grain boundary softening was amplified. The high-temperature tensile test was carried out at 500–650 °C at intervals of 50 °C. The experimental results showed the maximum prior β grain size of P/M TA15 alloy is 2.9 μm, and its tensile strength decreases from 579 to 389 MPa with the increase of tensile temperature from 500 °C to 650 °C. Combined with calculation according to the Read-Shockley formula and analysis by macro-fracture, which show that the grain boundary strength is higher than the grain strength at 500 and 550 °C, and there are obvious grain and phase boundary torsion. The fracture mode demonstrated as a trans-granular fracture. The specimens soften rapidly, grain boundary strength decreases to less than grain strength, which led to fracture mode changed to inter-granular fracture at tensile temperatures up to 600 °C. If the crack extends to the critical length, the stress at the crack tip reaches easily the fracture strength of P/M TA15 alloy, and crack propagates rapidly at the temperature above 600 °C. Moreover, which corresponds to the elongation of true stress-strain decreasing with the increase of test temperature. OM and EBSD result demonstrated that the equi-cohesive temperature of TA15 alloy between 550 °C and 600 °C. Our findings provide a promising route to improve service temperature of high temperature TA15 alloy by raising the equi-cohesive temperature area in zone Ⅱ to a higher temperature.

Forming Analysis and Heat Treatment of TC31 Titanium Alloy Component with High Ribs and Thin Webs

TC31 is a new type of high-temperature titanium alloy, but few researchers have studied the combination of forming and heat treatment of a component using this material. The component with high ribs and thin webs was studied by numerical simulation and trail production. Based on the establishment of the finite element model, the forming process was analyzed by simulation software, and the maximum forming load of the component was 1920 kN. Ultimately, there were no folding defects of the component during the forming process. The material flow law was revealed by selecting the typical section of the component, and then the forming process was verified and the fully filled component was obtained. After that, the component was subjected to post-processing, and three heat treatment methods were designed to conduct heat treatment experiments on it (heat treatment: solution treatment and aging treatment). By analyzing the influence of three heat treatment methods on mechanical properties, the optimal heat treatment method was obtained, namely a solution treatment at 960 °C for 2.5 h and aging treatment at 610 °C for 7 h. The ultimate tensile strength, yield strength, elongation, and section shrinkage of the component through forging forming and heat treatment are higher than those of original material; meanwhile, it also indicates that the designed heat treatment has a better effect on the high-temperature mechanical properties of this titanium alloy at 650 °C than that at 450 °C. The research on the combination of the forming and heat treatment of this component provides a reference for the engineering application of high-temperature titanium alloys.

Evolution and mechanism of combustion microstructure of 600 ℃ high temperature titanium alloy

Oxides formed in the combustion process significantly affect the flame retardancy of titanium alloys, however, the evolution mechanism and formation mechanism of the combustion products of 600 ℃ high temperature titanium alloy remain uncertain. Frictional ignition method is employed in this paper to study the combustion behaviors of 600 ℃ high temperature titanium alloy, and the flame retardancy is evaluated according to the friction time, oxygen content and combustion state. <i>In-situ</i> observation of the burning phenomenon at the friction position and morphology after combustion is investigated, and the combustion states can be divided into oxidation stage, ignition stage and extended combustion stage. Further microstructure analysis is conducted subsequently by focus ion beam (FIB) and high resolution transmission electron microscope (HRTEM) to characterize the oxidation products with different valences in different zones of combustion microstructure. Al<sub>2</sub>O<sub>3</sub>, Ti<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> are observed as the main combustion products in the heat-affected zone, melting zone and combustion zone, respectively. Notably, TiO<sub>2</sub> is found to be formed by Ti<sub>2</sub>O<sub>3</sub> under the combustion condition, which is different from the TiO<sub>2</sub> transformed from the TiO mesophase under oxidation condition. This results in a lax structure composed of spherical Ti<sub>2</sub>O<sub>3</sub> particles and porous Ti matrix in the melting zone. Thermodynamic calculations including Gibbs free energy and decomposition pressure are discussed to explain the evolution mechanisms and formation mechanisms of different oxides. It is revealed that an Al content of 6% is insufficient to form a continuous protective Al<sub>2</sub>O<sub>3</sub> layer at the interface of the melting zone and heat affected zone. The difference in reaction path between TiO<sub>2</sub> formed by TiO and by Ti<sub>2</sub>O<sub>3</sub> can be ascribed to the formation of gaseous TiO phase. The sharp increase of TiO vapor pressure at about 1800 K reduces the stability of titanium oxide, thus causing the as-formed TiO to evaporate rapidly and forcing titanium to transform into TiO<sub>2</sub> via a more stable phase, Ti<sub>2</sub>O<sub>3</sub>. The formation of the porous structure composed of Ti<sub>2</sub>O<sub>3</sub> and Ti at the melting zone provides a path for the rapid internal diffusion of oxygen, which severely deteriorates the oxygen prevention capability of as-formed oxide layers. Besides, the TiO<sub>2</sub> synthesized from Ti-O melt in the combustion zone can hardly protect the inner structure. Therefore, the flame retardancy of 600 ℃ high-temperature titanium alloy is far from satisfactory.

Microstructure and mechanical properties of particle reinforced high-temperature titanium composites

In this research, a novel high-temperature titanium alloy, Ti750, was used as matrix and SiCp, SiCw, B4C, and GNPs as reinforcements to prepare both ex situ and in situ composites using spark plasma sintering process. The microstructure and mechanical properties of the samples were then examined and evaluated. The results show that the microstructures and phase compositions of the ex situ composites contain mainly SiC particles homogeneously distributed in the α-Ti matrix. The in situ synthesized composite, however, mainly contains TiC and Ti5Si3 reinforced phases in the Ti-rich matrix. The in situ composite had the best mechanical properties among all the materials. It recorded 1164 HV and 924 MPa in Vickers microhardness and room temperature compressive tests respectively. It also had the lowest apparent porosity (4.89%) among the composites but slightly higher than matrix material (4.67%). The in situ composite thus presents a better option to the Ti750 alloy which is currently used for high-temperature applications.

Effect of hot isostatic pressing processing parameters on microstructure and properties of Ti60 high temperature titanium alloy

Hot isostatic pressing parameters are critical to Ti60 high temperature titanium alloy castings which have wide application perspective in aerospace. In order to obtain optimal processing parameters, the effects of hot isostatic pressing parameters on defects, composition uniformity, microstructure and mechanical properties of Ti60 cast high temperature titanium alloy were investigated in detail. Results show that increasing temperature and pressure of hot isostatic pressing can reduce defects, especially, the internal defects are substantially eliminated when the temperature exceeds 920 °C or the pressure exceeds 125 MPa. The higher temperature and pressure can improve the microstructure uniformity. Besides, the higher pressure can promote the composition uniformity. With the temperature increases from 880 °C to 960 °C, α-laths are coarsened. But with increasing pressure, the grain size of prior-β phase, the widths of α-laths and α-colony are reduced. The tensile strength of Ti60 alloy is 949 MPa, yield strength is 827 MPa, and the elongation is 11% when the hot isostatic pressing parameters are 960 °C/125 MPa/2 h, which exhibits the best match between the strength and plasticity.

Dynamic transformation of a near alpha high-temperature titanium alloy during hot deformation

The rapid drop of peak flow stress in the initial stage of hot compression experiment was found to be related to the occurrence of dynamic transformation from alpha phase (hcp) into beta phase (bcc) of a near α high-temperature titanium alloy. In order to predict the flow stress at all strain, the dynamic recovery (DRV) model and the Back-Error Propagation (BP) neural network architecture were established and comprehensively utilized to characterize the flow stress, which exhibited high accuracy in tracking the flow behavior at different deformation parameters. The variation of peak flow stress at initial stage of hot compression indicated that the rapid drop extent of peak value increased with the rise of deformation temperature, the decrease of strain rate and the increase of strain. It was worth noting that the dynamic transformation evolution in the microstructure exhibited the consistent variation of peak flow stress with different deformation parameters. The high-magnification microstructure analysis indicated that the dynamic transformation was accomplished by the immigration of α/β interface and the penetration of beta phase into alpha phase from edge to inside, all of which were related to the dislocation motion. The experimental result proved that the dynamic transformation was the dominant factor resulting in the rapid drop of peak flow stress at the initial stage of hot deformation.

The preparation of gradient titanium alloy through laser deposition

Functionally gradient materials (FGMs) with continuous variation in composition or microstructure can realize gradient properties in different positions of the same component. The layer-by-layer laser deposition additive manufacturing is one of the most promising technologies that prepare FGMs with gradient properties. The present study is focused on the preparation of gradient titanium alloy by laser depositing Ti2AlNb powders on the substrate of a near-α high temperature titanium alloy. The microstructure, composition, and micro-hardness of prepared gradient titanium alloy with and without transition layer were compared and analyzed. Results show that an obvious bonding interface with variant microstructure morphology and element contents formed during directly deposited Ti2AlNb powders on near-α titanium alloy substrate and the bonding interface exhibits higher micro-hardness than the substrate and the deposited zone. However, the microstructure and the element exhibit gradient distribution characteristics along the deposition direction after adding the mixed powders of both two alloys as intermediate transition layers between the near-α titanium alloy and the Ti2AlNb alloy. The gradient distributed micro-hardness from the substrate to the top deposited zone sufficiently demonstrates the feasibility of obtaining gradient properties of gradient titanium alloy with composition transition layer during laser depositing.

Influence of silicide and texture on the room temperature deformation size effect of Ti65 alloy sheets/foils and its constitutive model modification

In micro-scaled plastic deformation process such as micro-forming, material size effect is challenging to investigate and reveal using traditional material models. Since high-temperature titanium alloys have become the critical materials of micro-parts depending on outstanding mechanical properties, studying the effect of texture and silicide precipitate on size effect in microtensile deformation of a high-temperature titanium alloy is of great significance because the size effect of highly alloyed titanium alloys has been less studied. In the present study, various heating treatments were performed to regulate grain size and texture and obtain silicide precipitate. The room temperature tensile tests were carried out to investigate the effect of the texture and silicide precipitate on the size effect of plastic deformation behaviour. It is revealed that silicide precipitation in the heat-treated specimens can lead to a more obvious “smaller is weaker” phenomenon and the specimens with transverse textures show a better strength–ductility match. In addition, considering solution strengthening, grain boundary strengthening and precipitation strengthening, the material constitutive model is modified by the effect of silicide and texture on the size effect, allowing for an accurate description of the tensile deformation characteristics at the microscopic scale. The results of the physical experiments and the hybrid constitutive model provide a basis for understanding and further exploration of the microscale plastic deformation behaviour of high-temperature titanium alloys.

Characterization of Hot Deformation of near Alpha Titanium Alloy Prepared by TiH2-Based Powder Metallurgy.

TiH2-basd powder metallurgy (PM) is one of the effective ways to prepared high temperature titanium alloy. To study the thermomechanical behavior of near-α titanium alloy and proper design of hot forming, isothermal compression test of TiH2-based PM near-α type Ti-5.05Al-3.69Zr-1.96Sn-0.32Mo-0.29Si (Ti-1100) alloy was performed at temperatures of 1123–1323 K, strain rates of 0.01-1 s−1, and maximum deformation degree of 60%. The hot deformation characteristics of alloy were analyzed by strain hardening exponent (n), strain rate sensitivity (m), and processing map, along with microstructure observation. The flow stress revealed that the difference in softening/hardening behavior at temperature of 1273–1323 K and the strain rate of 1 s−1 compared to the lower deformation temperature and strain rate. The strain hardening exponents at temperatures of 1123 K are all negative under all strain rates, and the most severe flow softening with minimum value of n was observed at 1123 K and 1 s−1. The strain rate sensitives showed that the peak region with m value greater than 0.5 generally appeared in the high temperature range of 1273–1323 K, while strain rate sensitivity at low temperature behaved differently with strain rates. The processing map developed for strain of 0.6 exhibited high power dissipation efficiency at high temperatures of 1273–1323 K and a low strain rate of 0.01 s−1, due to microstructure evolution of β phase. The decrease of strain rate at 1323 K resulted in the formation of globularization of α lamellae. The instability domain of flow behavior was identified in the temperature range of 1123–1173 K and at the strain rate higher than 0.01 s−1 reflecting the localized plastic flow and adiabatic shear banding, and inhomogenous microstructure. The variation of power dissipation energy (η) slope with strain demonstrated that the power dissipation mechanism during hot deformation has been changed from temperature-dependent to microstructure-dependent with the increase of temperature for the alloy deformed at 0.1 s−1. Eventually, the optimum processing range to deform the material is at 1273–1323 K and a strain rate range of 0.01–0.165 s−1 (ln = −4.6–−1.8).

First-principles investigation of interaction between surface oxygen and other alloy atoms in α-Ti (0001) for designing high-temperature titanium alloy

The high-temperature titanium alloy faces the dilemma that the oxidation resistance decreases sharply with the increase of temperature. The first-principle calculation has been proved to reveal the antioxidant mechanism from the atomic perspective. Therefore, the changes in Ti-O interaction and oxygen diffusion barrier in α-Ti (0001) crystal plane doped with the alloying elements X have been systematically studied by first-principles calculations. The alloying elements that may improve the oxidation resistance of high-temperature titanium alloy were screened. On this basis, the effect of multi-alloying of Al and screening element Xt on oxygen adsorption and diffusion was further studied. The results show that the adsorption energy depends on the contribution of X-O/Ti-O covalent interaction. Compared with other alloying elements, Nb and Ta can weaken the adsorption of O and hinder the diffusion of surface O to sublayer, which is expected to improve the oxidation resistance of high-temperature titanium alloys. When Al-Ta co-doped, the hindering effects on oxygen adsorption and oxygen diffusion can be superimposed. When both elements are located on the surface, the adsorption and diffusion of oxygen are the most difficult. This work contributes to the rational design of high-temperature titanium alloys.

Producing high-temperature titanium alloys of Ti–Al–Zr–Si–Mo–Nb–Sn system by electron beam melting

The Paton Welding Journal, 2022, №07. 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.