Titanium alloys are widely used in the manufacture of aero-engine blisks due to their low density, high strength, and excellent performance at medium and high temperatures. However, there are few studies on dynamic mechanical properties and adiabatic shear sensitivities of titanium alloy forgings for blisks. In this work, the dynamic mechanical properties of forged TC17 and TC4 alloys at high strain rates were examined by SHPB apparatus, and OM, SEM, EBSD were used to study the adiabatic shear behaviors of the two kinds of alloy. As the strain rate increases, the strength of both alloys increases, thus exhibiting the strain rate strengthening effect. At the same strain rate, TC4 alloy exhibits higher plastic strain and dynamic absorbed energy than those of TC17 alloy. TC17 alloy obtains a basket-weave microstructure after β forging, in which lath α-phases and residual β phases form more phase interfaces. ASBs tend to form at phase interfaces, which lead to a tendency for ASBs to bifurcate during propagating processes. TC4 alloy obtains a bimodal microstructure after α+β forging, and equiaxed primary α-phases show good ductility, which improve the dynamic plastic deformation ability. The regular arrangement of secondary α-phases results in fewer phase interfaces, leading to the difficulty in bifurcation of ASBs during propagating processes. Under dynamic interrupted compression conditions, ASBs in TC17 alloy are occurred earlier, and the localization energy of ASBs is low. Therefore, TC17 alloy has higher adiabatic shear sensitivity, and adiabatic shear sensitivities of both alloys increase with the increase of strain rates.

High speed cutting is an effective technique to achieve high efficiency and high quality machining of titanium alloy and other difficult materials. The high speed cutting process of titanium alloy has the nonlinear dynamic characteristics of high temperature, high strain and high strain rate. In order to accurately describe the dynamic mechanical behavior of titanium alloy in high speed cutting, the research on dynamic constitutive model of titanium alloy is reviewed. The application conditions, advantages and disadvantages of Johnson-Cook model, Zerilli-Armstrong model and Bammann model are analyzed from the perspective of phenomenological model and physical model with Ti-6Al-4V as the research object. After comprehensive comparison, the Johnson-Cook model is selected for further exploration, and the Johnson-Cook modified model is classified based on the influence of temperature and competition mechanism. The prediction accuracy of the Johnson-Cook modified model is improved compared with that of the classical model. At the same time, it is proposed that the construction of phenomenology-physics composite constitutive model can be taken as the key direction to explore the dynamic constitutive model of titanium alloy, and the method of experiment and computer synchronization can be used to obtain the optimal solution of constitutive model parameters, so as to improve the prediction accuracy of dynamic constitutive model.

α+β titanium alloys have a wide application prospect in aero engine blisk manufacturing, owing to their high specific strength and good high-temperature performance. Whereas there are few studies on mechanical properties and plastic deformation modes of large-size blisk specimens at variable strain rate conditions. In this work, the effects of different strain rates on the mechanical properties of forged TC17 and TC4 alloys were examined by tensile testing machine, and Vickers hardness tester, OM, SEM, and EBSD were used to study the Vickers hardness, deformation microstructures and fracture morphologies. As increasing strain rate, the strengths of both alloys increase and the elongation decrease, showing positive strain rate sensitivities of flow stress, and the strain rate sensitivity coefficients decrease with true strain. Besides the solid solution strengthening of alloying elements, lath α-phases and residual β-phases in TC17 alloy with basket-weave microstructure are interweaved with each other, resulting in more phase interfaces. Phase interfaces are effective in blocking dislocations motion and lead to pile-up of dislocations, improving the strength of TC17 alloy. In addition, the voids are easier to nucleate at the phase interfaces and form dimples. Therefore, a lot of small dimples are observed on the fracture surface, which make the poorer ductility of TC17 alloy. Fewer phase interfaces exist in TC4 alloy with bimodal microstructure, which is related to the better plastic deformation capacity of equiaxed primary α-phases and the regular arrangement of secondary α-phases in transformed β-phases. The fewer phase interfaces increase the mean free path of dislocations and form fewer large dimples, which lead to a decrease in strength but an increase in ductility of TC4 alloy.

Aiming at improving the strength-plasticity match in the as-cast state of the most widely used Ti-6Al-4V the present work designs Ti-Al-V-Zr alloys on the basis of the dual-cluster formula of Ti-6Al-4V, α-{[Al-Ti₁₂]（AlTi₂）}₁₂ +β-{[Al-Ti₁₄]（V₂Ti）}₅: first, the alloys are more biased towards α-Ti by decreasing the number of β unit to 2, then, the stability of β-Ti is improved by increasing the number of V atoms in β unit to 3, and finally, Zr （x=1-5） replaces Ti in the β unit. Finally α-{[Al-Ti₁₂]（AlTi₂）}₁₅-β-{[AlTi_14-xZr_x]V₃）}₂ is obtained, Ti-（6.64-6.82）Al-（2.42-2.35）V-（1.44-7.02）Zr （mass fraction,%） alloy is designed. The alloy ingots are prepared by melting in a non-consuming vacuum are furnace, and the alloy bars are suction-cast in copper mould. The results show that the alloys are all in α' martensite structure, showing morphologies changing from acicular Widmannstatten structure at lower Zr contents to net-basket structure at higher Zr contents. Among the designed alloys, Ti-6.64Al-2.35V-7.02Zr （x=5） with a net-basket structure, has the best mechanical properties: yield strength of 806 MPa, tensile strength of 963 MPa, and elongation of 5.9%, which are respectively 23%, 19% and 51% higher than those of Ti-6Al-4V alloy under the same preparation condition. In particular, the specific strength and specific hardness are 217kN•m/kg and 0.71 GPa•cm³/g, which are 18% and 10% higher than Ti-6Al-4V alloy.

In the current aviation industry, laser melting is an ideal technique for repairing and surface treatment of TC4 alloy parts, which has advantages over traditional metal repair techniques in terms of process. In this work, laser melting repair processes were performed on the surface of alloy specimens by different laser scanning speeds at a power of 2 kW, and the changes in metallographic organization, electrochemical corrosion properties and mechanical properties of the repaired surfaces were detected and analyzed. The results show that the significant microstructural changes are occurred during the laser repair process. The best corrosion resistance of the repaired surface is achieved at a laser scanning speed of 150 mm/min. The best microhardness and wear resistance of the repaired surface are achieved at 200 mm/min.

Under the high-energy particle impingement and cascade effect, different types of radiation damage defects occur in metals. The aggregation and evolution of radiation damage defects can lead to the destruction of the internal structural stability and the deterioration of their properties of metals. Titanium alloy is a promising radiation resistant alloy due to its advantages of light weight, high strength, high temperature resistance and low radiation activity. Aiming at the improvement of the radiation damage resistance, this work summarizes the research progress on the radiation damage defects, the microstructural features and mechanical properties of titanium alloys. In addition, the formation and evolution of radiation damage defects and the influence mechanism of radiation dose, temperature and element species on defect migration and aggregation are analyzed. The microstructure evolution of titanium alloys induced by irradiation and the radiation damage effects such as radiation hardening, radiation embrittlement and radiation creep are discussed. The radiation damage resistance properties of titanium alloys are summarized and evaluated. The existing researches are lack effective methods to inhibit the radiation damage. Finally, the effective strategies to improve the radiation resistance of titanium alloys through composition regulation and interface microstructure design are prospected.

As a new high-temperature structural material, Ti₂AlNb-based alloy originated from titanium alloy has excellent room temperature toughness, crack resistance, high temperature strength, oxidation resistance and other advantages, showing a broad application prospect in the aerospace field. To study the microstructure transformation mechanism and related kinetics of Ti₂AlNb alloy is of great significance to the alloy composition design and process optimization to obtain the required properties. This paper summarizes the research progress and deficiency of the structure transformation and the dynamic mechanism in Ti₂AlNb-based alloy, focuses on the research status of the growth kinetics of B2 phase and O phase at home and abroad in recent years, and points out that there is lack of research on the order disorder transformation kinetics, defect density related dynamics of Ti₂AlNb-based alloy. In the future, Ti₂AlNb-based alloy needs to be combined with gradually comprehensive dynamics research results to establish a theoretical model of microstructure evolution, so as to optimize alloy composition and process to meet more complex and severe service environment.

Selective electron beam melting (SEBM), which is a powder-bed fusion additive manufacturing technology has unique advantages in the preparation of intermetallic materials with low room temperature plasticity. Recently TiAl alloy parts prepared by SEBM have been successfully used in advanced aeroengines. In this study, crack-free TiAl alloy low-pressure turbine blade simulation parts were prepared by SEBM using Ti-48Al-2Cr-2Nb powder. The tensile properties of the samples at room temperature and the thermal shock resistance of the blades were evaluated. The results indicate that the room temperature tensile strength of TiAl alloy prepared by SEBM can reach 515 MPa after heat treatment, and the elongation after failure is 1.13%. No cracks are found after 120 cycles of thermal shocks at 700 °C tested by the water quenching. The crack perpendicular to the radial direction is appeared in the aerofoil position after 6 times of accelerated thermal shocks tested at 900 °C. Combined with the analysis of crack propagation path and crack fracture, it is determined that the main mechanism of blade component failure under thermal shock conditions is due to the stress concentration caused by the large surface roughness.

The hot compression tests of TB9 titanium alloy sample were carried out on Gleeble-1500 thermal simulator at the temperature range of 750-1000 ℃ and the strain rate range of 0.01-10 s⁻¹. The stress-strain curves obtained by the experiment were subjected to friction correction and the processing map was drawn according to the corrected stress-strain curve .The results show that the stress-strain curve after friction correction is obviously lower than that before correction, and the stress difference between them increased with the increase of strain. The corrected stress−strain curve is $ \sigma {\text{ = }}\frac{{\arcsin h{{[\frac{{\dot \varepsilon \exp (\frac{Q}{{RT}})}}{A}]}^{\frac{1}{n}}}}}{\alpha } $, and can used to predict the stress of TB9 titanium alloy under different strain rates at 750 ℃ to 1000 ℃. Instable deformation of TB9 titanium alloy leads to localize the deformation bands which is about 45° to the compression direction appeared, resulting in the inhomogeneous microstructure. Stable deformation during hot working in suitable process window can bring dynamic recrystallization and recovery in the alloy, which can improve the microstructure and properties of the alloy. According to the processing map, the suitable thermal deformation process parameters of TB9 titanium alloy are obtained as follows: deformation temperatures of 850-1000 ℃ at deformation rates of 0.01-1 s⁻¹.

The microstructure characteristics and formation mechanism of linear friction welded (LFW) TC4-DT damage-tolerant titanium alloy joint were investigated . The microstructure of each zone of the joint was analyzed in detail by using an optical microscopy and a scanning electron microscopy; the microhardness distribution of the joint was tested by means of a microhardness tester. The results show that dynamic recrystallization occurs in weld zone (WZ); the WZ temperature exceeds the β-transus temperature during welding, and both β→α′ and β→α phase transformation occur in WZ under rapid cooling after welding, resulting in a large number of α′ martensite and secondary lamellar α are formed. Due to the high deformation resistance of TC4-DT titanium alloy, the thermo-mechanically affected zone (TMAZ) of this joint is relatively narrow. The structure of the TMAZ is elongated, deformed and broken seriously under the strong thermo-mechanically coupling effect. Moreover, a few α′ martensite and a large number of secondary lamellar α are formed in TMAZ under the condition of rapid cooling after welding. The microstructure characteristics of α colony with different orientation of the base metal (BM) is basically preserved in the heat affected zone (HAZ). However, due to the influence of heat, the mutual diffusion of elements occurs at the α/β phase boundary in α colony, the interlayer β is consumed, and the primary α grows up. The refined crystalline strengthening and second phase strengthening of the WZ microstructure, the strain strengthening and second phase strengthening of the TMAZ microstructure, and the growth of α phase in the HAZ make the microhardness of above zones higher than that of the BM.

For the TC17 titanium alloy, the influence of the leading end angle of the mandrel on the expansion strengthening effect of the hole structure was studied, the surface integrity of the hole expansion strengthened under different process parameters was characterized, the high temperature and low cycle of the original and strengthened samples were tested. Fatigue life and the morphological characteristics of fatigue fracture are analyzed. The results show that the lead angle of the mandrel has a significant effect on the surface roughness after expansion. The uneven plastic flow of the metal on the surface of the hole wall during the expansion process leads to uneven residual stress distribution on the hole wall after expansion, and the residual stress amplitude at the exit end of the expansion is the largest, and the hole wall has a certain depth of residual compressive stress gradient field after expansion. When the interference of the core rod is constant, the fatigue life increases with the increase of the rear lead end angle of the mandrel. When the rear lead end angle is 8°, the median fatigue life gain after strengthening can reach 1.74 times, and the strengthening effect is the best, its minimum cycle life is 16331 times, which is higher than the longest cycle life of the original sample (13965 cycles). After strengthening, the origin of the cracks is changed from the multi-source type in the middle of the hole wall to the single-source crack initiation at the inlet end of the expansion.

In order to study the effect of hole extrusion strengthening process on the fatigue performance of Ti₂AlNb alloy, a simulation analysis model of residual stress of hole strengthening process was established. The distribution law of surface residual stress and strengthening mechanism after hole extrusion process were discussed. In this work, the hole extrusion experiments were carried out. The high temperature and low cycle fatigue performance of the compressed and un-compressed specimens were tested respectively. Meanwhile, the microstructure characteristics of the fatigue fracture of the two specimens were compared. The results show that the hole extrusion process can produce a strong residual compressive stress layer around the small hole, which effectively delays and inhibits the initiation and propagation of fatigue cracks, and significantly improves the high temperature and low cycle fatigue performance of Ti₂AlNb specimens.

TiAl alloy was electrochemically anodized in ethylene glycol electrolyte containing with NH₄F to prepare anodic film. The influence of anodization treatment on the oxidation behavior and mechanical properties of the anodized TiAl alloy were then characterized. Results shown that based on the halogen effect a continuous and dense Al₂O₃ oxide scale will generate on the anodized TiAl alloy after high temperature oxidation. After oxidation at 1000 ℃ for 100 h, the weight gain of the anodized TiAl alloy was dramatically decreased from 85.86 mg/cm² to 0.67 mg/cm². Moreover, it is shown that the surface hardness and elastic modulus of the anodized TiAl alloy decreased first and then increased with the prolonging of oxidation time. Meanwhile, the friction coefficient of the anodized TiAl alloy increased comparing to the bare TiAl alloy. The surface wear resistance of the anodized TiAl alloy exhibited similar phenomena. This is because that during high temperature oxidation process, aluminum fluorides selectively transport to the surface through pores or micro-cracks, and are oxidized to Al₂O₃ at the surface region. The influence of anodization treatment on the mechanical properties of the anodized TiAl alloy is attributed to the Al₂O₃ content contained in the oxide scale.

Because of the variety and complexity of solid-state phase transformation characteristics of titanium alloys, the relationship between their microstructure and performance has always been one of the hot topics in the field of titanium alloy materials science. By adjusting the composition, processing technology and heat treatment process parameters of titanium alloys, the microstructure type and parameters of titanium alloy parts can be adjusted to a certain extent to achieve the best matches in strength, plasticity, toughness, fatigue and fatigue crack propagation rate, etc. In this paper, based on the comparison of four typical microstructure characteristics including equiaxed microstructure, bimodal microstructure, lamellar microstructure, basket weave microstructure and their thermo-mechanical controlling technologies, taking the TC21 titanium alloy, TC4-DT titanium alloy, TC32 titanium alloy and TB17 titanium alloy for aviation use as examples to review the properties of strength, plasticity, fracture toughness, fatigue life and fatigue crack propagation rate, which can provide a reference basis for reasonably choosing microstructure parameters, optimizing properties, stabilizing mass production quality of titanium alloy products.

In the present study, Ti-10V-2Fe-3Al (Ti-1023) alloy was prepared by vacuum consumable melting and forging technique. The structural stability, microstructural evolution and mechanical behavior of the alloy were systematically investigated by X-ray diffraction, transmitting electron microscopy and mechanical testing. It is indicated that the structural stability, microstructure and mechanical behavior of Ti-1023 alloy are closely related to the cold deformation and heat treatment. Regardless of the solution treatments in single β phase region (833 ℃) or α + β phase region (753 ℃), double yielding occurs in the stress-strain curves of the alloy. This suggests that the β phases in the alloys with above solution treatments possess low structural stability, and stress induces β→α" martensitic transformation, leading to double yielding behavior. Severe cold rolling deformation and stress/strain induced martensitic transformation gives rise to the refinement of β grains and martensite variants. Since numerous dislocations and grain/phase boundaries induced by severe cold deformation can be used as nucleating sites for the precipitation of α phase, a large amount of fine α phase is precipitated out of the cold rolled Ti-1023 alloy after short aging at 550 ℃, therefore,the alloy exhibits a good balance between strength and ductility.

Titanium and titanium alloys are important lightweight structural materials in the fields of aviation, aerospace and defense weapons. The low elastic modulus of Ti alloy gives it excellent elastic function, and it is applied to fasteners, springs and other elastic components in aviation, aerospace and other industries. The currently used high-strength Ti alloys exhibit high Young’s modulus that can not fully meet the application requirements. The balance between high strength and high elastic property of conventional Ti alloys needs to be further improved.This paper reviews the current research and development of high strength and high elasticity Ti alloys. Based on the comprehensive understanding of high strength and high elasticity Ti alloys and the existing problems, the composition design method based on electronic theories and the structure design strategy based on phase stability of β-matrix of Ti alloys with high strength and high elasticity is proposed in this paper. The research progress of novel Ti alloys with high strength and high elasticity based on the proposed alloy design strategy is also briefly presented. Finally, the future research direction of Ti alloys with high strength and high elasticity is prospected.

The research and development in liquid metal atomisation and forming technologies of high performance metallic materials with the emphases on gas atomised superalloy powders, spray formed superalloys, powder metallurgy TiAl alloys and spray formed high-speed steels at Beijing Institute of Aeronautical Materials are reviewed. The technology and equipment of argon atomisation and minus atmospheric pressure atomisation (i.e. atomisation in sub-atmospheric pressure atomising assembly) of superalloy powders were established. Major factors contributing to powder oxygen content, particle size and non-metallic inclusions have been identified. A variety of high-purity, fine-grained and high-quality spherical powders of superalloys were produced , which have been utilised in the research and production of hot section components, such as turbine disks in advanced aero-engines. Spray forming technologies of highly-alloyed materials were investigated and developed while taking the key technical issues for making sound performs into process consideration, such as formation and deposition of droplets, densification and shape control, and hot working of preforms. The relative densities of as-deposited performs of superalloys and high-speed steels could be higher than 99.0% after the optimisation of process parameters. Low cost and high performance spray formed superalloys and high-speed steels were developed. Spherical powders of TiAl alloys with high purity and low oxygen content were obtained using the argon atomization techniques, and high performance sheets were subsequently deformed.

Carbon nanomaterials with low density, high strength, high elastic modulus, excellent conductivity and thermal conductivity are the ideal reinforcing phases for TiAl-based alloy. In this paper, the preparation and surface treatment methods of TiAl-based alloy modified by carbon nanofibers, carbon nanotubes and graphene are reviewed. The influence of material and processing on the interface structure and mechanical properties are introduced, and strengthening mechanisms are also summarized. The preparation technology of graphene modified TiAl-based alloy will be the key development direction of future research. The key problems of graphene uniform dispersion technology, interface reaction control and action mechanism in TiAl- based alloy matrix are the difficulties in the research field of this technology.

β-Ti alloys have been used in many military/commercial aircraft since 1950s. Their high specific strength, good corrosion resistance, and high formability meet the special requirement of certain structures. Despite a further understanding of the relationship among chemistry, processing, and microstructure, as well as the expanding of performance data base, there is some stagnation in commercialization of new alloys over the past 20 years. This paper reviews the development and applications of β-Ti alloys, and summarizes the important processing parameters for microstructure control. The widely used 5 kinds of high-strength β-Ti alloys are discussed based on their processing-microstructure-property relationship. From the cost and performance perspectives, the challenges and opportunities of β-Ti alloys are identified. Future research will be focused on alloy compositions with more robust processing widows and better performance matching. The integrated computational materials design technology will be a prospect to accelerate the workflow development of chemistry-processing- microstructure-performance for high strength β-Ti alloys.

Deformation and phase transformation are two major topics in the study of titanium alloy materials. Titanium alloys usually require a series of complex thermo-mechanical treatments to obtain a microstructure corresponding to service performance. Its hot deformation behavior is a typical thermo-mechanical coupling process. Deformation and phase transformation may occur simultaneously and affect each other. It is one of the current research hotspots. However, due to the inevitable existence of dynamic recovery / recrystallization, microstructure fragmentation / spheroidization, a large number of deformation defects, deformation texture, and stress-induced phase transformation during hot deformation, coupled with the changes of the phase transformation kinetics characteristics and the crystallographic mechanism of the variant selection under thermo-mechanical coupling, directly leads to the extremely complicated dynamic phase transformation behavior of the titanium alloy during the hot deformation process, and it becomes quite difficult to reveal its evolution law in depth. This paper summarizes the main characteristics and laws of titanium alloy deformation and phase transformation in view of the dynamic phase transformation behavior of titanium alloy during hot deformation,mainly introduces the research progress of the dynamic phase transformation of the titanium alloy under the thermo-mechanical coupling from the three aspects of precipitation phase morphology characteristics, variant selection mechanism and phase transformation kinetics characteristics, and summarizes and prospects its research and development trend.

Stress intensity factors (SIF) and crack mouth opening displacements (CMOD) for three-point bending beams with arbitrary span-to-width ratios (S/W) were calculated by using the Wu-Carlsson analytical weight function for edge-cracked finite-width plate and the analytical solution of un-cracked stress by Filon. Based on the analytical weight function and tabulated SIF and CMOD data for power-law crack-line stresses, SIF and CMOD for general polynomial crack face loadings could be rapidly determined by simple arithmetic. The results obtained for several span-to-width ratios determined by using fundamentally different methods are in excellent agreement with those in literature. A brief discussion is made for calculating cohesive fracture toughness by analytical weight function method. The present study provides a high efficient and accurate method for fracture mechanics analysis of the three-point bending beam with arbitrary span-to-width ratio.

The experimentation adopted low energy ball milling combining, with hot pressing sintering, to design and fabricate 3.4%（volume fraction）TiB_w/TA15(Mo,Si) titanium matrix composites, for investigating the effects of heat treatment on the composites’ microstructure and mechanical properties. Through phase analysis about the composites via X-ray and transmission electron microscopy (TEM), while also analyzing the composites’ microstructure via scanning electron microscope, Several results the experimentation has observed. Firstly, the added TiB₂ generated in-situ synthesized TiBw reinforcement which was distributed around the TA15 titanium alloy powder and formed a network microstructure. Moreover, fine (Ti,Zr)₅Si₃ reinforcement was formed by solid solution and precipitation mechanism and then Mo element was solid solution in β phase after MoSi₂ solution at high temperature. Secondly, solution treatment with 1200 ℃ did not change the microstructure of TiBw neither the characteristics of the network microstructure of the composites, and the matrix was turned into martensite α'. (Ti,Zr)₅Si₃ reinforcement was re-dissolved and transformed to supersaturated solid solution. Thirdly, after aging treatment at 550-700 ℃, the martensitic matrix was decomposed, and the supersaturated silicon element was precipitated at the interface of both α/β interface and the network boundary. The acicular martensite α' was gradually transformed into lamellar (α + β) phase, and the amount of silicide precipitates was gradually increased with the increase of aging temperatures. Later, the experimentation further utilized Instron-5569 universal testing machine to test and analyze the composites’ mechanical properties. The experimental results show that the strength of titanium matrix composites is increased first and then decreased with the increase of aging temperature instead, and the plastic change is opposite to the strength change. The compressive strength of TiB_w/TA15(Mo,Si) composites at 1200 ℃/45 min solution treatment is 1751 MPa, and the strain at break is 6.7%. After 1200 ℃/45 min solution treatment + 600 ℃/90 min aging treatment, the compressive strength of the composites reaches 1900 MPa and the strain at break decreases to 3.6%.