Titanium Alloy Tube Research Articles

Research on the Springback of Square TA18 Titanium Alloy Tube on the Numerical Simulation

This paper focuses on how bending and springback process of the titanium tubes with different bending radius and bending angle affect the springback rate after unloading and analyses tube distributions and variations of stress and strain by establishing a three-dimensional elastic-plastic finite element model of square TA18 titanium alloy tube based on ABAQUS/explicit and ABAQUS/standard. It is shown that under the same process parameters, the sprignback rate obtained by numerical simulation is in good agreement with that measured in the experiments. The springback rate after unloading increases with the increase of the bending radius linearly, and it increases nonlinearly with the decrease of bending angle. The distribution of the tube-roundness and the relationship between its roundness and springback rate under different process parameters could be obtained by comparing the variation of the absolute value of its outer wall unit at the maximum principal strain before and after unloading.

Effect of Heat Processing Technique on Microstructure and Mechanical Properties of Extrusion Beta Titanium Alloy Tube Blank

The effects of extrusion temperature and heat treatment on the microstructure and mechanical properties of beta-CEZ titanium alloy tube blank were studied with an emphasis on the relationship between the heat processing technique and microscopic structure. The results show that the extruded tube blank of beta-CEZ titanium alloy at alpha-beta phase has better tensile strength and plasticity match, and the ductility of the alpha-beta phase extrusion is obviously better than that of the single beta-phase extrusion, especially the reduction of area. When the extruded tube is heat treated at 830°C and 860°C solid solution, with the increase of aging temperature, the strength of tube decreases and the plasticity increases. When the aging temperature is up to 600°C, the reduction of area of the tube increases obviously. When the extruding tube is aged at 550°C and 600°C, the strength of the tube increases and the plasticity decreases with the increase of the solid solution temperature. The titanium alloy of beta-CEZ is extruded below the phase transition point after low temperature solid solution and high temperature aging treatment, which can achieve good microstructure and performance matching. The tensile strength is greater than 1250MPa, the elongation is more than 15%, and the reduction of area is more than 40%. The microstructure was a fine and uniform equiaxed structure.

Significance analysis of process parameters on cross section distortion of high-strength TA18 tube in numerical control bending

To achieve the precise numerical control (NC) bending and improve the forming quality of high-strength TA18 titanium alloy tube (TA18-HS tube), the significance of process parameters on cross section distortion in the TA18-HS tube NC bending should be clarified. Taking the TA18-HS tube of 6.35 mm × 0. 4064mm (out diameter × wall thickness) as the objective, a three dimensional (3D) elastic plastic finite element (FE) model based on virtual orthogonal test was used to explore the effects of process parameters on cross section distortion behaviors in the TA18-HS tube NC bending. The results show that the clearance between tube and mandrel Cm, the clearance between tube and bending die Cb, the friction between tube and wiper die fw and the mandrel extension length e are significant factors for cross section distortion in the TA18-HS tube NC bending, and the significant factors on cross section distortion from high to low are the Cb, e, fw and Cm. The cross section distortion degree increases with the increase of the Cb, fw, Cm or with the decrease of the e.

Modelling of hot rotary draw bending for thin-walled titanium alloy tubes

Titanium alloys tubes are largely used to manufacture structural parts and piping elements that work at high temperature in many applications of transport industry, thanks to their high strength-to-weight ratio and excellent corrosion resistance. Among the available manufacturing methods, tube rotary draw bending is the most promising to achieve challenging shapes with high level of accuracy and process robustness, even if defects, such as wrinkling, over thinning, distortion of the cross-sections and springback, are still critical to be controlled. At the same time, titanium alloy tubes can be hardly shaped at room temperature due to their high yield strength and low ductility. The use of temperature-assisted processes might allow overcoming the above-mentioned limitations, but, at now, such processes have not been investigated in depth. In this context, the paper aims at investigating by numerical simulations the effects of selective heating in the rotary draw bending of thin-walled titanium alloy tubes. A numerical model of the process was developed to investigate different heating strategies and process temperatures. The obtained results show that selective heating is promising and capable to influence the quality of the bent tubes.

Experimental and modelling study of an approach to enhance gas bulging formability of TA15 titanium alloy tube based on dynamic recrystallization

In order to further improve the hot gas bulging formability of laser-welded TA15 titanium alloy tube, studies about the effects of initial microstructures on the formability were carried out at 800 °C. Vacuum annealing procedures were performed to obtain different microstructures. The formability of these TA15 titanium alloy sheets with different microstructures was subsequently investigated by hot tensile tests and hot gas free bulging. A unified physically based material model considering dislocation density, work hardening, recrystallization, grain size and damage was built to analyze the deformation process. Results show that a good agreement was achieved between the unified material model and experiment results. The evolution of physical variables such as recrystallization fraction, and grain size can be predicted properly by the model. In the unified material model, the initial dislocation density would affect the dynamic recrystallization (DRX) rate. The DRX rate would increase with the increasing dislocation density. Therefore more DRX occurred at the early stage of deformation of initial material with higher dislocation density, while most of the DRX occurred at the middle-late stage of deformation of the annealed material with lower dislocation density. The initial material demonstrated the best formability due to the wide occurrence of DRX at the early stage of deformation, which increased the fraction of high angle grain boundaries, refined the microstructure, promoted the occurrence of grain boundary sliding and enhanced the formability of the material. However, most of the DRX occurred at middle-late stage of deformation of annealed material, which may increase the softening rate and lower the formability. Hence increasing the occurrence of DRX at the early stage of deformation by increasing the initial dislocation density in the material is an efficient approach to improve the gas bulging formability.

Tribological behaviors in titanium sheet and tube forming at elevated temperatures: evaluation and modeling

Warm forming has been an efficient approach to exploiting the forming potential of titanium alloy sheet and tube materials. However, the tribological condition between Ti-alloy sheet/tube and tools at elevated temperatures is a non-trivial issue and has yet not been fully explored and articulated. Taking CP-3 tube and Ti-6Al-4V sheet as case study materials, the tribological behaviors between Ti-alloy sheet/tube and tools at elevated temperature are revealed and modeled. The main results show that (1) by using the high-temperature twist-compression test combined with the design of experiments, the suitable tool materials, surface modification approaches, and lubricants are determined for warm forming of Ti-alloy sheet/tube, and the significant influential factors and their affecting rules/mechanisms on the coefficient of friction are identified; (2) a pressure- and temperature-related dynamic friction model is developed and implemented in the 3D-FE simulation of warm forming via ABAQUS/VFRIC; taking warm rotary draw bending of CP-3 tube as an application, the proposed friction model is experimentally validated, and the comparisons between the experimental results and the simulated ones indicate that the proposed model is much better than the Coulomb friction model in prediction of forming defects, such as wall thinning/thickening and wrinkling instability.

Effect of geometrical parameters on forming quality of high-strength TA18 titanium alloy tube in numerical control bending

Abstract The forming quality of high-strength TA18 titanium alloy tube during numerical control bending in changing bending angle β, relative bending radius R/D and tube sizes such as diameter D and wall thickness t was clarified by finite element simulation. The results show that the distribution of wall thickness change ratio Δt and cross section deformation ratio ΔD are very similar under different β; the Δt and ΔD decrease with the increase of R/D, and to obtain the qualified bent tube, the R/D must be greater than 2.0; the wall thinning ratio Δto slightly increases with larger D and t, while the wall thickening ratio Δti and ΔD increase with the larger D and smaller t; the Δto and ΔD firstly decrease and then increase, while the Δti increases, for the same D/t with the increase of D and t.

Texture Development of Ti-3Al-2.5V Titanium Alloy Tubes

Abstract The anisotropy, which is one of key mechanical properties of Ti-alloy tubes, is usually described in terms of the contractile strain ratio (CSR) macroscopically and dependent on the micro texture evolution. In order to understand the variation of CSR, the texture evolution of Ti-3Al-2.5V titanium alloy tubes was studied by Electron Back-Scattered Diffraction (EBSD). The results show that the basal poles of the α-phase incline from the radial direction to circumferential direction and stabilize around 45° between these two directions, and the strongly preferred orientation of the β-phase is observed with the increase of axial plastic strain. This change of texture decrease the CSR values rapidly in the initial stage, then they decrease slowly until stabilizing in the final stage. The simple model between CSR and texture quantity parameter f is modified by incorporating the texture component in the axial direction. Comparison with experiment shows that the modified model is in better agreement with the experimental values than the simple model.

Correlation between softening mechanisms and deformation non-uniformity of laser-welded titanium alloy tube during gas bulging process

In this paper, post-weld annealing was carried out to adjust the flow stress difference between weld seam and base material (BM). Deformation non-uniformity of laser-welded titanium alloy tubes before and after annealing was evaluated by gas bulging at 800°C. Results show that after double annealing (950°C/2h, air cooling+600°C/2h, air cooling), weld seam and BM had similar peak stress at first during tensile test at 800°C, 0.001s−1, then the flow stress difference between them changed dynamically due to different softening rates. The maximum flow stress difference ratio was reduced from 36% to 17% after annealing. Deformation uniformity of the bulged tube was improved by 24.6% after annealing, but the higher softening rate of BM during gas bulging confined its further improvement. At early stage of gas bulging of the annealed tube, the main softening mechanism for weld seam was dynamic recovery and that for BM was globularization of secondary α and phase transformation of α to β. At middle-late stage of gas bulging, the main softening mechanism for weld seam was partial globularization of lamella α and that for BM was wide dynamic recrystallization.

Effect of recrystallization on hot deformation mechanism of TA15 titanium alloy under uniaxial tension and biaxial gas bulging conditions

To investigate the effect of recrystallization on hot deformation mechanism of TA15 titanium alloy, rolled sheet and laser-welded tubes before and after recrystallization annealing were tested by uniaxial tensile tests and biaxial gas bulging respectively. The results show that both of the initial rolled sheet and the as-welded tube consisted of equiaxed α microstructure with high initial dislocation density. During uniaxial tensile tests, a quasi-steady flow state was achieved at 800°C, 0.001s−1, which demonstrated the best formability with a maximum elongation of 536%. Significant recrystallization occurred at the early stage of tensile deformation and the grain size was found to decrease first and then increase. Significant recrystallization also occurred at the early stage of the biaxial gas bulging of the as-welded tube. During the bulging of the annealed tube consisting of equiaxed α with low initial dislocation density, dynamic recrystallization (DRX) was the main microstructure evolution characteristic, but most of the DRX occurred at the middle-late stage. The relatively coarse equiaxed α and increasing fraction of low angle grain boundaries during deformation may restrict the occurrence of grain boundary sliding (GBS), which resulted in the relatively worse formability of the annealed tube. However, recrystallization which happened widely at the early stage, increased the fraction of high angle grain boundaries, refined the microstructure, promoted the occurrence of GBS and enhanced the formability of the initial rolled sheet and as-welded tube. It was also found that the stress state had no effect on the DRX mechanism for TA15 at 800°C, which was confirmed to be discontinuous dynamic recrystallization under both uniaxial tension and biaxial gas bulging conditions.

Effect of Boosting Velocity on Forming Quality of High-Strength TA18 Titanium Alloy Tubes in Numerical Control Bending

In order to reveal the effect laws of boosting velocity on forming quality of tube bending. A three dimensional (3D) elastic plastic finite element (FE) model of whole process of high-strength TA18 tubes in numerical control (NC) bending was established based on the FE code of ABAQUS, and its reliability was validated by using the experimental results in literature. Then, the effect laws of boosting velocity on deformation behaviors of high-strength TA18 tubes in NC bending were explored with respect to multiple defects such as wall thinning, wall thickening, cross section deformation and springback. The results show that wall thinning ratio decreases with the increasing of boosting velocity; wall thickening ratio increases with the increasing of boosting velocity; cross section deformation ratio decreases with the increasing of boosting velocity; springback decreases slightly with the increasing of boosting velocity.

The Role of Simulation in the Design of a Semi-Enclosed Tubular Embolus Retrieval.

A numerical analysis of a semi-enclosed tubular mechanical embolus retrieval device (MERD) for the treatment of acute ischemic stroke (AIS) is presented. In this research, the finite element analysis (FEA) methodology is used to evaluate mechanical performance and provide suggestions for optimizing the geometric design. A MERD fabricated from nickel-titanium alloy (Nitinol) tubing is simulated and analyzed under complex in vivo loading conditions involving shape-setting, crimping, deployment, and embolus retrieval. As a result, the peak strain of the shape-setting procedure is proved to be safe for the device pattern. However, the MERD shows poor mechanical behavior after crimping into a catheter, because the peak crimping strain obtains a value of 12.1%. The delivery and deployment step demonstrates that the artery wall has little risk of serious injuries or rupture. In addition, the process of simulation of embolus retrieval and device system migration inside the cerebral artery lumen provides useful information during the design process.

Assessment of microstructure and tensile behavior of continuous drive friction welded titanium tubes

Friction welding process has been applied to join Grade 2 titanium alloy tubes of outer diameter 60 mm and wall thickness 3.9 mm. In this research work, five different friction times (24, 28, 32, 36 and 40s) were used to evaluate the ultimate tensile strength (UTS) and microstructure of welded tubes. Recording of the process parameters during welding was done. Optical microscopy, electron back scattered diffraction and transmission electron microscopy were used to study the microstructure. The results showed that the friction time had a significant influence on the microstructure and UTS. The rate of deformation increased with friction time and refined the grains in the weld zone. Coarse grain structure was observed from the center of the weld zone towards the flash. Identical grain structure was observed in the heat affected zone (HAZ) and the parent metal. It was found that a maximum joint efficiency of 98.3% was achieved at a friction time of 32s.The details of microhardness, failure location and fracture surface of the welded tubes were reported.

Modelling of heat transfer process in condensing unit with titanium alloy tubes

One of the most important units of heat transfer equipment of a nuclear power plant is the condenser. Currently, at the nuclear stations of concern “Rosenergoatom” work is actively underway to replace the tubes of copper containing alloys to various steels or titanium alloys. Also, active work is underway on modernization of heat-exchange equipment of operating units. It is necessary to make the modelling of the parameters of condenser, to ensure that after the upgrade, the unit will continue operating normally. For this purpose, was created the model of module of tube bundle of condenser unit of K-33160 with tubes of titanium alloy. The modelling process is based on the equation of heat balance. In this work were modelled condenser of NPP of K-33160 with WWER-1000 reactor and the tubes of a titanium alloy VT0-1. The calculation was carried out for three presented methods and the error was less than 2%.

Approach to Enhance Gas Bulging Formability of TA15 Titanium Alloy Tube Based on Dynamic Recrystallization

Abstract In order to further improve the gas bulging formability of laser-welded TA15 titanium alloy tube, studies about the effects of initial microstructures on the formability were carried out at 800 ℃.Vacuum annealing procedures were performed to obtain different microstructures. The formability of these TA15 titanium alloy sheets with different microstructures was subsequently investigated by hot tensile test and hot gas free bulging. The results show that after the recrystallization annealing in the two phases field, the initial dislocation density of the material was reduced greatly due to recrystallization and the grains became coarser. After the double annealing at the near β phase field, phase transformation of α to β happened, secondary α formed in the β matrix and the equiaxed α grew coarser. The strength of material at elevated temperature increased and the ductility decreased after the annealing. Under the uniaxial tensile deformation, the material consisting of equiaxed α microstructure with high initial dislocation density exhibited the best formability. During its deformation, lots of dynamic recrystallization (DRX) happened due to its high initial dislocation density at the early stage of deformation, which increased the fraction of high angle grain boundaries, refined the microstructure, promoted the occurrence of grain boundary sliding and enhanced the formability of the material. The bulging results are consistent with the tensile results. The annealed tubes deformed more slowly due to the higher strength at elevated temperature. The tube consisting of equiaxed α microstructure with high initial dislocation density also exhibited the best formability. Therefore increasing the occurrence of DRX at the early stage of deformation by increasing the initial dislocation density in the material is an efficient approach to improve the gas bulging formability.

Anisotropic and asymmetrical yielding and its distorted evolution: Modeling and applications

Characterizing the anisotropy/asymmetry-induced distortional yielding and subsequent evolution is still a challenge for potential usages of hard-to-deform materials. From perspective of multiple mechanisms, two types of yield functions are classified, viz., the principal shear stress-based models (SSM) and the stress invariants-based models (SIM); then a unified continuum-based discontinuous (CBD) framework is constructed, in which SSM and SIM are introduced to capture the distorted shape of the yielding, and an interpolation approach is adopted to smoothly present the nonlinear evolution of the distorted plasticity in the full stress space. Taking the CPB06 (Cazacu et al., 2006) and Yoon's criteria (Yoon et al., 2014) as typical SSM and SIM, the CBD framework is implemented in the explicit 3D-FE platform for practical usages by combining implicit algorithm and interpolation approach, and the Nelder-Mead (N-M) method and the genetic algorithm (GA) approach are evaluated for calibrating of CBD related to convergence, overlapping and accuracy. The evaluation proves that the GA-based method is suitable for CBD, and the SIM seems to be feasible for embedding into the CBD framework because of its solid physical basis and numerical robustness. Taking high strength titanium alloy tube (HSTT) as a case, the distorted plasticity evolution of the HSTT with six typical initial textures are characterized, then the correlations among initial textures, distorted behaviors and inhomogeneous deformation are quantitatively established to improve the multi-defect constrained formability in uniaxial tension/compression and mandrel bending.

Establishment of a thermal damage model for Ti-6Al-2Zr-1Mo-1V titanium alloy and its application in the tube rolling-spinning process

Rolling-spinning of titanium alloy tubes is an advanced plastic forming technology that has been developed due to the urgent need for light-weight, high-precision, and high-reliability components in high-tech fields, such as aviation and aerospace. However, due to the complexity of the rolling-spinning process and the sensitivity of titanium alloy to temperature and strain rate, it is easy to crack, which severely restricts the improvement of the forming quality and forming limit of components. In this study, the critical deformation of Ti-6Al-2Zr-1Mo-1V was obtained by a hot compression test under various temperatures and strain rates. The damage threshold was obtained through FE simulation for the hot compression process under these temperatures and strain rates. The relationship among damage threshold, temperature, and strain rate was established by introducing the Zener-Hollomon factor. A thermal damage model for Ti-6Al-2Zr-1Mo-1V was established by combining the Oyane ductile fracture criterion with the relationship among damage threshold, temperature, and strain rate. By coupling this thermal damage model into the FE model for rolling-spinning of a Ti-6Al-2Zr-1Mo-1V tube, the damage prediction for the process was realized. The results show that the stress triaxiality at the top and bottom ends of the rolling zone is positive, the accumulation of damage is fast, and the strain rate is large in the zone. Thus, these ends are the zones most prone to damage in rolling process. The stress triaxiality at the local inner surface area of the spinning region is positive, the accumulation of damage is fast, and the strain rate is large in the zone. Therefore, the inner surface of the spinning region is the zone most prone to damage.

Formability and microstructure evolution for hot gas forming of laser-welded TA15 titanium alloy tubes

A laser-welded TA15 titanium alloy tube with outer diameter of 40mm and thickness of 2mm was fabricated successfully by hot U–O forming process combining with laser beam welding. The formability of the laser-welded tube was tested at 800°C by hot gas free bulging on the self-designed high pressure gas forming platform. Both the microstructure evolutions of the weld seam and basal material during the hot gas free bulging were investigated by optical microscope and electron backscattered diffraction. It was found that the bulging limit of the laser-welded TA15 titanium alloy tube was 73.9% and the uniform bulging ratio was close to 43.8% taking into account shape deviation and uniformity of wall thickness in this article. Due to the lower forming temperature and shorter forming time, the microstructure of the basal material was obviously refined after the hot gas bulging, which is quite different from the traditional gas forming process like superplastic forming. The main microstructure evolution of the laser-welded TA15 titanium alloy tube during hot gas free bulging was dynamic recrystallization under these conditions, which is also the leading reason for grain refining.

Springback FE modeling of titanium alloy tubes bending using various hardening models

In this study, effect of various material hardening models based on Holloman\'s isotropic, Ziegler\'s linear kinematic, non-linear kinematic and mixture of the isotropic and nonlinear kinematic hardening laws on springback prediction of titanium alloy (Ti-3Al-2.5V) in a tube rotary draw bending (RDB) process was investigated with presenting the keynotes for a comprehensive step by step ABAQUS simulation. Influence of mandrel on quality of the final product including springback, wall-thinning and cross-section deformation of the tube was investigated, too. Material parameters of the hardening models were obtained based on information of a uniaxial test. In particular, in the case of combined iso-nonlinear kinematic hardening the material constants were calibrated by a simple approach based on half-cycle data instead of several stabilized cycles ones. Moreover, effect of some material and geometrical parameters on springback was carried out. The results showed that using the various hardening laws separately cannot describe the material hardening behavior correctly. Therefore, it is concluded that combining the hardening laws is a good idea to have accurate springback prediction. Totally the results are useful for predicting and controlling springback and cross-section deformation in metal forming processes.

Effects of the U–O forming process on microstructure evolution of TA15 tubes

In view of the difficulty of manufacturing titanium alloy tubes, a U–O forming process was proposed to manufacture tubes with TA15 titanium alloy. The effect of the U–O forming process on the microstructure evolution of typical regions of TA15 tubes was investigated using electron backscattered diffraction technique. Results showed that the grain size of the U-shaped part was uniform when deformed at 750°С. Through microstructure evaluation of the O-shaped part, there were only slight changes concerning grain size compared with the initial plate because of the deformation sequence. However, in general, no significant changes concerning the grain size of most regions were observed when comparing the O-shaped tube with the initial plate, which indicated that the U–O forming process did not cause obvious changes in the initial microstructure in terms of grain size.