Titanium Alloy Sheet Research Articles

Microstructure evolution and hydrogen absorption characteristics of gradient-hydrogenated Ti-4.5Al-3V-2Mo-2Fe alloys

Ti-4.5Al-3V-2Mo-2Fe rolled material is a dual-phase titanium alloy with an average grain size of less than 3 μm; its optimal superplastic forming temperature of 760 °C is at least 50 °C lower than the temperature required for diffusion bonding, making it challenging to carry out superplastic forming/diffusion bonding within a process window. The promotion of hydrogen on the low-temperature diffusion bonding of the alloy was verified through thermohydrogen processing, and the absorption characteristics of hydrogen in the alloy at various temperatures, holding times, and pressures were investigated. Subsequently, a mathematical model for achieving standardized hydrogen content was developed. X-ray polycrystalline diffractometer (XRD) analysis was utilized to preliminarily explore phase differences in samples with varying levels of hydrogen content. Furthermore, scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron back scatter diffraction (EBSD) and time of flight secondary ion mass spectrometry (TOF-SIMS) were employed to analyze microstructure changes and hydrogen distribution in both the surface and core regions of the titanium alloy following hydrogenation, demonstrating its feasibility for surface hydrogenation treatment of titanium alloy sheets

KEARNS TEXTURE PARAMETERS AND PROPERTIES OF HEXAGONAL MONO- AND POLYCRYSTALS

Problem statement. Polycrystals' physical and mechanical properties are determined by the corresponding properties of single crystals (crystallites) that make up the polycrystal, and their distribution by orientation in the polycrystal (texture). In metals with a hexagonal structure, the use of Kearns texture parameters, which show the degree of coincidence of the hexagonal axis of crystallites with a given direction in a polycrystalline sample, allows determining the property of a polycrystal in this direction, if the properties of a single crystal in the direction of its hexagonal axis and the perpendicular direction are known. It is also possible to solve the inverse problem: determining the properties of a single crystal in the direction of its hexagonal axis and the perpendicular direction based on the properties of the polycrystal and the determined of the Kearns texture parameters. Materials and methods. Elastic and mechanical characteristics of hexagonal alloys based on titanium (Grade 1 and VT1-0) and magnesium (Mg − 10 % Li and ZE10) were studied after different types of deformation − rolling, alternating bending, and twist extrusion. The Kearns texture parameters were determined by the X-ray method based on the data of the construction of inverse pole figures (IPF) in the normal direction (ND) to the sheets plane and the rolling direction (RD). The results of the experiment. It is shown that the specified method allows to calculate the elastic and mechanical properties of the specified polycrystals after they undergo various types of deformation with an error of no more than 5−10 %, as well as to solve the inverse problem of calculating the properties of single crystals with an error of no more than 5 %. Conclusions. Using the parameters of the Cairns texture and the characteristics of single crystals of magnesium alloys ZE10, Mg 5 % Li, titanium Grade1 and VT1-0 made it possible to calculate the corresponding properties of polycrystals and their anisotropy. The use of Cairns texture parameters, experimental values of the modulus of elasticity, tensile strength and yield strength of polycrystalline sheets of the studied magnesium and titanium alloys made it possible to evaluate the characteristics. There are strong correlations between the values of the modulus of elasticity, the mechanical characteristics of the studied sheets of magnesium and titanium alloys, on the one hand, and the corresponding parameters of the Cairns texture, on the other hand.

Anisotropic formability and deformation mechanism of near-α titanium alloy sheet under continuous nonlinear strain paths at high temperature

In the present study, the anisotropic formability and underlying deformation mechanism of near-α TA32 titanium alloy sheet under continuous nonlinear strain paths (CNSPs) at high temperature were investigated in depth. To achieve this goal, a new experimental method combining hot gas bulging with step-combined dies was proposed, and the hot CNSPs of metal sheets can be flexibly and conveniently realized by changing the number and shape of step-combined dies. Based on this method, the anisotropic deformation behavior and forming limits of TA32 sheet under fifteen CNSPs were tested at 800 ℃ with a strain rate of 0.001 s−1. Then, two advanced constitutive models with different scales were embedded into the classical Marciniak-Kuczyński (M-K) theory to predict the forming limits of TA32 sheet under different strain paths: the macro-scale viscoplastic model coupled with Hill48 yield criterion and non-associated flow rule (NAFR) as well as the meso-scale three-dimensional crystal plasticity finite element (CPFE) model coupled with cellular automata (CA). The results demonstrate that the CPFE-CA-MK coupled model exhibits higher accuracy in predicting the forming limits of TA32 sheet under linear and continuous nonlinear strain paths. Especially for the tension-tension strain paths, the CPFE-CA-MK coupled model improves accuracy by at least 3.1 % compared to macro-scale models. Due to the material anisotropy, the initial inclination angle of the groove in the CPFE-CA-MK model is closely related to the strain path and significantly affects the prediction accuracy. Based on the CPFE simulation, the effects of anisotropy and strain path change on the dislocation slip mode of different texture components was analyzed in depth, which provides a theoretical guidance for the optimization of hot forming process of TA32 titanium alloy complex components.

Закономерности износа плазмотронов при плазменной резке толстолистового проката на токе обратной полярности

The introduction describes the features of the process of plasma cutting of various metals and alloys using reverse-polarity plasma torches with and the features of cutting thick sheets. The purpose of the work is to study the wear process of plasma torches operating on reverse polarity current when cutting thick rolled sheets of aluminum and titanium alloys. Research methods include optical and scanning electron microscopy, filming of the cutting process and visual inspection of plasma torch elements after receiving specimens. Results and discussion. The section shows the appearance of the main working elements of the plasma torch after cutting in various modes, which led to both stable and gradual wear and to catastrophic failure of the plasma torch. The results of structural studies of the main characteristic zones of nozzles and electrodes after cutting are presented. The studies carried out made it possible to establish the main reasons for the failure of the working elements reverse-polarity plasma torches. The causes of catastrophic failure of plasma torches include failure to maintain the gap between the nozzle and the electrode and melting of the channel of gas supply into the discharge chamber. The wear of nozzles and electrodes in a stable mode can be intensified due to abnormal operation of the starting arc, the presence of manufacturing inaccuracies and excess gas pressure. In conclusion, the main conclusions based on the results of the research are formulated. The process of wear of electrodes, nozzles and body elements of plasma torches during operation at high electric arc power values is described.

Effect of Swing Amplitude on Microstructure and Properties of TC4 Titanium Alloy in Laser Welding

The welding of TC4 titanium alloy sheets with a thickness of 1 mm was successfully accomplished by a swinging laser. The microstructure and mechanical properties of the welding seam under different swing amplitudes were studied. In this paper, the microstructure, phase composition, mechanical properties, and fracture morphology of the weld with swing frequency of 50 Hz and different swing amplitudes (0.2 mm, 1 mm, 2 mm, and 3 mm) were tested and analyzed. The results show that basket-weave microstructures are present in the fusion zone of welds under different oscillation amplitudes, but the morphology of martensite within the basket-weave differs. The weld microstructure is mainly composed of acicular α′ martensite, initial α phase, secondary α phase, and residual β phase. The hardness of the weld is higher than that of the base metal, and the overall hardness decreases from the weld center to the base metal. When the oscillation amplitude A = 1 mm, the weld microstructure has the smallest average grain size, the highest microhardness (388.86 HV), the largest tensile strength (1115.4 MPa), and quasi-cleavage fracture occurs. At an oscillation amplitude of A = 2 mm, the tensile specimen achieves the maximum elongation of 14%, with ductile fracture as the dominant mechanism.

Grain refinement and phase precipitation simultaneously improve the strength and ductility of ultra-high strength titanium alloy sheets

The simultaneous high strength and high plasticity of metastable-β titanium alloy sheets remains a difficult challenge. In this work, a 1.2 ​mm thick sheet of Ti–15Mo–3Al-2.7Nb-0.25Si titanium alloy was obtained after rolling and annealing, and then subjected to a duplex-ageing treatment. The pre-ageing temperatures fell in the range of 300–390 ​°C for 0.5–2h. The re-ageing temperatures were in the range of 500–600 ​°C. After characterization, it was found that the alloy precipitates ω-phases during the pre-ageing process, and the distribution of such ω-phases evolves unevenly and increases in number with the increase of the pre-ageing temperature. Therefore, the strengthening mechanism of the alloy sheet is mainly α-phase nucleation assisted by ω-phase. Moreover, grain refinement appears as a mechanism to ensure the plasticity of the alloy. Finally the ω-phase evolution law is discussed in detail and the strengthening mechanism of the alloy sheet is also analyzed. At this work, a metastable-β titanium alloy sheet with strength of 1445.75 ​MPa and elongation of 6.55 ​% was obtained. This study provides a new idea for the microstructure design and process improvement of the metastable-β titanium alloy sheet.

Understanding the influence of forming condition on superplasticity elongation for SP700 Ti-alloy

The high-temperature tensile tests were conducted for SP700 Titanium alloy sheet under the temperatures of 755°C, 775°C, 795°C, 815°C, and the strain rates of 1×10−2 s−1, 1×10−3 s−1, 1×10−4 s−1, respectively. The microstructure evolution, Superplasticity deformation characteristics and elongation differences under different forming conditions were investigated. Results indicate that the steady-state flow duration is the longest under the deformation conditions of 775°C and a strain rate of 1×10−3 s−1, achieving a maximum elongation of 746 %. At 795°C with the same strain rate, fine porosities can be observed at the α/β phase boundaries in the uniform deformation and fracture zones, with larger porosities at P3 corresponding to more pronounced necking phenomena. At 775°C and a strain rate of 1×10−3 s−1, the average grain size of the α phase is maintained at 3–5μm, accounting for 78.6 % of the microstructure. It is suggested that maintaining an average grain size of approximately 4μm after tensile test can result in an even better superplasticity and elongation rate. Furthermore, at a strain rate of 1×10−3 s−1, the average grain size of the α phase initially increases and then decreases with the temperature increasing. At 795°C and a strain rate of 1×10−3 s−1, the α/β phase boundaries are curved. However, the α/β phase boundaries remain straight after tensile test, under 815°C and a strain rate of 1×10−3 s−1. Moreover, the observed dislocation is mainly in the α phase and only a few in the β phase. It shows that the superplastic deformation of SP700 alloy mainly occurs within the α phase, and the dislocation activity of the β phase may be limited.

Analysis of the Microstructure and Mechanical Performance of Resistance Spot-Welding of Ti6Al4V to DP600 Steel Using Copper/Gold Cold-Sprayed Interlayers.

In this article, an attempt was made to join DP600 steel and Ti6Al4V titanium alloy sheets by resistance spot-welding (RSW) using an interlayer in the form of Cu and Au layers fabricated through the cold-spraying process. The welded joints obtained by RSW without an interlayer were also considered. The influence of Cu and Au as an interlayer on the resulting microstructure as well as mechanical properties (shear force and microhardness) of the joints were determined. A typical type of failure of Ti6Al4V/DP600 joints produced without the use of an interlayer is brittle fracture. The microstructure of the resulting joint consisted mainly of the intermetallic phases FeTi and Fe2Ti. The microstructure of the Ti6Al4V/Au/DP600 joint contained the intermetallic phases Ti3Au, TiAu, and TiAu4. The intermetallic phases TiCu and FeCu were found in the microstructure of the Ti6Al4V/Cu/DP600 joint. The maximum tensile/shear stress was 109.46 MPa, which is more than three times higher than for a welded joint fabricated without the use of Cu or Au interlayers. It has been observed that some alloying elements, such as Fe, can lower the martensitic transformation temperature, and some, such as Au, can increase the martensitic transformation temperature.

A VFM-based identification method for anisotropic thermal-mechanical properties of sheet metals using the digital image correlation and infrared thermography assisted heterogeneous test

The accurate characterization of the anisotropic thermal-mechanical constitutive properties of structural sheet metals at elevated temperatures and under nonuniform stress/strain states is crucial for the precise hot plastic forming and structural behavior evaluation of an engineering sheet part. Traditional thermal-mechanical testing methods rely on the assumption of states homogeneity, leading to a large number of tests required for the characterization of material anisotropy and nonlinearity at various high temperatures. In this work, a highly efficient identification method is proposed that allows the simultaneous characterization of the anisotropic yielding, strain hardening and elasto-plasticity thermal softening material properties using the minimum number of tests, releasing the limitations of traditional identification methods. This is implemented by performing a digital image correlation and infrared thermography assisted heterogeneous high temperature test and processing the full-field measurement data based on the principle of virtual work. A double-notched tensile specimen configuration combined with a center-to-periphery temperature gradient is designed first to enable the high heterogeneity of stress/temperature states. Simulations of the heterogeneous tests are then performed to supply idealized reference data that can be used to evaluate the identification sensitivity of the proposed identification algorithm. After the numerical validation of the methodology, it is then applied to the TC4 titanium alloy sheet specimen using the self-developed experimental setup. The experimental identification results verify that the multiple anisotropic thermal-mechanical elasto-plasticity constitutive parameters can be accurately identified from the heterogeneous test with high computation efficiency, significantly simplifying the testing process in comparison to applying multiple traditional homogeneous tests. The current work provides an effective and convenient alternative to high temperature identification strategies used by the material processing community.

Investigation on mechanism in fabricating truncated cone with tooth features of titanium alloy via flexible free incremental forming at room temperature

It has been a challenge to efficiently make titanium alloy thin-walled components by sheet metal forming. Incremental sheet forming (ISF) method provides a promising way to increase the formability of low-ductility metallic sheets, but making titanium alloy sheet panels still needs heating by electricity or laser. The present work investigates the deformation mechanism in fabricating truncated cones of titanium alloy with tooth features realized by flexible free incremental sheet forming (FFISF) at room temperature. Experimental investigations on auxiliary sheets and tool path selections, analytical modeling, finite element simulation, and microstructure characterization have been conducted to evaluate the deformation mechanism in terms of the geometric deviation, thickness distribution and microstructure evolution of TA2 and TC4. Results indicate that the I-O loading path coupled with an optimized auxiliary sheets selection can ensure the successful fabrication of designed panel without defects. An analytical model is proposed to predict the free edge dependent law of thickness distribution in FFISF, indicating the material thinning is positively correlated with the distance from the free edge, while the thinning rate is inversely proportional to the yield strength. A more uniform thickness of TC4 panel is obtained compared with TA2. Finally, the improved formability of titanium alloys by FFISF can be attributed to grain subdivision, decreasing of intragranular deformation, and optimization of dislocation movement.

FORMABILITY CAPABILITIES AND MECHANICAL PROPERTIES OF TITANIUM TAILOR-WELDED BLANKS

Titanium alloys have many applications in aerospace, nuclear and automotive industries and in most parts are in sheet form and require joints of high integrity to meet the design requirements and achieve reliable welds. For weight and cost reduction, the technology of tailor-welded blanks (TWBs) is a promising technology in various components. TWBs are usually semi-finished metallic sheets made of different strengths, materials, and/or thicknesses and a forming process is often needed to manufacture the final components. In this paper, Grade-2 and Grade-5 titanium alloy sheets (Ti-TWBs) were laser welded and subjected to a forming process in U-profile geometry at elevated temperatures. The deformation behaviors of the weld joints after forming process were analyzed by mechanical tests such as tensile and hardness tests. The formability of the welded blanks is assessed based on variations in the geometric changes related to the springback angles. The results showed that there was significant increase in tensile strength with forming temperature increase and the failure mode was changed at 850 °C. The formability of the Ti-TWBs was found to be strongly dependent on the applied process temperatures and forming at 850 °C leads to the lowest springback angle.

Numerical simulation of electron beam welding and local heat treatment of TC4 titanium alloy sheet

Numerical simulation of electron beam welding and local heat treatment of TC4 titanium alloy sheet

Advanced FEM Insights into Pressure-Assisted Warm Single-Point Incremental Forming of Ti-6Al-4V Titanium Alloy Sheet Metal

This study employs the finite element (FE) method to analyze the Incremental Sheet Forming (ISF) process of Ti-6Al-4V titanium alloy. The numerical modeling of pressure-assisted warm forming of Ti-6Al-4V sheets with combined oil-heating and friction stir rotation-assisted heating of the workpiece is presented in this article. The thermo-mechanical FE-based numerical model took into account the characteristics of the mechanical properties of the sheet along with the temperature. The experimental conditions were replicated in FEM simulations conducted in Abaqus/Explicit, which incorporated boundary conditions and evaluated various mesh sizes for enhanced accuracy and efficiency. The simulation outcomes were compared with actual experimental results to validate the FE-based model’s predictive capacity. The maximum temperature of the tool measured using infrared camera was approximately 326 °C. Different mesh sizes were considered. The results of FEM modeling were experimentally validated based on axial forming force and thickness distribution measured using the ARGUS optical measuring system for non-contact acquisition of deformations. The greatest agreement between FEM results and the experimental result of the axial component of forming force was obtained for finite elements with a size of 1 mm. The maximum values of the axial component of forming force determined experimentally and numerically differ by approximately 8%. The variations of the forming force components and thickness distribution predicted by FEM are in good agreement with experimental measurements. The numerical model overestimated the wall thickness with an error of approximately 5%. By focusing on the heating techniques applied to Ti-6Al-4V titanium alloy sheet, this comparative analysis underlines the adaptability and precision of numerical analysis applied in modeling advanced manufacturing processes.

Mechanical properties of ultrasonic welded and self-piercing riveted joints in a 5A06 aluminum alloy and a TA1 titanium alloy

Abstract The self-piercing riveting (SPR) experiences problems of poor forming qualities and mechanical properties during joining aviation alloy sheet materials. To address this issue, a novel combined process nominated ultrasonic self-piercing riveting (USPR) is carried out to join a 5A06 aluminium alloy and a TA1 titanium alloy sheets. The forming qualities, mechanical properties, failure modes, and mechanisms of USPR and SPR joints are comprehensively investigated. The results showed that the mechanical properties of the USPR joints were enhanced due to the welding formation of a solid phase between the specimen sheets and the degree of solid phase. The investigation showed that the welding was mainly affected by the material of the upper sheet. However, the welding also increased the brittleness of the rivet to some extent. The failure modes of the joints are affected by the welding process. The results determined that APL, AFD, and AEA of USAA joints were improved by 25.6 %, 31.3 %, and 88.8 %, respectively. The performance of the USPR joints with 5A06 aluminum alloy as the upper sheet is improved more than 88.8 % after the welding process. The combined method can be advantageous and supportive for automotive and spacecraft applications.

Influence of Femtosecond Laser Surface Modification on Tensile Properties of Titanium Alloy.

Titanium alloy components often experience damage from impact loads during usage, which makes improving the mechanical properties of TC4 titanium alloys crucial. This paper investigates the influence of laser scanning irradiation on the tensile properties of thin titanium alloy sheets. Results indicate that the tensile strength of thin titanium alloy sheets exhibits a trend of initial increase followed by a decrease. Different levels of enhancement are observed in the elongation at break of a cross-section. Optimal improvement in the elongation at break is achieved when the laser fluence is around 8 J/cm2, while the maximum increase in tensile strength occurs at approximately 10 J/cm2. Using femtosecond laser surface irradiation, this study compares the maximum enhancement in the tensile strength of titanium alloy base materials, which is approximately 8.54%, and the maximum increase in elongation at break, which reaches 25.61%. In addition, the results verify that cracks in tensile fractures of TC4 start from the middle, while laser-induced fracture cracks occur from both ends.

Thickness Measurement of Titanium-Alloy Sheets Based on the Resistance-Frequency Eddy Current Method

Thickness Measurement of Titanium-Alloy Sheets Based on the Resistance-Frequency Eddy Current Method

Residual Stresses in Alpha Titanium Alloy Sheet after Punching at Moderate Strain Rates

Residual Stresses in Alpha Titanium Alloy Sheet after Punching at Moderate Strain Rates

Determining the hot forming limits of titanium alloy sheet under different strain paths by constant equivalent strain rate hot gas bulging tests

This study aims to determine the hot forming limit diagram (FLD) of titanium alloy sheet using constant equivalent strain rate hot gas bulging tests. A novel method was proposed to calculate pressure-time curves under different strain paths, ensuring that the equivalent strain rate during hot deformation remains constant. The key of this method is the development of a VUMAT material subroutine that accurately reflects anisotropic hardening and r-value evolution, and the pressure loading curves under different strain paths were determined by coupling with the VUAMP amplitude subroutine embedded with a PID control algorithm. Based on dies with different cavity structures and unbonded double-layer samples, the FLDs of TA32 titanium alloy sheet under linear and nonlinear strain paths were obtained by carrying out hot gas bulging tests at 800 ℃ with a strain rate of 0.001 s-1. The results demonstrate that the proposed approach is applicable for determining the pressure-time curves under various complex strain paths, and it is experimentally verified that the equivalent strain rate of the sample apex is maintained near the target value during the bulging process. Furthermore, the significant effects of anisotropy and strain path change on the forming limits were quantitatively analyzed. The developed method is not only beneficial for testing the hot biaxial mechanical properties of materials, but also useful for controlling the strain rate during the hot forming of complex thin-walled components to improve the formability of materials.

Study of the Law Motion of the Micro-EDM Drilling Process

Micro-EDM is an unconventional technology used to machine every type of electrically conductive material regardless of its mechanical properties. Material removal occurs through electrical discharges between the workpiece and the electrode immersed in a dielectric fluid. In drilling operations, the technology is able to realise microholes with excellent quality in terms of precision, quality surface, roundness, and taper to the detriment of the machining time, which is less than other technologies. Several efforts are being made to improve different features related to the process performance that are severely affected by both the operative conditions, such as the electrode material or the type of dielectric, and process parameters. The typical indexes used to characterise the performance are the machining time, the material removal rate, and the geometric indexes. These indexes are very effective and are easily measurable, but they do not give information about the evolution of the drilling process, which could be irregular due to the different phenomena occurring during machining. The aim of this paper is the development of a method able to elaborate the motion law of the electrode during the micro-EDM drilling operation. In order to do this, a single hole was manufactured in several steps, recording both the machining time and electrode wear for each step. In this way, the actual position of the electrode during the drilling can be measured without the use of a predictive model for electrode wear. It was tested to confirm that the multistep procedure did not introduce new phenomena, in contrast to the traditional drilling operation. This method was used to study the effects of the electrode diameter, the type of electrode, the length of the electrode out of the spindle, and the entity of the run-out on the process performance. The tests were executed on titanium alloy sheets using a tungsten carbide electrode and hydrocarbon oil as the dielectric. It was found that the descent of the electrode into the workpiece was not regular, but it depended on the level of debris concentration in the machining zone. The debris concentration was influenced by the type and diameter of the electrode, its length out of the spindle, and, to a lesser extent, the run-out. This method was found to be a useful method for an in-depth analysis of the micro-EDM drilling process, contributing to a better understanding of the physical aspects of the process.

Microstructure and mechanical properties of vacuum electron beam welded joints of Ti/Cu dissimilar metals

Sheets of TC4 titanium alloy and T2 pure copper were joined by vacuum electron beam welding with an offset on the copper side. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to study the microstructure of the welded joint, and the composition of the intermetallic compounds (IMCs) at the reaction layer was studied by energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM), followed by tensile testing to investigate the mechanical properties of the welded joints. The results show that electron beam welding can achieve an effective connection of Ti/Cu dissimilar metals. A multilayer structure composed of an IMCs layer, a final solidification zone, and a weld zone is formed at the Ti/Cu interface. The main composition of the IMCs layer is the faceted phase of TiCu and a small amount of the faceted phase of Ti2Cu, while the FS zone is composed of tiny equiaxed grains of copper. The tensile test results show that the ultimate tensile strength of the joints reaches 190 MPa, and the elongation rate reaches 4.27%. The joint presents brittle fracture characteristics with fracture occurring in the IMCs layer.