Titanium Alloy Sheet Research Articles

Development and applications of the titanium alloy sheet hot deformation control method by adjustment of its temperature field

Development and applications of the titanium alloy sheet hot deformation control method by adjustment of its temperature field

Numerical Simulation and Experiment of Electrically-Assisted Incremental Forming of Thin TC4 Titanium Alloy Sheet.

In order to integrally manufacture the large TC4 titanium alloy part, an electrically-assisted incremental forming process is cleverly proposed to solve the traditional hot forming disadvantages of expensive heating furnaces and long cycle period. The two-step simulation method including thermal-electricity coupling simulation and thermo-mechanical coupling simulation was selected to predict the temperature variations and the sheet deformation behaviors. The electrically-assisted incremental forming experiment of thin TC4 titanium alloy sheet was performed. The highest prediction error is 6% for springback angles. The thrice forming at 10.9 A/mm2 satisfies the precision requirement of the designed part. Therefore, the two-step simulation method can effectively calculate the electrically-assisted incremental process. The electrically-assisted incremental forming technique is very promising for the integral producing large titanium alloy part.

Formability prediction of Ti6Al4V titanium alloy sheet deformed at room temperature and 600 °C

Formability predictions of Ti6Al4V titanium alloy sheets deformed at room temperature and 600 °C, using D-Bressan’s shear stress rupture criterion and the critical strain gradient macroscopic modelling are presented and discussed in relation to limit strain results obtained experimentally. Ti6Al4V Forming Limit Strain Curves were predicted and compared with experimental curves at 25 °C and 600 °C and strain rate 0.1 s−1. The analytical models were calibrated by means of tensile tests performed on samples cut at 0°, 45° and 90° to the rolling direction at different temperatures and strain rates to obtain the Lankford coefficients and material strain and strain rate hardening behavior. The applied critical shear stress rupture criterion showed to give a fairly good fit with experimental limit strains outcomes, proving that the shear stress rupture nature of specimens deformed at room and elevated temperatures were well reproduced, despite a not-null strain rate sensitivity coefficient at 600 °C. Fracture occurrence by fast shear stress mechanism through thickness direction was corroborated by experimental fractograph observations close to fracture surfaces. It was shown that predicted limiting major true strain of fracture by shear stress curve is governed by normal anisotropy, strain hardening exponent, pre-strain and normalized critical shear stress parameter, which depends on temperature and strain rate whereas the strain hardening exponent depends largely on temperature. In contrast, the critical strain gradient modelling for onset of localized necking showed poor correlation with the experimental limit strains. Best fit of the critical shear stress criterion with experimental limit strain curves was given by specimens deformed near plane strain or FLCo. Hence, a common feature of various strain-rate independent metals, annealed or cold rolled, is that the main fracture mechanism of thin sheet metals can be considered as fast shear stress through sheet thickness without a visible localized necking in biaxial stretching.

Study on Hardness and Microstructural Properties of Ti-6Al-4V Alloy using Overlapped Multipass Laser Transformation Hardening under Optimized Test Conditions

In this research paper, overlapped multipass Laser Transformation Hardening (LTH) of Ti-6Al-4V titanium alloy sheet of 2 mm thickness was analyzed experimentally for uniformly intense, CW spherical beam moving with constant speed using 2 kW Nd: YAG laser. Experiments were conducted for optimized two sets of laser process parameters: 1. High Laser Process Parameter (HLPP), Lp = 800 Watts, Ss = 3000 mm/min, Fp = -10 mm, with heat input 180 J/cm and 2. Low Laser Process Parameter (LLPP), Lp = 600 Watts, Ss = 2000 mm/min, Fp = -10 mm, with heat input 160 J/cm respectively having same Fp = -10 mm. The maximum, minimum and average hardened depths of 0.27, 0.19 and 0.23 mm respectively, achieved for HLPP were found to be minimum, as compared to the maximum, minimum and average hardened depths of 0.38, 0.29 and 0.33 mm, respectively, for LLPP. Measurements of Vickers micro-hardness survey of the hardened zone of the laser processed Ti-6Al-4V alloy are presented. Vickers micro-hardness of an as-received two-phase (α+β) Ti-6Al-4V titanium alloy is 328 HV. The results showed that Vickers micro-hardness on top of the surface (TS), in hardened or fusion zone (Fz), at the interface of Fz -Haz, in the heat affected zone (Haz) is higher than the bulk material. The high hardness values of 450 HV and 445 HV were investigated on the top surface for high and low laser process parameters respectively. This can be the quality characteristics of the dissolution of small amounts of oxygen, nitrogen, and carbon with hard martensite α' (transformed β) formation, thereby ensuring an increase in wear resistance of laser treated hardened surface of Ti-6Al-4V considerably in relation to the untreated or base alloy.

EDM of Nickle and Titanium Alloy Sheets aided by Vibration

Nickel and titanium alloys are widely used as aero-engine blade materials due to their excellent properties such as high strength, light weight and resistance to high temperature. There are many methods available to machine materials to the required dimensions and with high blade accuracy. Electrical chemical machining (ECM) is one of them. However, the complexity of flow field and electric field on the leading and trailing edges of the blade during ECM results in large dimensional and shape errors. The edges must be dressed to the required dimensions and accuracy. Electric discharge machining (EDM) has the ability to remove any electrically conductive material regardless of its strength and hardness. In this paper, EDM aided by vibration is used to roughly dress the leading and trailing edges of the blade. To optimize machining parameters such as peak current, pulse on-time, amplitude and frequency of vibration, extensive experiments are carried out based on orthogonal method. Thin sheets of nickel and titanium alloys with cross section of 29 mm × 0.5 mm are cut off 2mm in length. The optimal machining parameters were verified by confirmation experiments. It was found that under optimal conditions and using graphite electrode, machining time of nickel alloy was 1.62 minutes and machining time of titanium alloy was 2.12 minutes. The corresponding electrode wear ratio and heat affected zone were analysed.

Effects of the properties of workpiece, electrode and dielectric fluid in micro-EDM drilling process

In the last years, the miniaturization of the components took place in many industrial sectors such as automotive, aerospace, biomedical. Significant industrial efforts were made to support this new manufacturing trend in order to propose effective solutions. In this scenario, Electrical Discharge Machining (EDM) finds use for a variety of drilling applications in automotive, aerospace, biomedical sectors on different materials such as stainless steels, titanium alloys and others metals regardless of their mechanical properties. The material removal occurs thorough electrical discharges between the electrode tool and the workpiece in a dielectric fluid. Dielectric, electrode and workpiece are the main factors involved during the discharges. Aim of this paper is to analyse the effects of the physical and thermal properties of the dielectric fluid and material of electrode and workpiece on the process performance of micro-EDM drilling operation. Two traditional (water and mineral oil) and an unconventional (vegetable oil) dielectrics were tested on sheets of stainless steel and titanium alloy using both brass and tungsten carbide electrodes. The performance were evaluated considering the material removal rate, the tool wear ratio and the geometrical characteristics of the holes. The results were correlated to the properties of the dielectric, electrode and workpiece. The results can be useful to both improve the knowledge and allow the optimization of the process.

Experimental evaluation of influence of temperature on nature of fracture in formability test of alpha-beta titanium alloy

In the present era, titanium alloys are the workhorse in aeronautical component production applications. The formability tests are carried out for alpha-beta titanium alloy sheet metal blanks using the Erichsen Cupping Test, under the different tribological conditions and at varying temperatures. Taguchi Method of optimization technique is used to optimize the process parameters and analysis of variance is also carried out to obtain percentage contribution of each parameter. The various forming conditions at different temperatures involved a varying range of stress. The fractures occurred after necking during formability test. Further these fractures are analyzed for their nature. The paper aims to disseminate the research highlights from a research project sanctioned from Science and Engineering Research Board, Directorate of Science and Technology, Govt. of India, vide file no. EMR/2016/007303 dated 20 Mar 2018.

Superplastic forming with diffusion bonding of titanium alloys

The ability of materials to display extensive plastic deformation at elevated temperature before permanent deformation without necking is known as super plasticity. The optimization of superplastic forming can be evaluated by application of gas pressure at elevated temperatures using hot superplastic forming set up. The diffusion bonding process involves keeping together the required titanium alloy sheets or titanium alloy with any other metal with the help of load at elevated temperatures and in an inert environment preferably in vacuum for the bonding process to complete. This method is used to eliminate many bonding defects such as distortions and cracking which can occur in conventional joining methods such as welding and brazing or riveting. The resulting micro structure at the interface can be evaluated using scanning electron microscope (SEM) photography and also the bond strength can be determined using micro hardness tester. Titanium based alloys are super- plastic in nature at elevated temperatures, and they also display exceptional mechanical properties such as a great strength to weight ratio, good fatigue life good corrosion resistance, high torsional rigidity and excellent bio compatibility. The components bonded using both super plasticity and diffusion bonding possesses high tensile strength which is makes it reliable for aerospace applications.

Modelling and optimization of different quality characteristics in electric discharge drilling of titanium alloy sheet

Abstract The present research work is concentrated around the machining of titanium grade 5 alloy using electric discharge drilling. The process response parameters viz. hole taper and hole dilation have been calculated by performing experiments. During the experiments titanium grade 5 alloy has been taken as a workpiece with brass electrode as a tool. The experimentally calculated process parameters have been optimized using grey relational analysis. The main objective of this research is to maximize the hole circularity along with minimum hole taper and dilation by selecting the optimal input parameters. From the results it has been found that discharge current is the most effective parameter for the given conditions.

Establishing relationship between fusion zone hardness and grain size of gas tungsten constricted arc welded thin sheets of titanium alloy

Ti–6Al–4V alloys are perfectly suited for fan compressor blade material in advanced aero engine components due to outstanding resistance to corrosion and specific strength was high in both room temperature and elevated temperature. For autogeneous welding of thin sheets of Ti–6Al–4V alloy, the gas tungsten constricted arc welding (GTCAW) was established to be beneficial than the gas tungsten arc welding process. The performance of welded joints depends on the fusion zone grain size (FZG) and fusion zone hardness (FZH), which need to be suitably optimized and controlled to attain advantageous mechanical characteristics of the joint. Hence, in this research study, efforts were taken to develop empirical relationships for predicting the FZH and FZG incorporating very important GTCAW parameters. Parameter optimization was performed using response surface methodology. Additionally, the influence of GTCAW parameters on FZG and FZH was analyzed. From the results, it is inferred that the inter-pulse frequency has better influence on FZG and FZH compared to other parameters.

Effect of the Application of Different Surface Treatment Methods on the Strength of Titanium Alloy Sheet Adhesive Lap Joints.

This study investigated the effect of the different surface treatment methods on the strength of Ti6Al4V titanium alloy sheet adhesive joints. The following surface treatment methods were used: alkaline degreasing, anodizing, vibratory shot peening, and anodizing with vibrational shot peening. The following tests/measurements were carried out during the experiment: surface roughness measurements; microhardness measurements (conducted by the Vickers hardness test method); and strength tests of single-lap adhesive joints fabricated with the use of two epoxy adhesives, rigid and flexible, both based on epoxy resin Epidian 5. It has been found that the application of anodizing followed by vibratory shot peening leads to increased strength of adhesive joints, irrespective of the type of applied epoxy adhesive.

V-shaped bending of Ti-6Al-4V titanium alloy sheet with elliptical hole

The internal elliptical hole defect in the Ti-6Al-4V titanium alloy sheet strongly affects the material mechanical properties during the bending process. In this study, the finite element method (FEM) is used to study the effect of internal hole on mechanical properties of the sheet subjected to the V-shaped bending. The fracture damage, the equivalent strain and the principal stress in the sheet with elliptical hole (the defect sheet) and the hole-free sheet (the perfect sheet) are analyzed contrastively under different punch speeds and radii. The results show that the load in the defect sheet and the perfect sheet has different trends during the bending process. Compared to the perfect sheet, both the damage and the equivalent strain in the defect sheet obviously increase, and the distribution of the principal stress in the bending zone of the defect sheet has a significant change. The hole causes the different evolution of the maximum damage, the equivalent strain, and the maximum tensile and compressive stresses with the increase of punch speed and radius for the defect and perfect sheets. The current results serve a feasible approach to predicting the fracture of the sheet with internal hole during the V-shaped bending process, and provide a guidance for the V-bending experiments of the defect and perfect sheets in the subsequent work.

Performances of regression model and artificial neural network in monitoring welding quality based on power signal

In this study, a systematic research was conducted to compare the performances of the regression model and artificial neural network in predicting the nugget diameter of spot-welded joints by monitoring the dynamic power signature. The TC2 titanium alloy with a thickness of 0.4mm was used as the welding material, and a high-frequency precision spot welder was used to join the titanium alloy sheets. The dynamic welding current curve was obtained using the Rogowski coil, while the voltage curve was detected via two leads clipped onto the upper and lower electrodes during the entire welding process. The variations in the welding power signal in the welding process were investigated, and the characteristics of the power signals for different welding currents and electrode forces were analyzed. The power signals of different types of welding joints varied significantly. Five characteristics were extracted from the power signal to describe the shape of the curve. The stepwise regression analysis and back propagation neural network were respectively used to classify the welding joints into three categories: bad welds, good welds, and welds with expulsion. The performances of the two established prediction models were compared, and their behavioral discrepancies were attributed to their own data-mapping capabilities.

EBSD analysis of the structure of a weld joining a chromium-nickel steel sheet and a titanium alloy sheet through a copper insert

The structure of the different zones of a C02 laser welded joint between a chromium-nickel steel sheet and a titanium alloy sheet, with a copper insert between them, is studied by EBSD analysis. The phase compositions of all the zones have been determined. The weld material has been found to consist of a Cu-based solid solution and unevenly distributed intermetallic particles of different stoichiometric compositions. The heat-affected zones consist of supersaturated iron- and titanium-based solid solutions. After laser welding, the microdeformations of the phase lattices are distributed unevenly over the cross section of the welded joint; namely, the maximum microdeformations and the resulting microstresses are concentrated in the heat-affected zone at the boundary between the weld and the titanium alloy.

Comparative Study of Pseudo-α and Pseudo-β Class Titanium Alloy Sheet Set of High-Tech Properties

A forming operations for the pseudo-α titanium alloys OT4-1, OT4-1V, OT4V that are used traditionally in aviation and aerospace transport structures, and a new advanced high-strength metastable β-titanium alloy VT47. It is shown that metastable β-titanium alloy VT47 provides the possibility of implementing manufacturing technology for preparing components of complex configuration by cold sheet forming with a degree of deformation equal to that of reference alloys (OT4-1, OT4-1V, OT4V). Additional ageing of VT47 workpieces provides a significant increase in strength properties.

Tensile deformation behavior of Ti-6Al-4V sheet at elevated temperature

The true strain-stress curves of Ti-6Al-4V titanium alloy sheet were obtained by uniaxial tensile tests under different temperatures using a Gleeble 3800 thermo-mechanical testing machine. And fractograph of failed sample was studied by means of scanning electron microscopy (SEM). The evolution of metallographic structure was observed by optical microscopy. The effect of deformation temperature was analyzed, and deformation mechanism was discussed. The results show that the flow stress of Ti-6Al-4V is controlled by deformation temperature. Flow stress decreases with the increase of the temperature. After 600 °C, elongation of the specimens will increase as tensile temperature increases, and there will be a maximum average 63% when the temperature is 850 °C, and necking phenomenon will become more obvious. Deformation mechanisms exhibit dynamic recovery and dynamic recrystallization at high temperature region.

Enhancement of sawing strategy of multiple surface quality characteristics in low power fiber laser micro cutting process on titanium alloy sheet

Being a promising non-traditional micro machining process laser micromachining may efficiently and fruitfully be used for hard machining materials without the hindrances of their hardness, toughness and brittleness. Superior specific strength, corrosion resistance and creep properties have made titanium alloy fit for many engineering applications as well as in medical purposes. High quality of cutting metal sheets to achieve intricate shapes and geometries etc has made laser to be an attractive tool and a popular mode. High cutting speed, high accuracy, narrow kerf and least material waste are the reasons for its high quality. Study and experimental analysis of the effect of sawing angle and constant Z height movement with other process parameters like power setting, duty cycle, scanning speed and pulse frequency related to the kerf taper and surface roughness of the 1 mm titanium alloy sheet (Ti-6Al-4V) have been done. Investigations on laser cutting for the attainment of optimization have found out better process control and better quality of final product.

Deformation path and springback behavior in double-curved bending at high temperature

In this work, integrated double-curved bending-sizing-unloading is simulated for a Ti6Al4V titanium alloy sheet. Bending radii R30 mm × R30 mm and R30 mm × R15 mm are used in the bending tests at 700 °C and 750 °C, respectively. A holding time of 0–600 s is applied to explore the effect of sizing time on forming accuracy. Similar experimental tests are performed for comparison with the finite element analysis results. Results show that bending behavior varies remarkably with the bidirectional radii. As for equal bidirectional curvature, bending along each direction occurs simultaneously. Given that bidirectional radii are different, the sheet consecutively experiences single small-, single large-, and double-curved bending. The deformation path results in nonuniform plastic strain distribution. The springback amount increases from the center to the marginal middle zone. Sizing at 700 °C or 750 °C in 600 s or 180–600 s can remarkably reduce the springback amount, respectively. The springback prediction via finite element method is consistent with that of the experiment.

Impact performance and microstructures of thick TA1 titanium alloy sheets welded by vacuum electron beam

Thick TA1 titanium alloy sheets were thoroughly bonded by vacuum electron beam welding (EBW). The results indicated that microstructures in the weld zone (WZ) consisted of coarse α columnar grains, serrated α as well as needle-shaped α′; the microstructure in the heat-affected zone near the WZ side was composed of α′ and α, while the microstructure near the base metal side consisted of α″ and α. The positional relation between the notches and rolling direction had an important role in the impact performance. The EBW joint exhibited higher absorbed impact energy at the weld seam after local heat treatment. Furthermore, lots of dimples were produced on the impact fracture surfaces, exhibiting ductile fractures.

Influences of cold rolling, recrystallization and surface effect on the transformation textures in a TA10 titanium alloy

A transformation treatment based on surface effect induced transformation is applied to cold rolled TA10 titanium alloy sheets to change and control transformation texture. This kind of treatment can promote the α-phase nucleation at sheet surface region during cooling and control the growth of surface α-grains into center layer of sheet. The results indicate that as the heating temperature increased, the transformation textures in the final HCP-structured TA10 sheets changed in helium atmosphere from the recrystallization type texture of <11-20>//RD to the transformation type texture of <11-20>//ND. The textures in sheets treated at low transformation temperature of 1000°C reveal texture memory effect, while those treated at high transformation temperature of 1100°C illustrate the effects of both transformation strain and anisotropy in elastic modules of HCP titanium crystals. The surface effect is promoted by cooling gas of helium, which leads to layered structures along sheet thickness direction. The surface region often shows small equiaxed grains with recrystallization orientations, while the center layer reveals coarse grains with either plate-like or equiaxed grain morphology corresponding to transformation orientation or recrystallization orientation, respectively. The special grain boundaries in plate-like α variants are different from those in equiaxed grains. These differences in morphologies, sizes and orientations are explained in terms of the mechanism change of the factors affecting variant selection.