Welded Titanium Alloy Research Articles

Optimisation of the rotary friction welding process of titanium alloy rods

This paper presents a study on the performance behaviour of friction welded titanium alloy rods. The Ti6Al4V alloy rods were friction welded with continuous-drive friction welding using different combinations of process parameters. The welding speed ranging from 1600 to 2700 RPM and the applied pressure ranging from 25 to 140 MPa were utilized for the welding process. The weld joints and the parent material were examined for microstructure characterisation, Vickers hardness and tensile properties. The microstructure of the weld joint revealed fine equiaxed grains with complete recrystallization. The presence of martensitic grains was obtained at process parameter combinations of low welding speed and high pressure. The tensile tests conducted revealed that the weld joints of low speed and high pressure had improved tensile properties when compared to that of the parent material. The ultimate tensile strength of 1040 MPa with the elongation of 26.5 % was obtained at a speed of 1900 RPM and 80 MPa pressure. The micro-hardness tests revealed an increase in hardness across all the weld zones when compared to the parent material, with the maximum hardness obtained at the weld nugget. Further study was conducted to evaluate the effect of parameters on the weld joint integrity.

Mechanical behaviors of electron beam welded titanium alloy up to very high cycle fatigue under different process conditions

The mechanical behavior of electron beam welded joints for titanium alloy has been investigated in static and cyclic loading up to very high cycle fatigue. It can be concluded that a higher welding voltage parameter and optimal heat treatment condition in combination will produce higher static and cyclic properties of titanium alloy welded joints. The metastable martensite α′ structures in the β grains of the fusion and heat-affected zones are wholly decomposed into small lamellar α phases, forming α + β phases through the post-weld heat treatment (PWHT). Hence, the welded joints by PWHT could transform the “concave” shape microhardness distribution into “convex” shape distribution. The fatigue cracks are initiated from the internal pores of the material in very high cycle fatigue regime. The higher voltage parameter applied to the welding process could reduce the density of pores in the material, which is in favour of the fatigue life of the welded joints. • A higher voltage and optimal heat treatment in combination produce higher mechanical properties of welded joints. • Microstructure and microhardness of welded joints were analyzed before and after heat treatment. • The higher voltage reduced the pores density in the welded joints, which improved fatigue life.

On the influence of tooling behaviour over axial shortening mechanisms in linear friction welding of titanium alloys and modelling plasticisation effects

Linear Friction Welding (LFW) has often been studied with the principal goal of describing complex physical interactions at the weld interface. Most published research has focused on the LFW process itself and under many assumptions: simplified welding geometries, over-constrained and rigid assemblies, and idealised clamping conditions. Equipment and tooling characteristics must be considered alongside the process itself for a more comprehensive understanding of LFW. The following study is aimed at addressing observed unaccounted variance in process outputs by investigating Ti6Al4V alloy welds processed under uniform conditions. A method for machine characterisation and a new experimental data analysis workflow is proposed, based on data processing techniques in spectral, temporal, and spatial domains. Research findings presented in this paper describe new plasticisation phenomena which accompany axial shortening in LFW welds. A new kinematic model is proposed, explaining macroscopic interactions at the contact interface. It allows for identification of shortening behaviour prevailing in the process, estimation of relative shape thickness of the thermo-mechanically affected zone, as well as potential for macroscopic misalignment between two joint substrates. Post-weld metrological investigations indicate a link between joint misalignment and effects observed, suggesting that tooling could influence weld shortening behaviour by disturbing planarity at the contact interface.

Mechanical properties and structure of welded joints of VT6 alloy through nanocrystalline interlayer of VT22

Experimental studies of the solid-phase weldability of the VT6 alloy through an interlayer of VT22 alloy in the temperature range of the low-temperature superplasticity (T=820 °C) of one of the elements to be joined have been carried out. Welding of dissimilar titanium alloys allows us to significantly reduce the temperature of pressure welding due to the use of alloys alloyed with different elements. The VT22 with nanocrystalline structure interlayer allows localizing deformation at the junction zone due to a significant difference between the values of the interlayer flow stress and welded billets. To improve the mechanical properties, the welds were heat-treated at T=900 °C. The optimal properties of welded joints are increased after the heat treatment of researched titanium alloys. This leads to the activation of diffusion processes and the disappearance of micropores. Thus, it can be concluded, that getting dissimilar titanium alloys high-quality solid-phase joint depends not only on the size of the interlayer grains but also on the material in the joint zone chemical and phase composition.

Analysis of the Microstructure and Mechanical Properties during Inertia Friction Welding of the Near-\u03b1 TA19 Titanium Alloy

The current research of titanium alloy on friction welding process in the field of aero-engines mainly focuses on the linear friction welding. Compared to the linear friction welding, inertial friction welding of titanium alloy still has important application position in the welding of aero-engine rotating assembly. However, up to now, few reports on inertial friction welding of titanium alloy are found. In this paper, the near-alpha TA19 titanium alloy welded joint was successfully obtained by inertial friction welding (IFW) process. The microstructures and mechanical properties were investigated systematically. Results showed that the refined grains within 15‒20 μm and weak texture were found in the weld zone due to dynamic recrystallization caused by high temperature and plastic deformation. The weld zone consisted of acicular α′ martensite phase, αp phase and metastable β phase. Most lath-shaped αs and β phase in base metal were transformed into acicular martensite α′ phase and metastable β phase in thermo-mechanically affected zone and heat affected zone. As a result, the microhardness of welded joint gradually decreased from the weld zone to the base metal. Tensile specimens in room temperature and high temperature of 480 °C were all fractured in base metal illustrating that the inertia friction welded TA19 titanium alloy joint owned higher tensile strength compared to the base metal.

Numerical simulations of friction stir welding of dual phase titanium alloy for aerospace applications

Dual phase titanium alloy is mainly used in aircraft industries due to low density, greater strength and superior thermal properties. However, titanium alloy is highly reactive to all materials and easy immersion of interstitial constituent leads to material embrittlement, so it is difficult to process and weld. So experimental investigation of friction stir welding (FSW) process is expensive. To overcome these, in the present work a finite element simulation has been developed in ABAQUS software for the FSW process to comprehend the process physics and to predict the mechanical properties of FSW component. The simulation has been carried out by changing the parameters and the performed simulation results such as stress strain plots, percentage elongation, yield and ultimate tensile strength has been verified and calibrated with experiment results. The FSW welding parameters have been optimized using Genetic algorithm to get better weld quality. The fitness function for genetic algorithm is evaluated using regression analysis. The optimized value of rotational and transverse speed to achieve maximum yield and ultimate tensile strength are 1000 rpm and 4 in./min respectively. The optimized results have also been compared with the Taguchi method.

Load Controlled Fatigue Behaviour of Microplasma Arc Welded Thin Titanium Grade 5 (6Al-4V) Sheets.

The current study investigates the load controlled fatigue properties of the microplasma arc welded thin titanium Grade 5 (6Al-4V) sheets. In order to explore the effect of weld geometry on the fatigue, two different welded joints were used in the experimental studies. Load controlled fatigue test results were evaluated to present an outlook on the behaviour of microplasma welded titanium alloy Grade 5 sheets under cyclic loading. Even though the previously published monotonic tests showed successful use of microplasma arc welding to join thin titanium Grade 5 sheets with mechanical properties comparable to the base metal, fatigue life of the welded joints was lower than the lives of samples without welds. In particular, the fatigue performance of overlap joints was very poor. This was presumed to be due to the changed material properties of the heat affected zone which was formed by the excess heat of the welding process as fractures often occurred at such locations. Based on experimental findings and fractographic observations, a clear adverse effect of welding process in material behaviour was discovered. Despite the concentrated heat of microplasma arc welding, post-weld heat treatment of the weld area is recommended to improve the mechanical behaviour of the welded joints.

Protection of Welded Joints from Oxidation at Welding of Titanium Alloys

Protection of Welded Joints from Oxidation at Welding of Titanium Alloys

Effect of Electron-Beam Welding Speed on Weld Metal Mechanical Properties of 5V Titanium Alloy

The results of metallographic studies of 5V titanium alloy welds obtained with the range of electron-beam welding speeds from 20 to 120 m/h are presented. It was established that at all welding speeds some identical microstructure of a weld metal is formed, which can differ only in sizes and shapes of the primary crystals. The results of Vickers hardness, ultimate tensile stress and yield stress estimation by sample-free indentation methods are shown. The weld metal hardness distribution in the transverse direction is homogeneous while from the top to the root an increase in hardness values at all welding speed modes is occurred. It was also revealed that both the hardness and strength of the weld metal grow with the rising welding speed, herewith the increase in these properties in the top of the weld is more significant than in the root. According to the analysis of the interrelation between structure and mechanical properties it was concluded that the main reason of mechanical properties fluctuations is a change in the weld metal chemical composition as a result of the volatile components evaporation during welding.

Influence of welding sequences on the microstructure and mechanical properties of dual-pass electron beam welded Ti60/V/Cu/GH3128 joints

Electron beam welding of Ti60 titanium alloy to GH3128 nickel-base superalloy was realized by using V/Cu composite interlayers, based on the element metallurgical compatibility. The effects of welding sequences on the microstructures and properties of the joints were analyzed. Microstructures and energy spectrum analysis shown that the reaction of Ti and Ni atoms to form brittle intermetallic compounds (IMC) can be effectively prevented by the interlayers. When the electron beam was first focused on the V foil, the copper foil was melted due to the high melting point of vanadium (1890 °C). Continuously distributed CuTi IMCs were produced near the Ti60 side. When the electron beam was first focused on the Cu foil, CuTi IMCs were replaced by the formation of (Ti,V) solid solutions at the interface of Ti60. A joint with a maximum tensile strength of 392 MPa, 49% of that of the GH3218 alloy was obtained. The fracture morphology proved that the fracture type belonged to brittle fracture.

Effect of pulsation in TIG welding on the microstructure, residual stresses, tensile and impact properties of Ti-5Al-2.5Sn alloy

Pulsation of current is widely employed in Tungsten Inert Gas (TIG) welding of titanium alloys. In the current study, the influence of welding speed and welding currents (peak and background) on the properties pulsed TIG welded Ti-5Al-2.5Sn alloy were investigated. The weldment characteristics which were analyzed included weld zone size, microstructure, residual stresses, tensile and impact properties. Increasing the welding speed and gradient of pulsed current enhanced grain strengthening in the fusion zone (FZ) which was attributed to increased cooling rate. Such a welding condition was also favorable in achieving full penetration weldments with a reduced; heat affected zone width, grain size in FZ and residual stresses. However, a tensile strength superior to the base metal was observed. The impact toughness reduced by increasing the pulsed current gradient and a high value of both peak and background currents were required to improve the impact toughness of the weldments.

Microstructure and texture investigation on electrically assisted friction stir welded titanium alloy

Microstructure, texture and mechanical properties of electrically assisted friction stir welding (EFSW) of Ti6Al4 V alloy were investigated. The base material (BM) and the heat-affected zone (HAZ) have a coarse equiaxed structure, and the fine equiaxed structure was observed in the stir zone (SZ). The boundary between the SZ and the HAZ changed abruptly from the FSW joint to the EFSW joint to make it smooth. The BM and the HAZ have a strong prismatic texture {100} and the texture of the SZ is randomly distributed. Hardness of the joints was explained by grain size, loss rate of elemental Al and dislocation density, as well as the advantages of the EFSW process in terms of improving mechanical properties as influenced by microstructure and texture.

Linear friction welding of a beta titanium alloy: experimental investigations on microstructure evolution and mechanical properties

ABSTRACT Linear friction welding was used to join Ti–3Al–8V–6Cr–4Mo–4Zr alloy under different pressures, and the microstructure, texture evolution and mechanical properties of the joint were investigated. Results show that the incomplete continuous dynamic recrystallisation (CDRX) occurs during welding, which refines the grains and produces a large number of subgrains in the thermo-mechanically affected zone (TMAZ) and weld centre zone (WCZ). At a higher friction pressure, the width of the WCZ becomes narrower, with the decrease of grain size and the increase of recrystallisation degree. In addition, the texture in the WCZ has changed from {112}<111> to {110}<111>, while the texture in the TMAZ remains at {110}<112>. The tensile properties of the two joints are similar to the base metal (BM), and the microhardness in WCZ and TMAZ are also close to that in BM due to the incomplete CDRX and the decrease of alpha phase.

A systematic review of fatigue behaviour of laser welding titanium alloys

In the existence era, the usage and need for Titanium (Ti) alloys has been increased for manufacturing weight-less products of machine-made automobile and aerospace tools with increased application of multi-material design. When compared to conventional manufacturing techniques, titanium and its alloys are categorized through better machinability, enhanced melting of temperature, great strength-to-weight ratio, lower thermal conductivity, and increased reaction to oxygen. In recent years, numerous assemblage systems have been pondered to manufacture Ti alloys but Laser Beam Welding (LBW) opens a worthwhile possibility towards other techniques for joining of titanium and alloys in industries due to its adaptability, great and explicit heat input, tractability. In optimal process circumstances, however there occurs a problem such as poor elongation and resistance to corrosion joined with lower fatigue properties, the strength-to-weight ratio of laser welded titanium alloys found to be approaching to unique material. In this study, a small review on the fatigue behaviour of laser welding titanium alloys has been analysed to enhance its mechanical properties, influence of process parameters, fracture mechanisms.

Laser Oscillating Welding of TC31 High-Temperature Titanium Alloy

The joining of high-temperature titanium alloy is attracting much attention in aerospace applications. However, the defects are easily formed during laser welding of titanium alloys, which weakens the joint mechanical properties. In this work, laser oscillating welding was applied to join TC31 high-temperature titanium alloy. The weld appearance, microstructure and mechanical properties of the laser welds were investigated. The results show that sound joints were formed by using laser oscillating welding method, and a large amount of martensite was presented in the welds. High mechanical properties were achieved, which was approaching to (or even equaled) the strength of the base material. The joints exhibited a tensile strength of up to 1200 ± 10 MPa at room temperature and 638 ± 6 MPa at 923 K. Laser oscillating welding is beneficial to the repression of porosity for welding high-temperature titanium alloy.

Arc Characteristics and Weld Bead Microstructure of Ti-6Al-4V Titanium Alloy in Ultra-high Frequency Pulse Gas Tungsten Arc Welding (UHFP-GTAW) Process

To resolve the problem of grain coarsening occurring in the fusion zone and the heat-affected zone during conventional gas tungsten arc welding(C-GTAW) welded titanium alloy, which severely restricts the improvement of weld mechanical properties, welding experiments on Ti-6Al-4V titanium alloy by adopting ultra-high frequency pulse gas tungsten arc welding (UHFP-GTAW) technique were carried out to study arc characteristics and weld bead microstructure. Combined with image processing technique, arc shapes during welding process were observed by high-speed camera. Meanwhile the average arc pressure under various welding parameters were obtained by adopting pressure measuring equipment with high-precision. In addition, the metallographic samples of the weld cross section were prepared for observing weld bead geometry and microstructure of the fusion zone. The experimental results show that, compared with C-GTAW, UHFP-GTAW process provides larger arc energy density and higher proportion of arc core region to the whole arc area. Moreover, UHFP-GTAW process has the obviously effect on grain refinement, which can decrease the grain size of the fusion zone. The results also revealed that a significant increase of arc pressure while increasing pulse frequency of UHFP-GTAW, which could improve the depth-to-width ratio of weld beads.

Influence of welding process on the properties of dissimilar titanium alloy weldments: a review

The extensive use of titanium alloys in a variety of complex industrial applications may be attributed to their properties of high strength-to-weight ratio, corrosion resistance and high temperature strength. Recently, the use of dissimilar titanium alloys has become popular to achieve contrasting characteristics in a single unit. In the fabrication of the structures, joining methods such as welding hold the key in the attainment of the desired characteristics. The present study is aimed at reviewing various state-of-the-art processes used for welding of dissimilar titanium alloys. In particular, the influence of different welding methods such as gas tungsten arc welding (GTAW), laser and electron beam welding on the microstructure, mechanical properties and other characteristics of dissimilar weldments of α, α + β and β titanium alloys has been emphasized. The underlying phenomena that govern the effect of weld processing parameters on the mechanical strength, microstructure and weld joint quality of the alloys were exploited. Moreover, detailed investigations on the fusion zone porosities and evolution of intermetallic concept at the interfacial regions have been examined. Furthermore, different remedial approaches to enhance the joint quality such as beam offsetting, process hybridization, aging and post-weld heat treatments are investigated thoroughly. The latest trends in dissimilar welding of titanium alloys to upheave further research in this area have been reported in the context of their application in industrial applications.

The effect of holding time on dissimilar resistance spot welding of stainless steel 316L and Ti6Al4V titanium alloy with aluminum interlayer

A combination of stainless steel and titanium alloy is obviously a good choice for the industrial application using resistance spot welding process. However, to provide good quality of the welded joint was difficult due to the different types of materials. To enhance the weld quality, aluminum was placed in between stainless steel and titanium alloy as an interlayer. The mechanical and physical properties of the welded joint were investigated. The results of the SS316L/Ti6Al4V joint show that the tensile-shear load was 895 N and the maximum hardness value was 367.3 HV under the weld current of 12 kA, welding time and holding time of 10 cycles and electrode force of 4 kN. The microstructure result shows that a very thin reaction layer was formed on the intermetallic compound of the SS316L/AA5754 interface. Meanwhile, a diffusion–reaction has occurred on the interface of AA5754/Ti6Al4V during resistance spot welding. The effect of holding time was investigated due to the void appears in the middle of the weld nugget. The existence of the void will significantly reduce weld strength. The increase of holding time successfully remove the void and increase the weld strength of the joint under the tensile-shear test.

Development and experimental study on linear friction welding titanium alloy blisk

Taking the advanced aeroengine compressor blisk as the application object, the development and experimental study on the TC11/TC17 different materials linear friction welding integral blisk was carried out. The microstructure of welded joint was analyzed, the tensile and stress rupture properties of base metal and welded joint were compared, the vibration fatigue test on welded blade test pieces, and the overrunning test and low-cycle fatigue test on welding blisk were developed. The results show that the TC11/TC17 linear friction welding joint consists of five typical zones, they are TC11 base metal zone, TC11 thermal influence zone, weld zone, TC17 thermal influence zone and TC17 base metal zone. The tensile strength of the welded joint is basically equivalent to that of the TC11 base metal, elongation is equivalent to TC17 base metal; endurance strength lower than TC17 base metal, but less higher than TC11 base metal. The median fatigue life of welded blade test pieces with three weld positions is respectively 1.501 × 106, 0.344 × 106, and 0.132 × 106 cycles, the fatigue crack isn’t at welding seam and thermal influence zone. The welding blisk pass the 115% overrunning test and 1000 cycles low-cycle fatigue test, the experiment results meet the requirement.

Identification of modes of welding using parametric studies during ytterbium fiber laser welding

Abstract Titanium-based Ti6Al4V alloy and SS 316L are most widely used materials in the manufacturing industry. Also, recent developments in fiber lasers offer remarkable benefits for welding of titanium and stainless steel alloys on account of high processing ability and accuracy. Moreover, identification of conduction and keyhole mode welding during fiber laser welding process is a promising task. Therefore, aim of the present work is identification of weld limits viz, conduction, transition and keyhole in Ti6Al4V alloy and SS 316L welds with respect to fundamental dimensional and non-dimensional parameters. Also, the influence of laser welding process variables and thermal physical properties of Ti6Al4V alloy and SS 316L welds are investigated using linear energy, laser interaction energy and absorbed heat flux. Moreover, the effect of non-dimensional numbers viz. melting efficiency, non-dimensional heat input index, non-dimensional linear energy, Marangoni number and Fourier number are examined. The non-dimensional numbers correlated the combined effect of laser welding process variables and alloy properties with thermal and fluid flow characteristics to analyze its impact on weld pool development. And, evaluation of weld characteristics in definitive weld regimes relative to dimensional and non-dimensional numbers. Moreover, macro and micro-structural analysis and micro-hardness estimation is carried out at distinct weld regimes to examine the weld behaviour.