Welded Joints In Titanium Alloys Research Articles

The Effect of Defect Characteristics on Prediction of Fatigue Life of TC4 Titanium Alloy Welded Joints

The size and depth of defects significantly affect fatigue performance; the main purpose of this article is to clarify the effect of stress correction factors caused by defects on the fatigue life of α + β Type titanium alloy welded joints. In order to investigate the fatigue characteristics of α + β Type titanium alloy welded joints, axial constant amplitude loading fatigue tests were performed with a stress ratio of −1. The test results show that the fatigue life continues to increase as the stress amplitude decreases, and the failure modes can be classified into two types: interior failure and surface failure. A fatigue parameter (λ) determined by both defect depth and size was proposed which allowed for a good generalization of the data point distribution in short and long-life regions. The stress correction factor (W) related to the S–N characteristics was constructed by combining the λ and average defect size, and it effectively improved the dispersion of the test data. Continuing, the fatigue life prediction model was established under the condition that the defect type and size can be estimated or detected on the basis of the dislocation energy method. The results indicated that the evaluated values of the new life model associated with W are in good agreement with the test results.

Investigation on corrosion tendency behaviour of TA2 titanium alloy welded joints under flow scouring conditions using the array electrode method

PurposeThe corrosion behaviour of titanium alloy surface when fluid with different flow rates flows through welded joints with different residual heights was explored.Design/methodology/approachThe experiment uses a combination of array electrodes and simulation.FindingsIt is found that when the weld reinforcement exists, the corrosion tendency of both ends of the weld metal is greater than that of other parts of the welded joint due to the influence of high turbulence kinetic energy and shear stress. The presence of weld reinforcement heights makes the fluid behind it fluctuate greatly. The passivation films of both the base metal (BM) at the rear and the heat-affected zone (HAZ) are more prone to corrosion than those of the front BM and HAZ, and the passivation film is rougher.Originality/valueThe combination of test and simulation was used to explore the influence of electrochemical and hydrodynamic factors on the corrosion behaviour of titanium alloy-welded joints when welding residual height existed.

Effect of Ultrasonic Impact on Corrosion Fatigue Properties of Titanium Alloy Welded Joints

Effect of Ultrasonic Impact on Corrosion Fatigue Properties of Titanium Alloy Welded Joints

Stress corrosion characteristics of electron beam welded titanium alloys joints in NaCl solution

The Ti6321 titanium alloy has stress corrosion sensitivity in 3.5% NaCl solution, and the sample with cracks will fracture in a short time. The aim of this paper is to reveal the key factors affecting the stress corrosion resistance and clarify the stress corrosion mechanism of different regions of the joint by studying the crack propagation and stress corrosion critical stress intensity factor of the different regions of titanium alloy welded joint. Stress corrosion cracking, fracture and crack propagation path of electron beam welded titanium alloy joint were analyzed, characteristics of microstructure, texture and electrochemical were studied. The results indicated that the stress corrosion intensity factor KISCC of the weld metal is >76.50 MPa • m 1 / 2 , and the maximum KISCC value of heat affected zone is 51.62 MPa • m 1/2 , so KISCC of weld metal is better than heat affected zone. The crack growth rate of weld metal is slightly higher than that of heat affected zone. The fractured surface of weld metal has no obvious stress corrosion characterization, while heat affected zone has. The propagation path of weld metal is more zigzag than that of heat affected zone. The results reveal that microstructure, texture and electrochemical properties are the main reasons for stress corrosion. • The stress corrosion of titanium alloy electron beam welded joint in different regions has been studied. • The stress corrosion resistance of weld metal is significantly higher than heat affected zone, which is related to composition, microstructure and microtexture. • The stress corrosion crack mechanism of titanium alloy welded joint is the combined action of crack propagation and potential corrosion under stress.

Characterization of Corrosion Behavior of TA2 Titanium Alloy Welded Joints in Seawater Environment.

Titanium alloy has been widely used in Marine pipeline system because of its excellent corrosion resistance. However, there are differences in microstructure and electrochemical properties because of the heterogeneous structure of the welded joint, the corrosion behavior is often different. In this paper, the corrosion behavior of TA2 titanium alloy welded joint in seawater at different temperatures was studied by traditional macro electrochemical test analysis combined with microelectrode array test and surface morphology analysis. Conventional macroscopic electrochemical analysis results show that the corrosion resistance of heat-affected zone is always the best, followed by the base metal and the weld. And the higher the temperature, the easier the formation of passivation film. The results of microelectrode array test show that the heat-affected zone is always the cathode region of the whole welded joint, and part of the cathode near the base metal region has the largest current density, which acts as the main cathode to slow down corrosion. At slightly higher temperatures, the polarity deflection will occur in the base metal zone and weld zone due to the different formation speeds of passivation film in early corrosion stage. With the prolongation of corrosion time, the base metal eventually becomes the cathode zone and the weld zone eventually becomes the anode zone.

Microstructure Evolution of Inertia Friction Welded Joints of TC21 Titanium Alloy

In this paper, TC21 titanium alloy welded joints were successfully formed through inertial friction welding (IFW) processes. Microstructure evolution of IFW joints was investigated by way of different analysis methods including optical microscope (OM), scanning electron microscope(SEM), Electron Back-Scattered Diffraction(EBSD), X-Ray Diffraction(XRD), and Energy Dispersive Spectrometer(EDS). The results indicate that large-sized equiaxial β grains, original α phases, and basketweave structure existing in the BM have completely disappeared in the WZ. Instead, fine equiaxial grains sized at 20–30 μm and very fine α + β lamellar microstructure are formed in the WZ. However, as transition zones, the microstructures of the TMAZ and HAZ are also in transition state while the microstructures existing in the BM partially remain in the TMAZ and completely remain in the HAZ. In addition, second α phases are precipitated and fine α + β lamellar microstructure are formed on the original β base in the TMAZ and HAZ. XRD and EBSD results reveal that the proportion of β phase in the WZ zone decreases greatly. EDS results show that there are aggregations of stabilizing elements of β phase in the BM, but no element aggregation in the WZ. Dynamic recrystallization during the IFW process and element distribution under the rapid cooling condition after the welding process are believed to be responsible for formation of the microstructure in the weld zone of IFW joints.

Multiscale Characterization of Erosion of TA2 Titanium Alloy Welded Joints

To prolong the service time of ship and seawater piping systems, titanium alloys have a series of excellent properties, such as their low density, high strength, and seawater corrosion resistance, and they have become the main material used in ocean engineering. A welded joint is a nonuniform structure that is composed of a weld seam (WM), base metal (BM), and heat-affected zone (HAZ). When an alloy is used, it is easier to form galvanic corrosion, stress corrosion, and pitting corrosion in a weld joint than when a single metal is used. Therefore, corrosion failure often occurs at a welded joint. In this article, classical electrochemical testing (EIS and Tafel) and surface morphology analysis (SEM and EDS) were used to study a welded joint, and microarray electrode (WBE) testing was added for the first time to study a welded joint. The corrosion behavior of each zone of a TA2 titanium alloy welded joint in flowing seawater and the overall corrosion tendency after coupling of three zones were studied at the macro- and submicroscales. Macroscopic results show that the HAZ and BM of a titanium alloy welded joint have better corrosion resistance in seawater. The microarray electrode shows that the WM is the main anode that accelerates corrosion, and at high flow rate, the electrode will change into the cathode. In conclusion, the data in this article provide a theoretical basis for the corrosion failure mechanism of TA2 welded joints.

Optimization of the weld characteristics of plasma-arc welded titanium alloy joints: an experimental study

ABSTRACT Titanium alloys especially Ti6Al4V have wide commercial applications in various sectors of aerospace manufacturing industries owing to their excellent physical, mechanical, and thermal characteristics. Titanium alloys are mostly welded by conventional gas tungsten arc welding process which gives compromisingly higher productivity. There are welding technologies like plasma arc welding that provide high arc energy density results in good-quality welds with higher productivity. In this present investigation, the efforts were put to study and optimize the important welding variables, such as weld current, speed, plasma gas flow rate, and constricted arc length. These parameters govern the most desired characteristics of weld bead such as weld bead width, complete penetration, fusion zone area, and prior β grain size. Optimum solutions were found through desirability-based multi-response optimization by response surface methodology. Microstructural features and mechanical properties were evaluated for the joints welded using the optimum process parameters and found that characteristics are well within the desired criteria.

Fatigue Performance of Titanium Alloy Welded Joints

Titanium alloys are widely used in aerospace, chemical engineering and medicine because of their excellent tensile, fatigue strength and corrosion resistance. For aerospace titanium alloys, fatigue performance is an important parameter, especially as a structural material. Welding is an indispensable method. After welding, there is a large unevenness in the structure and mechanical properties of the welded joint. Fatigue performance also has a profound effect. This article has done a deep research on the fatigue performance of titanium alloy welded streets, using ANSYS software to calculate and analyze the stress concentration of welded joints, observe and analyze the welding defects on fatigue fractures, and discuss the effect of welding defects on fatigue behavior The equivalent residual stress after spot welding at the center of the joint weld obtained by conventional laser welding near the welding end position is 547 MPa, of which the longitudinal residual stress along the weld direction is tensile stress, the magnitude is 482 MPa, and the transverse direction perpendicular to the weld direction The residual stress is a compressive stress of 114.0 MPa, and the equivalent residual stress of the weld is reduced after the use of SGCW technology. The equivalent residual stress at this point is reduced to 489 MPa, which is a reduction of nearly 12%.

Fracture toughness of friction stir welded TA5 titanium alloy joint

Fracture toughness of friction stir welded titanium alloy joints was investigated using Compact tension (CT) toughness specimens. The fracture toughness slightly decreases to about 90% of the fracture toughness of base metal. The fracture surface was mainly ductile fracture mechanism with a large number of dimples. The crack propagation path was straight and mixed with intergranular and transgranular fracture. The stir zone of joint has a large number of fine ɑ grains with some dislocations. For texture, the stir zone has hard orientation {0002} <112¯0>, the directions of cylinder and plate thickness are parallel. The reduction of fracture toughness in the stir zone is mainly related to microstructure and texture.

Fracture Toughness Evolution Induced by Hydrogen of TA10 Titanium Alloy Welded Joints

Fracture Toughness Evolution Induced by Hydrogen of TA10 Titanium Alloy Welded Joints

Applying Digital Image Correlation Technique for Studying the Growth of a Fatigue Crack in VT23 Titanium Alloy Welded Joints

We present results of applying a combined approach to studying fatigue fracture processes in VT23 titanium alloy with a laser-welded joint. The approach involves fractographic examination using scanning electron microscopy and analysis of strain fields at the sample surface (using digital image correlation technique). Samples with permanent connections are presented in two forms: in the initial state and subjected to post-welding treatment by ultrasonic forging and pulsed high-energy impact. It is shown that applying the proposed integrated approach to the analysis of fatigue fracture has allowed identifying features in the development of processes of nucleation and propagation of cracks and locating them in the bulk of the material, as well as determining running times after which transition from one stage to another takes place: crack initiation, stable growth, and rupture. The results have made it possible to explain the mechanisms of how post-welding treatment of permanent joints affects their fatigue properties.

Low-cycle fatigue of welded structures made from domestic and imported materials

In various branches of modern engineering, corrosion-resistant steels and titanium alloys are widely used as structural materials. At the same time, it is possible to connect parts made from domestic and imported alloys using automatic argon-arc electric welding, which leads to the formation of a material with unexplored properties in the weld. Welded joints are stress concentrators and currently there is no information about low-cycle fatigue of welded joints obtained by fusing domestic and imported materials. In the course of the research, the modes of welding and heat treatment of butt welded joints obtained from sheet titanium alloys and corrosion-resistant steel of domestic and foreign production have been developed. Resource tests for low-cycle fatigue of samples of welded joints were carried out. Tests on low-cycle fatigue were carried out on the upgraded testing machine UMM-10 with repeated static stretching with an asymmetry factor of +0.1 and at a frequency of 0.6–0.8 Hz. The maximum tensile stress was 80% of the temporary tensile strength of the weakest alloy in the pair. The main stress axis from external loading in all cases was perpendicular to the weld. The tests were carried out until the destruction of the sample. As a result of research, it was established that all welded joints were destroyed along the fusion line, which is explained by the simultaneous action of geometric and structural stress concentrators. In this case, the destruction of the samples, as a rule, began near the seam from the side of the weakest alloy in the pair. It was also established that the use of temperatures of incomplete annealing in comparison with the full one allows to increase the cyclic durability for welded joints of titanium alloys by 1.3–2 times. From the results of comparative tests of samples of corrosion-resistant steels, it follows that domestic and imported steels, as well as their welded joints, have similar properties, both in strength and in re-static durability.

An Entropy-Based Neighborhood Rough Set and PSO-SVRM Model for Fatigue Life Prediction of Titanium Alloy Welded Joints.

In order to obtain comprehensive assessment of the factors influencing fatigue life and to further improve the accuracy of fatigue life prediction of welded joints, soft computing methods, including entropy-based neighborhood rough set reduction algorithm, the particle swarm optimization (PSO) algorithm and support vector regression machine (SVRM) are combined to construct a fatigue life prediction model of titanium alloy welded joints. By using an entropy-based neighborhood rough set reduction algorithm, the influencing factors of the fatigue life of titanium alloy welded joints such as joint type, plate thickness, etc. are analyzed and the reduction results are obtained. Fatigue characteristic domains are proposed and determined subsequently according to the reduction results. The PSO-SVRM model for fatigue life prediction of titanium alloy welded joints is established in the suggested fatigue characteristic domains. Experimental results show that by taking into account the impact of joint type, the PSO-SVRM model could better predict the fatigue life of titanium alloy welded joints. The PSO-SVRM model indicates the relationship between fatigue life and fatigue life influencing factors in multidimensional space compared with the conventional least-square S-N curve fitting method, it could predict the fatigue life of the titanium alloy welded joints more accurately thus helps to the reliability design of the structure.

Hydrogen technologies in foundry and metallurgy: current state and perspectives (review)

The article presents an overview of achievements of hydrogen treatment of materials, – the field of materials science, which makes possible improvement of materials structure and properties with the help of a reversible hydrogen effect. Examples of the hydrogen technologies use in casting and metallurgy are shown. Thermohydrogen processing (THP) of titanium alloys consists of a number of successive operations: hydrogenation of the metal to specified concentrations, technological action on the metal, vacuum annealing to remove hydrogen from the metal to safe concentrations. THP allows plasticizing titanium alloys, increasing their antifriction properties. In welded joints of titanium alloys, the THP equalizes the plasticity of the welded joint and the base metal, increases the cyclic life of the products by 2–2.5 times. In the technologies of casting, the preliminary hydrogenation of a number of aluminum melts leads to an increase in the strength limit by 20–30%, and the relative elongation by 15–45%, and also increasing heat resistance after plastic deformation. With the help of hydrogen, it is possible to carry out controlled powdering of intermetallic compounds, to form nanostructures in materials, to accelerate the processes of chemical-thermal treatment, and to cause «artificial polymorphism» in metals that are not polymorphic by its nature.It is concluded that some of hydrogen technologies have already been commercialized, some are still waiting for wide use. In general, the prospects for the development of hydrogen processing of materials lie in the development of the application of metal– hydrogen systems, and international activity (in particular, schools and conferences), traditionally and regularly held on this topic, allow us to judge the intensive development of the theory and practice of hydrogen technologies.

Effect of Welding and Heat Treatment Regimes on the Mechanical Properties of Various Titanium Alloy Welded Joints

Results are provided for experimental study of automatic argon-arc electric welding and heat treatment regimes for butt welded joints of titanium alloy plates of domestic and foreign manufacture. Welded joint microstructure is studied and ultimate strength in breaking tests is determined.

Flaw inspection of welded joints in titanium alloys by the eddy current method

The eddy current transducer (ECT) of the transformer type is used to construct a sensor for investigating titanium sheets joined by a welded joint. The characteristics of the ECT are presented. The measurement method for controlling the occurrence of defects in the welded joints in titanium alloys is described. The experimental results obtained by the ECT on two welded titanium sheets are presented. The depth of penetration of the field of eddy currents into the investigated object is determined and the dependences describing the response of the ECT at different depths of the defect are outlined. The relationships can be used for evaluating the quality of welded joints and determining the reliability of welding.

Scanning the welded seams of titanium alloys by using subminiature eddy current transducers

The eddy current transducer (ECT) of the transformer type is used to construct a sensor for investigating titanium sheets joined by a welded joint. The characteristics of the ECT are presented. The measurement method for controlling the occurrence of defects in the welded joints in titanium alloys is described. The experimental results obtained by the ECT on two welded titanium sheets are presented. The depth of penetration of the field of eddy currents into the investigated object is determined and the dependences describing the response of the ECT at different depths of the defect are outlined. The relationships can be used for evaluating the quality of welded joints and determining the reliability of welding.

Welding of high-strength titanium alloys of large thicknesses for use in marine environments

The paper presents manual narrow groove welding of marine high-strength titanium alloys of large thickness using special flat devices (nozzle burners), double-sided electron beam welding, and welding technology producing combined high-strength titanium alloys of large thickness (over 200 mm). Electron beam welding technology with filler wire in the vertical and horizontal position of the seam has been developed to fill the gap. The technology for repair of welded joints of titanium alloys of large thicknesses by electron-beam melting has also been developed. The mentioned technologies have been implemented at shipbuilding sites and have passed interdepartmental tests.

Statistical analysis of tensile strength and elongation of pulse TIG welded titanium alloy joints using Weibull distribution

Abstract In this study, the tensile strength of a pulsed current tungsten inert gas welded Ti-6Al-4 V plate has been statistically analysed by Weibull distribution. Titanium alloy of 1.6 mm thickness was welded with pulsed current tungsten inert gas welding. Testing of mechanical properties was done to understand the influence of pulsing current on the fabricated joint. But the result obtained has to be consistent and repeatable. Hence, this paper investigates a method for predicting the reliability of values obtained for tensile strength and elongation with consistency. The tensile strength results obtained vary between 975 and 1160 MPa and percentage elongation vary between 2.4 and 5.9%. Using Weibull technique in conjunction with the experimental data, we can predict the output more accurately. Using Weibull distribution, the welded joint reliability can be obtained. The probability distribution according to which the joint will fail is estimated with the help of Weibull analysis.