Gas Tungsten Research Articles

Synergic investigation of microstructure, precipitation, and micro-segregation on Inconel 825 weldments: A comparative study between GTAW and EBW

Inconel 825, a Ni–Fe–Cr alloy highly regarded for its exceptional corrosion resistance and high-temperature strength. This investigation studies the effect of heat input, precipitation, and micro segregation of Inconel 825 weldments and compares the effectiveness of two welding techniques: gas tungsten arc welding (GTAW) and electron beam welding (EBW). The findings indicate that increasing heat input generally enhances weldment quality by reducing the lack of penetration. However excessive heat input in GTAW leads to root cracking and solidification cracking; while EBW demonstrates better control over undercut and maintains consistent weld quality even at higher heat inputs. Both GTAW and EBW samples exhibit dendritic grain morphologies with distinctive grain boundaries. Precipitates, such as Al4C3 and TiN, are observed in both processes, contributing to improved mechanical properties. While GTAW weldments show some degree of segregation for Mo, Cu, Ti, and Al, EBW weldments demonstrate negligible segregation for major alloying elements but micro-segregation of Ti and Al. EBW weldments additionally showcase higher average hardness, superior tensile strength, and ductility compared to GTAW weldments. This can be attributed to lower heat input, faster cooling rates, and a reduced rate of elemental segregation. Fractographic analysis reveals the presence of voids and micro-voids, indicating a ductile mode of failure for both GTAW and EBW samples. These void characteristics vary based on the heat input and microstructural features.

Metallurgical and mechanical properties evaluation of the activated flux tungsten inert gas weldments

The activated flux tungsten inert gas welding process is an attractive joining technique to increase the depth of penetration in a single pass. In the last two decades, the research on activated flux tungsten inert gas welding increased drastically. Despite enhanced weld penetration, activated flux tungsten inert gas is not frequently implemented in industries because of a lack of information about the process. However, research on activated flux tungsten inert gas welding has significantly increased in the last decade due to the widespread information related to the advancements in weld penetration and mechanical properties of the activated flux tungsten inert gas process. The activated flux tungsten inert gas welding process provides a high single pass depth of penetration along with good mechanical properties compared to the tungsten inert gas welding process. The current work offers an in-depth analysis of the activated flux tungsten inert gas welding process mechanism, advancement in activated flux tungsten inert gas methodology to improve weld bead geometry, and mechanical and corrosion behaviour of the weldments. The current work also highlights recent progress made in the field of dissimilar metal joining using the activated flux tungsten inert gas welding process.

Fabrication of Titanium Aluminide Alloys by Twin-Wire Tungsten Inert Gas Welding Applied with High-Frequency Induction Heating Wire Technology: Processing, Microstructure, and Properties

Fabrication of Titanium Aluminide Alloys by Twin-Wire Tungsten Inert Gas Welding Applied with High-Frequency Induction Heating Wire Technology: Processing, Microstructure, and Properties

Evaluation of Residual Stresses and Distortion of Ti-5Al-2.5Sn and SS 304 Gas Tungsten Arc Welded Joints under Hybrid Thermal Tensioning Technique: Transient Thermal Tensioning and Trailing Intensive Cooling

Evaluation of Residual Stresses and Distortion of Ti-5Al-2.5Sn and SS 304 Gas Tungsten Arc Welded Joints under Hybrid Thermal Tensioning Technique: Transient Thermal Tensioning and Trailing Intensive Cooling

A STUDY ON MULTI-OBJECTIVE OPTIMIZATION OF PULSED TIG WELDING PARAMETERS AND THEIR EFFECT ON JOINT PROPERTIES OF HIGH MANGANESE STEELS USING TAGUCHI-BASED GRA APPROACH

This investigation focuses on the study of the effect of process parameters like peak current ([Formula: see text], base current ([Formula: see text], pulse frequency ([Formula: see text], shielding gas flow rate ([Formula: see text] on mechanical properties like yield strength (YS), ultimate tensile strength (UTS) and flexural strength (FS) of the welded joints during pulsed TIG welding of SAILMA 450 and EN14 B steels. Taguchi’s L[Formula: see text] orthogonal array has been used for conducting the tests. Multi-objective optimization has been performed using Grey relational analysis (GRA) in order to maximize the mechanical strength and to find out the optimal set of parameters. The optimum parametric combination is obtained at a peak current of 220[Formula: see text]Amps, base current of 120[Formula: see text]Amps, pulse frequency of 5[Formula: see text]Hz and shielding gas flow rate of 17[Formula: see text]l/min. Analysis of variance (ANOVA) is used to predict the significant process parameters. It has been observed from the ANOVA analysis that peak current and pulse frequency have more influence on the output responses than the shielding gas flow rate and base current. The results of the confirmatory test show an improvement of 0.5801 in the GRG, which is satisfactory. A microstructure study has been performed using scanning electron microscopy (SEM) for the optimal set of process parameters.

Creep Performance Study of Inconel 740H Weldment Based on Microstructural Deformation Mechanisms

Abstract The creep behavior of Inconel 740H weldment at the temperature of 760 °C is investigated experimentally and analytically using the deformation-mechanism-based true stress (DMTS) model. The Inconel 740H weldment specimens are prepared with the gas tungsten arc welding technique. Creep testing is performed on the Inconel 740H weldment specimens under a range of stress levels from 190 MPa to 447 MPa at the temperature of 760 °C. The DMTS model is employed to analyze the creep curves and creep rates. The model parameters for Inconel 740H weldment are determined from the analyses of the creep testing data in combination with that from the previous studies of similar materials based on the same creep mechanisms that involve grain boundary sliding and intragranular dislocation climb-plus-glide with dislocation multiplication. The creep life predictions of the DMTS model for Inconel 740H weldment agree very well with creep rupture test data within a temperature range of 700–800 °C. The fractured surfaces and longitudinal sections of creep-tested Inconel 740H weldment specimens are examined using scanning electron microscopy, which corroborates the DMTS model inference that the creep failure of Inconel 740H weldment is in a mode of predominantly intergranular fracture. The present study suggests that grain boundary sliding is the most significant controlling factor for the creep failure of Inconel 740H weldment.

Microstructural and Corrosion Behavior of Thin Sheet of Stainless Steel-Grade Super Duplex 2507 by Gas Tungsten Arc Welding

<div>Super duplex stainless steel (SDSS) is a type of stainless steel made of chromium (Cr), nickel (Ni), and iron (Fe). In the present work, a 1.6 mm wide thin sheet of SDSS is joined using gas tungsten arc welding (GTAW). The ideal parameter for a bead-on-plate trial is found, and 0.216 kJ/mm of heat input is used for welding. As an outcome of the welding heating cycle and subsequent cooling, a microstructural study revealed coarse microstructure in the heat-affected zone and weld zone. The corrosion rate for welded joints is 9.3% higher than the base metal rate. Following the corrosion test, scanning electron microscope (SEM) analysis revealed that the welded joint’s oxide development generated a larger corrosive attack on the weld surface than the base metal surface. The percentages of chromium (12.5%) and molybdenum (24%) in the welded joints are less than those in the base metal of SDSS, as per energy dispersive X-ray (EDX) analysis. Corrosion modeling is done using the COMSOL Multiphysics software. Electrochemical corrosion modeling is used to determine the electrolyte potential (i.e., 0.09 V) and current density (i.e., 0.2 A/m<sup>2</sup> to 1.8 A/m<sup>2</sup>). An entire mesh model contains 6240 elements. The largest and smallest element sizes are 4 mm and 0.1 mm, respectively. The maximum element rate of growth is 1.2.</div>

Stress corrosion effects on ADC12 Al alloy tungsten inert gas welding joint in 3.5 wt% NaCl solution

The stress corrosion behavior of ADC12 Al alloy tungsten inert gas (TIG) welding joint (WJ) outside its elastic deformation range was studied using electrochemical testing methods combined with surface analysis techniques in 3.5 wt% NaCl solution at 30 °C. The results showed that, with the enlargement of imparted stress, the corrosion potential of the TIG WJ shifted positively, the corrosion current density increased, and the polarization resistance decreased, indicating that the corrosion rate of the TIG WJ increased with the enlargement of imparted stress. With the prolongation of immersion time, the corrosion rate of the TIG WJ increased and then subsequently decreased. In addition, the plasticity and ductility of the TIG WJ decreased with the enlargement of imparted stress. When the imparted stress was 2100 N and 4200 N, the corrosion products on its surface were mainly composed of Al2O3 and Al(OH)3. This study provided a theoretical basis for the selection of structural materials and welding methods in the automotive, marine and aerospace fields.

In situ chemical analysis of duplex stainless steel weld by laser induced breakdown spectroscopy

The high corrosion resistance and good mechanical properties of duplex stainless steel (DSS) are due to its special chemical composition, which is a balanced phase ratio of ferrite (α) and austenite (γ). Many industrial applications require the integration of DSS components. For this, Gas tungsten arc welding (GTAW) is an excellent choice, as it allows an automated operation with high reproducibility. However, when the weld pool solidifies, critical ratios of α- and γ- phases can occur, which lead to solidification cracking, increased susceptibility to corrosion, and a decrease in ductility and critical strength. Previous studies have shown that these defects can be caused by the accumulation of manganese and chromium in the heat affected zone (HAZ), requiring ongoing monitoring of this accumulation. A suitable method for such monitoring is laser-induced breakdown spectroscopy (LIBS), which can be used in two operating modes: calibration using standard reference samples and calibration-free. Unlike conventional quantitative LIBS measurements, which require reference samples to generate a calibration curve, calibration-free LIBS (CF-LIBS) allows chemical compositions to be determined solely from the emission spectrum of the plasma. Numerous publications show that CF-LIBS is a fast and efficient analytical method for the quantitative analysis of metal samples. In this work, CF-LIBS is applied to spectra obtained during GTAW DSS welding and the result is compared with those obtained by PLS analysis. A good correlation was found between both types of analysis, demonstrating the suitability of the CF-LIBS method for this application. The CF-LIBS method has a significant advantage over conventional LIBS due to the rapid in situ measurement of concentrations of major alloying elements without calibration procedure. This, combined with fast feedback and appropriate adjustment of welding parameters, helps prevent welding defects.

Investigations on the multiple-sector hard-copper X-band accelerating structures

The development of advanced, high gradient accelerating structures is one of the leading activity of the particle accelerator community. In the technological research of new construction methods for these devices, high-power testing is a critical step for the verification of their viability.Recent experiments showed that accelerating cavities made out of hard copper, fabricated without high-temperature processes, can achieve better performance as compared with soft copper ones. Recently, we have built cavities using Tungsten Inert Gas welding and the high-power experiments confirmed that this joining process is a robust and low-cost alternative to brazing or diffusion bonding. This is a good solution for high-gradient operation, with a gradient of about 150 MV/m in X-band, at a breakdown rate of 10−3/pulse/meter using a shaped RF pulse with a 150 ns flat part.We continue the design, construction and high power tests of three-cells standing-wave X-band accelerating cavities fabricated with a split-open geometry, made of hard copper and vacuum-sealed by welding. Our aim is the fabrication of accelerating structures made out of hard copper alloys by using innovative cost-effective technologies. Moreover, our method of multiple-sector structures opens the way to new technological approaches and design methods, for example providing the possibility of placing dampers of the parasitic higher-order modes. Such structures with dampers allow for acceleration of multi-bunch beams, both in standing and in travelling-wave accelerating modality.This paper describes the design of two cavities made of multiple sectors that were fabricated at the Italian Institute for Nuclear Physics in Frascati, Italy (INFN-LNF), assembled by means of clamping and then joined with the Tungsten Inert Gas welding in order to preserve the hardness of the metal. These are three-cell standing-wave X-band accelerating cavities, to be operated in the π-mode. We report the low-power RF tests of the first one, made of two halves, and the RF design of the second one, made of four quadrants. Both structures were built for high-gradient tests at SLAC National Accelerator Laboratory.

A Real-Time Monitoring Method for Droplet Transfer Frequency in Wire-Filled GTAW Based on Arc Sensing.

Droplet transfer frequency is a decisive factor in welding quality and efficiency in gas tungsten arc welding (GTAW). However, there still needs to be a monitoring method for droplet transfer frequency with high precision and good real-time performance. Therefore, a real-time monitoring method for droplet transfer frequency in wire-filled GTAW using arc sensing is proposed in this paper. An arc signal acquisition system is developed, and the wavelet filtering method filters out noise from the arc signal. An arc signal segmentation method-based on the OTSU algorithm and a feature extraction method for droplet transition based on density-based spatial clustering of applications with noise (DBSCAN)-is proposed to extract the feature signal of the droplet transition. A new conception of droplet transition uniformity is proposed, and it can be used to monitor the weld bead width uniformity. Numerous experiments for monitoring droplet transfer frequency in real time are conducted with typical welding parameters. This method enables the real-time observation of droplet transfer frequency, and the result shows that the average monitoring error is less than 0.05 Hz.

Search for high-creep-strength welding conditions considering HAZ shape factors for 2 1/4Cr–1Mo steel

The creep rupture life of ferritic heat-resistant steel weld joints is limited by Type IV cracking that occurs in the heat-affected zone (HAZ), whose shape affects creep damage accumulation. In this study, we address the inverse problem of extending the creep rupture life of weld joints by controlling HAZ shape via welding conditions. As reported separately, we have developed a workflow that predicts weld joint creep rupture life from the predicted HAZ shape from welding conditions and have implemented it in the material design system. Using this workflow, we presented a tandem Bayesian model for predicting the creep rupture life from welding conditions via the geometric features of HAZ shapes (HAZ shape factors), which are considered to determine the creep rupture life. The prediction model of a HAZ shape factor from welding conditions was formed by Gaussian process regression. The prediction model of the creep rupture life was formed by Bayesian linear regression. These models were probabilistically connected by Bayesian statistical mathematics. An algorithm to increase the creep rupture life was developed to search for welding conditions. This method was applied to a 2 1/4Cr–1Mo heat-resistant steel weld joint simulated with a plate I-bevel three-layer gas tungsten arc welding. The number of welding conditions combination reaches 78=5764801\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${7}^{8}=5764801$$\\end{document}. Start from 49 initial HAZ shape factors and 22 creep rupture life data, we performed forward calculations of 20 rupture lives to find welding conditions that can improve the creep rupture life by 12% over the initial data.

Interaction Mechanism of Arc, Keyhole, and Weld Pool in Keyhole Plasma Arc Welding: A Review.

The Keyhole Plasma Arc Welding (KPAW) process utilizes arc plasma highly constricted by a water-cooled cupper nozzle to produce great arc pressure for opening a keyhole in the weld pool, achieving full penetration to the thick plate. However, advanced control of welding is known to still be difficult due to the complexity of the process mechanism, in which thermal and dynamic interactions among the arc, keyhole, and weld pool are critically important. In KPAW, two large eddies are generally formed in the weld pool behind the keyhole by plasma shear force as the dominant driving force. These govern the heat transport process in the weld pool and have a strong influence on the weld pool formation process. The weld pool flow velocity is much faster than those of other welding processes such as Tungsten Inert Gas (TIG) welding and Gas Metal Arc (GMA) welding, enhancing the heat transport to lower the weld pool surface temperature. Since the strength and direction of this shear force strongly depend on the keyhole shape, it is possible to control the weld pool formation process by changing the keyhole shape by adjusting the torch design and operating parameters. If the lower eddy is relatively stronger, the heat transport to the bottom side increases and the penetration increases. However, burn-through is more likely to occur, and heat transport to the top side decreases, causing undercut. In order to realize further sophistication of KPAW, a deep theoretical understanding of the process mechanism is essential. In this article, the recent progress in studies regarding the interaction mechanism of arc, keyhole, and weld pool in KPAW is reviewed.

Effect of Cr on the high-temperature corrosion of dissimilar AISI 904L and Inconel 625 joints employed in the coal-fired thermal power plant tubes

ABSTRACT The hot corrosion behaviours of 5-mm-thick plates of dissimilar AISI 904L and Inconel 625 weldments produced by continuous current gas tungsten arc welding process using Ni-Cr-Mo-enriched filler wires (ERNiCrMo-4 and ERNiCrCoMo-1) were investigated. Optical microscopy was used to examine the microstructure of these weldments. The corrosion performance of the weldments and base metals was determined in the mixture of K2SO4 + 60% NaCl molten salt (MS) and air oxidation conditions at 700°C for 50 cycles. The thermogravimetric plots derived the corrosion kinetics of the weldments. The microstructure and the elemental analysis of the scales formed on the corroded samples were evaluated by scanning electron microscopy and energy-dispersive spectroscopy. The phases developed on the oxide layers during the corrosion were analysed using X-ray diffraction. The fusion zones of ERNiCrCoMo-1 weldment and AISI 904L base metal were vulnerable to degradation in the MS environment, causing severe cracks and spallation compared to ERNiCrCoMo-1 weldment.

Nickel-aluminide cladding on a steel substrate using dual wire arc additive manufacturing

In this study the nickel-aluminide intermetallic cladded on AISI 1010 steed using dual wire arc process. The nickel-aluminide is fabricated in situ through an arc provided by a gas tungsten arc welding process and changing aluminum wire feeding rate. The research findings reveal that at a constant Ni wire feeding rate of 450 mm/min, by decreasing the Al wire feeding rate lower than 800 mm/min, the instability of the melt pool prevents the formation of a uniform deposit on the substrate. Although deposition has been done at an Al wire feeding rate higher than 1600 mm/min, transverse cracks have formed in the clad layer. Increasing the aluminum wire feeding rate from 1000 to 1400 mm/min decreases the dendritic arm size from 9.2 ± 0.1 to 4.1 ± 0.3 μm. Although unreacted nickel is visible in the microstructure at the Al wire feeding rate of 1000 mm/min, at a high feeding rate (1400 mm/min), most of the microstructure contains AlNi and Ni3Al intermetallic compounds. With the rise in Al wire feeding rate from 1000 to 1400 mm/min, both yield strength and ultimate tensile strength increase from 521.45 ± 14.16 to 620.89 ± 16.08 MPa and from 762.11 ± 19.89 to 855.65 ± 21.54 MPa, respectively. Intriguingly, the clad layer's tensile toughness decreases from 26.51 ± 2.43 to 18.32 ± 2.56 MJ m−3. By increasing the wire feeding rate from 1000 to 1400 mm/min, the wear rate at room temperature, 500 °C, and 800 °C increases by 61.2, 45.7, and 44.3%, respectively.

Improving the Formation and Quality of Weld Joints on Aluminium Alloys during TIG Welding Using Flux Backing Tape

This work aimed to compare the quality and properties of the welded joints of AMg6 aluminium alloy produced via conventional TIG welding with the properties of those produced with flux backing tape. This study focussed on the relative length of oxide inclusions (Δoi) and the amount of the excess root penetration (hroot) of the AMg6 alloy weld beads. The results show the influence of the thickness of the flux layer of the backing tape on the formation and quality on the AMg6 alloy welds, along with the effect of flux backing tape and edge preparation on the mechanical properties of the 6 and 8 mm thick welded plates. In accordance with the results obtained, the joints produced by means of TIG welding with flux back backing tape and without edge preparation have higher mechanical properties. Moreover, the TIG welding of AMg6 alloy using flux backing tape reduces the total welding time by 55%, reduces filler wire consumption by 35%, reduces shielding gas consumption by 43% and electricity consumption by 60% per 1 linear meter of the weld line.

Review of coupled inductors in power electronics: From concept to practice

With the increasing complexity of power electronics converters, magnetic components like inductors, transformers in different configurations, etc., play important roles in shaping a power controller to meet its desired performance effectively and efficiently. Now, coupled inductors have emerged as one important category of magnetic components that can improve the performance of several types of power controllers used in different domains. They are used to improve the control response, reduce ripple content of output control variables, improve efficiency, enhance power density, etc. This review paper deals with coupled inductors in two ways. Firstly, it details the application prospects as well as design requirements for different applications of coupled inductors. Later, it deals with the design and practical validation of one coupled inductor essentially required for one complex application where the leakage inductance of each winding should be minimal. This review has analyzed that the magnetic circuit design would play a dominant role where both the soft magnetic material and winding layout would be extremely important. While designing a practical coupled inductor, this review article has further analyzed that a core material with low loss density, high saturation flux density and interleaved winding would make the ideal magnetic circuit. The proposed magnetic circuit has been thoroughly validated in a parametric-sensitive power controller for alternating current tungsten inert gas (AC TIG) welding.

Metallurgical, mechanical, and corrosion behavior of AISI 304L joints welded using variable arc energy inputs and subjected to thermal aging

The effect of three levels of welding arc energy input on the metallurgical, mechanical, and corrosion behavior of AISI 304L stainless steel was studied with the aim of investigating and recommending the most useful range of process parameters for improved performance of engineering structures made from this industrially important alloy. The gas tungsten arc welding process was employed, and all the joints were butt-welded using a single-V groove design. With an increase in heat input, the δ-ferrite phase changed from lathy to vermicular, besides the heat-affected zones of all the welds exhibiting grain coarsening effects. Postweld thermal aging led to the preferential occurrence of carbides in the interdendritic regions, which degraded their corrosion performance. Thermal aging did not affect the tensile strength of these welds, but their ductility was significantly impacted. The extent of segregation of Cr and C, especially, was observed to be the least in the case of low heat input welds. This study establishes that while designing welding procedures for AISI 304L structures, low welding arc energy should be used as it promotes better mechanical as well as corrosion properties.

A new method for refinement of Ti-6Al-4 V prior-β grain structure in the alternating magnetic field assisted narrow gap gas tungsten arc welding (AMF-GTAW) via filler wire oscillation

This study presents a new method for refining Ti-6Al-4 V prior-β grain in the alternating magnetic field assisted narrow gap gas tungsten arc welding (AMF-GTAW) process by stirring the molten pool, which is accomplished directly through the use of an oscillating filler wire. The wire feed rate can be increased from 1.8 m/min to 2.2 m/min by filler wire oscillation in the traditional AMF-GTAW process with minimal heat input. This method greatly increases welding efficiency by efficiently utilizing the energy of the arc and molten pool. Using a high-speed camera, the flow behavior of the molten pool was investigated under different filler wire oscillating amplitudes. The results showed that the oscillation of the filler wire can cause a violent stir in the molten pool. By increasing the oscillating amplitude of filler wire, one can refine the columnar prior-β grain structure and attain a morphology of the upper layer of the welded joint that is nearly equiaxed with crystallographic texture, all while maintaining a fixed heat input. This is because the wire's insertion into the molten pool also creates a negative thermal gradient and the filler wire's high-frequency and high-amplitude oscillation creates an intense convection that prevents randomly oriented nuclei and/or dendrite fragments from remelting and promotes nucleation activation. The oscillating amplitude of 6 mm and the oscillating frequency of 100 Hz are the ideal values for this effect.

Tribological Behavior and Residual Stresses of Gas Tungsten Arc Welded Dissimilar Joint of sDSS 2507/X-70 Pipeline Steel

Tribological Behavior and Residual Stresses of Gas Tungsten Arc Welded Dissimilar Joint of sDSS 2507/X-70 Pipeline Steel