Tungsten Inert Gas Welding Technique Research Articles

Development of a novel autogenous double pulse tungsten inert gas welding technique for joining IN625 in concentrated solar power plants

The research focuses on the challenges of joining the IN625 alloy for high-temperature applications. Tungsten inert gas (TIG) welding has drawbacks such as higher heat input (HI), which causes elemental segregation and secondary phases, ultimately affecting the quality of weldments. Previous literature indicates that single-pulsed TIG (SP-TIG) welding has shown improvements over TIG welding. In this study, a new technique called double-pulsed TIG (DP-TIG) welding was developed to address the HI and elemental segregation issues during the welding process. The study also compares the improvements in properties of DP-TIG with SP-TIG welding. The results demonstrate that DP-TIG significantly reduces HI by 53% compared to SP-TIG. It effectively decreased residual stress by 26% and suppressed secondary phase formation. Moreover, DP-TIG exhibits superior mechanical properties, with an 11% increase in hardness and a 10% increase in tensile strength compared to SP-TIG. These findings establish DP-TIG as the preferred method for joining the IN625 alloy.

Correlation between Microstructure and Bending of FSW and TIG Welded Mg-Rich Aluminium Alloy Joints

This paper reports on the mechanical properties in relation to the microstructure of the Mg-rich aluminium alloy joints fabricated through friction stir welding (FSW) and tungsten inert gas (TIG) welding techniques. The microstructure, tensile, and bending tests were conducted on friction stir, and TIG welded joints. Most coarse grains (27.81mm) dominated the joint produced using the TIG welding technique, while the refined grains (11.26 mm) mostly dominated the joint made through the FSW technique. The ultimate tensile strength (UTS) of the joint fabricated using the FSW technique was higher (379 MPa) compared to the TIG-welded joint (260 MPa). However, the inverse behaviour was observed when looking at the tensile elongation of the very same joints. The bending results correlated with UTS results, and this phenomenon was attributed to the microstructural grain size.

PRELIMINARY INVESTIGATION INTO MECHANICAL PROPERTIES AND MICROSTRUCTURAL BEHAVIOUR OF INCONEL ALLOY UNDER WELDED AND UNWELDED CONDITIONS

This work focusses on analysing mechanical properties and microscopic assessment into Inconel-718 plates in welded and unwelded conditions. Welding was performed by tungsten inert gas welding technique. Two mechanical tests such as tensile test and hardness were performed on both the types of plates to compare the properties of welded joint and unwelded plate. Although Inconel 718 possesses good weldability, the strength, ductility, and hardness of welded joint were reported lesser than these of Unwelded plate. The microstructural images revealed that metal carbides present in Inconel plate had reduced after welding. The ultimate tensile stress and elongation before breaking of welded joint were 16% and 72% lower than Unwelded plate. The fractography analysis of the ruptured part revealed that Unwelded plate possessed higher ductility than welded plate.

Characterization of the microstructure and mechanical properties of activated tungsten inert gas welded and hot-wire tungsten inert gas welded super austenitic stainless steel AISI 904L

Super austenitic stainless steel AISI 904L is a premium stainless steel variant known for its superior properties and ability to retain the same in highly challenging conditions. This study investigates the feasibility of welding 10-mm thick plates of AISI 904L through activated tungsten inert gas welding and hot-wire tungsten inert gas welding methods. The fabricated joints are then subjected to solidification mode study, ferrite number analysis, microstructural characterization, and mechanical tests. Results of the solidification mode study indicated primary austenitic solidification in both the weld joints. The ferrite number measurement revealed that the hot-wire tungsten inert gas weld joint had a higher δ-ferrite content of 1.58 over 0.99 of the activated tungsten inert gas weld joint. A microstructure study confirmed the presence of refined equiaxed grains in the fusion zone of the hot-wire tungsten inert gas weld joint, while the activated tungsten inert gas weld joint displayed equiaxed grains crammed between the columnar grains and dendrites. Liquid penetrant inspection of bend-tested samples proved the soundness and quality of both weld joints. The hot-wire tungsten inert gas weld joint excelled over the activated tungsten inert gas weld joint with a higher microhardness value. During tensile tests, activated tungsten inert gas and hot-wire tungsten inert gas weld joints displayed average ultimate tensile strength values of 521 and 514 MPa, respectively. The impact toughness of the activated tungsten inert gas weld joint was 248 J, while it was 220 J for the hot-wire tungsten inert gas weld joint. Field emission scanning electron microscope analysis equipped with energy-dispersive spectroscopy and elemental color mapping provided details about weld microstructure and the reasons for the material's failure. The study proved the efficiency and soundness of the 10-mm thick joints of AISI 904L fabricated by activated tungsten inert gas and hot-wire tungsten inert gas welding techniques.

The effect of SiC content in aluminum-based metal matrix composites on the microstructure and mechanical properties of welded joints

Aluminum metal matrix composites of the varying percentage of SiC reinforcement were welded using the tungsten inert gas welding technique. For all the conditions of the specimen, the welding parameters were kept identical. The welded composites were thermally aged to peak age-hardening conditions. Significant differences in microstructure exist between aged and non-age hardened composites in terms of misorientation, grain boundary fractions and stored energy. These differences in microstructure were seen through identical changes in the mechanical behavior of the welded composites. After aging, microstructure showed refinement in grain size and preferential orientation. Hardness and tensile strength increased at different rates with increase in SiC content indicating that hardness was a clear function of stored energy and strength had a dependence on the misorientation. EBSD measured suggests that due to age hardening, a rearrangement in dislocation substructures occurred with precipitation of Mg2Si or increasing SiC content followed by dynamic recovery of the weld metal region which leads to enhancement of hardness. The increase in tensile strength with decreased misorientation was a clear indication that the effect of annihilation of dislocations as a result of recovery was less pronounced and precipitation strengthening was dominant. The present study aims to address the role of SiC addition in aluminum metal matrix composites on the welded microstructure and finally relating the microstructural changes to the observed mechanical behavior of the welded joints. The study reveals that strength not only depends on the average value of misorientation but also on the distribution of misorientation in the microstructure.

Effect of hydrogen additions to shielding gas on activated TIG austenitic stainless steel weld

In tungsten inert gas (TIG) welding, less penetration depth is achieved in a single pass which adversely affects productivity, Activated TIG (A-TIG) welding techniques achieve better performances and higher penetration depths compared to conventional TIG welding. Pure argon does not have the potential to provide adequate penetration in austenitic stainless steel. Argon–hydrogen shielding gas mixture provides high heat flux, thereby influencing the arc voltage and penetration. In the present study, hydrogen is added to base shielding gas argon to study the effect on weld geometry during TIG and A-TIG of 310S stainless steel. The result shows a higher weld depth to width ratio and a significant reduction in the angular distortion. Also, higher tensile strength is obtained in A-TIG weld metal with 1% hydrogen addition, due to more efficient cooling of the weldment. However, increasing the hydrogen concentration in shielding gas resulted in defect formations in the weldment due to the interaction between activated flux and the hydrogen.

Investigation on the Pulsed TIG Welding of Nickel-Base Alloy for Improved Microstructure and Weld Penetration

In this study, a novel pulsed tungsten inert gas (TIG) welding technique that is capable of effectively improving the weldabilities of nickel-based alloys was developed.  The correlation between process parameters and material properties was studied. The effects of ratios of pulse to background welding currents on hardness and penetration in welds and heat-affected zones (HAZs) of Inconel 718 alloy were investigated experimentally by using the pulsed TIG welding technique. It is found that with an increasing ratio of the pulse to background welding current, the hardness in welds increased from 2% to 3.5%, compared to that in constant current TIG welding at the same level of heat input. When the ratio of pulse to background welding current is higher than 6, the penetration in weld was improved significantly by up to 61%. Research work has demonstrated that the pulsed TIG welding technique is an effective approach to control the microstructure and reduce cracking susceptibilities.

Effect of TIG, pulsed TIG and Interpulse TIG welding techniques on weld strength of dissimilar joints between Monel 400 and AISI 316

Abstract Dissimilar welds of Monel 400 and AISI 316 are extensively used in boiler feedwater heat exchanges, petrochemical industries, nuclear industries where moderate weld strength and high corrosion resistance are required. In this paper, dissimilar welded joint between Monel 400 and AISI 316 have been developed by employing Tungsten Inert Gas (TIG), pulsed TIG and Interpulse TIG welding techniques. The heat input rates and filler wire for joining the base metals were same for three welding techniques. The developed weldments have been inspected by employing X-ray Radiography Test (XRT) to determine the macro/micro defects. The tensile properties of weldments have been evaluated. The ultimate strength of TIG, pulsed TIG and Interpulse TIG weldments were observed to be 528 MPa, 542 MPa and 588 MPa, respectively. The tensile properties of Interpulse TIG weldments are superior to that of welds made of other two welding techniques.

Evaluation of Marginal Misfit of Metal Frameworks Welded by Gas-Torch, Laser, and Tungsten Inert Gas Methods.

Purpose The objective of this study was to evaluate the marginal fit and the flexural resistance of nickel-chromium frameworks welded by different techniques, gas-torch, laser, and tungsten inert gas (TIG), compared with that of frameworks made via one-piece casting. Methods To evaluate the marginal fit, a master model was fabricated simulating four implants. Transfers and replicas were used to transfer the positions of the implants to the model, using a silicone matrix. The bars were waxed up and casted. Three assessments of misfit were performed for each implant using a stereomicroscope before and after welding in two predetermined regions, totaling six readings for each implant. To evaluate the flexural resistance, one group was made casting the specimens in one piece. Other 3 groups using gas-torch, laser, and TIG welding techniques were made after sectioned transversally. The data showed normal distribution and two-way ANOVA for marginal fit and one-way ANOVA for flexural resistance, and Tukey's posttest (α=0.05) was performed. Results For the marginal fit, the three welding methods presented similar results and were different from one-piece casting. For the flexural resistance, significant differences were observed among the studied groups (p < 0.001), and the one-piece group presented higher resistance compared to the three welding techniques. Conclusions Within the limits of this study, the three welding techniques yielded similar misfit results, and the laser and TIG techniques presented similar flexural resistance but lower than gas-torch and one-piece casting.

Effect of welding current on microstructures and mechanical properties of welded Ni-base superalloy INC738LC

PurposeThe Ni-base superalloy INC738LC is a precipitation strengthened alloy and is widely used in hot sections of gas turbine engines owing to its excellent high-temperature strength and high hot corrosion resistance. The purpose of this study is to determine the appropriate welding current of Ni-base superalloy INC738LC after two passes of applying the tungsten inert gas (TIG) welding technique.Design/methodology/approachNi-base superalloy INC738LC plates were joined by TIG welding technique by varying the welding current (30, 40 and 50 A). Welded specimens were investigated using optical microscopy, tensile tests, Vickers’s micro-hardness tests and X-ray diffraction (XRD). Optical microscopy was used to characterize fusion zone, heat-affected zone and base metal. Tensile test was conducted to characterize weld strength by determining ultimate tensile strength. Scanning electron microscopy was used to investigate the fracture surfaces after tensile tests. Micro-hardness test was conducted to characterize the welded joint. XRD was applied to determine precipitates formed after welding.FindingsThe ultimate tensile strength results show that the optimum weld current out of the three weld currents was found to be 40 A, which is the closest to that of the base metal.Originality/valueMany researchers have worked to optimize welding parameters such as current and speed from the microstructural observations and mechanical properties of welded joints. The optimum weld current out of the three weld currents was found to be 40 A.

Fracture Energy and Fracture Morphology after Three-Point Bending Test of Welded Joints Made of Cast Steel Designed for Use in Power Sector, with and without the Addition of Rare Earth Metals

The paper reports the three-point bending test results of welded joints. The joints were made of chromium-molybdenum cast steel designed for the use at elevated temperatures. TIG (tungsten inert gas) welding technique was used. The fracture energy for particular joint zones and the stretch zone width (SZW) under the notch bottom were determined in a qualitative fracture toughness assessment. Fracture surface morphology was analyzed. The stretch zone measurement indicated a qualitative relationship between its width and the values of fracture energy. The results confirmed the influence of the modification on the character of fracture and the portions of brittle and ductile fracture in particular areas of welded joints.

Atmospheric Corrosion of Welded Mild Steel

Mild steel is commonly used for structural purposes in Mauritius. Arc welding is one of the main joining methods used, with Manual Metal Arc (MMA), Metal Inert Gas (MIG) and Tungsten Inert Gas (TIG) welding techniques being the preferred ones. This paper compares the corrosion resistance of mild steel, joined using these welding techniques. Mild steel samples, welded using MMA, MIG and TIG welding techniques, were exposed outdoors for a very short duration of 9 days, according to ASTM G50, and subjected to alternative immersion tests, according to ASTM G44, for 130 cycles. For the atmospheric exposure tests, digital image processing techniques were used to determine the amount of corrosion in the samples. For the alternate immersion tests, the weight loss method was used. The results of the three welding techniques were then compared. The microstructure of the weld area was also analysed to this end. For the atmospheric exposures, it was observed that the MIG welded specimens suffered from preferential weld corrosion, whereas for the TIG welded specimens, the welded area corroded the least. For the alternative immersion tests, it was again observed that the MIG welded samples were less corrosion-resistant compared to the other samples. Also, the TIG welded specimens were found to be the most corrosion resistant.

Study of 7075 Aluminium Alloy Joints

Abstract High-strength EN AW 7075 Al-based alloy (Al-Zn-Mg-Cu) is currently employed in many industrial fields where excellent mechanical performances of structural components are required. In contrast to the many positive features this alloy presents, it is not fusion weldable, because it is subjected to solidification and liquation cracking. In this paper, the possibility to weld low thickness plates, made of 7075 aluminum alloy, by the tungsten inert gas welding technique will be presented. Two types of welding have been performed: for the former one, welding involves only one surface, while for the second one, welding has been carried out on both faces of the plates. After welding, microstructural analysis and mechanical properties investigations have been carried out. The present research highlights that the mechanical properties evolution is affected by the welding procedure. In particular, the mechanical strength reached for the samples welded on both faces, in the proposed setting, is comparable to that of the un-welded alloys.

Cable Twist Pitch Variation in $\hbox{Nb}_{3}\hbox{Sn}$ Conductors for ITER Toroidal Field Coils in Japan

In March 2010, the Japan Atomic Energy Agency (JAEA) was the first to start the mass production of toroidal field (TF) conductors among the six parties who were procuring TF conductors in the International Thermonuclear Experimental Reactor project. The height and width of the TF coils are 14 m and 9 m, respectively. The conductor is a cable-in-conduit conductor with an operating current of 68 kA. A circular multistage superconducting cable is inserted into a circular stainless steel jacket with a thickness of 2 mm. A total of 900 Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands and 522 copper strands are cabled around the central spiral and then wrapped with stainless steel tape whose thickness is 0.1 mm. The superconducting cables are inserted into the jacket assembled using the automatic butt Tungsten Inert Gas welding technique. Cable insertion is one of the key technologies in the jacketing process because the gap between the inner surface of the jacket and the outer diameter of the superconducting cable is only 2 mm in diameter. It was observed that the cabling pitch of the destructive sample is longer than the original pitch at cabling. JAEA carried out the tensile tests of the cable and the measurement of the cable rotation during the insertion to investigate the cause of the elongation. The cause of elongation was clarified, and the results are described in this paper.

Study of Type 316L Stainless Steel TIG Welding with MoO&lt;sub&gt;3&lt;/sub&gt; Powder

In the present work, a specific oxide flux was used to systematically investigate the effects of activated tungsten inert gas (TIG) welding on the surface appearance, weld morphology, angular distortion, residual stress, and ferrite structure in type 316L stainless steel plates. MoO3 flux used was packed in powdered form. The results showed that MoO3 flux assisted TIG welding technique can produce a significant improvement in power density of heat source and weld aspect ratio, resulting in low angular distortion and residual stress levels. The MoO3 flux assisted TIG welding associated with a rapid cooling rate of the welds, therefore exhibiting higher ferrite content in austenitic stainless steel 316L weld metals during the solidification after welding.

Effect of Aging on the Toughness of Austenitic and Duplex Stainless Steel Weldments

In the present study, the effect of aging heat treatment at 650, 750, and 850°C on the impact toughness of 316L austenitic stainless steel, 2205 duplex stainless steel and their weldments has been investigated. Welding process was conducted using the TIG (tungsten inert gas) welding technique. Instrumented impact testing, at room temperature, was employed to determine the effect of aging treatment on the impact properties of investigated materials. Aging treatment resulted in degradation in the impact toughness as demonstrated by the reduction in the impact fracture energy and deformation parameters (strain hardening capacity, fracture deflection, and crack initiation and propagation energy). The degree of embrittlement was more noticeable in duplex stainless steel parent and weld-metal than in 316L stainless steel and became greater with the increase of aging temperature. The degradation in impact toughness was discussed in relation to the observed precipitation of the intermetallic sigma phase in the microstructure of the stainless steel weldments and the corresponding fracture surface morphology.

Manufacturing Technology and Material Characterization of Ti&lt;sub&gt;44&lt;/sub&gt;Ni&lt;sub&gt;47&lt;/sub&gt;Nb&lt;sub&gt;9&lt;/sub&gt; Alloy Fastener Ring by Tungsten Inert Gas Welding

The advanced manufacturing technology of TiNiNb wide hysteresis shape memory alloy fastener ring was performed by using the tungsten inert gas (TIG) welding technique. It was found that transformation temperatures of the joint were about 20 °C higher than these of the base alloy, which should be ascribed to the heat treatment in the joint caused by welding. The strain recovery behavior of the ring after the diameter expanding process was studied. For the ring with the diameter expansion of 16% and without the heat treatment after welding, the strain recovery began at 55°C and ended at 75°C. It is concluded that, by appropriate expanding diameter process, TIG welding technique is suitable for the production of TiNiNb wide hysteresis shape memory fastener ring.

Improvement of wear resistance of hot working tool steel by hardfacing Part 1 – Effect of microstructure and hardness

Hardfacing is one of the most useful and economical ways to improve the performance of components subjected to severe wear conditions. The aim of the present work was to investigate the influence of hardfacing on the hardness and wear resistance of a hot working tool steel. Two cobalt based and one nickel based superalloys were used as hardfacing materials. Stellite 6 and 21 were deposited on H11 steel via tungsten inert gas (TIG) and shielded metal arc welding and Inconel 625 was deposited by TIG welding techniques. The pin on disc high temperature wear tests were carried out on hardfaced materials. The worn surfaces were also characterised using SEM and X-ray diffraction methods. The results showed that TIG hardfacings process having a low dilution, owing to the refined solidification structure and high capacity of work hardening enhances better wear resistance.

A comparison between FSW and TIG welding techniques: modifications of microstructure and pitting corrosion resistance in AA 2024-T3 butt joints

An experimental investigation has been carried out, in present paper, on microstructure and corrosion resistance of weld butt joints of AA 2024-T3. Two different welding processes have been considered: a conventional tungsten inert gas (TIG) process and an innovative solid state welding process known as friction stir welding (FSW). Micro-hardness measurements allow pointing out a general decay of mechanical properties of TIG joints, mainly due to high temperatures experienced by material. In FSW joint, instead, lower temperatures involved in process and severe plastic deformations induced by tool motion allow rising of a complex situation: by a general point of view a slight decay of mechanical properties is recorded in nugget zone, flow arm and thermo-mechanically altered zone (TMAZ), while in heat-affected zone (HAZ), due to starting heat treatment of alloy under investigation, a light improvement of such properties is appreciated. In flow arm and in nugget zone, however, a light recovery of hardness, w.r.t. TMAZ zone, is recorded, due to the re-crystallisation of a very fine grain structure. Polarisation curve tests and electrochemical impedance spectroscopy, performed in this paper, allow assessing a generalised nobler behaviour of weld bead with respect to parent alloy. In FSW joint, however, the differences between the three examined zone are not so evident as in TIG joint; what is more, inside FSW weld bead, retreating zone shows a behaviour nobler than advancing one.

The microstructure and mechanical properties of a welded molybdenum alloy

Wrought TiZrMo (TZM) alloy has been welded using electron beam, laser and tungsten-inert gas welding techniques. The microstructure, tensile properties and fracture surfaces of these welded samples have been examined. Although the welds have been found to be defect free, a disparity in grain size leading to large strength differences exists between the weld and parent metal. Tensile tests have revealed that fusion zone strengths are typical of those expected for the grain size in the weld metal. However, brittle behavior is also always observed, with fracture initiating at grain boundaries and propagating by intergranular and cleavage modes. Auger electron spectroscopy analysis has eliminated oxygen or other interstitial elements as sources of grain boundary embrittlement. It is proposed that brittle behavior is a result of local high strain rates in the weld zone. These local high strain rates arise from the strength difference between the wrought parent metal and the weld metal as a result of the strong grain size dependence of TZM. It is shown that, either by reducing the strain rate of testing or by removing the grain size difference between the parent and weld metals by heat treatment, significant ductility can in fact be achieved in tensile-tested butt-welded TZM. Thus, it is proposed that TZM welds are not inherently brittle as had commonly been believed.