Pulsed Current Gas Tungsten Arc Welding Research Articles

Pulsed directed energy deposition-arc technology for depositing stainless steel 309L: Microstructural, elements distribution, and mechanical characteristics

In recent years, additive manufacturing has increased in prominence as a primary method of manufacturing around the globe. Modern metal additive manufacturing presents an innovative approach to manufacturing complex structures for the aerospace, energy, and construction sectors, due to technological advancements. In the present study, the austenitic stainless steel 309L (SS-309L) thick wall component was manufactured employing pulsed current gas tungsten arc welding (PC-GTAW) WAAM technology. The metallurgical characteristics of the as-deposited SS-309L thick wall part were evaluated. The investigation of material characteristics in the manufactured areas encompasses a study of cross-sectional (CS) and transverse-sectional (TS) regional portions, specifically the upper, middle, and lower regions. The microstructures of the CS and TS planes showed austenite, columnar, and delta ferrite dendrites in the upper, middle, and lower regions, respectively. The CS sample reveals the greatest grain size at 159.4 μm, following the EBSD investigation. The average size of the grains across the TS is 127.09 μm. The thermal cycles in multi-layer production result in changes in grain size. The microhardness in the transverse sectional regions is higher than in the CS regions, measuring average values of 257 HV, 253 HV, and 251 HV for the upper, middle, and lower sections, respectively. The ultimate tensile strengths (UTS) in the cross-sectional parts are 656 MPa, whereas in the transverse regions it was 661 MPa for the topmost regions. This study investigates the correlation among the mechanical and metallurgical properties of wire arc additively fabricated SS-309L austenite steel material.

Experimental investigation on solidification cracking & intergranular corrosion of AISI 321 & AISI 316 L dissimilar weld on pulsed current gas tungsten arc welding (PCGTAW)

Dissimilar metal combinations are frequently employed in the power generation and nuclear industries. Where stainless steel piping systems are connected to pressure vessels made of low-alloy steel, the subsystems of liquid rocket engines also have different, dissimilar material combinations. Dissimilar welding plays a vital role in ensuring the integrity, performance, and reliability of components and structures operating in cryogenic environments, in this study, plates of AISI 316L and AISI 321, each 5 mm thick, were successfully joined using the pulsed current gas tungsten arc welding (PCGTAW) technique with optimized process parameters. These weld joints are mostly present in rocket engines subjected to a cryogenic environment. Due to the low temperature environment, the metallurgical properties of these joints change, which affects their mechanical properties. As it is a structural part, PCGTAW welding is most common method for joining this kind of material.In this work, Microstructural analysis of the weldment revealed a combination of vermicular, lacy, and acicular ferrite morphologies in the fusion zone at the root, mid, and crown locations.Furthermore, no solidification cracking was detected in the weldments based on the optical micrograph and SEM results. Intergranular corrosion (IGC) testing indicated the absence of a ditch structure, suggesting that the heat-affected zone (HAZ) on both sides of the weld joint was not being susceptible to sensitization. However, the HAZ of the AISI 316L side exhibited coarser grains compared to AISI 321. Analysis of tensile properties revealed a significant influence of the testing environment on the tensile strength of the dissimilar welded joints. At room temperature, the average ultimate tensile strength (UTS) was measured as 621 MPa. Remarkably, at cryogenic conditions, the average tensile properties significantly increased to 1319 MPa.Microhardness analysis showed the highest hardness associated with the AISI 321 side. The fusion zone exhibited a large deviation in the hardness profile (205 ± 10 HV), with the highest average hardness observed in the middle part of the weld. However, the hot cracking behavior of the weld was investigated by using a suutula diagram at various locations of the weld. The investigation revealed that the Creq/Nieq ratio exceeded the critical threshold value, effectively diminishing the propensity for hot cracking in the fusion zone. Overall, these findings underscore the effectiveness of the PCGTAW technique in joining dissimilar materials, as well as the importance of microstructural and mechanical property evaluations, especially under extreme operating conditions such as cryogenic temperatures.Paraphrase.

The Taguchi and Response Surface Method for Optimizing Orbital Pipe Welding Parameters in Pulsed Current Gas Tungsten Arc Welding (PC-GTAW) for SS316L

The Taguchi and Response Surface Method for Optimizing Orbital Pipe Welding Parameters in Pulsed Current Gas Tungsten Arc Welding (PC-GTAW) for SS316L

An innovative pulsed current arc welding technology for armor steel: Processes, microstructure, and mechanical properties

This study presents a novel pulsed current arc welding technology, specifically pulsed current gas tungsten arc welding (PC-GTAW), single and double pulse gas metal arc welding (SP/DP-GMAW), and dual process welding (D-process). This study aims to investigate the effectiveness of these welding techniques for armor steel weldments. This research focused on investigating the welding processes, resulting microstructures, and mechanical properties of welded joints. Based on the macrography analysis, it was determined that the weldments exhibit no signs of porosity, inclusions, or inadequate penetration. This finding substantiates the optimum settings for the weldment production process. The weldment optical microstructure, fusion, and heat-affected zone were examined in the weld interface. The microstructural properties of the FZ include δ-ferrite, austenite, bainite, and acicular martensite. The HAZ has a bainite-untempered martensite microstructure. The chemical composition and variations across the weldment (base, weld and HAZ) were identified. The grain borders contained greater quantities of Cr, Ni, Mn, Si, and Mo than those of the grain cores. EBSD revealed average weld zone grain sizes of 17.7 µm, 32.6 µm, 30.8 µm, and 24.6 µm for PC-GTAW, SP-GMAW, DP-GMAW, and D-Process, respectively.Furthermore, the hardness measurements showed a progressive transition across different regions. Additionally, the D-Process-fabricated material exhibited a maximum ultimate tensile strength of 872 MPa and an elongation of 4%. The mechanical properties exhibited by this new process variant exceed those of other weldments, indicating its potential for fabricating armor steel. The impact toughness demonstrated superior performance in all the weldments. Within this context, the new use of pulsed current advanced welding methods has shown the ability to generate welded parts of exceptional quality.

Evaluate Effect of Pulsed Current Gas Tungsten Arc Welding Process Parameter on Intergranular Corrosion of SS304L Weld

Austenitic stainless steel (ASS) is the most common type of stainless steel which offers excellent weldability and mechanical properties. ASS is being used for various applications i.e. automotive, oil and gas and chemical industries in which the welding process plays a prominent role. Welding process selection is the main factor that emphasizes mechanical and corrosion resistance properties in various aggressive environments. There are various corrosion occurs in ASS but intergranular corrosion (IGC) forms during welding at elevated temperatures. IGC mainly occurs at grain boundaries of structure and resulting chromium depletion due to precipitation of chromium carbide at the grain boundary. In present work pulsed current gas tungsten arc welding (PCGTAW) process was used to investigate intergranular corrosion by oxalic acid test as per ASTM A262 Practice A. Experiments performed based on Taguchi L9 using design of experiments and corrosion rates are evaluated at base metal, heat affected zone and weld zone. This work is aimed to optimize process parameters followed by regression analysis to IGC susceptibility in the weldment. In this investigation, it has been found from ANOVA and main effects plots that peak current and base current are the most significant parameters in the PCGTAW process. The results of the corrosion test revealed that heat affected zone is more susceptible to IGC. At the end, it has been observed that the optimum value of peak current, base current and frequency based on regression analysis are 100 A, 50 A and 6 Hz respectively.

Mechanical behavior of austenitic stainless-steel welds with variable content of [formula omitted]-ferrite in the heat-affected zone

δ-ferrite solidified in the fusion zone (FZ) mitigates the microfissuring susceptibility in multi-pass welded joints performed on austenitic stainless steel (ASS). The herein investigation studied welded joints between two 304L grade ASS with different chemical compositions, which varied δ-ferrite content in the heat-affected zone (HAZ). The pulsed-current gas tungsten arc welding (GTAW-P) process was used along with filler metals ER 308L and ER309L. Additionally, an autogenous joint was made with stainless steel (SS) of high δ-ferrite content (10%). A thermo-mechanical finite element (FE) model was applied to estimate the thermal history, residual stress (RS) and distortion distributions on SS joints. Then, numerical results were correlated with the fracture analysis. The tensile test corroborated the increment in ductility due to δ-ferrite content increasing in the HAZ. The enhancement of mechanical strength observed in the autogenous welded joint was associated with the pinning effect produced by δ-ferrite stringers formed in the HAZ, which inhibited grain growth. Despite the high joint efficiency of SS 304L weldments, the FZ was fractured due to the microfissuring and precipitated particles. The FZ rupture starts in the FZ-HAZ interface of the first weld bead related to the ductility loss with the heat input. Microfissures found in the FZ of all weldments were related to the tensile stress concentration caused by the uneven distortion distribution and the ductility increment (up to 39%) provided by the high δ-ferrite content. Some chromium carbides in the FZ acted as stress raisers.

Effect of constant current and pulsed current gas tungsten arc welding process on microstructure and mechanical properties of superalloy 59 joints

This research paper investigates the microstructure, microsegregation and mechanical behaviour of Ni-based superalloy 59 which is an important candidate in the pollution control application. The weld joints were produced with continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) by applying both autogenous mode and filler wire ERNiCrMo-13. Weld flaws and weld aspect ratio of weld joints were identified using a macro analysis. An optical microscope (OM) and scanning electron microscope (SEM) were used to examine the microstructure of the welded joints. PCGTA weldments exposed refined grain structure, reduced heat-affected zone and narrow weld bead compared to CCGTAW. Microsegregation of the alloying elements at the weld center (WC) and weld interface (WI) was examined using Energy Dispersive x-ray spectroscopy (EDS). The findings of the metallurgical characterisation proved that the PCGTA weldments offer minimal microsegregation at the interdendritic region in comparison to CCGTA weldments. X-Ray Diffraction (XRD) examination reveals that there is a 16.7% enhancement in grain refinement in the autogenous mode and a 17.4% improvement in the filler wire ERNiCrMo-13 when switching from CCGTA to PCGTA welding. Tensile, Charpy impact and microhardness tests were used to assess the strength, toughness and hardness of the weld joints. Weld joints fabricated by PCGTAW offers higher tensile strength (∼1.4 to 1.6%), higher toughness (∼4.4 to 5.4%), and higher hardness (∼4.8 to 7.7%) than CCGTAW weld joints.

Mechanical characterization and simulation of PCGTAW welded thin sheet of SDSS material

In this research paper, Pulsed Current Gas Tungsten Arc Welding (PCGTAW) process is used to weld the thin sheet of Super Duplex Stainless Steel (SDSS). From the Bead on Plate (BoP) trials the parameters for full penetration butt joint were identified. Heat input obtained from the welding parameter is 0.144 kJ/mm. Microstructural characterization of Welded joint revealed the coarse grain microstructure in the Heat Affected Zone (HAZ) and Weld Zone (WZ) due to weld thermal cycle and slows cooling rate concern. Due to this high temperature in the WZ austenite grains are changed in the shape of Widmanstatten austenite, grain boundary austenite, and intragranular precipitates created from ferrite grains. The tensile strength of welded joints (800Mpa) is 3.75% less as compared to base metal tensile strength (830Mpa). The ductility of the weld joint is decreased as compared to base metal due to the presence of coarse grain in the HAZ and WZ. PCGTAW joint's micro-hardness is 0.7 HRC lower than the base metal due to weld thermal cycle involvement. Abaqus software is used to validate the tensile test result. The numerical analysis result is similar to the experimentally obtained tensile test result with a maximum error percentage is of 0.8%.

The effect of pulse current changes in PCGTAW on microstructural evolution, drastic improvement in mechanical properties, and fracture mode of dissimilar welded joint of AISI 316L-AISI 310S stainless steels

In this paper, the effect of pulse current changes in the Pulsed Current Gas Tungsten Arc Welding (PCGTAW) on the various properties of dissimilar welding of AISI 316L-AISI 310S stainless steels was investigated. 10 mm thickness steel sheets were joined by the PCGTAW process with the background current (Ib) of 55, 70 and 85A, as well as the peak current (Ip) of 110, 130 and 150A. Then, optical microscopy (OM) and Field Emission Scanning Electron Microscopy (FE-SEM) techniques were used to study the microstructural evolution in different areas of the welded joints. Also, tensile, Charpy impact and Vickers microhardness tests were used to evaluate the effect of the pulsed current changes on mechanical properties. Finally, the fracture surfaces of Charpy impact and tensile tests samples were studied by FE-SEM. The weld metal (WM) microstructure consisted of austenite dendrites together with a low amount of delta ferrite in the grain-boundaries. Results also showed that by increasing Ib and decreasing Ip, the microstructure of the WM was changed from columnar dendritic to coaxial, and a very fine, dendritic one. This condition led to the reduction of the size of the dendrites and the amount of delta ferrite ingrain boundaries of the WM, as well as a reduction in the width of Unmixed Zone (UMZ) area. Moreover, all the welded joints were fractured from the AISI 316L stainless steels side. However, the results of the Charpy impact and microhardness tests showed that with the above variation in the welding parameters, hardness value and fracture energy of the WM increased significantly. Fractography of the surfaces showed a completely ductile fracture for both tensile and Charpy impact tests samples.

Improvement of hot corrosion resistance of dissimilar weldments by current pulsing in a simulated power plant environment

Hot corrosion studies are of utmost importance for welded components in the power plant industry as well as for industries which deal with exposure to the high-temperature corrosive environment. The failure of welded components at high temperatures has often led to the reduced service life of a component and catastrophic disasters. This has been a significant engineering challenge in the design of welded components. It is generally seen that the failure of the welded sections mostly occurs because of the deposition of molten salt over the weldments which accelerate the hot corrosion reactions. In this present research work, two dissimilar base materials, AISI 4340 and AISI 304L have been welded with two different welding processes namely continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) while making use of ERNiCr-3 as filler material. A comparative study of the dissimilar welded plates was carried out by simulating a molten salt environment at 600°C involving hot corrosion behavior. By analyzing the microstructure and thermo-gravimetric data, it is concluded that the pulsed current gas tungsten arc welding process has superior corrosion resistance properties while using ERNiCr-3 as the filler material as compared to the continuous current gas tungsten arc welding process.

Development of arc welding technique to preclude microsegregation in the dissimilar joint of Alloy C-2000 and C-276

Hastelloy C-2000 and C-276 are widely used in Flue Gas Desulphurization (FGD) system and Chemical Processing Industries (CPI). Current work is focused on weld microstructure, and mechanical properties (structure-property relationship) of the dissimilar combination of alloy C-2000 and C-276. Multi-pass Pulsed Current Gas Tungsten Arc (PCGTA) welding was adopted for joining the dissimilar alloys using the filler ERNiCrMo-17. Microstructural characteristics of the weld joint were assessed by Optical and Scanning Electron Microscope (SEM). Weld interface microstructure examination revealed the presence of grain coarsening near the Heat Affecting Zone (HAZ) of the alloy C-276 side. SEM analysis shows the absence of secondary Topologically Closed Packed (TCP) phases in the Inter-Dendritic (ID) regions of the dissimilar weld. Micro-segregation of alloying elements in the weldment was assessed by Energy-Dispersive X-ray Spectroscopy (EDS). X-Ray Diffraction (XRD) analysis had been carried out to identify the phase constitution and average grain size. Strength, toughness, and hardness of the dissimilar weld were evaluated with the support of the tensile test, Charpy impact test, and Vicker’s hardness test. Tensile study showed that all the tensile fracture occurred at the base metal side of alloy C-276. The average toughness of the dissimilar alloy joint was noted about 84 J. Hardness test results indicated that fusion zone (FZ) hardness value was 6.19% and 2.27% superior to the candidates’ material (C-276 and C-2000) employed in this study. The refined grain structure and absence of microsegregation resulted in the highest hardness in the dissimilar weld FZ. Results revealed the substantiated use of PCGTA welding for the effective joining of dissimilar alloys of C-2000 and C-276 through the evaluation of metallurgical and mechanical characteristics.

Prospects of pulsed current arc welding on aerospace grade Hastelloy X

The conventional constant current arc welding of Hastelloy X (Ni-Cr-Fe-Mo) leads to the solidification and liquation cracks in the weldment. The higher heat supplied in constant current weldment develops the secondary carbide precipitates. It promotes the development of hot cracks in the weldment. In this study, joining of Hastelloy X plates was carried out by constant current gas tungsten arc welding (GTAW) and pulsed current gas tungsten arc welding (PCGTAW) with C263 filler wire. The result discovered that no hot cracks were formed in the weldment. In constant current mode, Cr-rich and Mo-rich Cr23C6 (M23C6), Fe2MoC, Fe3Mo3C (M6C), and Cr2Ti precipitates were observed. Whereas, in pulsed current mode, Ni3(Al, Ti), Ni3Ti, Co3Ti, Cr2Ti precipitates are found due to the segregation of Co, Al, and Ti. No Cr-rich and Mo-rich carbide phases identified in pulsed current weldment due to rapid cooling rate and higher thermal gradient observed during solidification. The tensile results revealed that 8.23% increase in the ultimate tensile strength and a 29.62% increase in elongation of pulsed current mode welding compared to constant current welding. Further, the microhardness and impact toughness of PCGTAW is 3.32% and 5.45% higher than GTAW, respectively. In pulsed current welding, better mechanical properties were identified compared to constant current welding. The nonappearance of Cr and Mo-rich phases and refined microstructure in the weldment are the main reason for better strength.

A Proposed Mechanism of Hot-Cracking Formation During Welding Fan-Shaped Test Specimen Using Pulsed-Current Gas Tungsten Arc Welding Process

Solidification cracking is a significant problem during the welding of fully austenitic stainless steels. The present work is considered as the first trial to investigate and propose a mechanism of hot cracking formation when welding the Fan-shaped cracking test specimen, using the pulsed current gas tungsten arc welding process (PCGTAW). The specimen lateral expansions perpendicular to welding line due to thermal effects, plus the transverse expansion due to crack opening are sensed and recorded to detect the crack behavior with time. The stages of crack formation are filmed by a high-speed photography of the weld pool and solidification process at a speed of about 1000 fps. Additionally, some microscopic examinations using Scanning Electron Microscope (SEM) and Electron Probe Micro-Analyzer (EPMA) are performed on the welds. The results helped in establishing a proposed mechanism for the formation of hot cracks in full–austenitic stainless steel welds done on a Fan-shaped test specimen. The proposed mechanism suggests three stages during hot cracking formation; the crack initiation, propagation, and ceasing. The occurrence of a hot crack during welding mainly depends on the way by which the molten zone solidifies, and which solid phase will primarily solidify. This affects, in turn, the segregation of the chemical elements, which found to have a great role in crack initiation. Moreover, the weld metal structure type, together with the thermal stresses in conjunction with the applied strains on the weld joint play a great role in the crack expansion and ceasing. The present work is considered the first trial done to propose a mechanism of hot-cracking formation during welding the Fan-Shaped test specimen using Pulsed-Current Gas Tungsten Arc welding process.

Multipass dissimilar joints for SS316L to Inconel625 using gas tungsten arc welding

Dissimilar material welding of SS316L and Inconel625 joints growing in heat exchanger applications like nuclear, power plants and petrochemical industries. The current work reports on multipass welding of SS316L and Inconel625 dissimilar material analysis effect of Gas Tungsten Arc Welding (GTAW) process. Four trials were conducted with L4 orthogonal array. These welds are prepared by using ErNiCrMo-3 and ERNiCr-3 filler wire. The analysis of weldability, distortion, residual stress, and tensile strength of the weldments. Least distortion was observed for pulsed current GTAW process. Tensile residual stress was spotted at welding zone. Tensile strength shows the fracture occurred in the base plate of the SS316L for all the trails.

Evaluation of hot corrosion performance of HVOF coatings on PCGTA welded Fe-based alloy A-286 in Na2SO4%-7.5%NaVO3%-5%NaCl environment

This research article investigated the hot corrosion behaviour of the pulsed current gas tungsten arc (PCGTA) welded Fe-based alloy A-286. PCGTA welding is employed to obtain a similar joint of 6 mm plates of A-286 alloy using ER-320LR filler material. A high-velocity oxy-fuel (HVOF) coating is carried out to deposit Cr3C2-25%NiCr and Ni-20%Cr coating on the PCGTA weldments. The microstructure and elemental analysis of the surface and cross-sections of the coatings were examined by Scanning electron microscope (SEM) combined with energy dispersive spectroscopy (EDS). Hot corrosion study is carried out on bare, and HVOF coated PCGTA weldments in Na2SO4-7.5%NaVO3-5%NaCl environment at 850 °C. The corrosion frate of the weldments was determined by thermogravimetric analysis. The reaction products present in the weldments were characterized by SEM and x-ray diffraction (XRD) analysis. Depths of corrosion attack and elemental distribution on the weldments at cross-section are analyzed using EDS with the x-ray mapping technique. The Cr3C2-25%NiCr coated weldment exhibits the superior corrosion resistance than bare and the Ni-20%Cr coating due to the development of chromium oxide (Cr2O3) scales. The chromium carbide coating has a reduced weight gain of 56% and 25% compared to uncoated, and Ni-20%Cr coated specimens.

A simulation-based approach to characterise melt-pool oscillations during gas tungsten arc welding

Development, optimisation and qualification of welding and additive manufacturing procedures to date have largely been undertaken on an experimental trial and error basis, which imposes significant costs. Numerical simulations are acknowledged as a promising alternative to experiments, and can improve the understanding of the complex process behaviour. In the present work, we propose a simulation-based approach to study and characterise molten metal melt pool oscillatory behaviour during arc welding. We implement a high-fidelity three-dimensional model based on the finite-volume method that takes into account the effects of surface deformation on arc power-density and force distributions. These factors are often neglected in numerical simulations of welding and additive manufacturing. Utilising this model, we predict complex molten metal flow in melt pools and associated melt-pool surface oscillations during both steady-current and pulsed-current gas tungsten arc welding (GTAW). An analysis based on a wavelet transform was performed to extract the time-frequency content of the displacement signals obtained from numerical simulations. Our results confirm that the frequency of oscillations for a fully penetrated melt pool is lower than that of a partially penetrated melt pool with an abrupt change from partial to full penetration. We find that during transition from partial to full penetration state, two dominant frequencies coexist in the time-frequency spectrum. The results demonstrate that melt-pool oscillations profoundly depend on melt-pool shape and convection in the melt pool, which in turn is influenced by process parameters and material properties. The present numerical simulations reveal the unsteady evolution of melt pool oscillatory behaviour that are not predictable from published theoretical analyses. Additionally, using the proposed simulation-based approach, the need of triggering the melt-pool oscillations is expendable since even small surface displacements are detectable, which are not sensible to the current measurement devices employed in experiments.

Comparison of metallurgical and mechanical properties of dissimilar joint of AISI 316 and Monel 400 developed by pulsed and constant current gas tungsten arc welding processes

Dissimilar weldments of AISI 316 and Monel 400 are extensively used in boiler feed water heaters where the weld roots are exposed to high pressure and hot corrosive environments. In this research, metallurgical and mechanical properties of dissimilar weldments of AISI 316 and Monel 400 obtained by pulsed current gas tungsten arc welding (PCGTAW) and constant current gas tungsten arc welding (CCGTAW) processes were compared. The heat input rate and filler wire were same in both welding techniques. Metallurgical properties are studied by employing optical microscope (OM) and scanning electron microscope (SEM). Mechanical properties of dissimilar weldments are determined by tension test and Vickers hardness. The metallurgical study has revealed fine grain structures with clear grain boundaries at the heat-affected zone in PCGTAW weldment. The ultimate tensile strength in PCGTAW and CCGTAW weldments was observed as 554 and 542 MPa, respectively. The ratio of yield strength to ultimate tensile strength is higher in PCGTAW weldment than CCGTAW weldment. The weldment developed by using PCGTAW technique has shown a higher microhardness value at HAZ of both the base metals than the weldment developed in CCGTAW technique.

Influence of Filler Wires to Suppress the Microsegregation and to Improve Mechanical Properties of Conventional Arc-Welded Nickel-Based Superalloy Incoloy 20

Elemental segregation leads to hot fissuring in the Incoloy 20. The present investigation examines the possibility of lessening the elemental segregation in the conventional arc welding techniques. In the present investigation, Incoloy 20 plates were fused by continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) with two different nickel-based filler wires (ERNiCrMo-2 and ERNiCrMo-3). The result of the macroexamination shows that steady fluid flow with crack-free welding was succeeded in all the weldments. Optical and scanning electron microscope proves the columnar and cellular structure in CCGTAW specimens and fine equiaxed dendritic structure in PCGTAW specimens. Energy-dispersive spectroscopy (EDS) and X-ray diffraction results exhibit that the weld joint produced by CCGTAW ERNiCrMo-2 shows Cr segregation that leads to the formation of M23C6 phases in the interdendritic regions, whereas ERNiCrMo-3 shows the presence of NbC instead of M23C6. The elemental segregation is suppressed when it comes to PCGTA weldments in both filler wires. Electron backscatter diffraction analysis shows that the CCGTA weldments show coarser grain structure in the heat-affected zone (HAZ). In all the cases, the formation of secondary phases affects the strength of the weld joints at HAZ. Refined microstructure obtained in the PCGTAW in both filler wires shows the marginally higher ultimate tensile strength and toughness compared to the corresponding CCGTA weldments. From the corrosion study, PCGTAW specimens exhibit higher corrosion resistance than the CCGTAW specimens for both filler wires.

Effect of Pulsed Current Frequency on Microstructure and Mechanical Properties of Gas-Tungsten-Arc-Welded Joints of UNS R30155

Thin sheets of UNS R30155 alloy with a thickness of 0.6 mm with AMS 5832 filler metal were welded using pulsed current gas tungsten arc welding (PC-GTAW). The aim of this research is to study the effect of frequency on the microstructure and mechanical properties of the joints. The results of the tests indicated that increasing the frequency up to the optimal level expands the region of fine equiaxed grains that contains equiaxed dendrites. It restricts the growth of epitaxial grains that contain columnar dendrites, resulting in an increase in the elongation, microhardness, tensile and shear strengths. Increasing the frequency causes uniform distribution of alloying elements in the weld metal, and increasing it more than the optimal level causes heterogeneity in the chemical composition and the formation of dispersed islands of equiaxed dendrites in the weld metal. Using non-pulsed current with higher heat input leads to the expansion of the epitaxial grains, which weakens the mechanical properties.

Combined Effect of Gas Tungsten Arc Welding Process Variants and Post-Weld Heat Treatment on Tensile Properties and Microstructural Characteristics of Ti–6Al–4V Alloy Joints

In aerospace and chemical industries, Ti–6Al–4V alloys are mostly used due to outstanding resistance to corrosion and high specific strength. Gas tungsten arc welding (GTAW) process is generally preferred to join Ti–6Al–4V alloy, but width of bead and heat-affected zone are wider in these joints. To overcome these problems, pulsed current gas tungsten arc welding (PC-GTAW), one of the variants of GTAW process, was employed to join Ti–6A–4V alloy. Recently, gas tungsten constricted arc welding (GTCAW) process, a new advanced variant of GTAW process, was developed. It creates high-frequency current level variation in the arc to produce low heat input, narrow fusion zone and heat-affected zone with deeper penetration compared to conventional GTAW and PC-GTAW processes. The present research work is focused to understand the influence of the post-weld heat treatment on tensile properties, microhardness and microstructure of Ti–6Al–4V alloy joints welded by GTAW, PC-GTAW and GTCAW processes. High frequency resulted in appreciable refinements of prior β grains prime to higher tensile properties, hardness and elongation of joints in the as-welded condition. The post-weld heat treatment (PWHT) at 910 °C resulted in enhancement in elongation and deterioration in tensile strength due to coarsening of α and disintegration of α-martensite into symmetrical α and β. However, pulsed gas tungsten constricted arc welded (P-GTCAW) joints showed greater tensile elongation even in PWHT conditions.