Search Results (119)

The microstructural evolution and tensile behavior of Inconel 617 welded joints produced by gas tungsten arc welding (GTAW) with ERNiCrCoMo-1 filler were systematically investigated. Detailed microstructural characterization revealed that Cr-rich M₂₃C₆ and Ti-rich MC carbides are the dominant precipitates, while Mo-rich M₆C forms locally along grain boundaries after thermal exposure. The fusion and weld zones exhibit fine dendritic morphologies with uniformly distributed precipitates, resulting in significant strengthening through precipitation and dislocation–pinning mechanisms. Owing to the low heat input and compositional compatibility between the weld and base metals, the heat-affected zone remains extremely narrow and free of compositional transitions. The welded joint attains tensile strengths of 920 MPa at room temperature and 605.5 MPa at 750 °C, corresponding to joint efficiencies of 117% and 121%, respectively, with fracture consistently occurring in the base metal. Deformation analysis shows that plasticity at room temperature is governed by planar slip and dislocation entanglement, whereas deformation twinning predominates at elevated temperatures owing to the reduced stacking-fault energy and the pinning effect of M₂₃C₆ carbides. These results provide key insights into the deformation and strengthening mechanisms controlling the high-temperature performance of GTAW-welded Inconel 617 joints and offer guidance for their application in advanced nuclear and high-temperature energy systems. Full article

Weld root reinforcement is a critical geometric parameter governing stress concentration and structural performance in thin-walled stainless-steel piping systems designed to ASME B31.3. While current codes specify permissible dimensional limits, they do not explicitly quantify how incremental variations in root height influence stress distribution under realistic service loading conditions. This study integrates finite element analysis (FEA) with experimentally validated GTAW weld profiles to evaluate the structural influence of weld root height in 316L stainless-steel pipe joints. An experimentally manufactured 4 in schedule 10S joint with a measured root height of less than 1.5 mm was adopted as the baseline geometry. Additional models with reinforcement heights of 1.138, 2.0, 2.5, and 3.0 mm were evaluated under two representative load cases: (i) internal pressure combined with drag and axial thrust (LC-1), and (ii) internal pressure with thrust only (LC-2). The results demonstrate that reinforcement heights exceeding 2.0 mm increase von Mises, hoop, longitudinal, and radial stress gradients, with peak stresses shifting toward the weld toe under drag-inclusive loading. In contrast, reinforcement ≤2 mm provides smoother load transfer and reduced stiffness discontinuity across the weld interface. The combined numerical and experimental findings support a stress-informed upper limit of 2 mm for weld root reinforcement in thin-walled stainless-steel pipelines, offering a performance-based complement to existing dimensional acceptance criteria. Full article

Damage is inevitably induced in titanium alloy laser-welded (LW) joints after prolonged service, making weld repair an economical and effective restoration method. This study employed gas tungsten arc welding (GTAW) to repair pre-damaged TC4 LW joints, with a systematic investigation on the microstructural and mechanical properties of the repaired joints. The results indicate that both the LW and the GTAW-repaired (GTAW-R) joints exhibit acicular α′ martensite in the fusion zone (FZ). However, the maximum length and width of the α′ phase in the FZ of the GTAW-R joint are 67% and 78% larger than those in the LW joint, respectively. The heat-affected zone (HAZ) of both types of joints comprises α′, α, and β phases. Similarly, due to the higher heat input in GTAW, the α′ phase in the HAZ of the GTAW-R joint is coarser. Differences in acicular martensite size result in an average microhardness of 356.3 HV in the FZ of the GTAW-R joint, which is 15.2 HV lower than that of the LW joint. The higher heat input of GTAW leads to a prolonged duration at elevated temperatures in the HAZ, promoting the formation of acicular α′ phase and, consequently, a slightly higher microhardness compared to the HAZ of the LW joint. The average tensile strength of the GTAW-R joint is 1032 MPa, equivalent to 98.4% of the LW joint strength (1049 MPa) and 96.8% of the BM strength (1066 MPa). Tensile fracture in the LW joint occurs in the BM region, whereas the coarser microstructure in the repair weld leads to fracture in the FZ for the GTAW-R joint. This study demonstrates that when the damage length in an LW joint is less than 20%, GTAW repair can effectively restore the joint strength. Full article

Arc welding techniques for applying austenitic stainless steel cladding to low-carbon steels are common. Cladding enhances surface properties, increases corrosion resistance, improves product performance, extends service life, and reduces maintenance costs associated with surface corrosion. The hot-wire gas tungsten arc welding (HW-GTAW) method offers several benefits, making it appealing for cladding applications. This research investigates the use of HW-GTAW to clad low-carbon steels with super-austenitic stainless steel, examining macro and microstructures, mechanical strength, corrosion resistance, and wear performance. Two conditions were tested: one without a hot-wire, called CW-GTAW (cold-wire), and one with a hot-wire, called HW-GTAW. The HW-GTAW process reduced the dilution rate, thereby benefiting cladding. Microstructural analysis showed that both conditions exhibited elongated columnar dendrites in the heat-affected zone and a shallow region of equiaxed dendrites near the surface. The HW-CL condition displayed slight improvements in corrosion and wear resistance, but both samples outperformed the uncoated base material. These findings support the expanded application of super austenitic stainless steels and HW-GTAW in cladding processes. Full article

This study aims to develop a library of Cu-CuAl material compositions and evaluate their mechanical properties. Various compositions are fabricated using Wire Arc Additive Manufacturing (WAAM) with GMAW and GTAW processes. The produced materials are characterised through hardness testing, eddy current measurements, and tensile testing supported by Digital Image Correlation (DIC). The hardness analysis reveals that increasing the CuAl content leads to higher hardness values. All compositions display stable and consistent eddy current measurements, except for the alloy with 25% Cu and 75% CuAl, which shows comparatively higher values. The load–displacement curves indicate that higher Cu content enhances ductility, resulting in a lower maximum load. Conversely, a higher CuAl fraction is directly associated with greater ultimate tensile strength. Overall, compositions with higher CuAl content exhibit improved mechanical performance, although they do not reach the levels of commercial materials due to defects inherent to the additive manufacturing process. Full article

Weld quality plays a critical role in ensuring the structural integrity and long-term performance of critical piping systems used across petrochemical, oil and gas, marine, and healthcare sectors. Although gas tungsten arc welding, shielded metal arc welding, and gas metal arc welding are widely applied in pipe fabrication, existing studies often examine these processes independently and provide limited insight into the comparative influence of process parameters on weld morphology, microstructure, and mechanical performance. This review consolidates findings from recent research to evaluate how welding current, arc voltage, heat input, travel speed, shielding gas composition, and joint preparation interact to affect weld bead geometry, heat-affected zone evolution, tensile properties, hardness, and overall weld integrity in piping systems. The primary objective of this review is to critically compare fusion welding process parameter optimization strategies and to identify unresolved challenges in achieving controlled weld root geometry for high-integrity piping applications. Recent industrial failure investigations, particularly in ethylene oxide service piping, further underscore the importance of weld root control. Several documented leak events were traced to excessive root protrusion and inadequate interpretation of non-destructive testing data, where elevated reinforcement disrupted internal flow and promoted turbulence-induced degradation. These recurring issues highlight a broader industry challenge and strengthen the need for improved root-height optimization in critical piping applications. A significant research gap is identified in the limited optimization of weld root reinforcement, particularly in gas tungsten arc welding processes, where most reported studies document root heights exceeding 3 mm. Achieving a root height below 2 mm, which is an important requirement for reducing flow-induced turbulence and meeting industry acceptance criteria, remains insufficiently addressed. This review highlights this gap and outlines future research opportunities involving advanced parameter optimization and improved process monitoring techniques. The synthesis presented here provides a comprehensive reference for enhancing weld quality in critical piping systems and establishes a pathway for next-generation welding strategies aimed at producing high-integrity weld joints compliant with the American Society of Mechanical Engineers B31.3 requirements. Full article

Three different Gas Tungsten Arc Welding methods—DC single electrode, DC double electrode, and PC double electrode—were analyzed using SS304 steel as the base material. Numerical models were developed to simulate the arc plasmas and calculate heat flux, current density, and wall shear stress on the surface of the workpiece. These data were used as input to simulate the weld pools across all three configurations. Experimental validation showed a good agreement with the numerical results. In the double-electrode setup, electromagnetic interaction caused the arcs to deflect, resulting in an 8% reduction in the maximum heat flux and a 4% decrease in the maximum current density. Marangoni stress had a notable effect on the weld pool shape, creating a -shaped pool with the stationary single-electrode setup, whereas the double-electrode setup produced a -shaped pool after 2 s. In the moving weld pool configurations, the sizes of the pools were maximum at the trailing electrodes. The pool was 1.7 mm deep and 5.6 mm wide in DC double- and 1.4 mm deep and 5.4 mm wide in PC double-electrode configurations. The pool depth and width were only 1.0 mm and 4.2 mm when a DC single-electrode setup was used. Comparing the three methods, the DC double-electrode setup produced the largest pool size. The findings of this research offer guidance for enhancing different arc settings and electrode arrangements to attain the intended welding quality and performance. Full article

Super duplex stainless steels (SDSS) are materials known for their exceptional mechanical strength and high resistance to corrosion due to their dual- phase microstructure consisting of ferrite and austenite in roughly equal proportions. However, the Gas Tungsten Arc Welding (GTAW) process used to join SDSS often causes microstructural imbalances, mainly ferritic structures, or the formation of harmful intermetallic phases, which can weaken the material’ s desirable properties. This study examines the effect of substrate preheating on the microstructure, mechanical properties, and corrosion resistance of UNS S32750 SDSS welds produced by GTAW. Preheating the substrate was considered as a strategy to improve phase balance in the fusion zone by extending the time within the ferrite- to- austenite transformation temperature range, thus slowing the cooling rates. Four conditions were tested: welding at room temperature (RT) and preheating to 100 °C (T100), 200 °C (T200), and 300 °C (T300). Welding parameters remained constant. The fusion zone microstructure was analyzed using metallographic techniques, while mechanical properties were evaluated through microhardness tests. Corrosion resistance was assessed with potential dynamic polarization in a 3.5% NaCl solution. The results showed significant improvements in microstructural balance with higher preheating temperatures. The austenite volume fraction in the fusion zone increased from about 16% at RT to 42% at T 300. Mechanical testing indicated a decrease in microhardness from 341 HV at RT to 314 HV at T 300, reflecting the increased austenite content and its associated toughness. Corrosion tests demonstrated enhanced resistance under preheated conditions, with T 300 exhibiting the highest corrosion potential and the lowest corrosion current, nearing the performance of the base metal. These findings suggest that preheating is a practical, cost- effective method for optimizing the GTAW process for SDSS, eliminating the need for expensive filler materials and stabilizing the microstructure elements. Full article

In the context of Industry 4.0, new methods of manufacturing, monitoring, and data generation related to industrial processes have emerged. Over the last decade, a new method of part manufacturing that has been revolutionizing the industry is Additive Manufacturing, which comes in various forms, including the more traditional Fusion Deposition Modeling (FDM) and the more innovative ones, such as Laser Metal Deposition (LMD) and Wire Arc Additive Manufacturing (WAAM). New technologies related to monitoring these processes are also emerging, such as Cyber-Physical Systems (CPSs) or Digital Twins (DTs), which can be used to enable Artificial Intelligence (AI)-powered analysis of generated big data. However, few works have dealt with a comprehensive data analysis, based on Digital Twin systems, to study quality levels of manufactured parts using 3D models. With this background in mind, this current project uses a Digital Twin-enabled dataflow to constitute a basis for a proposed data analysis pipeline. The pipeline consists of analyzing metal AM-manufactured parts’ surface roughness quality levels by the application of a Deep Neural Network (DNN) analytical model and enabling the assessment and tuning of deposition parameters by comparing AM-built models’ 3D representation, obtained by photogrammetry scanning, with the positional data acquired during the deposition process and stored in a cloud database. Stored and analyzed data may be further used to refine the manufacturing of parts, calibration of sensors and refining of the DT model. Also, this work presents a comprehensive study on experiments carried out using the CW-GTAW (Cold Wire Gas Tungsten Arc Welding) process as the means of depositing metal, resulting in hollow parts whose geometries were evaluated by means of both 3D scanned data, obtained via photogrammetry, and positional/deposition process parameters obtained from the Digital Twin architecture pipeline. Finally, an adapted PointNet DNN model was used to evaluate surface roughness quality levels of point clouds into 3 classes (good, fair, and poor), obtaining an overall accuracy of 75.64% on the evaluation of real deposited metal parts. Full article

In this study, surface alloying technology based on Gas Tungsten Arc Welding (GTAW) was used to synthesize in situ NiTiTa coatings on a NiTi substrate using commercially pure Ta foils. The influence of different Ta contents (0.91, 1.42, and 2.91 at.%) on the microstructure, phase formation, hardness, corrosion resistance, and X-ray visibility of the prepared coatings were systematically studied. These results show that the NiTiTa coatings fabricated by GTAW were free of microcracks with good surface quality and superior adhesion to the NiTi substrate. The NiTiTa coatings are mainly composed of columnar austenitic NiTi (B2), and martensitic NiTi (B19’) with (Ti, Ta)2Ni precipitating at the grain boundaries. The proportion of B19’ martensite and the Ta content dissolved in the NiTi matrix increases with the increasing addition of Ta. In addition, β-Ta appeared in the coating formed with 1.42 at.% Ta and precipitated abundantly when the Ta amount was increased to 2.91 at.%. Changes in phase composition and secondary phases lead to a decrease in the material nanohardness. To simulate the body fluid environment, corrosion tests were conducted in Hank’s solution at a rate of 0.5 mV/s. Electrochemical tests show that the NiTiTa coatings exhibit superior corrosion resistance, where the corrosion potential, Ecorr, increased with increasing Ta content. The enhanced X-ray visibility of the newly formed coatings was also revealed. This work provides a cost-effective method for in situ synthesis of NiTiTa coatings on NiTi alloys, highlighting its potential for improving the corrosion resistance and X-ray visibility of NiTi shape memory alloys. Full article

This study investigates the combined effects of oxygen content in the purging gas and pre-weld surface finish on the discoloration and corrosion resistance of AISI 316L pipe joints, with relevance to pipe welding where internal cleaning is constrained. The hybrid GTAW–FCAW process was used. Welds were produced at two oxygen levels (500 and 5000 ppm) and two finishes (40- vs. 60-grit). Discoloration and oxide morphology were examined by SEM/EDS, and corrosion behavior was evaluated without oxide removal using cyclic polarization and electrochemical impedance spectroscopy. The results reveal that higher oxygen levels in the purging gas produced more porous, less protective oxide layers, along with intensified oxidation around surface defects such as micro-holes. Surface roughness was also found to influence corrosion behavior: rougher surfaces exhibited higher resistance to pit initiation, whereas smoother surfaces were more susceptible to initiation but offered greater resistance to pit propagation. The corresponding governing mechanisms were identified and discussed in terms of how surface preparation affects crystallographic texture, heterogeneities and recrystallization. Taken together, the results link oxide morphology and near-surface microstructure to electrochemical response and offer practical guidance for pipe welding when internal cleaning is constrained, balancing purging control with surface preparation to preserve corrosion performance. The findings further highlight the critical roles of both purging-gas composition and surface preparation in the corrosion performance of stainless steel welded pipes. Full article

The purpose of this paper is to study the weldability of two specific steels, UNS S31803 (duplex) and UNS S 32760 (super duplex), by making heterogeneous butt joints using gas tungsten arc welding technology. These materials are widely used in applications that take advantage of their superior corrosion resistance, strength, or both, such as chemical plants, oil and gas equipment, offshore sector, marine and other high-chloride environments. Although the joining technique of DSS and SDSS steels is a well-established industrial method, there are several process parameters that can play a key role in the correct execution of welds and in their final achievable properties. Starting from this assumption, this paper investigates some specific aspects such as the influence of heat input and shielding gas composition on the joint’s microstructure and the consequent changes in the ferrite/austenite ratio, also after post-welding heat treatments. Effects on both mechanical and corrosion resistance properties of the alloys are addressed. Full article

Three types of CoCr alloy welding wires were deposited on the surface of a single-crystal alloy using gas tungsten arc-welding (GTAW) technology to enhance its wear resistance. Comparative studies were conducted on the microstructure, microhardness, friction and wear properties, and tensile properties of the deposited alloy layers. The results showed that the deposited CoCr alloy layers formed good metallurgical bonding with the substrate, and the microstructure mainly consisted of planar crystals, coarse columnar dendrites, and fine, dense equiaxed dendrites. The microhardness of joints formed by depositing CoCr alloy welding wires increased with increasing distance from the interface, exhibiting a distribution pattern where the center of the deposition layer had the highest hardness, followed by the interface, while the base material had the lowest hardness. The highest hardness of the deposited layers of the S1 alloy was 119.5 HRC, with significant fluctuations in the deposition layer area. The wear resistance was significantly improved after depositing, and decreased significantly with increasing service temperature. The tensile strengths of the three welding wires were similar. The joint strength gradually decreased as the test temperature increased, with the S12 alloy joint exhibiting superior performance at high temperatures. Full article

This study investigates the use of YOLOv8 deep learning models to segment and classify thermal images acquired from the rear of the weld pool during the Gas Tungsten Arc Welding (GTAW) process. Thermal data were acquired using a two-color pyrometer under three welding current levels (160 A, 180 A, and 200 A). Models of sizes from nano to extra-large were trained on 66 annotated frames and evaluated with and without data augmentation. The results demonstrate that the YOLOv8m model achieved the best classification performance, with a precision of 83.25% and an inference time of 21.4 ms per frame by using GPU, offering the optimal balance between accuracy and speed. Segmentation accuracy also remained high across all current levels. The YOLOv8n model was the fastest (15.9 ms/frame) but less accurate (75.33%). Classification was most reliable at 160 A, where the thermal field was more stable. The arc reflection class was consistently identified with near-perfect precision, demonstrating the model’s robustness against non-relevant thermal artifacts. These findings confirm the feasibility of using lightweight, dual-task neural networks for reliable weld pool analysis, even with limited training data. Full article

Aluminum alloy, due to its low melting point and high thermal conductivity, deforms and contracts significantly during welding. To mitigate this and achieve full penetration in a single pass, this study uses GTAW (Gas Tungsten Arc Welding) additive manufacturing and optimizes welding groove parameters via the Box-Behnken Response Surface Methodology. The focus is on improving tensile strength and penetration depth by analyzing the effects of groove angle, root face width, and root gap. The results show that groove angle most significantly affects tensile strength and penetration depth. Hardness profiles exhibit a W-shape, with base material hardness decreasing and weld zone hardness increasing as groove angle rises. Root face width reduces hardness fluctuation in the weld zone, and an appropriate root gap compensates for thermal expansion, enhancing joint performance. The interaction between root face width and root gap most impacts tensile strength, while groove angle and root face width interaction most affects penetration depth. The optimal welding parameters for 7xxx aluminum alloy GTAW are a groove angle of 70.8°, root face width of 1.38 mm, and root gap of 0 mm. This results in a tensile strength of 297.95 MPa and penetration depth of 5 mm, a 90.38% increase in tensile strength compared to the RSM experimental worst group. Microstructural analysis reveals the presence of β-Mg₂Si and η-MgZn₂ strengthening phases, which contribute to the material’s enhanced mechanical properties. Fracture surface examination exhibits characteristic ductile fracture features, including dimples and shear lips, confirming the material’s high ductility. The coexistence of these strengthening phases and ductile fracture behavior indicates excellent overall mechanical performance, balancing strength and plasticity. Full article