Tungsten Inert Gas Arc Research Articles

Surface modification by in-situ grown TiC in the bainitic matrix using TIG arcing

In the current study, surface modification of the steel was carried out with the in-situ formation of TiC in the bainite matrix using tungsten inert gas (TIG) arcing. The actual arcing parameters were optimised after thermal simulation considering the final phase transformation. Various characterisation techniques revealed the formation of fine nano as well as micron-sized in-situ grown titanium carbide precipitate within the bainite matrix. The morphology and coherency of fine TiC were analysed by high-resolution transmission electron microscopy. Mechanical properties of the modified surface were significantly improved owing to the combined effect of bainite and TiC formation. The coherent precipitates indicate superior wear resistance with the absence of pull-out particle during sliding wear.

In situ measurement of ultrasonic behavior during lap spot welding with laser ultrasonic method

Understanding the joining process in real time during welding can help improve welding quality, reliability, and manufacturing process efficiency. For this purpose, a laser ultrasonic method that can detect in situ welding quality without contact during welding would be useful. However, the behaviors of ultrasonic propagation as well as melting and joining with increasing temperature remain unclear. Therefore, this study aimed to experimentally investigate the in-process ultrasonic behavior when using the laser ultrasonic method. Lapped tungsten inert gas (TIG) arc spot welding was used for the ultrasonic measurements, wherein the ignition of the TIG arc from the specimen's top surface and laser irradiation for the ultrasonic measurement from the bottom surface occur simultaneously. In this welding, the melting width at the interface of the lapped plates is an important parameter. We investigated the type of ultrasonics used to measure the melting width and examined whether the melting behavior during welding could be experimentally captured. The results show that the ultrasonic velocity decreases as the temperature increases. The echo from the interface between the plates disappears, and the echo from the top surface appears. The disappearance and appearance of each echo facilitate the understanding of the melting behavior during welding.

Study on the weld formation, microstructure and mechanical properties of AZ31B Mg alloy in AC/DC mixed gas tungsten arc welding process

In this work, a new welding electrical signal waveform of the AC/DC mixed waveform is purposed to improve the welding quality of magnesium alloy TIG. The method is named as AC/DC mixed tungsten inert gas arc (MIX-TIG) welding. The AZ31B Mg alloy welded joints were obtained by AC-TIG and MIX-TIG. Through investigation of the weld formation, microstructure and mechanical properties of welded joints, the results showed that when the welding current of 90A∼110 A, the completely penetration of welded joints could be obtained. There was no obvious difference for the geometrical parameters of the weld cross-section between the AC-TIG and MIX-TIG. The microstrcuture of fusion zone consisted of α-Mg matric and β-Mg17Al12 phase. At the same welding conditions, the average grain size and β phase number in the MIX-TIG were less than that of the AC-TIG. The microhardness of the AC-TIG fusion zone was slightly larger than that of the MIX-TIG owing to the increase of β phase number. The strain of the AC-TIG welded joint was reduced by approximately 24% compared with that of the MIX-TIG welded joint.

Simultaneous multipoint emissivity measurement via Zebra-patterned blackbody spray method and application to gas tungsten arc welding process

Thermography is a temperature measurement method that can measure low temperatures but requires an emissivity setting. Because emissivity depends on the material, surface condition, and temperature, referring to a database is generally difficult in practical measurements. Hence, it is desirable to measure emissivity based on an object. Herein, a new emissivity measurement method, termed the zebra-patterned blackbody spray method, is proposed. By spraying a blackbody in a striped pattern and calculating the temperature at the unsprayed area via interpolation, the luminance and true temperatures of the measurement area are measured simultaneously; subsequently, the emissivity is calculated. In addition, simultaneous, multipoint, and multitemperature measurements are performed by heating the back of the sample. The emissivity of stainless steel and mild steel measured via this method agrees well with the emissivity measured using a thermocouple. In addition, bead-on-welding using a tungsten inert gas arc is performed and the difference in emissivity between the welded bead and the base metal is presented based on the welding current. The emissivity of a 200 A bead is higher than that of the base metal and a 100 A bead, and the variation increases with the variation in the surface condition. Additionally, the temperature during TIG welding is measured. When a constant emissivity is used, the temperature distribution across the beads becomes discontinuous. Applying the emissivity obtained using this method yields a continuous temperature distribution.

Exceptional grain refinement of Mg-Zr master alloy treated by tungsten inert gas arc re-melting with ultra-high frequency pulses

The Zr distribution in a commercial Mg-30Zr master alloy was modified by tungsten inert gas arc re-melting with ultra-high frequency pulses (UHFP-TIGR) leading to the most substantial grain size reduction using a Mg-Zr master alloy. The results show that the Zr particle size is well refined, and higher contents of soluble Zr (Zrs) and nanoscale (∼10 nm) Zr particles (Zrnp) can be obtained. Zrs provides considerable constitutional supercooling (CS) for the nucleation of α-Mg grains on Zrp (∼100 nm particles). An exceptional improvement in the grain refinement efficacy (54%) of Zr master alloys is achieved with a holding time of 5 min. Consequently, a new approach to the design and fabrication of high-efficiency grain refiners is proposed.

Humping Formation and Suppression in High-Speed Laser Welding.

Increasing welding speed can promote the productivity of laser welding. However, humping defects often occur, which limits the application of this strategy. The existing explanations for the humping formation remain vague, and mitigation and suppression methods are limited. In this research, high-speed imaging experiments and numerical simulation of the high-speed laser welding process are performed. Through careful examination, the humping phenomenon is explained. At high welding speed, the high-speed melt flow caused by recoil pressure is hindered by the solidified region in the melt pool, leading to the occurrence of a swelling. The swelling then grows, forming a valley in front of the swelling under the effect of surface tension. The solidification of the valley results in the occurrence of a second swelling. This process repeats and humping defect forms. Marangoni force and viscous force also have influence on this process. In addition, it is found that adding a Tungsten Inert Gas arc behind the laser beam can effectively suppress the humping.

Formation mechanism of Al-Zn-Mg-Cu alloy fabricated by laser-arc hybrid additive manufacturing: Microstructure evaluation and mechanical properties

A novel additive manufacturing followed by a hybrid process involving pulsed laser and tungsten inert gas (TIG) arc was proposed to balance the element vaporization, microstructure uniformity, and mechanical properties of the Al-Zn-Mg-Cu alloy. The amount of vaporized Zn in the laser-arc hybrid additive manufacturing (LAHAM) reduced by merely 2.5%, whereas the Zn vaporization loss of the WAAM specimens reached up to 8.3%. Compared with the grain sizes of specimen obtained via WAAM, those obtained via LAHAM decreased by approximately two times. The < 100 > texture in the LAHAM specimen was decreased significantly, due to the appearance of equiaxed grains and grain refinement. Furthermore, in contrast to WAAM specimen, the eutectics contained Al, Zn, Mg and Cu were evenly distributed in the LAHAM specimen, resulting in uniform element distribution. Nano-precipitates were dispersedly distributed within the grains in the LAHAM specimen, whereas they merely appeared around the grain boundaries in the WAAM specimen. Owing to microstructure changes, LAHAM improved the ultimate tensile strength and yield strength by up to 11.4% and 29.9%, as compared with WAAM. The substantial improvement in yield strength was primarily attributed to precipitation strengthening, instead of grain boundary strengthening or solid solution strengthening.

Advancement in cermet based coating on steel substrate: A review

Ceramic and metals mixed phases are a category of materials known as cermet to produce materials that have the best characteristics of both such as high hardness, abrasion wear resistance, resistance to corrosion-erosion resistance and deformation resistance against high temperature. Several thermal spray procedures e.g., high velocity air or oxygen fuel, spraying by plasma, detonation gun, and other cladding techniques, such as laser cladding, Tungsten inert gas arc cladding, have been widely utilised for the cladding of cermet powders on steel in recent decades. Cermet-based coatings on steel have gained popularity in recent years as a potential approach for improving metallurgical, mechanical, corrosion, erosion, and wear properties. This paper summarises the research that has been done to create cermet coating on steel.

Fatigue life estimation of welded structures enhanced by combined thermo-mechanical treatment methods

Different post-weld treatment methods are used to strengthen welded joints that are subjected to cyclic loading. Combining High-Frequency Mechanical Impact (HFMI) treatment with Tungsten Inert Gas (TIG) remelting is rather a new concept. In this paper, the fatigue lives of welded transverse attachments treated by HFMI-treatment, TIG-remelting, or the combination of both are estimated using fatigue damage modelling and finite element deletion. The change in local topography and residual stresses due to treatment are evaluated numerically and incorporated in the analysis. The local hardness is measured by a Vickers tester and incorporated by increasing the elemental ultimate strength. The analysis demonstrates the superiority of the combined treatment because of the introduced compressive residual stress and the improvement in topography. The analysis also shows that the damage is less distributed after the combined treatment than both individual treatments. Besides, the capability of the TIG-HFMI combination in treating existing welded structures with remaining embedded fatigue crack is proven. Besides, available fatigue test results on combined TIG-HFMI treatment shows that this combination gives always longer fatigue life than the characteristic fatigue lives of the treated details by any of the treatment methods. However, many aspects such as TIG arc and HFMI indenter positioning, and indentation and fusion depth should be taken into consideration when the combined treatment is to be applied to existing structures.

A numerical study of the effects of cathode geometry on tungsten inert gas type electric arcs

In this paper we address the question of the influence of cathode tip geometry on the physical quantities relevant to Tungsten Inert Gas (TIG) arc welding. Although cathode geometry is known to influence arc-plasmas, a thorough quantification of the Lorentz phenomenon, which is the dominant source of momentum in the fluid flow of TIG arcs has not been strongly investigated. Therefore, we have performed a numerical parametric study at a constant inlet electric current and arc height, for different cathode sizes and shapes (pointed, chamfered and rounded tips), parameterised by the truncation angle and tip radius. To this end, we developed a coupled steady-state magneto-hydrodynamic finite element model in a 2D axi-symmetric configuration, implemented in the [Display omitted] toolbox. The paper characterises, quantifies and analyses the influence of tip geometry on TIG arcs and the workpiece. The model reveals that tip size and truncation angle similarly influence the magnitude of the transported quantities of the arcs. We find that the imparted momentum and transferred heat flux to the workpiece vary about 4 and 2-fold between the bluntest and sharpest cathodes, respectively. This signifies the importance of the choice of cathode tips in numerical TIG welding simulations. Agreement between the literature and the current work is analysed and discussed and the importance of coupling the cathode and arc domains is highlighted.

Suppression mechanism of weld appearance defects in tandem TIG welding by numerical modeling

In high-speed tungsten inert gas (TIG) welding, the premature solidification of liquid metal in low-temperature zone of molten pool results in the formation of weld appearance defects (WADs) such as undercut and humping weld. Tandem TIG welding was developed to prevent the formation of the WADs and realize high-speed welding. A three-dimensional model of arc and molten pool was developed to investigate the heat and mass transfer behavior in molten pool of tandem TIG welding process. The results indicate that, because of the thermo-mechanical control effect on the molten pool by the assistant TIG arc, a stable swelling zone forms between the two arcs and the formation of trail accumulation was prevented. The maximum backward velocity driven by the main TIG arc is decreased significantly, which suppresses the backward flow and premature solidification of liquid metal. The existence time of liquid metal is evidently longer by 70% than that of single TIG welding, which leads to the liquid flow at the tail of weld pool sufficiently moving forward to suppress the instability of depression zone. The heat and mass transfer in molten pool indicates that during tandem TIG welding process, the thermo-mechanical effect of assistant TIG arc prolongs the existence time of liquid metal and improves its flowing back, so the WADs were efficiently suppressed.

Introducing Compressive Residual Stresses into a Stainless-Steel T-Pipe Joint by an Overlay Weld

Microcracks are always present in the deposited metal of nickel-based alloys and austenitic stainless steels, which affects the safety of the pressure pipes. If compressive stress can be introduced into the cracked position by overlay welding, the time required with ordinary gouging repair welding technology will be significantly reduced, which is practical significance for pressure pipes repair welding. In this work, a stainless-steel T-pipe joint was fabricated using manual metal arc welding with an ER316L wire, and an overlay weld was fabricated using tungsten inert gas arc welding with an ERNiCrFe-7A wire. The overlay thickness was about 10 mm. The contour method was employed to measure the residual stress in the T-pipe joint. The results show that compressive residual stress about 50 MPa is formed in the original ER316L weld, which proves that the residual compressive stress can be obtained in the original weld by surfacing 10 mm thick nickel base alloy on the original weld surface.

Fe2O3 Nanowire Flux Enabling Tungsten Inert Gas Welding of High-Manganese Steel Thick Plates with Improved Mechanical Properties

Economic welding of thick steel plates is an emerging challenge for various engineering applications. However, tungsten inert gas (TIG) arc welding, as an economic and widely used method, is not regarded as a suitable tool to weld thick steel plates due to the shallow penetration in a single-pass operation. In this technical progress, the joining of austenitic high manganese steel of 8 mm thickness was successfully performed using nanowire flux activated TIG welding with a full penetration and a narrow bead geometry. Fe2O3 nanowire was used as flux and compared with microscale Fe2O3 flux. Experimental results showed that with nanowire fluxes, the welding yielded the maximum of more than 8 mm thick penetration (full penetration and melt over the plate) with proper operating parameters in a single pass. In sharp contrast, the penetration is only less than 4 mm for a single pass welding without Fe2O3 flux with the similar parameters. Arc voltage—time variation during welding process was analyzed and the angular distortion was measured after welding to understand the activating effect of optimized flux mixture. Compared to welding joint without flux and with microscale Fe2O3 flux, nanoscale Fe2O3 flux has a larger arc voltage and higher energy efficiency, higher joint strength and less angular distortion. The developed joint with nanowire flux qualified the tensile test with tensile strength of 700.7 MPa (82.38% of base material strength) and 34.1% elongation. This work may pave a way for nanotechnology-enabling welding innovation for engineering application.

Microstructural Control of the Interface Layer for Strength Enhancement of Dissimilar Al/Cu Joints via Ni Addition during TIG Arc Brazing

Dissimilar metal joining between Al and Cu is effective for reducing the weight and cost of electrical components. In this study, dissimilar lap joining of pure Al to pure Cu with an Al-Ni filler material was conducted using tungsten inert gas (TIG) arc brazing, and the effect of Ni on the joint strength associated with the microstructure of the intermetallic compound (IMC) layer at the dissimilar interface was examined. The addition of Ni effectively increased the interfacial strength of the joints. Regardless of the addition of Ni, the joints fractured in the thick Al2Cu layer formed at the Al/Cu interface. However, the Ni addition reduced the thickness of the IMC layer and led to the formation of Al7Cu4Ni particles in the weakest Al2Cu layer. Both the thickness reduction and reinforcing Al7Cu4Ni particle formation are thought to contribute to the increase in joint strength of the Al/Cu dissimilar interface.

Physical and thermodynamic simulations of gamma-prime precipitation in Haynes® 282® using arc heat treatment

Haynes 282 is a Ni-based gamma prime (γ′) strengthening alloy with a balanced combination of high temperature properties and fabricability. This paper aims to study the evolution of the microstructure and hardness using a novel physical simulation method called arc heat treatment, followed by thermodynamic modeling of γ′ precipitation. For the arc heat treatment, a steady state temperature gradient was generated using a stationary tungsten inert gas arc on a sample mounted onto a water-cooled chamber. The steady state condition ranged from room temperature to the liquidus and was achieved within the first few seconds. Aged and solutionized samples were arc heat treated for 1.5 min, 30 min, and 4 h. The experiments were complemented with temperature modeling, equilibrium calculations, and γ′ precipitation simulations. A unique graded microstructure formed in the arc heat-treated samples. It consisted of a fusion zone with a dendritic microstructure; a region with the dissolution of all secondary phases (MC carbides, grain boundary carbides, and γ′); a region with MC and grain boundary carbides; a γ′ precipitation zone; and the base metal. The temperature range of the dissolution area extended to lower temperatures with increasing arc heat treatment dwell time. The γ′ precipitation zone showed a distinct etching response coupled with high hardness. The hardness and the temperature range of the γ′ precipitation zone increased with increasing arc heat treatment time. The γ′ radii increased with increasing time and temperature. The γ′ precipitation model, simulated with TC Prisma, showed very good agreement with the experimental results. Finally, the results were used to develop time-temperature precipitation and hardness diagrams.

The Effect of Post Weld Heat Treatment (PWHT) on the Microstructure, Microhardness and Sulphide Stress Corrosion Cracking (SSCC) of Ni-Base Superalloy IN625 Hot Wire TIG Cladding on AISI 4130 Steel

This study aims to investigate the effect of post-weld heat treatment (PWHT) on the microstructure, microhardness, and sulfide stress corrosion cracking (SSCC) of IN625 weld overlay on AISI 4130. In this paper, cladding was conducted by TIG (tungsten inert gas arc welding) technique, then PWHT was carried out at 650, 750, and 850°C temperatures with the constant time of 1 h. Also, the SSCC test was performed for 720 h. According to the results, columnar dendrites with MC carbide in g solid solution matrix comprise the microstructure. Furthermore, there was not any crack in the Weld Overlay (WO), tempered martensite, bainite in the base metal (BM), coarse tempered martensite, and ferrite in the heat-affected zone (HAZ). The results demonstrate that as the temperature of PWHT rises, the hardness of BM and HAZ reduces while hardness in the WO increases; it can be seen that at 750°C γ'' phase rapidly emerged and changed to stable δ at 850°C by the shearing mechanism. Furthermore, the results of the magnetic test showed stress crack in samples that heat-treated at 850°C. SEM images reveal that stress cracks in BM continued along grain boundaries and reached the WO.

Phase and chemical structure characterization in double sided TIG arc welding of HARDOX 450 and AISI 430 steel

In this study, HARDOX 450 and AISI 430 grades are combined using double-sided tungsten inert gas (TIG) welding process. Microstructural properties of weld zone were evaluated with optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), electron back scatter diffraction (EBSD), elemental mapping analysis. After tensile testing, fracture surface morphology was evaluated using SEM. The width and depth of the weld seam increased with the increase in current. Carbon and chrome diffusion gradients were formed on the HARDOX 450 steel side by FSS in welded joints. The crystallographic plane was dominated by blue and, concentrated in the direction of {101}, {001}, {111}.

Thermal analysis of TIG-WAAM based metal deposition process using finite element method

The Tungsten Inert gas welding-based wire and arc additive manufacturing (TIG-WAAM) process is one of the most energy-efficient processes among the direct energy deposition processes. The TIG-WAAM process involves layer by layer deposition of a material using wire and arc. The path planning in the metal deposition process affects the temperature distribution during the layer by layer deposition in wire arc additive manufacturing (WAAM) process. The distribution of the temperature affects the quality of the metal deposition and its dimensional accuracy. In this paper, a Finite element analysis (FEA) based model for TIG-WAAM process was developed for analyzing the effect of the temperature distribution on the metal deposition process. The developed model has been used for simulating metal deposition using TIG-WAAM process for a single layer of low carbon steel. The distribution of temperature across the deposited material has been recorded. The results showed that the concentration of the temperature takes place at all turning points in the deposition path which may lead to deteriorating the quality of deposition. The developed model can be used further for the development of the feedback-based temperature management system to provide smooth metal deposition with better quality.

Wear Resistance under Different Temperatures of NiCr-Cr3C2 Coating Remelted by Tungsten Inert Gas Arc

In this work, a NiCr-Cr3C2 coating was prepared on the AISI 1045 steel substrate by plasma spraying, then subjected to tungsten inert gas arc (TIG) remelting treatment. The microstructure, hardness and the wear test under different temperatures (25, 200, 400, and 600 °C) of the NiCr-Cr3C2 coatings before and after remelting were studied comparatively. The results show that after TIG remelting, the internal structure of the coating was dense, and the defects were greatly reduced. The hardness of the remelted coating surface became uniform and increased from 1007 HV0.1 to 1141 HV0.1, with an increase of 13.3%. At different temperatures, the weight loss of the remelted coating was always less than that of the sprayed coating, with a significant reduction of about 75%. The friction coefficients of the remelted coating and sprayed coating at 25 and 200 °C were basically the same, while the friction coefficients of the remelted coating at 400 and 600 °C were smaller than that of the sprayed coating. The wear mechanism of the remelted coating under different temperature were abrasive wear and adhesive wear, while that of the sprayed coating were fatigue wear, abrasive wear, and adhesive wear. Therefore, the TIG remelting treatment can optimize the microstructure of the NiCr-Cr3C2 coating and remarkably improve the wear resistance.

Surface modification of AISI 8620 steel by in-situ grown TiC particle using TIG arcing

In-situ grown titanium carbide (TiC) reinforced steel matrix was produced with tungsten inert gas (TIG) arcing by the metallurgical reaction between titanium and graphite powder on bearing steel (AISI 8620). Microstructure, chemical composition, and formation of TiC precipitate particles were thoroughly analysed primarily for basic understanding of transformation characteristics and morphology of the TiC particles as a function of the process parameters. The microstructure was analysed with the help of several tools like field emission scanning electron microscope (FESEM) equipped with energy dispersive spectroscopy (EDS), electron probe micro analyzer (EPMA), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The treated surface was practically free from cracks and porosity. The modified surface consists of in-situ synthesized titanium carbide precipitate in the martensite matrix. The XRD results confirmed the presence of titanium carbide precipitate. The changes in TIG arcing parameters have been found to vary the dilution of the modified zone which has subsequently affected the concentration of TiC precipitates in the modified region. Considerable enhancement in the mechanical properties of the modified surface was examined using microhardness and wear test. The average hardness of the modified surface with flux of lowest current reached to about 2.15 times that of the base metal. The wear test reveals the effectiveness of the TiC precipitate with the enhancement in wear resistance of about 4.6 times that of as received sample. Surface modification of the substrate was also carried out by employing TIG arcing without the addition of the flux coating to make a comparative study on the evolution of microstructure and its effect on mechanical behavior to find out the utility of using the flux coating for an exclusive benefit of the surface modification for superior properties.