Gas Tungsten Arc Welding Method Research Articles

Laser and GTAW torch processing of Fe–Cr–B coatings on steel

A comparison of a coating of Fe–Cr–B alloy powder processed on a plain carbon steel by surface melting using either laser or gas tungsten arc welding (GTAW) torch was made. The alloy powder was injected in laser melted surface, while the preplaced powder was melted using the GTAW technique. The topography of the GTAW tracks showed a relatively smooth surface, but the laser track surface was very rough. Because of high energy input, the GTAW method produced very wide and deep tracks with a high dilution compared to those of the laser tracks. Pores and fine cracks were seen in laser tracks; the cracks were elongated across the track width, and some of them propagated down to the melt depth. The GTAW track produced at a low energy was free from any cracking, but a centreline crack was present when processed at a high energy input.

A Comparative Study of the Tribological Behavior of Tin Powder Clad on the JIS SKD11 Tool Steel with the GTAW Method

This work focused on the wear performance of the clad layers which were formed with cladding titanium nitrides (TiN) powder on the JIS SKD11 tool steel by the gas tungsten arc welding (GTAW) method. A rotating type tribometer was used to evaluate the wear behavior of the clad specimens under different sliding conditions. Furthermore, a nanoindenter was used to measure the hardness and elastic modulus of the reinforcements. According to the wear test results, the wear performance of the specimens cladded with TiN powder was better than that of the JIS SKD11 tool steel specimens. During dry sliding wear test, the clad layers exhibited a strong wear resistance because they contained the hard TiN reinforcements. Therefore, the wear performance of the clad layers was substantially better than that of the SKD11 specimens under all the test conditions in this study. In addition, produced oxide films might influence the wear behavior of different specimens during the wear testing, and oxidation wear would even dominate the wear behavior of the clad layers under some conditions.

The Effect of Shielded Metal Arc and Gas Tungsten Arc Welding Methods on 308L Stainless Steel Weldments

Shielded metal arc (SMA) and gas tungsten arc (GTA) weldments were investigated to study the welding effects on the mechanical behavior of 308L austenitic stainless steel weldments, respectively. Both SMA and GTA weldments showed dendritic microstructure. The observed austenitic stainless steel welds solidified to give primary ferrite and secondary austenite as the ferritic-austenitic solidification mode (FA-mode) solidification. However, the lower heat input with larger Cr-versus-Ni ratio in SMA weld process led to lathy ferrite morphology and more residual ferrite in the SMA welds, while vermicular ferrite morphology was shown in GTA weldments. The yield strength of the welds significantly increased with decreasing elongation, which was mainly due to the dual phase strengthening effect after rapid solidification during welding

Characteristics of surface layer of sintered stainless steels after remelting using GTAW method

The study presents the results of the investigations concerning the effect of remelting using gas tungsten arc welding (GTAW) process on the microstructure and selected properties of the surface layer in sintered multi-phase steels obtained from powders of 304L and 434L steels. The effect of surface treatment was evaluated based on macro- and microstructural observations, EDS analysis, X-ray phase analysis and measurements of surface roughness and microhardness. It was found that remelting of surface layer leads to elimination of open porosity and homogenization of the structure, which was confirmed by microscopic observations and microhardness tests. A cellular or mixed cellular and dendritic structure was formed in the remelted zone in the sinters. Growth of columnar crystals occurred along the direction of heat transfer. Using the energy dispersive spectroscopy (EDS), the authors found higher concentration of alloy elements in the intercellular zones compared to cell cores. X-ray analysis demonstrated that the remelting used is conducive to formation of the austenitic phase in the remelted material.

Microstructures and wear properties of various clad layers of the Fe–W–C–B–Cr system

In this study, using the gas tungsten arc welding method, various hard boride and carbide phases inside clad layers were synthesized in situ from Fe, C and Cr-containing SKD61 or SKD11 substrates spread over with tungsten boride powder. According to the results concerning hardness and microstructures, the clad layers of the Fe–W–C–B–Cr system had a high hardness because of the precipitation hardening of various precipitates. Additionally, the high C and Cr content of WB-SKD11 specimens led to clad layers with hard and complicated structure. The clad layers of the Fe–W–C–B–Cr system were quite thick, with a mean thickness of 6mm. By observing scanning electron microscopic images, it was evident that the soft regions in the heat-affected zones of the WB-SKD11 specimen had a bainite and retained austenite structure that was due to the high C and Cr content in the substrate. However, the WB-SKD61 specimen had no soft regions; its heat-affected zone was only composed of a martensite structure. The hardness of the WB-SKD61 specimen gradually decreased along the direction deep into the clad surfaces. The WB-SKD11 specimen was treated with cryogenic treatment that could reduce some of the retained austenite structures and significantly improve the hardness of the heat-affected zone. During the dry sliding wear test, the hard vein-shaped phase in the WB-SKD11 clad layers provided strong mechanical interlocking. Therefore, the wear performance of the WB-SKD11 clad layers was substantially better than that of the other specimens under all test conditions in this study.

Geometry of Remeltings and Efficiency of the Surface Remelting Process Applied to Cobalt Alloy Castings

Abstract The paper summarises results of measurements of remelting area geometry, thermal efficiency and melting efficiency characterising the surface remelting process applied to castings of MAR-M-509 cobalt alloy. The remelting process was carried out with the use of GTAW (Gas Tungsten Arc Welding) method in protective atmosphere of helium, at the electric current intensity in the range from 100 A to 300 A, and the electric arc scanning velocity vs in the range from 200 mm/min to 800 mm/min. The effect of current intensity and electric arc scanning velocity on geometrical parameters of remeltings, thermal efficiency, and melting efficiency characterising the remelting process has been determined.

Microstructural characterization and formation of α′ martensite phase in Ti–6Al–4V alloy butt joints produced by friction stir and gas tungsten arc welding processes

The obtained microstructures of a Ti–6Al–4V alloy welded by Gas Tungsten Arc Welding (GTAW) and Friction Stir Welding (FSW) were investigated and evaluated quantitatively. In the GTAW method, the effect of current was examined so that the samples were subjected to various currents between 90 and 120A. In the FSW process, samples were welded by different rotational speeds (450–850rpm). Non-destructive tests including Visual and Radiography Tests (VT and RT) were used to identify defect-free samples. The microstructural studies by electron microscopes revealed formation of different phases in the weld area of the samples welded via mentioned methods. The recorded peak temperatures in the weld regions compared favorably with the expectations about the evolved microstructures. A bi-modal microstructure was just obtained in the FSWed sample with a peak temperature below β transus temperature (T<995°C). α′ martensite phase, which is an acicular and strengthening phase in this alloy, was only observed in FSWed specimens.

Reinforcements affect mechanical properties and wear behaviors of WC clad layer by gas tungsten arc welding

This work deals with the surface analysis, mechanical properties and wear performances of the clad layer, which is made from tungsten carbide (WC) powders on SKD61 die steel by the gas tungsten arc welding method. According to the experimental results, due to the high hardness and elastic modulus reinforcements (Fe3W3C and M7C3) existing in the WC clad layer, the WC clad specimen has excellent wear performance at different sliding speeds.According to the wear analysis, wear behaviors of the WC clad layer are two-body abrasion and oxidation wear. In addition, oxidation wear dominates the wear behaviors of the SKD61 die steel specimen at different sliding speeds.

Effect of Zirconium Addition on Welding of Aluminum Grain Refined by Titanium

Aluminum and its alloys solidify in large grains columnar structure which tends to reduce their mechanical behaviour and surface quality. Therefore, they are industrially grain refined by titanium or titanium + boron. Furthermore, aluminum oxidizes in ordinary atmosphere which makes its weldability difficult and weak. Therefore, it is anticipated that the effect of addition of zirconium at a weight percentages of 0.1% (which proved to be an effective grain refiner on the weldability of aluminum grain refined by Ti) is worthwhile investigating. This formed the objective of this research work. In this paper, the effect of zirconium addition at a weight percentage of 0.1%, which corresponds to the peritctic limit on the aluminum-zirconium phase diagram, on the weldability of aluminum grain refined by Ti is investigated. Rolled sheets of commercially pure aluminum, Al grain refined Ti of 3 mm thickness were welded together using Gas Tungsten Arc Welding method (GTAW), formerly known as TIG. A constant air gap was maintained at a constant current level, 30 ampere AC, was used because it removes the oxides of the welding process under the same process parameters. Metallographic examination of weldments of the different combinations of aluminum and its microalloys at the heat affected zone, HAZ, and base metal was carried out and examined for width, porosity, cracks and microhardness. It was found that grain refining of commercially pure aluminum by Ti resulted in enhancement of its weldability. Similarly, addition of zirconium to Al grain refined by Ti resulted in further enhancement of the weldment. Photomicrographs of the HAZ regions are presented and discussed.

Microstructure evolution of Al/Mg butt joints welded by gas tungsten arc with Zn filler metal

Abstract Based on the idea of alloying welding seam, Gas tungsten arc welding method with pure Zn filler metal was chosen to join Mg alloy and Al alloy. The microstructures, phases, element distribution and fracture morphology of welding seams were examined. The results indicate that there was a transitional zone in the width of 80–100 μm between the Mg alloy substrate and fusion zone. The fusion zone was mainly composed of MgZn 2 , Zn-based solid solution and Al-based solid solution. The welding seam presented distinct morphology in different location owning to the quite high cooling rate of the molten pool. The addition of Zn metal could prevent the formation of Mg–Al intermetallics and form the alloyed welding seam during welding. Therefore, the tensile strengths of joints have been significantly improved compared with those of gas tungsten arc welded joints without Zn metal added.

Corrosion behavior of aluminum 6061 alloy joined by friction stir welding and gas tungsten arc welding methods

Wrought aluminum sheets with thickness of 13mm were square butt-welded by friction stir welding (FSW) and gas tungsten arc welding (GTAW) methods. Corrosion behavior of the welding zone was probed by Tafel polarization curve. Optical metallography (OM) and scanning electron microscopy together with energy dispersive spectroscopy (SEM-EDS) were used to determine morphology and semi-quantitative analysis of the welded zone. FSW resulted in equiaxed grains of about 1–2μm, while GTAW caused dendritic structure of the welded region. Resistance to corrosion was greater for the FSW grains than the GTAW structure. In both cases, susceptibility to corrosion attack was greater in the welded region than the base metal section. T6 heat treatment resulted in shifting of the corrosion potential towards bigger positive values. This effect was stronger in the welded regions than the base metal section.

Remelting treatment of the non-conductive oxide coatings by means of the modified GTAW method

The primary objective of the study was to adapt the GTAW (Gas Tungsten Arc Welding) technique for the purposes of the surface remelting processing of non-conductive plasma sprayed coatings. Modification concerned the surface layer of complex oxide compositions based on ZrO2 and Al2O3, which had been applied onto a steel substrate using the plasma spraying technique. In the course of research it was demonstrated that the process of surface remelting of non-conductive oxide coatings may be successfully conducted using welding sources of heat provided that the standard welding station is previously redesigned and additionally equipped. The methodological and apparatus-related work undertaken led to the development and construction of a welding set with a free independent arc, in which the active participation of the oxide coating in the creation of the electric arc and its stabilisation has been eliminated.The effects of the remelting treatment on the structure of the plasma sprayed coatings have been investigated. The microstructures of both the as-deposited and the remelted coatings were observed by optical microscope and scanning electron microscope (SEM). Observation of the remelted coating structure allowed to distinguish areas with characteristic structural and morphological effects and changes in the structure thereof. On the basis of regularities noted and observations made, a zonal model of the remelted coating structure was put forward and elaborated.

Elucidation of microstructure and wear behaviors of Ti–6Al–4V cladding using tungsten boride powder by the GTAW method

Tungsten boride (WB) powder was used as a wear-resistance material, then clad on a Ti–6Al–4V substrate by the gas tungsten arc welding (GTAW) method. The titanium boride (TiB) reinforcing phase was formed in situ in the clad layer during the cladding process. Since the TiB and tungsten (W) reinforcing phase exist in the clad layer, the hardness of the clad layer is double that of the substrate. Wear test results reveal that the tribological performance of the WB-clad layer is superior to that of the Ti–6Al–4V substrate. This investigation also discusses the forming mechanism of the clad layer microstructure.

Microstructural properties of M7C3 eutectic carbides in a Fe–Cr–C alloy

Abstract The microstructure of Fe–Cr–C coatings was investigated with optical microscope (OP), scanning electron microscope (SEM), electron dispersive spectrograph (EDS), respectively. The coatings were formed by means of gas tungsten arc welding method on the AISI 4340 steel. The microstructures of the coatings are found to compose of primary M7C3 carbides in eutectic of austenite matrix. The hypereutectic microstructure consisted of M7C3 and M7C3 + austenite (γ). The hardness values of M7C3 carbides varied between 1050 and 1500 HV, while the hardness of M7C3 + austenite (γ) matrix measured between 500 and 750 HV. The lower hardness of matrix of the coating microstructure was related to the relatively low concentrations of Cr and C.

Studies on characteristics of temperature field during GTAW with a trailing heat sink for titanium sheet

The characteristics of temperature field have been studied numerically and experimentally for a titanium alloy sheet when welded with an improved gas tungsten arc welding method, in which a trailing spot heat sink is introduced to control the welding stress and distortion. The impinging jet model is employed to describe the intense heat transfer between the cooling media and the top surface of the workpiece. By comparing this improved technique to the conventional gas tungsten arc welding (GTAW) process, the influence of the spot heat sink is investigated. Results show that a low temperature region exists where the heat sink is applied; a saddle backed temperature field, with the lowest temperature at the centre and higher temperatures at both sides, is formed during the improved welding method; and the time that the metal spends at high temperature is shortened in the improved welding process. Experimental measurements of the thermal histories compare well with the calculations, which prove the validity of the finite element model and the impinging jet heat transfer model in simulating the gas tungsten arc welding process with a trailing heat sink.