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Wire arc additive manufacturing (WAAM) is advantageous for fabricating large-scale metallic components; however, a high geometric accuracy as that of other AM techniques cannot be achieved because of the deposition process with a large layer. This study focuses on the WAAM process based on gas metal arc welding (GMAW). To clarify the influence of shielding gas used to protect a molten metal during fabrication on the geometric accuracy of the built part obtained via the GMAW-based WAAM process, the influence of the metal transfer behavior on the geometry and surface roughness of the fabricated structures was investigated via visualization using a high-speed camera when single and multilayer depositions were performed under different heat inputs and gases. It is known that Ar gas is not suitable for welding steel because it cannot provide the desired arc stability and weld bead characteristics. The results reveal that the arc is stable in the multilayer deposition of the WAAM process, and the short-circuit of the metal transfer at the heat input of 1.17 kJ/cm enables smoothing of the fabricated surface with large irregularities. Better arc stability under Ar gas is achieved when the oxygen content of the fabricated surface is 22 wt%. Furthermore, the short-circuit between the metal droplet and the fabricated surface, where the molten pool is insufficiently formed, resulted in a hump formation. The results indicate that proper use of Ar gas can improve the surface quality when depositing on rough surfaces. [ABSTRACT FROM AUTHOR]

Atmospheric pressure cold plasma has the advantages of high reactive species content, free from the limitation of vacuum environment and low cost in polymer films pattern etching. However, due to the extension phenomenon of the jet, there are problems in the pattern etching, such as low processing accuracy and difficulty in process precise control. In this paper, an atmospheric pressure cold plasma jet diffusion limited etching model is established to simulate the etching process and surface etching morphology under different conditions, and a plasma jet processing platform is built for experimental confirmation. The effect of diffusion coefficient and move probability on the etching results is studied by numerical simulation. The experiment observes the extension phenomenon of the plasma jet hitting the glass slide under the influence of working voltage or nitrogen flow, and the color reaction of Starch-KI test paper. The results show that the simulated etching results are consistent with the extension phenomenon of the jet impinging on the glass slide. The greater the probability of the active particles moving downward, the greater the contact line width and the etching depth, which is the same as the experimental result of increasing the working voltage. The shielding gas can isolate the air, reduce the diffusion coefficient, and reduce the loss of particles, which is beneficial to plasma etching. It is hoped that the research results in this paper can provide a certain reference for realizing high-precision and controllable etching and process optimization of atmospheric pressure cold plasma jet. [ABSTRACT FROM AUTHOR]

This paper presents an investigation into effect of nitrogen content of shielding gas mixture on weld geometry, microstructure and hardness of pulsed laser welded 2205 duplex stainless steel. Full penetration autogenous welding was performed on 2 mm thick plates using a low power pulsed Nd: YAG laser. light and scanning electron microscopy were used to study the resulting microstructures. It is observed that 2 mm full penetrated joint decreases to 1.8 mm by dominating nitrogen in argon-nitrogen mixture. Different morphologies of austenite phase as well as an increase of 8% of its content can be observed in pure nitrogen shielded welds. Average weld grain size in sample which is welded in nitrogen atmosphere stands at approximately 41 μm which is smaller than that of argon atmosphere which is about 51 μm. Micro-hardness test reveals that hardness values increase from 280 HV in base metal to 307 HV in weld center line and the shielding gas mixture does not significantly influence the weld hardness.

Abstract Background Aim of the present study is the evaluation of ultrasound as a physical method for virus inactivation in human plasma products prior to transfusion. Our study is focused on achieving a high level of virus inactivation simultaneously leaving blood products unaltered, measured by the level of degradation of coagulation factors, especially in third world countries where virus contamination of blood products poses a major problem. Virus inactivation plays an important role, especially in the light of newly discovered or unknown viruses, which cannot be safely excluded via prior testing. Methods Taking into account the necessary protection of the relevant coagulation activity for plasma, the basis for a sterile virus inactivation under shielding gas insufflation was developed for future practical use. Influence of frequency and power density in the range of soft and hard cavitation on the inactivation of transfusion-relevant model viruses for Hepatitis-(BVDV = bovine diarrhea virus), for Herpes-(SFV = Semliki Forest virus, PRV = pseudorabies virus) and Parvovirus B19 (PPV = porcine parvovirus) were examined. Coagulation activity was examined via standard time parameters to minimize reduction of functionality of coagulation proteins. A fragmentation of coagulation proteins via ultrasound was ruled out via gel electrophoresis. The resulting virus titer was examined using end point titration. Results Through CO2 shielding gas insufflation—to avoid radical emergence effects—the coagulation activity was less affected and the time window for virus inactivation substantially widened. In case of the non-lipidated model virus (AdV-luc = luciferase expressing adenoviral vector), the complete destruction of the virus capsid through hard cavitation was proven via scanning electron microscopy (SEM). This can be traced back to microjets and shockwaves occurring in hard cavitation. The degree of inactivation seems to depend on size and compactness of the type of viruses. Using our pre-tested and subsequently chosen process parameters with the exception of the small PPV, all model viruses were successfully inactivated and reduced by up to log 3 factor. For a broad clinical usage, protection of the coagulation activities may require further optimization. Conclusions Building upon the information gained, an optimum inactivation can be reached via raising of power density up to 1200 W and simultaneous lowering of frequency down to 27 kHz. In addition, the combination of the two physical methods UV treatment and ultrasound may yield optimum results without the need of substance removal after the procedure.

Welding of ferritic steel tube material T91 (9Cr-1Mo), was used because of high temperature withstanding, mechanical properties, compatibility with chemicals and adequate weldability. The main objective of this project is to find out near optimum welding parameters with appropriate shielding gas in gas tungsten inert gas welding (GTAW) of T91 tube. The quality and productivity of the weld joint strongly depends on welding parameters. The perfect arc during welding is produced when the welder uses the optimum welding parameters. The composition of shielding gas plays an important role ensuring sound quality of welds. The composition of shielding gas with the molten pool has a marginal influence in the depth of penetration. The optimized parameters with three samples were prepared with different purging gases Viz. 100% helium, 100% Argon, Argon 50% plus Helium 50% for welding of 2.9 mm thick T91 tube with ER 505 filler wire.

As improving fuel economy and performance through weight reduction in vehicles are recognized as important tasks, the defense industry is researching ways to reduce the weight of armor plates for combat vehicles and increase bulletproof performance and durability. Most armor plates in combat vehicles are manufactured using weld joints. High-hardness armor (HHA) is used to make armor plates; however, its mechanical properties deteriorate because of hydrogen embrittlement and high-temperature softening during welding. Welding defects, such as pores and cracks, occur frequently. In this study, HHA steel was subjected to single-pulse gas metal arc welding (GMAW), and the welding performance of the shielding gas and heat input was analyzed by the United States army tank-automotive and armaments command (TACOM) standard. The specimen cross-section was visually examined, and hardness, tensile, and impact tests were used to identify the mechanical properties based on the welding conditions. Additionally, flux cored arc welding (FCAW) and GMAW were used and compared, and spatter image analyses were used to assess the integrity of the welding process of the HHA plate applied to a combat vehicle. As a result of the experiment, as the CO2 content and heat input increased, the mechanical strength of the welded zone and the integrity of the welding process deteriorated.

[Display omitted] • In-house developed activated flux for welding of 316L(N) stainless steel. • Identification of optimum shielding gas mixture based on arc stability studies. • Full-depth of penetration in 11 mm thick plate in single pass welding with optimised parameters at reduced heat input. • Joining of 20 mm thick plate by double side A-TIG welding technique. In the present study, type 316L(N) bead-on-plates were welded using Activated-Tungsten Inert Gas (A-TIG) welding process with argon and helium gas at various ratios to evaluate the arc characteristics. The welding process parameters including shielding gas composition were optimized using the design of experiments to join 11 mm thick plate in a single pass. In addition, the A-TIG welding technique using optimized process parameters was developed to weld plates up to 20 mm thickness with significantly reduced heat input. High power density of helium arc shielding leads to constricted arc column that enhances arc efficiency and produces deeper penetration. [ABSTRACT FROM AUTHOR]

It is common to use argon as the shielding gas for laser conduction welding of thin aluminum parts with a filler wire in the automotive industry. However, defects such as skips (i.e., discontinuities), holes in the weld, or a rough weld surface are commonly found when using argon as a shielding gas due to poor wettability. A new shielding gas mixture was developed in this study. With the addition of small amounts of active gases to an argon-based mixture, the wettability of the weld pool was significantly improved, yielding decreases in defectivity, improved penetration of the weldment, as well as a more stable welding process. The developed shielding gas mixtures could improve weld quality when compared to pure argon in laser wire conduction welding of different types of aluminum alloys in coach joint configuration. Energy dispersive spectroscopy (EDS) and wavelength dispersive spectroscopy (WDS) were used to detect the nitrogen and oxygen concentrations in the weld. The results show there is no noticeable increase in the oxygen or nitrogen concentration in the weld zone compared to the base metal when using the developed gas mixtures as shielding gas. Rising displacement testing was performed, it is shown that the weld strength obtained with the developed shielding gas mixtures is no less than that obtained with argon. [ABSTRACT FROM AUTHOR]

An 80%Ar-10%CO2-10%He ternary gas mixture was used as the shielding gas during the narrow-gap welding of thick Q690E high-strength steel plates. Complete and defect-free welded joints were obtained, and the microstructure and mechanical properties of the welded joint were investigated. The weld zone consists of a solidification area and interlayer zone, and the heat-affected zone consists of a coarse-grain heat-affected zone (CG-HAZ) and a fine-grain heat-affected zone (FG-HAZ). The microstructures of the weld zone are mainly lath bainite (LB), acicular ferrite (AF), and granular bainite (GB). The microstructure of the CG-HAZ is lath martensite (LM) and the microstructure of FG-HAZ is GB. Methods with different heat inputs were used to study their effects on the mechanical properties of the welded joint. It was found that the microstructure and mechanical properties of the welded joints are better with lower heat input. With tandem wire narrow-gap GMA welding, the tensile strength of the joints declined from 795.3 to 718.3 MPa and the impact toughness at −40 °C resulted in a weak position in the weld zone, which declined from 76~81 J to 55~69 J, when the welding speed reduced from 350 to 250 mm/min. With oscillating-arc narrow-gap GMA welding, the tensile strength achieved 853.4 MPa and the impact toughness at −40 °C was around 69~87 J. The results indicated that, under the appropriate heat input, the tensile strength of the joint exceeds 770 MPa and the low temperature impact toughness at −40 °C exceeds 69 J. A 155 mm-thick Q690E steel welded joint was obtained and the mechanical properties of the welded joint meets the requirements of the offshore drilling platforms.

The metal transfer behavior of gas metal arc welding in a pure argon shielding gas was evaluated through experiments using a standard solid wire and a metal-cored wire. The investigation was conducted using observation techniques based on recording images by a high-speed camera equipped with laser assistance and bandpass filters in a range of welding currents. It was observed that the metal transfer mode became a streaming transfer mode when the welding current increased in the solid wire. Meanwhile, in the metal-cored wire, the droplet transfer frequency increased, and the droplet diameter decreased without changing the metal transfer mode in the globular transfer mode. We surmised that the streaming transfer in the solid wire would be caused by the spread of argon plasma at the wire tip, which decreases the effect of the electromagnetic force on droplet detachment. Conversely, due to the presence of flux inside the metal-cored wire, the argon plasma could not spread and was attached close to the iron vapor plasma at the overhead of the droplet. Hence, the electromagnetic force acting on the side of the unmelted flux was ineffective at promoting droplet detachment, preventing the transition to a streaming transfer mode. Furthermore, weld bead formation in the metal-cored wire was better than that in a conventional solid wire.

Growing awareness for occupational safety in the welding environment needs a sustainable welding system. Welding gases releases toxic tiny particles and gases that inflict severe health consequences in the weld zone are unsolicited. Some of the other main adverse effects are lung disease, hemoptysis, pulmonary inflammation, pneumoconiosis, etc. GMAW procedure has been used for welding 316L stainless steel plates of 3 mm, 5 mm, and 6 mm. Various current configurations with gas flow rate of 5 LPM, 10 LPM and 15 LPM were also used to achieve optimum butt joint performance and to reduce the production rate of fume contributing to cost-effectiveness. In this research a cost-effective fume extraction hood was fabricated for measuring Emission factor produced during welding. Various shielding gas compositions including Pure Argon, Pure CO2, 92% Ar+8% CO2 and 88% Ar+12% CO2 were used to determine the best operating parameters in the GMAW method. To satisfy the latest Permissible Exposure Limit (PEL) legislation, optimum technical parameters for efficient welding were acknowledged with the lowest emission factor. A maximum reduction of Emission factor can be achieved by using Pure Argon. The inclusion of CO2 as a shielding gas mixture gives higher emission factor when compared to Pure Argon. Very low emission factor were witnessed in this research when compared to previous investigations. Lower emission factor of 2941.17 mg/kg of electrode, 4411.76 mg/kg of electrode and 7352.94 mg/kg of electrode were obtained for pure argon as shielding gas with 150 A welding current. [ABSTRACT FROM AUTHOR]

This paper present the algorithm for calculating the electric arc as a heat source in the arc welding processes, but also the dependence between it and the calorific value developed, because the quality of welded seams has a decisive influence in terms of reliability of welded structures. [ABSTRACT FROM AUTHOR]

Wire arc additive manufacturing (WAAM) is the process by which large, metallic structures are built, layer-by-layer, using a welding arc to melt wire feedstock. In this process, the proper selection of the shielding gas plays a vital role in the achievement of structurally acceptable part geometries and quality surface finishes. In this study, the authors used either a ternary mix (He, Ar and CO2) or a binary mix (Ar and CO2) of shielding gases to deposit wall geometries using an open loop-controlled WAAM system developed at Oak Ridge National Laboratory’s Manufacturing Demonstration Facility. The binary blend produced a wider and shorter geometry, while the ternary blend resulted in a narrower build that was more equivalent to the CAD geometry. The data indicated that the binary blend provided a higher oxygen concentration in the weld as compared to that of the ternary blend. The results imply that the arc characteristics and heat input had a significantly higher impact on the weld penetration than the surface tension effect of surface active elements. This was further verified by developing and applying a high-fidelity computational fluid dynamics (CFD) model of the thermophysical properties of gas mixtures. The results from the model showed that, while the influence of increased oxygen concentration on the surface tension for the binary blend led to a deeper penetration, the ternary blend gave rise to heat flux to the workpiece.

This paper presents an investigation into effect of nitrogen content of shielding gas mixture on weld geometry, microstructure and hardness of pulsed laser welded 2205 duplex stainless steel. Full penetration autogenous welding was performed on 2 mm thick plates using a low power pulsed Nd: YAG laser. light and scanning electron microscopy were used to study the resulting microstructures. It is observed that 2 mm full penetrated joint decreases to 1.8 mm by dominating nitrogen in argon-nitrogen mixture. Different morphologies of austenite phase as well as an increase of 8% of its content can be observed in pure nitrogen shielded welds. Average weld grain size in sample which is welded in nitrogen atmosphere stands at approximately 41 µm which is smaller than that of argon atmosphere which is about 51 µm. Micro-hardness test reveals that hardness values increase from 280 HV in base metal to 307 HV in weld center line and the shielding gas mixture does not significantly influence the weld hardness. [ABSTRACT FROM AUTHOR]

The effect of a shielding gas on the plasma flow of an electric arc and molten metal is studied. The effect of the shielding gas on the plasma flow of the electric arc of molten metal is simulated, and a mathematical model is developed that describes the flow of the plasma-forming gas inside a device that forms the necessary directions of plasma flows to form a droplet of molten electrode metal of the required size. It is established that the shielding gas and its pressure affect the gas outflow rate and the formation and size of an electrode metal drop. The time of the formation and detachment of the droplet changes at the increase in the pressure of the shielding gas, the higher the gas pressure, the smaller the volume of the droplet. Argon and carbon dioxide have different effects on the plasma flow of the electric arc, the length of the arc, the formation and detachment of the droplet. The process of the droplet formation can be controlled by changing the gas composition, pressure, and gas velocity. It is determined that the gas flow rate increases from 1.2 to 5.2 m/s and the volume of a droplet of molten electrode metal decreases at the increase in the gas flow from 10 to 30 L/min. The droplet volume can be changed on average by 65% depending on the shielding gas. [ABSTRACT FROM AUTHOR]

Blue light emitted during arc welding is known to potentially cause photoretinopathy. To help prevent retinal injury, it is important to identify the hazards associated with various welding conditions. The present work conducted experiments involving gas metal arc welding of mild steel under various conditions, and measured the spectral radiance of the arcs. The effective radiance values, as used by the American Conference of Governmental Industrial Hygienists (ACGIH) to quantify exposure level of blue light, were subsequently calculated from the data. The resulting values were in the range of 5.0-118 W/cm 2 /sr, corresponding to hazardous levels according to ACGIH guidelines. The effective radiance was increased at higher welding currents and when pulsed currents were used rather than steady currents. The blue light hazard was also affected by the type of shielding gas employed. These data confirm that it is very hazardous to stare at arcs during gas metal arc welding of mild steel. As such, appropriate eye protection is necessary during arc welding, and directly staring at the arc should be avoided.

The intention of this study was to create information for welders and engineers in regards to 202 (200-series) austenitic grade stainless steel as a low cost alternative for the replacement of 300-series stainless steel. The content of this paper discusses the effects of different heat inputs and different nitrogen mixes in the argon shielding gas using the GTA welding process. This paper discusses the effects to the microstructure, mechanical properties and corrosion resistance of the weld metals. The results of this study indicate that reducing the heat input when welding caused the width of the face and root of the weld bead to be narrower. The microstructure (delta ferrite, dendrite length and interdendrite spacing) tended to decrease and the hardness and ultimate tensile strength tended to rise. In addition, the percentage of elongation decreased while the pitting corrosion resistance increased. An increase of nitrogen in the argon shielding gas did not cause the width of the weld bead to change. However, the volume of delta ferrite, dendrite length and inter-dendrite spacing reduced and the hardness and ultimate tensile strength increased. The percentage of elongation was shown to decrease and the pitting corrosion resistance tended to increase. The test results of this work focused on increasing productivity and reducing the cost of production from the use low nickel stainless steel in the fabrication industries of Southeast Asia.

This research aims to find an inexpensive solution for the problem of welding stainless steel. Cheaper grade stainless steel is popular in Southeast Asia. In this present study, weld bead shape, microstructure, mechanical properties and corrosion behavior of SUS 201 austenitic stainless steel weld joint through the GTA welding process with filler metal grade RE 310 SS are studied. Welding was undertaken under four different conditions with shielding gases at 100%Ar, 1%H2 + 99%Ar, 3%H2 + 97%Ar and 5%H2 + 95%Ar were compared. The results gained from this investigation indicate that the weld joint mixtures of hydrogen with increased argon shielding gas showed no defects of the weld, increased weld bead size (slightly increased due to the welding speed increased in tandem), reduced delta-ferrite, decreased hardness and ultimate strength. However, the pitting corrosion area occurred at the interface between the delta-ferrite phase and the austenite phase because of low chromium in this region.

The laser welding of magnesium alloys, largely used in many fabrication applications, has gained considerable interest especially in aerospace, electronics, automotive industry etc. Unfortunately, this process is associated to an undesired phenomenon which is “oxidation”. For this reason, a good shielding system of the welding zone is of major importance. This paper presents a numerical study using computational fluid dynamics (CFD) of a laser welding process employing a moving volumetric heat source. Starting with the turbulence model validity, a parametric study of this welding process in a vertical position aiming to optimize the design of protection gas device, the gas jet inclination, the appropriate welding direction and the gas type is, then, proposed. The optimum parametric combination ensuring the largest gas coverage area is the one where the shielding gas is Argon, supplied by the coaxial nozzles at a downward inclination angle with respect to the laser beam axis, and a downward welding direction.

CO2 gas-shielded arc welding, which is widely used in the industrial world, has been recognized as an efficient and economical GMA welding process. However, its characteristic repelled transfer produces a large amount of spatter which results in costly cleanup and, thus, practical methods to overcome this weakness have been highly demanded. In the series of this study, 'Pulsed Gas MAG' welding was proposed as a new approach to reducing spatter, in which Ar gas pulses were periodically injected into CO2 shielding gas so that gas composition of arc atmosphere was largely modified in a very short period of time and a metal droplet formed at the electrode tip during CO2 atmosphere was released before repelled transfer had occurred. In this report, the influence of parameters of Ar gas injections, such as frequencies, average gas flow rates and gas injection periods, on the metal transfer was investigated. It was found that synchronous metal transfer stimulated by pulsed Ar gas injections was achieved at any frequencies from 35 to 65 Hz under the conditions of gas injection periods longer than 4 ms and of Ar gas volumes larger than approximately 1mL/pulse. This is because Ar gas injections below these critical levels resulted in lack of time for arc shape changes and metal drop detachment. From these experimental results, a model to explain the metal transfer phenomena was developed. The amount of spatter was reduced to the levels as low as that of the conventional MAG welding with 80 %Ar +20 %CO2 shielding gas mix and penetration profiles were round shape like those obtained in CO2 arc welding. [ABSTRACT FROM AUTHOR]

Background: Aim of the present study is the evaluation of ultrasound as a physical method for virus inactivation in human plasma products prior to transfusion. Our study is focused on achieving a high level of virus inactivation simultaneously leaving blood products unaltered, measured by the level of degradation of coagulation factors, especially in third world countries where virus contamination of blood products poses a major problem. Virus inactivation plays an important role, especially in the light of newly discovered or unknown viruses, which cannot be safely excluded via prior testing. Methods: Taking into account the necessary protection of the relevant coagulation activity for plasma, the basis for a sterile virus inactivation under shielding gas insufflation was developed for future practical use. Influence of frequency and power density in the range of soft and hard cavitation on the inactivation of transfusion-relevant model viruses for Hepatitis-(BVDV = bovine diarrhea virus), for Herpes-(SFV = Semliki Forest virus, PRV = pseudorabies virus) and Parvovirus B19 (PPV = porcine parvovirus) were examined. Coagulation activity was examined via standard time parameters to minimize reduction of functionality of coagulation proteins. A fragmentation of coagulation proteins via ultrasound was ruled out via gel electrophoresis. The resulting virus titer was examined using end point titration. Results: Through CO2 shielding gas insufflation—to avoid radical emergence effects—the coagulation activity was less affected and the time window for virus inactivation substantially widened. In case of the non-lipidated model virus (AdV-luc = luciferase expressing adenoviral vector), the complete destruction of the virus capsid through hard cavitation was proven via scanning electron microscopy (SEM). This can be traced back to microjets and shockwaves occurring in hard cavitation. The degree of inactivation seems to depend on size and compactness of the type of viruses. Using our pre-tested and subsequently chosen process parameters with the exception of the small PPV, all model viruses were successfully inactivated and reduced by up to log 3 factor. For a broad clinical usage, protection of the coagulation activities may require further optimization. Conclusions: Building upon the information gained, an optimum inactivation can be reached via raising of power density up to 1200 W and simultaneous lowering of frequency down to 27 kHz. In addition, the combination of the two physical methods UV treatment and ultrasound may yield optimum results without the need of substance removal after the procedure. [ABSTRACT FROM AUTHOR]

is shown in the work that at laser-plasma welding of 3 mm stainless steel SUS304, using disc laser radiation, a stable manifestation of the synergistic effect and a ratio of powers of the laser and plasma components of 1:1 – 1:3 were found, that allows the penetration depth to be increased by approximately 25% without any change in the welding speed. The stability of the synergistic effect and increase of penetration depth are affected by the ratio of powers of the process components, method of feeding and composition of the shielding gas. In order to improve the hybrid welding effectiveness at coaxial feed of shielding and plasma gases, it is rational to use an additive of 2 – 3% oxygen to shielding gas argon. Stabilization of the synergistic effect due to selection of the mode parameters and shielding gas composition allows replacing up to 40% of the laser power by plasma power. The strength of joints of stainless steel SUS304, produced by hybrid laser-plasma welding, is equal to approximately 95% of that of the base metal. [ABSTRACT FROM AUTHOR]

It is shown in the work that laser-plasma welding of 3 mm SUS304 stainless steel, using disc laser radiation, a stable manifestation of the synergistic effect and a ratio of powers of the laser and plasma components of 1:1-1:3 were found that allows penetration depth to be increased by approximately 25 % without any change in the welding speed. The stability of the synergistic effect and increase of penetration depth are influenced by the ratio of powers of the process components, method of feeding and composition of the shielding gas. In order to improve the hybrid welding effectiveness at coaxial feed of shielding and plasma gases, it is rational to use an additive of 2-3 % oxygen to shielding gas argon. Stabilization of the synergistic effect due to selection of mode parameters and shielding gas composition, allows replacing up to 40 % of the laser power by plasma power. The strength of joints of SUS304 stainless steel produced by hybrid laser-plasma welding is equal to approximately 95 % of that of the base metal. 8 Ref., 1 Table, 7 Figures. [ABSTRACT FROM AUTHOR]

Featured Application: Wire arc additive manufacturing has been applied in aerospace (such as stiffened panels, wing ribs), nuclear energy, marine (such as ship's propeller) and architecture (such as steel bridge) industries. Wire arc additive manufacturing (WAAM) has been considered as a promising technology for the production of large metallic structures with high deposition rates and low cost. Stainless steels are widely applied due to good mechanical properties and excellent corrosion resistance. This paper reviews the current status of stainless steel WAAM, covering the microstructure, mechanical properties, and defects related to different stainless steels and process parameters. Residual stress and distortion of the WAAM manufactured components are discussed. Specific WAAM techniques, material compositions, process parameters, shielding gas composition, post heat treatments, microstructure, and defects can significantly influence the mechanical properties of WAAM stainless steels. To achieve high quality WAAM stainless steel parts, there is still a strong need to further study the underlying physical metallurgy mechanisms of the WAAM process and post heat treatments to optimize the WAAM and heat treatment parameters and thus control the microstructure. WAAM samples often show considerable anisotropy both in microstructure and mechanical properties. The new in-situ rolling + WAAM process is very effective in reducing the anisotropy, which also can reduce the residual stress and distortion. For future industrial applications, fatigue properties, and corrosion behaviors of WAAMed stainless steels need to be deeply studied in the future. Additionally, further efforts should be made to improve the WAAM process to achieve faster deposition rates and better-quality control. [ABSTRACT FROM AUTHOR]

To reduce the consumption of gas metal arc welding shielding gas and improve welding quality, three spiral-diffusion nozzles with different structures were designed in this study. The four evaluation indexes of the flow field quality of shielding gas were determined by analyzing the protective airflow field with the computational fluid dynamics simulation method. Isight software was used to optimize the multi-objective parameters of the three spiral-diffusion nozzles with the self-adaptive mutation genetic algorithm. Combined with the computational fluid dynamic simulation results, the optimized value of each nozzle and the percentage of parameters such as gas reduction were obtained. Three new double-helical spiral-diffusion stainless nozzles were created using 3D printing, and the gas metal arc welding of the Q235 and A36 steel plates was performed using 80% Ar + 20% CO2 mixed shielding gas with three nozzles. The tensile test and impact test were conducted to inspect tensile strength and impact toughness, and the hardness and average grain grade of microstructures in the weld seam were analyzed. The experimental results were consistent with the optimization simulation results. In terms of welding quality, compared with the shielding gas consumption of the conventional nozzle, that of the optimized spiral-diffusion nozzles I, II, and III could be reduced by 29.22%, 33.19%, and 27.31%, and the effective protection range could be increased by 34.53%, 19.79%, and 19.69%, respectively. [ABSTRACT FROM AUTHOR]

Ferrite number (FN) is a crucial parameter for austenite steel welding product, since it has significant influences on the crack sensitivity and ductility at cryogenic temperature. Normally, the FN is measured using a Feritscope or predicted according to WRC-1992 and the results generally match. This investigation detected the FN of 304L stainless steel multi-pass GTAW joint protected by mixed shielding gas with different N2 additions; the measured FN did not match with the FN predicted through WRC-1992 as the N2 content was more than 1%. The microstructure showed that a fully austenitized zone formed at the inter-bead of the joint shielded with Ar–1.0%N2 and Ar–1.5%N2, which resulted in the inaccuracy of the FN predicted through WRC-1992. The formation mechanism of the fully austenitized zone was proposed based on the nitrogen solubility and equilibrium phase transformation map. It is suggested that traditional prediction diagrams cannot give an accurate prediction of the FN during the multi-pass process shielded with N2 addition. [ABSTRACT FROM AUTHOR]

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In this research article, the effect of welding process parameters such as arc welding current, arc voltage, wire feed speed, and shielding gas flow rate on mechanical and metallurgical properties of IS 2062 Grade A steel bonded by MIG welding was investigated. In this experimental work, parent metal was welded by an ER70S-6 filler wire in the presence of a mixture of 75%Ar+25% CO gases for shielding purpose. The Toughness of weldment was 2 determined as mechanical properties. In metallurgical investigation of the weldment, Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were used. Fracture surfaces of notched toughness specimens were examined after toughness test. From experimental results, it was observed that on increasing the arc voltage, toughness value of weldment decreased and the grain size of microstructure of weldment varied throughout the weldment surface. Microstructure of weldment was also found influenced by the composition of shielding gases. [ABSTRACT FROM AUTHOR]

Today, the quality of welded seams is often examined off-line with either destructive or non-destructive testing. These test procedures are time-consuming and therefore costly. This is especially true if the welds are not welded accurately due to process anomalies. In manual welding, experienced welders are able to detect process anomalies by listening to the sound of the welding process. In this paper, an approach to transfer the “hearing” of an experienced welder into an automated testing process is presented. An acoustic measuring device for recording audible sound is installed for this purpose on a fully automated welding fixture. The processing of the sound information by means of machine learning methods enables in-line process control. Existing research results until now show that the arc is the main sound source. However, both the outflow of the shielding gas and the wire feed emit sound information. Other investigations describe welding irregularities by evaluating and assessing existing sound recordings. Descriptive analysis was performed to find a connection between certain sound patterns and welding irregularities. Recent contributions have used machine learning to identify the degree of welding penetration. The basic assumption of the presented investigations is that process anomalies are the cause of welding irregularities. The focus was on detecting deviating shielding gas flow rates based on audio recordings, processed by a convolutional neural network (CNN). After adjusting the hyperparameters of the CNN it was capable of distinguishing between different flow rates of shielding gas.

The use of shielding gases in laser beam welding is of particular interest for materials interacting with ambient oxygen, e.g., copper, titanium or high-alloy steels. These materials are often processed by remote laser beam welding where short welds (e.g., up to 40 mm seam length) are commonly used. Such setups prevent gas nozzles from being carried along on the optics due to the scanner application and a small area needs to be served locally with inert gas. The article provides systematic investigations into the interaction of laser beam processes and parameters of inert gas supply based on a modular flat jet nozzle. Based on the characterization of the developed nozzle by means of high-speed Schlieren imaging and constant temperature anemometry, investigations with heat conduction welding and deep penetration welding were performed. Bead-on-plate welds were carried out on stainless steel AISI 304 for this purpose using a disc laser and a remote welding system. Argon was used as shielding gas. The interaction between Reynolds number, geometrical parameters and welding/flow direction was considered. The findings were proved by transferring the results to a complex weld seam geometry (C-shape).

Ferrite number (FN) is a crucial parameter for austenite steel-welding products, since it has a specific relationship with crack sensitivity and other important properties. In this paper, artificial neural network (ANN) models were built to predict FN, based on the GTAW tests of 304L plates produced by two different steelworks, Dongfang Special Steel hot-rolled sheet (DFSS) and Anshan Iron and Steel cold-rolled sheet (ASIS). The results show that a high performance, of more than 98% accuracy, can be achieved when the models of DFSS and ASIS are modeled separately, and that accuracy is also above 96% when an integrated model is built. The influences of nitrogen content and multiwelding parameters, such as travel speed, wire-feed rate, welding current and arc length, on FN are also analyzed through the FN-prediction model for DFSS. The results show that FN increases monotonously with the increase of nitrogen content, but the influences of either of the other two parameters on FN are nonlinear.

Vacuum laser beam welding enables deeper penetration depth and welding stability than atmospheric pressure laser welding. However, contaminated coupling glass caused by welding fumes in the vacuum space reduces laser transmittance, leading to inconsistent penetration depth. Therefore, a well-designed protective system is indispensable. Before designing the protective system, the contamination phenomenon was quantified and represented by a contamination index, based on the coupling glass transmittance. The contamination index and penetration depth behavior were determined to be inversely proportional. A cylindrical protective system with a shielding gas supply was proposed and tested. The shielding gas jet provides pressure-driven contaminant suppression and gas momentum-driven contaminant dispersion. The influence of the shielding gas flow rate and gas nozzle diameter on the performance of the protective system was evaluated. When the shielding gas flow was 2.0 L/min or higher, the pressure-driven contaminant suppression dominated for all nozzle diameters. When the shielding gas flow was 1.0 L/min or lower, gas momentum-driven contaminant dispersion was observed. A correlation between the gas nozzle diameter and the contamination index was determined. It was confirmed that contamination can be controlled by selecting the proper gas flow rate and supply nozzle diameter. [ABSTRACT FROM AUTHOR]

Statistical models were developed to study the effect of gas metal arc welding process parameters (i.e., wire feed speed, voltage, travel speed, and shielding gas chemistry) on the resultant weld bead width, penetration, and reinforcement height, using a factorial design of experiment. Analysis of variance (ANOVA) indicated that the weld width depended on voltage, travel speed, gas type, and the interactions between these factors. The weld penetration depended only on wire feed speed and gas type, as well as the two-way interactions of wire feed speed with travel speed and gas type. Reinforcement height depended on travel speed, wire feed speed, and their two-way interactions with gas type. Residual analysis revealed that all assumptions inherent in the regression analysis were satisfied over the range of welding parameters considered in this study. The predictive power of the statistical models was validated using intermediate process parameter values in the experimental design, and it was found that predicted values were mainly in agreement with the measured values for a 95% prediction interval. [ABSTRACT FROM AUTHOR]

The laser-arc hybrid welding test of high nitrogen steel was carried out to solve the porosity and nitrogen loss of high nitrogen steel during welding. The effects of shielding gas composition, welding wire composition and ultrasonic vibration on the porosity and nitrogen content of welded joint were investigated. The results show that, when the shielding gas is Ar+N2, the nitrogen content of welded point increases with the proportion of nitrogen in the shielding gas, and the porosity decreases first and then increases. When 2% O2 is added to Ar+N2, the nitrogen content and porosity increase obviously. With the increase in the proportion of nitrogen, the nitrogen content in welded joint increases, but the porosity changes irregularly. With the increase in nitrogen content in the welding wire, the nitrogen content of welded joint increases first and then decreases, and the porosity decreases first and then increases. With the increase in ultrasonic power, the nitrogen content of welded joint decreases slightly, and the porosity decreases first and then increases. Appropriate shielding gas and welding wire composition can be used to improve the nitrogen content of welded joint, and inhibit the formation of weld porosity. The porosity is suppressed in the best effect when the ultrasonic power is 180 W. [ABSTRACT FROM AUTHOR]

The Nd: YAG pulsed laser welding process with different speed and shielding gas was applied on 2205 duplex stainless steel. The effects of different parameters on the microstructural evolutions and mechanical properties were investigated. Four different zones with different secondary austenite contents were observed in the weld microstructure. By changing the shielding gas from argon to nitrogen, the secondary austenite percentage was not significantly varied. The secondary austenite fraction was showed about 38% reduction with increasing the welding speed. The weld penetration depth decreased with changing the shielding gas from argon to nitrogen (about 26% and 14% reduction at speed of 3.8 and 8.3 mm/s, respectively) and increasing the welding speed (about 43% and 34% reduction under shielding gas of argon and nitrogen, respectively). The variations in microhardness values along the weld line were correlated to the microstructural characterizations. Changing the welding speed had no significant effect on the microhardness variations, but changing the shielding gas from argon to nitrogen caused a significant increase of microhardness. [ABSTRACT FROM AUTHOR]

The paper deals with the evaluation of the shielding gas influence on the properties of titanium Grade 2 weld joints produced with disk laser. Butt weld joints were produced under different shielding gas types, namely Ar, He, Ar + 5 vol.% He, Ar + 30 vol.% He, and without shielding weld pool. Light and electron microscopy, microhardness measurements, computed tomography, and tensile testing were used for evaluation of weld joint properties. He-shielded weld joints were the narrowest ones. On the other hand, Ar-shielded weld joints exhibited the largest weld width. The choice of shielding gas had a significant influence on the porosity of welds. The lowest porosity was observed in the weld joint produced in Ar with the addition of 30 vol.% He shielding atmosphere (only 0.03%), while the highest level of porosity was detected in weld joint produced without shielding gas (0.76%). Except for unshielded titanium Grade 2 weld joint, the lowest tensile strength was recorded in Ar-shielded weld joints. On the contrary, the highest average microhardness, except unshielded weld joint, was measured in He-shielded weld joints. [ABSTRACT FROM AUTHOR]

Shielding gases are used in laser welding mainly for protecting the weldment from contamination during welding and solidification. However, the change in shielding gas composition has shown to alter the properties of the laser welds. In the present work, the effect of shielding gases in CO2 laser welding on metallurgical, hardness and indentation creep properties of P92 material was studied. Experiments were carried out in bead on plate mode using three different shielding gases, viz., Ar, He and Ar + 20% N2. Defect-free welding could be achieved with a wide range of parameters with all the three shielding gases used for experimentation. With respect to bead geometry characteristics, He resulted in good penetration with narrow width followed by Ar + 20% N2 and then Ar. The microstructural analyses indicated that welds had tempered martensitic structure after post-weld heat treatment (PWHT) with no deleterious δ-ferrite phase for a wide range of heat inputs. δ-ferrite phase could be observed at very high heat inputs (> 360 J/mm). The amount of δ-ferrite is dependent on the shielding gas composition. High heat input welds made with Ar + N2 gas mixture had very low δ-ferrite content compared to welds made with He. Hardness values were comparatively higher for welds made with Ar + N2 mixture in both as-welded and PWHT conditions. Indentation creep properties of welds were better than the base material. Among the three shielding gases experimented, welds made with Ar + N2 mixture had superior indentation creep properties followed by welds made with Ar and finally He. [ABSTRACT FROM AUTHOR]

Abstract The mixing of hydrogen in Ar-N 2 shielding gas could produce a Fe-15.7 wt.% Cr-8.5 wt.% Mn steel weld bead shape in accordance with ISO 5817 quality level B at the welding speed of 5.4 mm s–1. At this speed the acceptable weld bead shape could not be obtained when using Ar-N 2 as the shielding gas. The beneficial role of hydrogen could improve the welding productivity. At the same welding speed, the addition of hydrogen in the Ar-N 2 shielding gas reduced the concentration of nitrogen dissolved in the weld, thus reducing the austenite stabilising effect due to nitrogen and increasing the delta ferrite content in the weld. Mixing hydrogen in the Ar-N 2 shielding gas considerably reduced the weld oxidation rate, possibly from the hydrogen dissolved in the oxide. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Analyzing the perpendicular and longitudinal sections of the laser welded joints of AA6061-T6, it was confirmed that adding an interface gap between two plates could improve the esthetic appearance and reduce porosity formation. The use of helium as shielding gas yielded a further increase of the weld seam quality in terms of porosity and mechanical properties. The resultant microstructure in the weld zone was analyzed in terms of cooling rate and temperature gradient calculated from the predictive 3D welding model. The failure mechanisms during tensile-shear and cross-tension tests are also analyzed via finite element modeling based on the measured micro-hardness distributions. [ABSTRACT FROM AUTHOR]

The requirements of microfeature-based systems are essentially increasing due to their usage in every major field. Market needs microproducts with more functionality, information processing ability integrated together with compact size. Electro-discharge deposition process is an emerging nonlithographic, additive process to manufacture high aspect ratio 3D microfeatures. The current research work develops and investigates the application of magnetic field and shielding gas in the electro-discharge deposition process with experimental work and simulation model. Response surface methodology model is developed to perform parametric analysis and to ascertain the significance of introducing magnetic field and shielding gas in an electro-discharge deposition process. Results from atomic force microscope and optical image microscope shows that at higher magnetic field the deposition height increases with reduced width. From the EDAX compositional analysis, it is noted that the presence of shielding gas increases the percentage of copper composition and reduces the carbon and oxygen composition in the deposited material. The obtained results confirmed that the presence of magnetic field and shielding gas significantly improves the deposition process. [ABSTRACT FROM AUTHOR]

Abstract Deposition of superhydrophobic coatings on glass substrates from hexamethyldisiloxane (HMDSO) precursor using an argon plasma jet at a relatively low power frequency (11.5 kHz) was studied. The coating hydrophobicity was first found to be strongly dependent on the gaseous shield. Nitrogen (N 2) rather than inert gases (argon, Ar, and helium, He) had an excellent shielding effect against the interference of ambient air on the plasma jet. The evolution of water contact angle (WCA) of the prepared coating was investigated upon the variations of the operating parameters, such as N 2 /Ar ratio, HMDSO concentration, deposition time and nozzle-to-substrate distance. Generally, the measured WCA gradually increased with increasing the values of these parameters and then leveled off at some specific values, except for the nozzle-to-substrate distance. The wettability of glass was completely switched from hydrophilicity to superhydrophobicity with the WCA reaching 168° and the sliding angle of about 3° at optimum conditions. The surface morphology analyses by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that the prepared coating had a very high surface roughness and micro-nano structure, which intensely promoted the water repellence property. The chemical examination by X-ray photoelectron spectroscopy (XPS) clearly showed the shielding effect on the surface chemical composition of the coating. N 2 shield preserved a high carbon content (in CH 3 groups) from the precursor, while minimizing the incorporation of oxygen into the coating surface. Also, it was found that O (from O and OH radicals) has replaced C to form silica-like coating in case of without shielding gas or with Ar and He shields. Highlights • Superhydrophobic coatings using atmospheric pressure plasma jet • N 2 possessing an excellent shielding effect due to its high ionization potential • Plasma jet capable of producing micro-nano structured coatings [ABSTRACT FROM AUTHOR]

• He can more effectively suppress the inverse bremsstrahlung absorption. • He can improve the transmittance rate of laser energy. • He can improve the absorption efficiency of materials to laser energy. • A larger gas flow can suppress the electron density and the IB absorption. According to the theory of plasma sheath layer, the charge-voltage of plasma was measured by the principle of plasma probe to investingage the effect of shielding gas on the plasma plume in bead-on-plate welding by pulsed laser. The electron temperature, electron density, IB linear absorption coefficient of plasma and transmittance rate are interrelated and important parameters to estimate the energy absorption mechanism in laser welding. The results showed that Helium atmosphere suppresses the plasma eruption in laser welding more effectively than the Argon atmosphere, which is shown to reduce the electron temperature of plasma and shorten the duration of plasma eruption. Compared with the suppressing effect of Argon atmosphere, Helium atmosphere can more effectively suppress the inverse bremsstrahlung absorption effect of plasma induced in laser welding, improve the transmittance rate of laser energy, so as to improve the absorption efficiency of materials to laser energy, which is conducive to higher welding efficiency. In addition, a larger shielding gas flow can also suppress the increase of electron density and the inverse bremsstrahlung absorption effect of plasma, and increase the transmittance rate of laser energy. So, a larger shielding gas flow in laser welding is beneficial to suppress the plasma eruption either in Helium atmosphere or in Argon atmosphere. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Argon-Hydrogen shielding gas mixture induced a steep temperature gradient and enhanced the instantaneous cooling rate of the weld. The welds obtained by Argon-Hydrogen have finer grain structure than the Argon-Shielded welds. The reduction of laves phase segregated at the interdendritic region has lower Niobium concentration which improves the corrosion resistance of the welds. [ABSTRACT FROM AUTHOR]