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Flux Bounded Tungsten Inert Gas Welding (FBTIG)
Published in P. Chakravarthy, M. Agilan, N. Neethu, Flux Bounded Tungsten Inert Gas Welding Process, 2019
P. Chakravarthy, M. Agilan, N. Neethu
The less stable metal oxides occupy higher positions in the Ellingham diagram as shown in Figure 4.15. Silica, calcium oxide and titania are the most commonly used flux materials, out of which silica has the lowest bond dissociation energy (less stable), which makes it a strong candidate for the choice of flux in flux-assisted welding processes. Since it has low dissociation energy, silica decomposes with lesser energy input and also ensures higher concentrations of SAE at the weld pool. This facilitates a lower amount (coating thickness) of flux at the joint surface for the FBTIG welding process, which provides the required SAE. Thinner coating also ensures less entrapment of flux particles in the case of ATIG welding. When the oxides that occupy lower positions in the Ellingham diagram are used as fluxes, thicker coatings are required with higher current and voltages during the welding process to ensure the critical amount of SAE. Neethu et al. (2019) investigated the shape of the welding arc for different fluxes as depicted in Figure 4.16. The arc formed during TIG welding is much wider than those using fluxes. When an activating flux is used, the arc constricts and caves causing an increased DWR. This happens because of the influence of insulation effect and the arc constriction effect. The former channels the arc root to the flux gap while the latter constricts the overall distribution of the arc. The most constricted arc is observed for SiO2 which yields a higher DWR. The low stability of SiO2 paves way for easier decomposition and better consequences of the mechanisms.
A systematic overview on activated-Tungsten inert gas welding
Published in Welding International, 2022
K. B. Vysakh, A. Mathiazhagan, S. Krishna Prasad
The stability of oxides formed during the A-TIG welding process from Ellingham diagram, which is a plot of the Gibbs free energy change (ΔG) for each oxidation reaction vs temperature, was inspected by Jayakrishnan et al. [15]. The authors compared the stability of TiO2 and SiO2 fluxes based on Ellingham diagram and observed that TiO2 flux is more stable than SiO2 which is based on the respective position of these fluxes in Ellingham Diagram. This implies that a high value of energy and temperature is needed to liquefy the TiO2 flux with respect to SiO2 flux. The existence of high amount of oxygen in the molten pool can result in an increased depth of penetration. The oxides with higher thermodynamic stability and melting points like ZrO2 and CaO are not preferred for austenitic SS [10]. The oxides in the top part of Ellingham diagram are the most stable oxides and as we move to the bottom portion of the diagram, the oxides become harder to reduce. However, if the decomposed oxygen content in the weld pool is excessive, inward Marangoni convection weakens, altering the flow to outwards and reducing weld penetration [24,25].