Hamidreza Pooreskandari, Masoud Goodarzi, Rouholah Ashiri,
Volume 9, Issue 2 (Journal OF Welding Science and Technology 2026)
Abstract
The superalloy Inconel 738LC is considered one of the most challenging alloys in welding processes due to its widespread use in gas turbine blades and its high microstructural sensitivity to heat. The most significant limitation in welding this alloy is its high susceptibility to hot cracking in the heat-affected zone (HAZ), which arises from the formation of intergranular liquid films during the welding thermal cycle. In this study, the effect of activated tungsten inert gas (A-GTAW) welding on the behavior of the heat-affected zone, liquid film thickness, and hot cracking susceptibility in Inconel 738LC superalloy was investigated. For this purpose, specimens were welded with various fluxes under approximately constant heat input conditions, and the effect of the active flux on weld geometry, HAZ width, and liquid film thickness was evaluated. The results showed that the use of active flux, by inducing arc constriction and altering the molten metal flow pattern due to the reverse Marangoni effect, leads to more effective heat transfer into the depth of the workpiece and reduces lateral heat dissipation. This resulted in a reduction of HAZ width and a decrease in liquid film thickness in some specimens. It was also found that cracking behavior is a function of the interaction between liquid film thickness and the contraction stress of the weld pool. In the flux-free specimen, despite the formation of a greater number of liquid films, none developed into hot cracks, which was attributed to greater stability of the liquid films and their ability to fill discontinuities. Overall, the results of this study indicate that the A-GTAW process can influence hot cracking susceptibility in Inconel 738LC superalloy by controlling the heat transfer pattern and liquid film formation conditions.
H.r. Pooreskandari, M. Goodarzi, R. Ashiri,
Volume 12, Issue 1 (Journal OF Welding Science and Technology 2026)
Abstract
Nickel-based superalloys are among the most critical materials used in high-temperature components of gas turbines, where their replacement costs and potential turbine damage necessitate effective protection and repair strategies. Optimizing repair methods to enhance efficiency and reduce costs has therefore been a continuous focus. The aim of this study is to improve the repair process of Inconel 738LC superalloy by reducing the susceptibility to liquation cracking. Activated tungsten inert gas (A-TIG) welding was performed on Inconel 738LC using a welding current of 60 A. Titanium dioxide (TiO2) powder was employed as an activating flux, and weldments with four flux concentrations were examined. The microstructure was characterized using optical microscopy and scanning electron microscopy. The results revealed that flux concentration had a significant influence on penetration depth, with a concentration of 1 g/mL producing the maximum effect. At this concentration, weld penetration increased by 68% and weld pool volume by 63%, while the heat-affected zone width decreased by 12%. Arc imaging and quantitative/qualitative analysis demonstrated a constricted and focused plasma arc column in the presence of TiO2 flux. Microstructural examinations further revealed suppression of columnar dendrite growth. It was found that TiO2 flux enhances weld penetration and pool volume by constricting the arc and activating a reversed Marangoni flow, while simultaneously reducing HAZ width. However, the increased weld pool volume also intensified contraction stresses, leading to liquation cracking in the weld with the largest pool volume.
