Critical grain boundary liquid film thickness range for liquation cracking susceptibility of IN738LC superalloy

• This study investigates the underlying mechanisms, critical requirements, and methods for suppressing liquation cracking during the Welding of IN738LC superalloy. • It specifically demonstrates a critical grain boundary liquid film thickness range that dictates the susceptibility of IN738LC superalloy. • It also tries to explain the phenomenon of liquation cracking. This study investigates how the thickness of liquid films at grain boundaries affects liquation This study investigates how the thickness of liquid films at grain boundaries affects liquation cracking in the heat-affected zone (HAZ) of welded IN738LC superalloy. Welds were produced using gas tungsten arc welding (GTAW) operated in constant-current and pulsed-current modes in ain a butt joint while keeping the total heat input the same across conditions. Constant-current welding was compared to pulsed-current welding at 5 Hz and 30 Hz. Polished cross-sections were examined using optical microscopy and scanning electron microscopy and grain-boundary liquid-film thickness was measured using ImageJ. Our findings show that cracking does not simply increase with film thickness; instead, it peaks within an intermediate range. Regions with very thin (2.37–2.81 µm) and very thick (21.50–25.02 µm) films were crack-free. The 30 Hz pulsed condition exhibited the least cracking, likely because higher frequency reduces thermal stress and limits harmful microstructural changes in the HAZ. Thus, using high-frequency pulsed current is an effective strategy to improve the weldability of IN738LC.