Reza Sahihi, , ,
Volume 9, Issue 2 (Journal OF Welding Science and Technology 2025)
Abstract
In this study, the effect of gas tungsten arc welding (GTAW) in both constant and pulsed current modes with frequencies of 5 and 20 Hz was investigated on the weldability, microstructure, and mechanical properties of Inconel 738LC superalloy. The main objective was to evaluate the susceptibility to liquation cracking in the heat-affected zone (HAZ) and to identify the mechanisms responsible for improving weldability. The results revealed that applying pulsed current, particularly at a higher frequency of 20 Hz, significantly reduced the extent of liquation cracking and improved the overall joint quality. The average crack length decreased by more than 50% compared to the constant current condition. Increasing the pulse frequency transformed the solidification morphology from columnar dendritic to equiaxed, reduced interdendritic segregation, and led to a more uniform and finer distribution of MC carbides. The ultimate tensile strength increased from 751 MPa (constant current) to 802 MPa (20 Hz pulsed current), representing an improvement of approximately 6.7%, while the total elongation improved from 7.96% to 9.83% (about 23% increase). The weld metal hardness also increased from 446 to 468 HV. Overall, pulsed GTAW at a moderate frequency (20 Hz) effectively reduced solidification stresses and thermal gradients, providing an efficient approach to mitigate liquation cracking and enhance the mechanical performance of Inconel 738LC welds.
