Ultrasonic-driven grain refinement in high-frequency pulsed welding of Inconel 690 alloy: Interplay between ultrasonic and molten pool dynamic

This study investigates the influence of pulse frequency on high-frequency pulsed gas tungsten arc welding (HFP-GTAW) of Inconel 690 alloy. The results reveal that increasing pulse frequency significantly modifies arc morphology through electromagnetic constriction and thermal delay effects, leading to concentrated heat input. At 20 kHz, pronounced grain refinement occurs, marked by reduced columnar grain proportion to 66.15 % and improved grain misorientation uniformity, driven by ultrasonic cavitation and acoustic streaming effects. However, as the pulse frequency exceeds 20 kHz, ultrasonic effects weaken and heat source concentration dominates, resulting in coarser grain structures and reduced orientation uniformity. The theoretical analysis explores molten pool resonance further highlights the interplay relationship between frequency-selective of arc-induced ultrasonic and molten pool dynamics (thermal gradient) on grain growth. This study provides novel insights into the ultrasonic effect in HFP-GTAW, offering a foundation for optimizing welding processes to achieve superior microstructure in nickel-based alloys.