A Comparative Study on High-Temperature Oxidation Behavior, Microstructure Characterization, and Texture of UNS R30155 Superalloy Weldment Joint Using Pulsed Current and Constant Current Gas Tungsten Arc Welding.

This study focuses on welding UNS R30155 alloy thin sheets using IN718 filler metal, employing two welding modes: pulsed current gas tungsten arc welding and constant current gas tungsten arc welding. The main goal was to examine the combined effects of pulsed current and optimal frequency on the microstructure and oxidation behavior across the weldment, comparing it to the constant current mode using electron backscatter diffraction. The results show that employing an optimal frequency of 240 Hz induces turbulence in the molten pool, limiting epitaxial grain growth by fragmenting dendritic arms and generating solid particles as modifiers. This phenomenon results in an expanded zone featuring equiaxed grains with random orientations, causing the weld metal's texture intensity to shift from the preferred growth direction, < 001> (with a texture intensity of about 0.92 mrd (multiples of random texture distribution)), to random orientations. In contrast, constant current welding ensures extensive growth of epitaxial grains, maintaining a high texture intensity of 2.61 mrd, aligned with the preferred growth direction, < 001>. Oxidation tests reveal that the sample welded with the optimal frequency of 240 Hz, facilitating uniform distribution of alloying elements during solidification, forms alternating protective layers of Cr₂O₃ and NiCr₂O₄. This reduces damage to the substrate, resulting in the thinnest oxide layer and a lower parabolic rate constant (Kp) compared to other welded specimens. Specifically, the Kp values for the sample were 0.158 × 10⁻¹⁰ g² cm⁻⁴ s⁻¹ for up to 4 hours and 0.027 × 10⁻¹⁰ g² cm⁻⁴ s⁻¹ after 4 hours. [ABSTRACT FROM AUTHOR]