Electrolyte-driven phase-selective dissolution for nanostructure fabrication on single-crystal superalloys

Micro-nanostructures are widely used for heat transfer, friction reduction, and drag reduction. This study proposes a new electrolyte composition and optimizes current density to fabricate concave–convex nanostructures on single-crystal superalloys. Based on the selective dissolution mechanism of γ/γ′ phases, two types of nanostructures are precisely formed: a grid-like structure with mildly raised γ phases (∼12 nm) and wide channels (∼500 nm), and a columnar structure with prominently raised γ′ phases (∼54 nm) and narrow channels (∼50 nm). The results reveal distinct electrochemical responses depending on the electrolyte and current density (0.5–20 A cm⁻²). In sodium chloride, protective elements such as Cr and W enrich in the γ phase, making the γ′ phase the primary dissolution pathway, whereas in sodium nitrate, the γ phase dissolves preferentially. Water-based solutions showed high sensitivity to current density, affecting surface morphology, while glycol-based solutions exhibited reduced sensitivity, facilitating smoother, more refined nanostructures. Thus, the surface morphology can be finely tuned through electrolyte-driven selectivity. Furthermore, the resulting nanostructures provide a controllable basis for tailoring surface characteristics in single-crystal alloys.