Chemically Engineered Micro/Nanostructures on Additively Manufactured 316L Stainless Steel and CuCrZr Copper Alloys...

Recent advances in surface micro/nanostructuring techniques have enabled efficient two-phase cooling. With the growing adoption of metal additive manufacturing (AM) in thermal hardware, it is critical to establish scalable micro/nanostructuring strategies tailored to AM alloys, whose altered surface chemistry, composition, and grain boundaries differ significantly from their conventional counterparts. In this study, by elucidating the interplay between bubble nucleation characteristics and microstructural length scales, we develop and optimize facile and highly scalable surface structuring techniques that enable the fabrication of micro/nanostructures on AM stainless steel (316L) and copper (CuCrZr) alloys, achieving substantial pool boiling enhancement with HFE-7100. For AM stainless steel, electrolytic etching in oxalic acid selectively amplifies sub-grain boundaries through localized anodic dissolution and oxide formation, yielding uniform microneedles (0.5-2 µm) with enhanced wickability. The optimized surface (AMSS-C(27)) exhibits a maximum heat transfer coefficient enhancement of 110.2 and 90.2% over plain and conventional microstructured stainless steel, respectively, attributed to favorable ∼5 µm cavity distributions. For AM copper, immersion etching in ferric-chloride/hydrochloric-acid solution promotes redox-driven dissolution of Cu and redeposition of Cu2O/CuO phases, forming 10-30 µm deep crevices, while post-heat treatment (AM-CuCrZr-H) achieves a maximum heat transfer coefficient enhancement of 85.6%. Hierarchical incorporation of 0.5-2 µm knife-like CuO nanostructures further increases the maximum heat transfer coefficient by 15.7% compared to its single-tier etched counterpart through optimized cavity tuning and surface-energy modification. This work develops scalable structuring methods for AM 316L and CuCrZr with substantial boiling enhancements, establishing a class of chemically engineered, high-performance heat-transfer surfaces applicable to a broad range of engineering fluids, and suitable for next-generation energy and cooling systems.