Abstract: Selective laser melting (SLM), an advanced powder-bed fusion technique, utilizes high-intensity lasers to consolidate metallic powder layer-by-layer, enabling fabrication of complex components with tailored microstructures. However, the intricate relationship between microstructural anisotropy and corrosion behavior in SLM-fabricated medium-entropy alloys (MEAs) remains inadequately understood. This study systematically investigates the microstructure-corrosion correlation in SLM-processed CoCrNi MEAs. Multi-scale analysis demonstrates that pronounced microstructural anisotropy can be induced by the 67 ° rotation scanning strategy of SLM, which is characterized by heterogeneous grain morphologies and crystallographic plane-dependent texture intensities governed by the solidification dynamics of MEAs. Notably, a unique composite band structure comprising stacking faults and nanotwins is identified, which is favorable for the optimal passive film stability via the increase of the interfacial energy barrier. The crystallographic orientation-dependent corrosion performance is governed by the synergistic interplay of texture, dislocation substructures, and passive film stability. Enhanced corrosion resistance of the SLM-fabricated CoCrNi alloy is attributed to weak texture and well-distributed dislocation networks resulting from ultra-rapid solidification and intense thermal cycling, as well as the formation of oxide-rich passive films that are stabilized by the inherent multi-elemental synergy of MEAs. These findings provide fundamental insights into microstructure-controlled corrosion behavior and establish strategic guidelines for designing high-performance SLM-fabricated MEAs for demanding service environments.

Key words: Cocrni medium-entropy alloy, Selective laser melting, Microstructural anisotropy, Passive film formation, Corrosion resistance