Comparing electrochemical pitting behavior and passive films of Fe-Cr-B alloy coatings manufactured via high deposition rate and conventional laser directed energy deposition

This study conducted a comparative analysis of the microstructural features and electrochemical pitting performance of high deposition rate laser directed energy deposition (H-LDED) and conventional laser directed energy deposition (LDED) Fe-Cr-B alloy coatings. It aimed to reveal the impact of process-induced microstructural differences on pitting performance. The microstructure of both coatings consists of a Fe-rich matrix phase and (Fe, Cr)2B phase. In comparison to LDED coatings, H-LDED coatings offer advantages due to their rapid solidification, resulting in significantly finer microstructure, reduced microelement segregation, and significantly lower dilution rates. However, H-LDED coatings exhibit higher porosity (0.06 %) compared to LDED coatings (0.02 %). Under identical chemical composition conditions, the thickness, structure, and composition of the passive film in both coatings are similar, indicating that microstructural differences have minimal impact on passive film formation. In cases of consistent coating thickness, dilution rate emerges as the most significant factor influencing corrosion resistance, while porosity plays a prominent role under uniform coating chemical composition conditions. In summary, the advantages of H-LDED coatings encompass high deposition efficiency and low dilution rates, allowing for the production of thin coatings that meet service requirements.