Effects of nanoscale Sn segregation on corrosion behavior of laser powder bed fusion Cu-15Ni-8Sn alloy

Corrosion resistance of laser powder bed fusion (LPBF) Cu-15Ni-8Sn alloys is crucial towards its practical application in marine engineering. In this work, corrosion behavior of LPBF Cu-15Ni-8Sn alloy was comprehensively investigated. The results suggest that LPBF Cu-15Ni-8Sn alloy exhibits superior corrosion resistance than the conventional casting counterpart and their corrosion behavior is highly associated with Sn segregation. Generally, a triple-layer film will be formed on the surface of LPBF Cu-15Ni-8Sn alloy when being exposed to 3.5 wt% NaCl solution. To be more detailed, the abundance of nanoscale Sn-rich precipitates at the molten pool boundaries promotes the initial formation of a thick inner layer, where Ni and Sn tend to be distributed at inner and outer positions of the layer, respectively. In contrast, the inner layer on molten pools is much thinner ascribed to a lower Sn content, facilitating the earlier nucleation and growth of a compact middle layer that is mainly composed of numerous Cu-rich nanoparticles. At the outmost position, CuO, Cu(OH)₂ and Ni(OH)₂ constitute the major composition of the loose layer. The results of this study could contribute to the optimal design and processing of additively manufactured Cu-Ni-Sn alloys.