Fatigue behavior of powder bed Fused–Laser beam (PBF-LB) 70/30 Copper-Nickel (CuNi30)

• HCF of PBF-LB CuNi30 quantified across build orientations and heat treatments. • Heat treatment homogenized micro-segregation, preserving grain size and cellular substructure. • Build orientation governed strength–ductility trade-offs; HT favored horizontal builds. • Fatigue life controlled by defect- and facet-driven crack initiation from fractography. The 70/30 Cu–Ni alloy (CuNi30) is widely employed in marine systems due to its excellent corrosion resistance and mechanical reliability. Despite its industrial relevance, its behavior under additive manufacturing (AM), particularly powder bed fusion–laser beam (PBF-LB) processing, has received limited attention in the context of fatigue-critical applications. This study presents the first systematic assessment of the microstructure, defect population, mechanical properties, and fatigue performance of PBF-LB 70/30 Cu–Ni in both the as-built and heat-treated conditions, with specific attention to the role of build orientation using horizontally and vertically fabricated specimens. The applied heat treatment increased mechanical strength and produced a marked improvement in the stress–life (S–N) response of the alloy. Detailed microstructural characterization and post-mortem fractography showed that fatigue cracks predominantly initiated from surface or subsurface crystallographic facets induced by local embrittlement in the matrix. The results provide essential guidance for designing fatigue-resistant Cu–Ni components and support the broader adoption of PBF-LB 70/30 Cu–Ni in demanding marine and naval environments. Furthermore, this work establishes a foundation for future investigations into the corrosion-fatigue behavior of the alloy.