Evolution of nanosized Cu-rich clusters in a Fe–15Cu–15Ni alloy produced by laser powder bed fusion

Designing a metastable microstructure with a coherent nano-sized precipitation phase in the matrix is an effective strategy in improving the strength of materials. Recently, the rapid fusion and solidification cycle associated with laser-based additive manufacturing (AM) has emerged as a promising strategy to design unique microstructures with lattice distortion, solute segregation, and nano-sized precipitations. In this study, the evolution of nano-sized Cu-rich clusters in an AM-processed Fe–15Cu–15Ni alloy (wt.%) was investigated by conducting multiscale microstructural characterization. The results reveal that nano-sized Cu-rich clusters were generated inside the matrix due to a phase decomposition induced by the intrinsic heat treatment during the AM process. The heat energy generated by the laser beam not only initiated Cu-rich cluster formation, but also induced precipitation growth. Therefore, the average Cu-rich cluster size increased with an increase in the volumetric energy density. The hardness of the AM-processed Fe–15Cu–15Ni alloy at first increased with an increase in the energy density until a medium energy density level (140 J/mm3), due to formation of Cu-rich clusters. The hardness decreased with further increase in energy density (185 J/mm3), due to the Cu-rich cluster growth and retained austenite. The results reveal that laser-based AM successfully induces nano-cluster without the need for post-treatment and that the mechanical properties of materials can be optimized by adjusting the processing parameters in a way to enable nano-sized cluster and phase formation.