Silicon effects on the formation of heterogeneous intermetallic compound phases in Cu-Ni-Si(-Mn) alloys under homogenization treatment

This study investigates the role of silicon in the formation and evolution of heterogeneous intermetallic compound phases in Cu-Ni-Si(-Mn) alloys subjected to homogenization treatment at 980 °C. Si plays a critical role in both the intragranular and grain boundary precipitation behavior. An increase in Si content significantly enhances the volume fraction and size of intragranular δ-Ni₂Si precipitates. Furthermore, it promotes morphological changes at the grain boundaries, increasing the aspect ratio of boundary precipitates and transforming them into thin, film-like G-phase structures (Mn₆Ni₁₆Si₇) in Mn-containing alloys. While the overall volume fraction of grain boundary phases remains relatively stable, these Si-induced morphological changes alter the grain boundary characteristics and impact mechanical performance. In Mn-free Cu-Ni-Si alloys, higher Si content leads to the coarsening of grain boundary δ-Ni₂Si precipitates, degrading both strength and ductility. In contrast, in Mn-containing alloys, the grain boundary G-phase remains stable without coarsening, even with increased Si content, which helps retain ductility (∼10 %) and enhances overall mechanical properties. These findings highlight Si as a key element in tailoring microstructures and optimizing the mechanical performance of Cu-Ni-Si(-Mn) alloys through control of intermetallic phase formation.