Effect of GPa-level pressure on the microstructure and properties of Cu-8Ni-1.8Si alloy

Reducing or completely eliminating the reticular grain boundary phases in alloys is crucial for enhancing the mechanical and electrical properties of Cu-Ni-Si alloys with high nickel and silicon content (Ni + Si > 5 wt%). In this study, we investigated the microstructure, mechanical properties, and electrical conductivity of Cu-8Ni-1.8Si (wt%) alloy prepared by high-pressure solidification (HPS) and subsequent aging treatment. The interfacial growth stabilizes as the pressure reduces the crystal growth rate, inhibits the diffusion of solute atoms, and increases the solute partition coefficient. The reticulated Ni₃₁Si₁₂ and granular Ni₂Si phases disappear under 6 GPa pressure, forming a complete Cu (Ni, Si) solid solution. After direct aging treatment, the precipitated phase of the HPS alloy is β-Ni₃Si at the early stage of aging. At the peak aging state, β-Ni₃Si and δ-Ni₂Si phases coexist in the matrix. Additionally, the Avrami equations for the phase transition kinetics of HPS alloys at different aging temperatures were derived from the electrical conductivity data, and the strength contributions from solid solution strengthening and precipitation strengthening were calculated. The alloy aged at 450 °C exhibited the largest volume fraction and the smallest average size of precipitates, resulting in a more pronounced obstruction effect of nano precipitates on dislocation bypassing and demonstrating the best precipitation strengthening effect. At the peak aging states, the alloy's hardness reaches 367.5 HV, and the compressive yield strength reaches 788.2 MPa. These results indicate that high pressure is an effective method to improve the solid solution degree of alloying elements and enhance the mechanical properties of Cu-Ni-Si alloys.