High-pressure solidification of Cu–Ni–Si-(Cr)-(Zr) alloys: Microstructural evolution and properties

High-solute Cu–Ni–Si alloys (Ni + Si ' 5 wt%) are attractive precipitation-strengthened copper materials for advanced electrical and structural applications, yet their practical potential is constrained by solidification heterogeneities and the difficulty of simultaneously optimizing strength, conductivity, and ductility. In this work, GPa-level high-pressure solidification progressively suppressed dendritic segregation and coarse intermetallic formation, while markedly reducing the grain size in Cu–Ni–Si-(Cr)-(Zr) alloys. These pressure-induced changes arose from enhanced solubility of Cr and Zr in the Cu matrix, concomitant stabilization of the solid-liquid interface, and the simultaneous promotion of nucleation and suppression of crystal growth under high pressure. Cr further promoted the formation of coherent L1₂-type β-(Ni, Cr)₃Si during solidification and improved the coarsening resistance of the strengthening precipitates during subsequent aging, whereas Zr mainly contributed to grain refinement. The elevated solid solubility achieved under high pressure further enhances the roles of Cr and Zr in optimizing microstructure and properties, resulting in a marked improvement in the performance of the high-pressure-solidified alloys. Among the investigated alloys, the Cu–8Ni-1.8Si-0.4Cr-0.2Zr alloy exhibited the most favorable overall property combination after high-pressure solidification and aging, achieving a hardness of 385.2 HV, a compressive yield strength of 850.1 MPa, and a maximum electrical conductivity of 34% IACS. The present findings provide a mechanistic basis for the design of high-performance precipitation-strengthened copper alloys via the combined effects of high-pressure solidification and targeted microalloying.