Microstructure evolution and properties of a quaternary Cu–Ni–Co–Si alloy with high strength and conductivity

Abstract

An in-depth exploration of the microstructure evolution and characterization of the precipitates in a quaternary Cu–Ni–Co–Si alloy under different aging conditions was conducted. The precipitates were confirmed to be δ-(Ni, Co)2Si and exhibited different morphological features with high-resolution transmission electron microscopy. The three-dimensional atom probe technique revealed the quantitative atomic distribution and corresponding content changes in the precipitates. Combined with the above analysis, these results allowed the evolution of the δ-(Ni, Co)2Si precipitates to be determined. The precipitation phase was divided into two zones: unstable zone I at the edge and zone II comprising pure δ-(Ni, Co)2Si in the core. As aging progressed, the thickness of zone I decreased, and that of zone II increased continuously, accompanied by the replacement of Cu atoms in the precipitates by external Ni atoms. In the peak-aged state, the Ni, Co and Si atoms exhibited a substantial amount of cosegregation, and the corresponding atomic concentrations were 40 at.%, 25 at.% and 35 at.%, respectively. The studied alloy exhibited excellent comprehensive properties, including a hardness of 318 HV, an electrical conductivity of 37.1% IACS, a tensile strength of 1003 MPa, a yield strength of 929 MPa, and an elongation of 4.5%, after the introduction of a multistage thermomechanical treatment process. Theoretical analysis was conducted for different strengthening mechanisms, and the findings coincided well with the experimental results.