Phase-composition design of high-hardness and high-electric-conductivity Cu-Ni-Si Alloy

Abstract

Cu-Ni-Si alloy has good electrical conductivity, thermal conductivity, high strength, and high hardness, and is widely used in electronic components and other fields. When the compositions of the Cu-Ni-Si alloy are designed, the determination of the phase component is critical. In this work, the composition of Cu-Ni-Si alloy is designed according to the "precipitation phase" by cluster-plus-glum-atom model. Following the cluster selection criteria, the δ-Ni<sub>2</sub>Si, γ-Ni<sub>5</sub>Si<sub>2</sub> and β-Ni<sub>3</sub>Si phase clusters are determined, respectively, and the corresponding cluster formulas are [Ni-Ni<sub>8</sub>Si<sub>5</sub>]Ni,[Si-Ni<sub>10</sub>]Si<sub>3</sub>, and [Si-Ni<sub>12</sub>]Si<sub>3</sub>. the compositions of a series of Cu-Ni-Si alloys are designed according to the different precipitated phases of δ-Ni<sub>2</sub>Si, γ-Ni<sub>5</sub>Si<sub>2</sub>, and β-Ni<sub>3</sub>Si each with Cu atom content being 93.75%, 95%, 95.8%, 96.7% and 97.5%, respectively. The alloy raw material is melted into alloy ingot in an argon-filled vacuum arc furnace. The ingots undergoes solid-solution at 950 ° C for 1 hour and water quenching then aging treatment at 450 ° C for 4 hour and water quenching. The conductivity and Vickers hardness of the alloy are tested by conductivity meter and hardness meter, respectively. The microstructure of the alloy is characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). In general, the electrical conductivity of Cu-Ni-Si is the main consideration in the design of alloy composition, the content values of matrix Cu atoms are in the ranges of 90%-95.63% and 95.63%-97.5% respectively, the precipitated phases are designed according to δ-Ni<sub>2</sub>Si and γ-Ni<sub>5</sub>Si<sub>2</sub> respectively; the content of matrix Cu atoms is over 97.5%, it can be designed according to any phase of δ-Ni<sub>2</sub>Si, γ-Ni<sub>5</sub>Si<sub>2</sub> and β-Ni<sub>3</sub>Si, with no difference in electrical conductivity among them. If the strength of the alloy is the main factor in the composition design, the content values of Cu atoms in the matrix are in the ranges of 90% — 93.93%, 93.93% — 94.34%, 94.34%— 95.63%, and 95.63%—96.12% respectively, according to the composition intervals the precipitated phases are designed as δ-Ni<sub>2</sub>Si, γ-Ni<sub>5</sub>Si<sub>2</sub>, β-Ni<sub>3</sub>Si, and γ-Ni<sub>5</sub>Si<sub>2</sub>, respectively. Once the content of Cu in the matrix is greater than 96.12%, the precipitated phase can be designed according to any of the phases of δ-Ni<sub>2</sub>Si, γ-Ni<sub>5</sub>Si<sub>2</sub> and β-Ni<sub>3</sub>Si.