Netted structure of grain boundary phases and its influence on electrical conductivity of Cu–Ni–Si system alloys

Abstract

Cu-Ni-Si alloys with four different Cu contents were fabricated by means of smelting. Subsequently, isothermal aging and hot rolling followed by aging treatment were carried out. The microstructure and phase composition were characterised by optical microscope, transmission electron microscope and X-ray diffractometer. Electrical conductivity was measured by using an eddy current based technique. The results show that the electrical conductivities of as cast Cu-Ni-Si alloys decrease obviously with a decline in Cu content. Isothermal aging is favourable to enhance the electrical conductivities of Cu-Ni-Si alloys with higher than 90%Cu content rather than that with ,90%Cu content containing an integrated netted structure of grain boundary phases. The electrical conductivities of as rolled Cu-Ni-Si alloys can obviously be increased by subsequent aging treatment. The above results suggest that the disintegration of the integrated netted structure at the grain boundary is a promise to achieve high electrical conductivity for Cu-Ni-Si alloys.

Investigation of Cu-diamond/Cu-diamond-high-entropy alloys bi-layer coating via mechanical alloying

“…The conductivity of T2 pure Cu matrix is 98.7% IACS and the Cu–diamond/Cu–diamond-Cu2NiAlAgZn bi-layer leads to a significant decrease in conductivity. The electrical conductivity of copper and copper matrix composites can be expressed by the following equation 39 : where ρ 0 is the matrix resistivity; ρ pho , ρ pre , ρ sol , ρ def and ρ int are the contributions to the resistivity from phonon scattering, precipitation scattering, solid solution scattering, defect scattering and interfacial scattering, respectively; σ and ρ are the electrical conductivity and resistance, respectively. It follows that a large number of second phases and interfaces are present in MA-II, which leads to a significant increase in electrical resistance.…”

Effect of multiple forging on the microstructure and properties of an as-cast Cu–Ni–Si alloy with high Ni and Si contents

“…With increasing number of forging passes, the electrical conductivity first increased and then decreased, while the hardness increased continuously until it slightly decreased when the number of forging passes exceeded 18. According to the electron mechanism, electrical conductivity is affected by phonon scattering, dislocations, solution atoms, precipitates, grain boundaries, interfaces, and impurities [27,28]. However, for precipitation-strengthened Cu-Ni-Si alloys, the most important factors are the solution atoms and precipitates [29].…”

“…However, for precipitation-strengthened Cu-Ni-Si alloys, the most important factors are the solution atoms and precipitates [29]. Considering the microstructural evolution of the as-cast Cu-Ni-Si alloy after multiple forging for different numbers of passes, it can be easily confirmed that the increase in electrical conductivity is due to the destruction of the reticular Ni 31 Si 12 phase, which is located on the grain boundaries and has poor conductivity; hence, it has a very negative effect on the electrical conductivity [20]. The decrease in electrical conductivity is the result of the dissolution of Ni 2 Si precipitates because the atoms degrade the electrical conductivity considerably more in solid solution than as precipitates [30].…”

“…Therefore, increasing the quantity of Ni-Si precipitates in the alloy is considered to be an effective way to improve the strength of Cu-Ni-Si alloys. For this reason, in recent years, some scholars [20][21][22][23][24] have attempted to increase the Ni and Si contents in the alloy and increase the number of precipitated phases, achieving good results. However, when the Ni and Si contents increase, a reticular phase easily forms in the alloy structure.…”

Experimental investigation on phase transformation of Cu–Ni–Si alloy melts during cooling

“…Such a case is true to Cu–Ni–Si alloys with low Ni and Si addition, in which δ -Ni 2 Si precipitates have significant influence on the strength as well as the directional movement of electrons. However, for high Ni and Si addition, besides δ -Ni 2 Si precipitates in the copper matrix, the influence of Ni 3 Si phases formed at the grain boundaries on tensile strength and electrical conductivity must also be taken into consideration 11. Thus, it is very important to realise an excellent combination of strength and electrical conductivity by controlling effectively the amount, distribution as well as size of nickel silicides.…”