Discontinuous precipitates in age-hardening CuNiSi alloys

Microstructural Subsequence and Phase Equilibria in an Age-Hardenable Cu-Ni-Si Alloy

“…The electrical resistance of the specimens was measured using a standard DC four-probe method with an Agilent 34420A micro-ohm meter with an accuracy of ±10 μΩ, which was then used to calculate the electrical conductivity. The precipitates formed in the aged specimens were separated using the following extraction procedure, the details of which are described in the literature 17,22) : the surfaces of the aged specimens were mechanically polished again to remove the contaminated surface layer. After the specimens had been thoroughly rinsed in pure ethanol, they were cut into small pieces.…”

“…It is generally recognized that the strengths and electrical conductivities of Cu-Ni-Si alloys are closely dependent on their microstructure; at an early stage of aging, the strength of the alloys increases owing to the continuous nucleation and growth of the nano-scaled δ-Ni 2 Si precipitates (i.e., continuous precipitates (CPs)) in the matrix of Cu solid-solution phase [10][11][12][13][14][15][16][17] . Here, δ-Ni 2 Si has an orthorhombic structure (Space group: Pnma, lattice parameter: a = 0.504 nm, b = 0.364 nm, c = 0.708 nm) 14,17,18) . At a later stage of a prolonged aging, the strength decreases, which is primarily caused by the development of coarse cellular components consisting of the Cu solid-solution and ber-shaped δ-Ni 2 Ni phase (i.e., discontinuous precipitates (DPs)), accompanied by the consumption of the ne δ-Ni 2 Ni hardening species 17,[19][20][21] .…”

“…Here, δ-Ni 2 Si has an orthorhombic structure (Space group: Pnma, lattice parameter: a = 0.504 nm, b = 0.364 nm, c = 0.708 nm) 14,17,18) . At a later stage of a prolonged aging, the strength decreases, which is primarily caused by the development of coarse cellular components consisting of the Cu solid-solution and ber-shaped δ-Ni 2 Ni phase (i.e., discontinuous precipitates (DPs)), accompanied by the consumption of the ne δ-Ni 2 Ni hardening species 17,[19][20][21] . Meanwhile, the electrical conductivity of the al-loys increases monotonically during aging, because the amount of solute Ni and Si elements in the matrix decreases as a result of the formation of ne CPs and ber DPs of δ-Ni 2 Si.…”

“…Thus, to control the mechanical and electrical properties of the alloys, it is important to understand the precipitation behavior in association with the microstructures. The purpose of the present study is, therefore, to investigate the microstructural subsequence and phase equilibrium of commercial Cu-4.3 at% Ni-2.2 at% Si alloy during isothermal aging over a wide temperature range of 698 K-873 K. As a particular feature of this study, a chemical extraction technique was used to quantitatively analyze the microstructure of the aged-specimens 17,22,23) . The adopted chemical extraction procedure allowed direct and reliable examination of the structure, volume fraction, and compositions of the constituent phases.…”

Behaviour of Small Fatigue Cracks in CU-5.5NI-1.28SI Alloy Round-Bar Specimens

“…For Cu-Ni-Si alloys with high solute concentrations, on the other hand, phase transformation studies have been conducted mainly to control the microstructure of the alloy [7], [8]. In addition, discontinuous precipitates (DPs) that were fibre-shaped, stable δ-Ni2Si intermetallic compounds were formed in the Cu matrix [9], [10]. The formation of DPs in Cu-Ni-Si alloys is detrimental to their mechanical properties.…”