Calculation of Cu-rich part of Cu-Ni-Si phase diagram

The thermodynamic calculation of phase equilibria in the Cu-Ni-Si alloy system was carried out using the CALPHAD method. The calculations show that there are three two-phase areas and two three-phase areas in the Cu-rich parts of the isothermal section of the phase diagram at 300-600 ℃,and the three two-phase areas are FCC-A1(Cu-rich)+γ-Ni5Si2,FCC-A1(Cu-rich)+δ-Ni2Si and FCC-A1(Cu-rich)+ε-Ni3Si2,two three-phase areas are FCC-A1(Cu-rich)+γ-Ni5Si2+δ-Ni2Si and FCC-A1(Cu-rich)+δ-Ni2Si+ε-Ni3Si2. For this reason,an alloy located in the Cu-rich portion may precipitate γ-Ni5Si2,δ-Ni2Si or ε-Ni3Si2;the proportion of each phase depends on the alloy composition and aging temperature. The transmission electron microscope analysis of the Cu-3.2Ni-0.75Si alloy indicates that the precipitates are mainly δ-Ni2Si with only a few γ-Ni5Si2 phase particles,which agrees well with the thermodynamic calculations of phase equilibria.

The thermodynamic calculation of phase equilibria in the Cu-Ni-Si alloy system was carried out using the CALPHAD method. The calculations show that there are three two-phase areas and two three-phase areas in the Cu-rich parts of the isothermal section of the phase diagram at 300-600 ℃ , and the three two-phase areas are FCC-Al（Cu-rich）＋γ-Ni5Si2, FCC-Al（Cu-rich）＋δ-Ni2Si and FCC-Al（Cu-rich）＋ε-Ni3Si2, two three-phase areas are FCC-Al（Cu-rich）＋）,-Ni5Si2＋δ-Ni2Si and FCC-Al（Cu-rich）＋δ-Ni2Si＋e-Ni3Si2. For this reason, an alloy located in the Cu-rich portion may precipitate γ-Ni5Si2, δ-Ni2Si or ε-Ni3Si2; the proportion of each phase depends on the alloy composition and aging temperature. The transmission electron microscope analysis of the Cu-3.2Ni-0.75Si alloy indicates that the precipitates are mainly δ-Ni2Si with only a few γ-NisSi2 phase particles, which agrees well with the thermodynamic calculations of phase equilibria.