Phase equilibria of the Cu–Ni–Si system at 700 °C

The phase equilibria at the isothermal section of the Cu–Ni–Si system at 700 °C were experimentally investigated. Thirty Cu–Ni–Si alloys were prepared by arc melting and annealed at 700 °C for 30 or 80 days, and examined with optical microscopy, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy and electron probe microanalysis. Twelve three-phase regions were determined. The existence of the ternary compound τ1-Cu56.8–63Ni10.4–16.1Si26.6–27.3 reported in literature was confirmed and a new compound τ2-Cu45.8Ni25Si29.2 with nearly no homogeneity range was observed. The θ-Ni2Si compound, which exists above 820 °C in the binary Ni–Si system, was found to be stable at 700 °C and the composition range of Cu is 12.7–20.6 at.% Cu. The ternary solubilities of binary compounds were measured and noticeably the Cu56Si11 compound can dissolve Ni up to 21.9 at.%.

► The phase diagram of the Cu–Ni–Si system at 700 °C was measured for the first time.
► The existence of the ternary compound τ1 reported in literature was confirmed.
► A new compound τ2-Cu45.8Ni25Si29.2 with no solubility was observed for the first time.
► The Ni2SiH compound was found to be stable at 700 °C in the ternary system by dissolving Cu.