Phase equilibria of the Ni–Si–Zn system at 600 °C

The phase equilibria at 600 °C of the Ni–Si–Zn system were investigated by using 19 alloys and four reaction diffusion couples. The alloys were prepared by melting the pure elements in the alumina crucibles capsulated in evacuated quartz tubes. The samples were examined by means of optical microscopy, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, and electron probe microanalysis. The presented isothermal section at 600 °C is characterized by the existence of five ternary phases, which are labeled as T1, T2, τ3, τ4 and β′, respectively. Three previously reported ternary compounds, viz. Ni3Si0.33Zn0.67 (T2), Ni2SiZn3 (τ3), and Ni3Si2Zn (τ4), were confirmed to exist at 600 °C. β′-NiZn was assumed to be the Si-stabilized β-NiZn phase in the Ni–Zn binary system. T1 is a newly found ternary compound. It should be noted that the phase relationships at 600 °C are significantly different from the previously reported ones at 800 and 297 °C. γ1-NiZn3, the existence of which is still controversial in the literature, was observed at 600 °C. The solubilities of Zn in Ni31Si12, Ni3Si2 and NiSi, and those of Si in γ1-NiZn3 and γ-Ni2Zn11 are negligible. The solubilities of Zn in α-NiSi2 and δ-Ni2Si were determined to be 8.5 and above 3.1 at.% Zn, respectively. α-NiSi2 and δ-Ni2Si extend into the ternary system at constant Ni content with Zn substituting for Si.