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

Abstract

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 T 1, T 2, τ 3, τ 4 and β′, respectively. Three previously reported ternary compounds, viz. Ni 3Si 0.33Zn 0.67 ( T 2), Ni 2SiZn 3 ( τ 3), and Ni 3Si 2Zn ( τ 4), 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. T 1 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. γ 1-NiZn 3, the existence of which is still controversial in the literature, was observed at 600 °C. The solubilities of Zn in Ni 31Si 12, Ni 3Si 2 and NiSi, and those of Si in γ 1-NiZn 3 and γ-Ni 2Zn 11 are negligible. The solubilities of Zn in α-NiSi 2 and δ-Ni 2Si were determined to be 8.5 and above 3.1 at.% Zn, respectively. α-NiSi 2 and δ-Ni 2Si extend into the ternary system at constant Ni content with Zn substituting for Si.