Thermochemical and phase diagram studies of the Sn–Zn–Ni system

The phase diagram Sn–Zn–Ni was studied by means of DSC and electron microprobe analysis. The samples were positioned in three isopleth sections with nickel contents of 0.04 (section 1), 0.08 (section 2) and 0.12 (section 3) mole fractions. The mole fractions of Sn corresponding to the particular sections were as follows: from 0.230 to 0.768 (section 1), from 0.230 to 0.736 (section 2); from 0.220 to 0.704 (section 3).Mixtures of pure metals were sealed under vacuum in quartz ampoules and annealed at 350 °C. The solid phases identified in the samples were: γ-(i.e. Ni5Zn21), (Zn) and the ternary phase T1. Unidentified compositions were observed. One of them: UX1 (XNi = 0.071 ± 0.005, XSn = 0.439 ± 0.009 and XZn = 0.490 ± 0.010) might indicate another (stable or metastable) ternary compound (T3) in the system Sn–Zn–Ni.Considering the data obtained by combining DSC with microstructure observations, the studied alloys could be divided in two groups (A and B). A ternary eutectic reaction at around 190 °C is common for the A-group alloys. The phases taking part in this reaction are, probably, Ni5Zn21, (Zn), (βSn) and liquid. B-group samples do not show ternary eutectic reaction and are also characterized by the presence of the ternary compound T1 (absent in the A-group alloys).Four other groups of thermal arrests were registered (TA1–TA4). It was found that TA2 peaks were characteristic for most of the A-group samples, while TA1 peaks were registered with all B-group samples.

► Sn–Zn–Ni phase diagram in the vicinity of the Sn–Zn system.
► Unidentified compositions (UX1–UX4) are repeatedly observed.
► This indicates up to 6 ternary compounds in the system.
► A ternary eutectic reaction at around 190 °C is found.