Diffusion couple studies of the Ti‐Bi‐Zn system

Abstract

The system Ti-Bi-Zn has been investigated using diffusion couples consisting of solid Ti and liquid (Bi+Zn) phase. The diffusion paths at 400, 500, 700 and 800°C have been traced by means of electron microprobe analyses. The growth constants of the diffusion layers are roughly assessed. The phase diagram data obtained in this investigation are compared with previous studies of equilibrated alloys. The existence of the ternary compound TiBiZn has been confirmed. The formation of another phase with approximate formulae Ti 4 Bi 3 Zn to Ti 9 Bi 7 Zn 4 has been observed at high temperatures. The latter compound as well as the ternary extension of the Ti X Bi Y (X≈ 5, Y≈6) phase react easily with air.

Phase diagram studies of the Ti–Bi–Zn system

“…Its crystals exhibit fissures and are always in contact with the TiBiZn phase. Layers having similar composition have been observed in solid (␣-Ti)/liquid (Bi + Zn) diffusion couples annealed at 700 and 800 • C [1]. Taking into account the present results and the authors' previous data [1,32], we assume the existence of two stable ternary phases in the Ti-Bi-Zn system (TiBiZn and ∼Ti 4 Bi 3 Zn).…”

“…In specimen no. 12, annealed at 900 • C, except the recently found TiBiZn [1,32], another phase corresponding approximately to the formula Ti 4 Bi 3 Zn has been observed (Fig. 5).…”

“…1. Four phase fields could be distinguished in the quenched sample: ∼Ti 4 Bi 3 Zn crystals [1], Ti Y Bi X (with X ≈ Y) (probably related with the compound Ti 8 Bi 9 [26]) and Bi-rich and Zn-base areas (actually, both of them appertain to the liquid phase where separation occurs due to the Bi-Zn miscibility gap with critical temperature around 600 • C).…”

“…For this reason the application of long annealing times at high temperatures should be avoided. Nevertheless, our experience gives evidence that when such a reaction is observed the result is the formation of reactionary layers along the walls [1].…”

“…Thus, the knowledge of the pertinent phase diagrams could be a source of important information. Recently, we revealed, the existence of two ternary compounds in the Ti-Bi-Zn system (TiBiZn and ∼Ti 4 Bi 3 Zn) [1]. Nevertheless, their simultaneous presence in the phase diagram was questionable.…”