Experimental investigation and thermodynamic re-assessment of the Ti–Zn system and atomic mobility of its bcc phase

Abstract

Detailed thermodynamic and kinetic descriptions of the Ti–Zn system are of especial significance for designing novel titanium alloys. However, there are still inconsistencies between the literature data and the existing phase diagram of the Ti–Zn system. Besides, little report about the kinetics of the Ti–Zn system is available. In the present work, the Ti–Zn system has been revisited via experimental, ab initio and CALPHAD (CALculation of PHAse Diagrams)-type investigations with a thermodynamic database being in good agreement with experimental information. A Ti/Zn diffusion couple and a Zn-rich equilibrated alloy were employed to contribute to the knowledge of the phase equilibria at 500 °C and 600 °C. The formation enthalpies of the intermetallic Ti–Zn compounds were computed via ab initio calculations, while those of body-centered cubic (bcc) and hexagonal-close packed (hcp) phases were obtained with the special quasirandom structure (SQS) method. In addition, another diffusion couple of bcc Ti/Ti-3at.% Zn was assembled and annealed at 900 °C and 1100 °C respectively for 72h to extract interdiffusion coefficients. Based on the newly developed thermodynamic description in this work and our experimental results, the atomic mobility parameters of the bcc phase for the Ti–Zn system were assessed.