Thermodynamic assessment of bio-oriented ti-ta-sn system

Abstract

The alloying elements Ta and Sn can effectively increase the stability of β-bcc phase, reduce Young’s modulus and improve the shape-memory property of Ti-based biomedical alloys. The development of the thermodynamic database for Ti-based biomedical alloys promises thermodynamic predictions in composition design and process optimization. In this work, one key sub-ternary Ti-Ta-Sn system has been thermodynamically assessed based on critical evaluation of experimental phase equilibria. A self-consistent thermodynamic description for the Ti-Ta-Sn system including one ternary compound Ti36Ta28Sn36 and six binary compounds considering the solubility of the third element has been obtained. Two isothermal sections at 973 and 1173 K and the liquidus projection have been calculated. Comparisons between the calculated and experimental phase equilibria vali-date the reliability of the present thermodynamic description. The influence of Ta and Sn contents on the transformation temperature and amount of α_hcp-Ti phase in β_bcc-(Ti,Ta) phase has been investigated based on thermodynamic calculations. The solidified phases in Ti-20Ta-xSn (x = 5, 15 and 25 at.%) as-cast alloys have been thermodynamically calculated based on Scheil solidification simulations. The presently developed thermodynamic description of the Ti-Ta-Sn system would promote the establishment of muti-component Ti-based thermodynamic database and guide the development of Ti-based alloys.