Transactions of Nonferrous Metals Society of China
JOURNAL OF RAILWAY SCIENCE AND ENGINEERING
|Vol. 12 No. 4 August 2002|
Ti-25Al-25Nb melt during induction skull
（School of Materials Science and Engineering,
Harbin Institute of Technology, Harbin 150001, China）
Abstract:Based on activity calculation model, the activity coefficients of Ti, Al and Nb components of Ti-25Al-25Nb (mole fraction, %) melt, the vapor pressures of corresponding components and the evaporation loss rates were calculated. Utilizing these activity coefficients and the vapor pressures, the relative evaporation coefficient is used to judge the evaporation tendency of these components. The evaporation tendency among the three components were compared and the result shows that the evaporation tendency is that: AlTi>Nb. Evaporation loss rate increases with the increase of melting temperature and decreases with the increase of chamber pressure. There exists an impeding pressure pimpe of Al element evaporation during induction skull melting process of Ti-25Al-25Nb alloy. The impeding pressure can be written as pimpe=8.1pe, where pe represents the equilibrium partial pressure. The calculation of evaporation loss of Al element also showed that when chamber pressure exceeds pimpe, the Al volatilization losses could be ignored. In order to pr event the evaporation loss of components, the pressure in the vacuum chamber should not below pimpe.
Key words: Ti-25Al-25Nb alloy；ISM process； multi-components evaporation