Evaporation of multi-components in Ti-25Al-25Nb melt during induction skull melting process

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 vapor pressures, the relative evaporation coefficient can be used to judge the evaporation tendency of these components. The evaporation tendency was found to be Al≫Ti>Nb. Evaporation loss rate increases with the increase of melting temperature and decrease with the increase of chamber pressure. There exists an impeding pressure P_impe of Al element evaporation during induction skull melting process of Ti-25Al-25Nb alloy. The impeding pressure can be written as P_impe=8.1P_e, where P_e represents the equilibrium partial pressure. The calculation of evaporation loss of Al element also shows that when chamber pressure exceeds p_impe, the Al volatilization loss can be ignored. In order to prevent the evaporation loss of components, the pressure in the vacuum chamber should not below p_impe.