Evaporation loss of components during induction skull melting of Ti-13Al-29Nb-2.5Mo

Saturated vapour pressures of the Al, Ti and Nb components in Ti-13Al-29Nb-2·5Mo (wt-%) melts were calculated at arbitrary temperatures. The calculated values at 2150 K for Ti, Al and Nb were 2·0, 30·7 and 0·17 Pa, respectively. From the thermodynamic point of view, the principal evaporation loss is of the Al component. Based on the saturated vapour pressure, the mass transport coefficient of the Al component, evaporation loss rates of the Ti, Al and Nb components and the evaporation loss of the Al component were calculated. When the melt temperature is 2100 K, the evaporation control changes from the double control mode to the single interface volatilisation control mode with increasing chamber pressure at a transition pressure of about 4 Pa. The rates of evaporation loss of the components are N_AI≈15N_Ti≈46N_Nb. A critical chamber pressure of about 13-33 Pa exists during induction skull melting of the Ti-13Al-29Nb-2·5Mo alloy. In order to prevent the evaporation loss of Al, the chamber pressure should be kept above 13·33 Pa. The theoretical calculation of the evaporation loss of the Al component is in good agreement with experimental values.