Evaporation behavior of aluminum during the cold crucible induction skull melting of titanium aluminum alloys

Taking the Ti-Al binary alloy as an example, this article studied the evapo ration behavior of Al during the cold crucible induction skull melting (ISM ) process of titanium alloys. A formula was deduced to predict the activity of Al in a molten Ti-Al binary system. The calculated activity of Al negat ively deviates from an ideal solution. A model was established to judge the evaporation controlling mode and, on this basis, several conclusions were obtained. (1) The evaporation controlling mode of Al in molten Ti-Al transf ers from the evaporation reaction controlling mode to the double controllin g mode (diffusion and evaporation reaction) with increasing melt temperatur e (T-ms) and/or Al content (x(Al)) and/or decreasing pressure (P) in the me lting chamber. (2) The expression P less than or equal to P-crit (P-crit ap proximate to 0.44 P-e(Al)) is a criterion used to judge whether the evapora tion is in the state of free evaporation. (3) The term P-impe (P-impe = (3. 5 to 4) P-e(Al)) is a critical value which impedes the evaporation loss. Al most all of common used ternary additions could enhance the activity of Al in molten Ti-Al and, accordingly, aggravate the evaporation of Al, except f or Zr. The enhancing sequence is Y, Ni, Nb, Mn, V, Fe, Cr, Mo, Cu, Si, W, M g, B, and Sn. The Al evaporation mass-transfer losses, measured from the me lting experiments of several titanium aluminum alloys, were in reasonable a greement with the calculated results.