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

Abstract

Taking the Ti-Al binary alloy as an example, this article studied the evaporation 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 negatively 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 transfers from the evaporation reaction controlling mode to the double controlling mode (diffusion and evaporation reaction) with increasing melt temperature (T ms ) and/or Al content (x Al ) and/or decreasing pressure (P) in the melting chamber. (2) The expression P Յ P crit (P crit Ϸ 0.44 P e(Al) ) is a criterion used to judge whether the evaporation is in the state of free evaporation. (3) The term P impe (P impe ϭ (3.5 to 4) P e(Al) ) is a critical value which impedes the evaporation loss. Almost all of common used ternary additions could enhance the activity of Al in molten Ti-Al and, accordingly, aggravate the evaporation of Al, except for Zr. The enhancing sequence is Y, Ni, Nb, Mn, V, Fe, Cr, Mo, Cu, Si, W, Mg, B, and Sn. The Al evaporation mass-transfer losses, measured from the melting experiments of several titanium aluminum alloys, were in reasonable agreement with the calculated results.

Microstructural Evolution during Pressureless Sintering of Blended Elemental Ti-Al-V-Fe Titanium Alloys from Fine Hydrogenated-Dehydrogenated Titanium Powder

“…This is higher than the furnace vacuum level of 2 × 10 −3 Pa thus suggesting that the Al is in a state of free evaporation [29,30]. The evaporation rate of aluminum and vanadium are 1.48 × 10 −4 and 1.48 × 10 −12 g·cm −2 ·s −1 respectively at a temperature of 1150 • C seen from Figure 13.…”

“…The presence of vanadium-rich "coral-like" material with a smooth cellular wall is considered to be correlated with the evaporation of aluminum according to the following analysis. Theoretical calculation of the evaporation of binary alloys can be determined based on the Miedema model and Langmuir equation [23,29,30]. For instance, Guo and co-workers calculated the theoretical elemental evaporation of a Ti-Al melt during casting with this model, which had reasonable agreement with the experimental data [29,30].…”

“…Theoretical calculation of the evaporation of binary alloys can be determined based on the Miedema model and Langmuir equation [23,29,30]. For instance, Guo and co-workers calculated the theoretical elemental evaporation of a Ti-Al melt during casting with this model, which had reasonable agreement with the experimental data [29,30]. Chen et al [23] and Xu et al [31] also utilized this model to calculate the evaporation of PM fabricated Fe-Al and Fe-Mn alloys in good accordance with experimental observations.…”

“…The Langmuir constant (K L ) is equal to 4.37 × 10 −4 when the partial pressure is described in Pascal [29,30]. ε is the condensation constant (for metals = 1) [29,30].…”

“…ε is the condensation constant (for metals = 1) [29,30]. P e A indicates the saturated vapor partial pressure of element A in the system and P g A is the partial pressure of the component.…”