Chemical Vapor Synthesis of Titanium Aluminides by Reaction of Aluminum Subchloride and Titanium Tetrachloride
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tanium aluminides (TiAls) are an important class of materials for the automotive and aerospace industries.[1,2] Intermetallic compounds of titanium (TiAl, Ti3Al, TiAl3) are characterized by superior mechanical and chemical properties: low density, high-temperature oxidation, and corrosion resistance. However, these alloys also have low ductility at room temperature, and mechanical postprocessing of ingots, therefore, is complicated. Powder metallurgy (PM), including three-dimensional printing technology, is considered an effective method for automotive components production. Currently, much investigation has been carried out on techniques for the production of TiAl powder.[3–5] However, combining aluminum and titanium powders for the production of TiAl alloys has limitations due to the differences in the densities and melting temperatures of these metals. Several strategies have been proposed to overcome these limitations, for example, the use of additional techniques such as hydrogenation of titanium, milling, and prealloying.
ROMAN A. ZAKIROV, OLEG G. PARFENOV, and LEONID A. SOLOVYOV are with the Institute of Chemistry and Chemical Technology of SB RAS, Akademgorodok 50/24, Krasnoyarsk 660036, Russia. Contact email: [email protected] Manuscript submitted on June 6, 2017. Article published online November 14, 2017. METALLURGICAL AND MATERIALS TRANSACTIONS B
The main objective of this study is to develop a facile technique for the fabrication of TiAl alloys powder, which involves the preparation of aluminum subchloride (AlCl) as the reducing agent and its reaction with titanium tetrachloride (TiCl4). A similar metallothermic approach has been reported previously.[6] In that report, TiAls were produced via the co-reduction of TiCl3 and AlCl3 by magnesium. It is known that metallic aluminum has very low vapor pressure and, therefore, cannot be used as a gas-phase reducing agent. On the other hand, aluminum subhalides are highly stable in the gas phase at temperatures ‡ 1173 K (900 C). In the 20th century, the subhalide method for aluminum extraction attracted the attention of researchers as an alternative route for aluminum production.[7,8] We have published several articles concerning the application of AlCl as the reducing agent.[9–11] In addition, the possibility of silicon tetrachloride reduction by AlCl has been investigated.[12,13] Thermodynamic calculations for the application of AlCl to the synthesis of aluminum alloys have been reported,[14] but the results have not yet been validated experimentally. Therefore, in this report, we demonstrate the feasibility of using the AlCl method for the synthesis of TiAl alloys in a laboratory experiment. Aluminum chloride (98 pct, purified by sublimation), metallic aluminum (> 99 pct), and TiCl4 (99.9 pct) were used as the starting reagents. Argon was additionally purified using P2O5 and magnesium. The experimental setup is shown in Figure 1. The reactor consisted of two coaxial ceramic tubes (1, 2), a ceramic boat (3), gas-tight flanges (4), chloride vaporizers (5, 6)
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