Titanium aluminide

Titanium aluminide (chemical formula TiAl), commonly gamma titanium, is an intermetallic chemical compound. It is lightweight and resistant to oxidation ^[1] and heat, but has low ductility. The density of γ-TiAl is about 4.0 g/cm³. It finds use in several applications including aircraft, jet engines, sporting equipment and automobiles.^{[citation needed]} The development of TiAl based alloys began circa 1970. The alloys have been used in these applications only since about 2000.

Titanium aluminide has three major intermetallic compounds: gamma titanium aluminide (gamma TiAl, γ-TiAl), alpha 2-Ti₃Al and TiAl₃. Among the three, gamma TiAl has received the most interest and applications.

Applications of gamma-TiAl

Gamma TiAl has excellent mechanical properties and oxidation and corrosion resistance at elevated temperatures (over 600 °C), which makes it a possible replacement for traditional Ni based superalloy components in aircraft turbine engines.

TiAl-based alloys have potential to increase the thrust-to-weight ratio in aircraft engines. This is especially the case with the engine's low-pressure turbine blades and the high-pressure compressor blades. These are traditionally made of Ni-based superalloy, which is nearly twice as dense as TiAl-based alloys. Some gamma titanium aluminide alloys retain strength and oxidation resistance to 1000 °C, which is 400 °C higher than the operating temperature limit of conventional titanium alloys.^{[not specific enough to verify][3]}

General Electric uses gamma TiAl for the low-pressure turbine blades on its GEnx engine, which powers the Boeing 787 and Boeing 747-8 aircraft. This was the first large-scale use of this material on a commercial jet engine^[4] when it entered service in 2011.^[5] The TiAl LPT blades are cast by Precision Castparts Corp. and Avio s.p.a. Machining of the Stage 6, and Stage 7 LPT blades is performed by Moeller Manufacturing.^{[6][citation needed]} An alternate pathway for production of the gamma TiAl blades for the GEnx and GE9x engines using additive manufacturing is being explored.^[7]

In 2019 a new 55 g lightweight version of the Omega Seamaster wristwatch was made, using gamma titanium aluminide for the case, backcase and crown, and a titanium dial and mechanism in Ti 6/4 (grade 5). The retail price of this watch at £37,240 was nine times that of the basic Seamaster and comparable to the top of the range platinum-cased version with a moonphase complication.^[8]

Alpha 2-Ti₃Al

TiAl₃

TiAl₃ has the lowest density of 3.4 g/cm³, the highest micro hardness of 465–670 kg/mm₂ and the best oxidation resistance even at 1 000 °C. However, the applications of TiAl₃ in the engineering and aerospace fields are limited by its poor ductility. In addition, the loss of ductility at ambient temperature is usually accompanied by a change of fracture mode from ductile transgranular to brittle intergranular or to brittle cleavage. Despite the fact that a lot of toughening strategies have been developed to improve their toughness, machining quality is still a difficult problem to tackle. Near-net shape manufacturing technology is considered as one of the best choices for preparing such materials. {date=July 2022}^{[citation needed]}

References

External links

• Machining Gamma Titanium Aluminide Components - Moeller Manufacturing
• Titanium Aluminide Applications in the HighSpeed Civil Transport
• Titanium Aluminides - Intermetallics on azom.com.
• Power House (GEnx TiAl LPT Blade Announcement)
• Edward A. Loria (2001). "Quo vadis gamma titanium aluminide". Intermetallics. 9 (12): 997–1001. doi:10.1016/S0966-9795(01)00064-4.
• Donachie, Matthew J (2000). Titanium: a technical guide. ASM International. p. 131. ISBN 978-0-87170-686-7.
• Kassner, Michael E, Pérez-Prado, María-Teresa (2004). Fundamentals of creep in metals and alloys. Elsevier. p. 175. ISBN 978-0-08-043637-1.