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

Names
IUPAC name aluminum;titanium
Identifiers
CAS Number	12003-96-2 Y
3D model (JSmol)	Interactive image
ChemSpider	8466204
PubChem CID	10290735
InChI InChI=1S/Al.Ti Key: KHEQKSIHRDRLMG-UHFFFAOYSA-N
SMILES [Al].[Ti]
Properties
Chemical formula	AlTi
Molar mass	74.849 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

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

Pole figures displaying crystallographic texture of gamma-TiAl in a rolled sheet of alpha2-gamma alloy, as measured by high energy X-rays.^[2]

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

Alpha 2-Ti₃Al is an intermetallic compound of titanium and aluminum, belonging to the Ti-Al system of advanced high-temperature materials. It is primarily used in aerospace and other high-performance applications due to its balance of strength, lightweight properties, and oxidation resistance.

It has an ordered hexagonal (D0₁₉) crystal structure, which makes it distinct from the more commonly known γ-TiAl (gamma titanium aluminide).

Higher strength than conventional titanium alloys, especially at high temperatures. More brittle than pure titanium but tougher than γ-TiAl, making it useful in applications requiring a trade-off between toughness and lightweight properties.

Improved high-temperature oxidation resistance compared to pure titanium, but generally not as good as γ-TiAl or other high-temperature alloys like nickel-based superalloys. Often used with coatings to further enhance oxidation resistance.

Density and Lightweight Properties:

Lower density than traditional nickel-based superalloys, making it attractive for aerospace applications where weight reduction is crucial.

Operates effectively at 600–800°C, making it useful in jet engines, turbine components, and hypersonic vehicles.

Applications of Alpha 2-Ti₃Al:

Aerospace: Used in jet engine components, compressor blades, and airframe structures where high strength and lightweight properties are needed.

Automotive (High-Performance Vehicles): Some high-end applications in racing engines. Military and Defense: Structural components in hypersonic aircraft and advanced missiles.

Energy Sector: Potential use in turbine components for power generation.

Challenges and Limitations:

Brittleness: More brittle than conventional titanium alloys, requiring careful processing and potential use of composite materials.

Manufacturing Complexity: Difficult to process and fabricate due to its intermetallic nature, often requiring advanced techniques like powder metallurgy, additive manufacturing, or specialized forging methods.

Oxidation Resistance: While better than standard titanium, it still requires protective coatings for long-term use in extreme environments.

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]}