Titanium aluminide

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Titanium aluminide
Names
IUPAC name
aluminum;titanium
Identifiers
3D model (JSmol)
ChemSpider
PubChem CID
  • InChI=1S/Al.Ti
    Key: KHEQKSIHRDRLMG-UHFFFAOYSA-N
  • [Al].[Ti]
Properties
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).

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.

Contents

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. MAUD-MTEX-TiAl-hasylab-2003-Liss.png
Pole figures displaying crystallographic texture of gamma-TiAl in a rolled sheet of alpha2-gamma alloy, as measured by high energy X-rays.

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 ]

Related Research Articles

<span class="mw-page-title-main">Titanium</span> Chemical element, symbol Ti and atomic number 22

Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in sea water, aqua regia, and chlorine.

A cermet is a composite material composed of ceramic (cer) and metal (met) materials.

<span class="mw-page-title-main">General Electric GEnx</span> Turbofan jet engine

The General Electric GEnx is an advanced dual rotor, axial flow, high-bypass turbofan jet engine in production by GE Aviation for the Boeing 787 and 747-8. The GEnx is intended to succeed the CF6 in GE's product line.

<span class="mw-page-title-main">Intermetallic</span> Type of metallic alloy

An intermetallic is a type of metallic alloy that forms an ordered solid-state compound between two or more metallic elements. Intermetallics are generally hard and brittle, with good high-temperature mechanical properties. They can be classified as stoichiometric or nonstoichiometic intermetallic compounds.

<span class="mw-page-title-main">Inconel</span> Austenitic nickel-chromium superalloys

Inconel is a registered trademark of Special Metals Corporation for a family of austenitic nickel-chromium-based superalloys.

Titanium alloys are alloys that contain a mixture of titanium and other chemical elements. Such alloys have very high tensile strength and toughness. They are light in weight, have extraordinary corrosion resistance and the ability to withstand extreme temperatures. However, the high cost of both raw materials and processing limit their use to military applications, aircraft, spacecraft, bicycles, medical devices, jewelry, highly stressed components such as connecting rods on expensive sports cars and some premium sports equipment and consumer electronics.

<span class="mw-page-title-main">Superalloy</span> Alloy with higher durability than normal metals

A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, good surface stability, and resistance to corrosion or oxidation.

<span class="mw-page-title-main">Titanium hydride</span> Chemical compound

Titanium hydride normally refers to the inorganic compound TiH2 and related nonstoichiometric materials. It is commercially available as a stable grey/black powder, which is used as an additive in the production of Alnico sintered magnets, in the sintering of powdered metals, the production of metal foam, the production of powdered titanium metal and in pyrotechnics.

Nickel aluminide typically refers to the one of the two most widely used compounds, Ni3Al or NiAl, however is generally any aluminide from the Ni-Al system. These alloys are widely used due to their corrosion resistance, low-density and easy production. Ni3Al is of specific interest as the strengthening γ' phase precipitate in nickel-based superalloys allowing for high temperature strength up to 0.7-0.8 of its melting temperature. Meanwhile, NiAl displays excellent properties such as low-density (lower than that of Ni3Al), good thermal conductivity, oxidation resistance and high melting temperature. These properties, make it ideal for special high temperature applications like coatings on blades in gas turbines and jet engines. However, both these alloys do have the disadvantage of being quite brittle at room temperature while Ni3Al remains brittle at high temperatures as well. Although, it has been shown that Ni3Al can be made ductile when manufactured as a single crystal as opposed to polycrystalline. Another application was demonstrated in 2005, when the most abrasion-resistant material was reportedly created by embedding diamonds in a matrix of nickel aluminide.

Electron-beam additive manufacturing, or electron-beam melting (EBM) is a type of additive manufacturing, or 3D printing, for metal parts. The raw material is placed under a vacuum and fused together from heating by an electron beam. This technique is distinct from selective laser sintering as the raw material fuses having completely melted.

<span class="mw-page-title-main">Directional solidification</span>

Directional solidification(DS) and progressive solidification are types of solidification within castings. Directional solidification is solidification that occurs from farthest end of the casting and works its way towards the sprue. Progressive solidification, also known as parallel solidification, is solidification that starts at the walls of the casting and progresses perpendicularly from that surface.

<span class="mw-page-title-main">Turbine blade</span>

A turbine blade is a radial aerofoil mounted in the rim of a turbine disc and which produces a tangential force which rotates a turbine rotor. Each turbine disc has many blades. As such they are used in gas turbine engines and steam turbines. The blades are responsible for extracting energy from the high temperature, high pressure gas produced by the combustor. The turbine blades are often the limiting component of gas turbines. To survive in this difficult environment, turbine blades often use exotic materials like superalloys and many different methods of cooling that can be categorized as internal and external cooling, and thermal barrier coatings. Blade fatigue is a major source of failure in steam turbines and gas turbines. Fatigue is caused by the stress induced by vibration and resonance within the operating range of machinery. To protect blades from these high dynamic stresses, friction dampers are used.

<span class="mw-page-title-main">Waspaloy</span> Nickel-based superalloy, United Technologies Corp trademark

Waspaloy is a registered trademark of United Technologies Corp that refers to an age hardening austenitic nickel-based superalloy. Waspaloy is typically used in high temperature applications, particularly in gas turbines.

In materials science, the yield strength anomaly refers to materials wherein the yield strength increases with temperature. For the majority of materials, the yield strength decreases with increasing temperature. In metals, this decrease in yield strength is due to the thermal activation of dislocation motion, resulting in easier plastic deformation at higher temperatures.

<span class="mw-page-title-main">Selective laser melting</span> 3D printing technique

Selective laser melting (SLM) is one of many proprietary names for a metal additive manufacturing (AM) technology that uses a bed of powder with a source of heat to create metal parts. Also known as direct metal laser sintering (DMLS), the ASTM standard term is powder bed fusion (PBF). PBF is a rapid prototyping, 3D printing, or additive manufacturing technique designed to use a high power-density laser to melt and fuse metallic powders together.

<span class="mw-page-title-main">General Electric Passport</span> High bypass turbofan aircraft engine

The General Electric Passport is a turbofan developed by GE Aviation for large business jets. It was selected in 2010 to power the Bombardier Global 7500/8000, first run on June 24, 2013, and first flown in 2015. It was certified in April 2016 and powered the Global 7500 first flight on November 4, 2016, before its 2018 introduction. It produces 14,000 to 20,000 lbf of thrust, a range previously covered by the General Electric CF34. A smaller scaled CFM LEAP, it is a twin-spool axial engine with a 5.6:1 bypass ratio and a 45:1 overall pressure ratio and is noted for its large one-piece 52 in (130 cm) fan 18-blade titanium blisk.

<span class="mw-page-title-main">General Electric GE9X</span> High-Thrust Turbofan Jet Engine

The General Electric GE9X is a high-bypass turbofan developed by GE Aviation exclusively for the Boeing 777X. It first ran on the ground in April 2016 and first flew on March 13, 2018; it powered the 777-9's maiden flight in early 2020. It received its Federal Aviation Administration (FAA) type certificate on September 25, 2020. Derived from the General Electric GE90 with a larger fan, advanced materials like ceramic matrix composites (CMCs), and higher bypass and compression ratios, it was designed to improve fuel efficiency by 10% compared to the GE90. It is rated at 110,000 lbf (490 kN) of thrust, which is 5,000 lbf less than the GE90 highest thrust variant, the GE90-115 rated at 115,000 lbf (510 kN).

Ti-6Al-2Sn-4Zr-2Mo, also known as Ti 6-2-4-2, is a near alpha titanium alloy known for its high strength and excellent corrosion resistance. It is often used in the aerospace industry for creating high-temperature jet engines and the automotive industry to create high performance automotive valves.

<span class="mw-page-title-main">Inconel 625</span> Nickel-based superalloy

Inconel Alloy 625 is a nickel-based superalloy that possesses high strength properties and resistance to elevated temperatures. It also demonstrates remarkable protection against corrosion and oxidation. Its ability to withstand high stress and a wide range of temperatures, both in and out of water, as well as being able to resist corrosion while being exposed to highly acidic environments makes it a fitting choice for nuclear and marine applications.

Iron aluminides are intermetallic compounds of iron and aluminium - they typically contain ~18% Al or more.

References

  1. ↑ Voskoboinikov, R.E.; Lumpkin, G.R.; Middleburgh, S.C. (2013). "Preferential formation of Al self-interstitial defects in γ-TiAl under irradiation". Intermetallics . 32: 230–232. doi:10.1016/j.intermet.2012.07.026.
  2. ↑ Liss KD, Bartels A, Schreyer A, Clemens H (2003). "High energy X-rays: A tool for advanced bulk investigations in materials science and physics". Textures Microstruct. 35 (3/4): 219–52. doi: 10.1080/07303300310001634952 .
  3. ↑ Thomas, M.; Bacos, M. P. (November 2011). "Processing and Characterization of TiAl-based Alloys : Towards an Industrial Scale". Aerospace Lab. 3: 1–11.
  4. ↑ Bewlay BP, Nag S, Suzuki A, Weimer MJ (2016). "TiAl alloys in commercial aircraft engines". Materials at High Temperatures . 33 (4–5): 549–559. doi:10.1080/09603409.2016.1183068. S2CID   138071925.
  5. ↑ "GE Aviation Rolls Out its 1,000th GEnx Engine". AviationPros. 21 October 2015. Retrieved 10 August 2017.
  6. ↑ Moeller Manufacturing, Aerospace Division, in Wixom, Michigan, USA
  7. ↑ Heidi Milkert (18 August 2014). "GE Uses Breakthrough New Electron Gun For 3D Printing – 10X's More Powerful Than Laser Sintering". 3D Print.com.
  8. ↑ Tim Barber (31 August 2019). "The new Omega Seamaster Aqua Terra is made of titanium and weighs just 55g". Wired .
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