Titanium aluminides

When titanium aluminide (TiAl) is intermetallic compounds of titanium and aluminum . They can be represented both as a structural material and as a coating material .

structure

In the binary phase diagram of titanium-aluminum according to Murray, McCullough and Huang, there are at least four intermetallic phases. The two most important are the hexagonal α ₂ Ti ₃ Al, which may contain up to 35% of aluminum at room temperature is about 25 and the γ-TiAl with 50 to 55% aluminum, L1 ₀ - About structure and a tetragonal distorted face-centered cubic unit cell . Some of the technically important Ti-Al alloys also consist of a mixture of these two phases with aluminum contents between 35 and 50%.

There are also the less temperature-resistant phases TiAl ₂ with about 65% and η – Al ₃ Ti with about 75% aluminum. The ordered phases Ti ₂ Al ₅ and Ti ₅ Al ₁₁ have not yet been adequately investigated.

properties

Texture pole figures made of gamma-TiAl in a rolled sheet of an alpha2-gamma two-phase alloy.

Titanium aluminides have very good strength and rigidity properties at a low density (3.8 g / cm³) and can replace nickel alloys with a significantly higher density (8.5 g / cm³) for certain components (e.g. gas turbines and engines ) . The big advantage of the low weight, however, are the problems

• high price as well
• high surface oxidation compared to.

The surface oxidation limits the maximum working temperature to approx. 750 ° C. Research projects are therefore trying to open up further areas of application for the material:

• In 2005, a more cost-effective manufacturing process was developed and patented at the TU Chemnitz. It uses waste from titanium and aluminum production, which is processed into titanium tripuminides in a sintering process .
• The DECHEMA research institute is working on protective surface coatings through halogenation , which significantly improve the oxidation resistance and thus extend the usable temperature range to over 1000 ° C.
• The Institute for Machining Production (ISF) at the Technical University of Dortmund is working on the use of γ-titanium aluminide as a material for connecting rods and valves in motor vehicle engines.

literature

• JH Westbrook, Robert L. Fleischer (Eds.): Intermetallic Compounds: Principles and Applications. 2 Volume Set: Principles / Practice v. 1 & 2 . John Wiley & Sons, 1994, ISBN 0-471-93453-4 .
• JH Westbrook, Robert L. Fleischer (Ed.): Intermetallic Compounds: Progress: 3 . John Wiley & Sons, Chichester 2002, ISBN 0-471-49315-5 .
• Gerhard Sauthoff : Intermetallics . Wiley-VCH, 1995, ISBN 3-527-29320-5 .

swell

1. ↑ ^{a b} Tom Majewski: Trace determination of metallic impurities in γ-TiAl and the high-purity starting materials Al and Ti by means of ICP mass spectrometry. Dissertation, University of Hanover 2002, DNB 965453219/34 , p. 5. and sources [14] - [19]
2. ↑ Liss KD, Bartels A, Schreyer A, Clemens H: High energy X-rays: A tool for advanced bulk investigations in materials science and physics . In: Textures Microstruct. . 35, No. 3/4, 2003, pp. 219-52. doi : 10.1080 / 07303300310001634952 .
3. ↑ Titanium aluminide - MTU Aero Engines develops a new material for turbine blades. In: pressebox.de. MTU Aero Engines , March 23, 2015, accessed on December 16, 2017 . 
4. ↑ TU Chemnitz: New manufacturing process for titanium aluminides ( Memento from January 6, 2013 in the web archive archive.today ).
5. ↑ Dechema project on the halogen effect on titanium aluminides in the high-temperature materials working group
6. ↑ Page no longer available , search in web archives: Gamma-Titanaluminide connecting rod  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.