Titanium aluminide

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

Structure

In the binary phase diagram of titanium aluminum to Murray, McCullough and Huang least four intermetallic phases exist. The two most important are the hexagonal α2 - Ti3Al which may contain about 25 to 35 % of aluminum at room temperature and the γ -TiAl to 50 to 55 % aluminum, L10 on the structure and a tetragonally distorted cubic face-centered unit cell. Some of the industrially important Ti-Al alloys with aluminum contents between 35 and 50 % from a mixture of these two phases.

There are also the less temperature-resistant phases TiAl2 with about 65 % and η - Al 3 Ti with about 75 % aluminum. The ordered phases Ti2Al5 and Ti5Al11 are not yet sufficiently investigated.

Properties

Titanium aluminides have at low density ( 3.8 g / cc) to very good strength and stiffness properties and can be used for certain components (e.g., gas turbines) alloys with much higher density (8.5 g / cc) to replace. The great advantage of low weight are, however, problems

• High surface oxidation over.

The surface oxidation limits the maximum operating temperature to about 750 ° C. In research projects will therefore seek to develop the material further application areas:

• At the TU Chemnitz 2005, a cost- effective manufacturing process was developed and patented. It uses waste from the titanium and aluminum production, which are processed in a sintering process to Titantrialuminiden.
• 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 above 1000 ° C.
• The Institute of Machining Technology (ISF ), TU Dortmund University is working on the use of γ - titanium aluminide as a material for connecting rods and valves in car engines.