Advanced Coatings for Protection of Titanium Aluminide against Embrittlement

The titanium aluminide alloys are known to be sensitive to environmental embrittlement which deteriorates the mechanical properties. This is still a critical issue, for e.g. the aeronautic and automotive industry, if titanium aluminide alloys are chosen as a substitute for Ni-based superalloys. It is anticipated that the project will lead to a greater understanding of the environmental embrittlement of TiAl and provide an insight into how microstructure and composition may influence the phenomena. As the main task new coatings and a special halogen surface treatment based on fluorine will be developed to decrease the embrittlement sensibility of TiAl alloys. The aim of this project is to develop coatings or scales which may act as a physical barrier against hot gases and preserve the mechanical properties. The combination of advanced coatings with graded composition and the halogen effect (controlled surface treatment with fluorine) is thought to be an efficient way to protect TiAl alloys against hot gas embrittlement for the two envisaged applications (aeronautic and automotive) and others. The coatings and the F-treatment will be applied on two types of alloys (one with high ductility and one with high strength). Physical (HVOF, triode sputtering) and chemical (MOCVD,) techniques will be used to produce the coatings. The oxidation resistance of coated and F-treated specimens will be tested under isothermal and cyclic (1hhot cycle) conditions for temperatures up to 850 °C. Hot corrosion by molten salt deposit (chloride/sulphate mixture) will also be investigated. For corrosion resistant coatings, coated specimens will be tested under tensile, creep, impact and fatigue conditions in order to investigate whether mechanical properties are affected.

BMWi/AiF Project:

“Vermeidung der Versprödung von Legierungen auf Basis TiAl mittels Beschichtungen mit funktionellen Eigenschaften, um die mechanischen Eigenschaften zu erhalten” (IGF-No. 24EBG)

Partners:

DECHEMA Gesellschaft für Chemische Technik und Biotechnologie e.V. (DECHEMA)
Materialscluster GmbH (MCL)
ATZ Entwicklungszentrum (ATZ)
GKSS-Forschungszentrum Geesthacht GmbH (GKSS)
Österreichisches Gießerei-Institut (ÖGI)
TU Bergakademie Freiberg
Technische Universität Wien, Institut für Fertigungstechnik (VUT/IFT)