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Oxidation Protection

Complex microstructure of an oxide layer on a coated Ti-Al-Nb alloy. View enlargement

To utilize the full potential of modern Ti alloys, Ti aluminides and fibre reinforced Ti alloys, an effective oxidation protection is necessary. The growth of the oxide layer and its stability as well as the embrittlement of the material due to incorporation of oxygen are of major importance. For Ti-base alloys two effects must be considered: oxide layer formation and solution of non-metals in the outer layers.

Coatings for Ti-alloys and Ti-aluminides

In general, three different ways to improve oxidation behaviour are possible:

1. alloying
2. pre-oxidation and
3. coatings.

The last option is the preferred choice for developments in the institute as it provides optimal balance between improved oxidation behaviour and maintenance of  the mechanical properties of the base material. Examples of  such coatings are Al-Ti-Cr layers or nano-structured multilayer made of  nitrides/oxides.

Development goals

Based on the magnetron sputtering technique the major focus is on:

1. good adhesion of the coatings
2. long-term stability of the coatings
3. maintenance of the substrate mechanical properties
4. thermal protection of Ti-aluminides with thermal barrier coatings
5. high temperature application of coatings for Ti-based alloys up to 900°C

Testing of oxidation protection coatings

To evaluate the potential of the coatings, analytical characterization methods are used. Test rigs are operated ranging from standardised thermocyclic testing, oxidation experiments, to testing the influence of the coatings on the mechanical behaviour of the base materials, e.g. by fatigue tests.