Graded plasma-anodised oxide coatings for wear and corrosion protection on titanium aluminides

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Titanium aluminides show the potential to substitute Ni-based alloys in temperature ranges up to 800 °C. However, a broad use as light-weight construction materials - e.g. in aircraft turbines - is not yet opened up due to their brittleness at room temperature and their low resistances against wear as well as high-temperature oxidation. As a conclusion, protective coatings have to improve the wear and oxidation behaviour. To face these demands, the present project investigates the plasma-electrolytic anodic oxidation (PAO, or plasma-electrolytic oxidation PEO), that is already generally accepted in its application on tiitanium alloys. The scientific aim of the project is the development, investigation and description of a process that produces graded ceramic protive coatings on titanium aluminides that show alumina-rich top layers. This aim will be achieved by two separated scientific branches. The first approach investiagtes a two-staged process using a preliminary aluminium donator coating that will be fully oxidised during the plasma-electrolytic anodising to form a dense alumina protective top layer. The second approach investigates the influences of electrolyte additives (aluminates) to achieve a one-staged plasma-anodising process for the direct production of alumina-rich graded PAO coatings on titanium aluminides. Both approaches will provide basic knowledge concerning formation, microstructure and behaviour of PAO coatings on titanium aluminides.