MOCVD processed platinum–aluminum coatings on titanium alloys

Reduced oxidation and corrosion resistance at high temperature are limiting factors to the application of titanium alloys in aero gas turbine engines despite their interesting mechanical properties in view of their low density. Adapted protective coatings such as platinum–aluminum based films can be applied on the surface of titanium alloys in order to replace heavier materials such as steels that are currently used in parts of turbines operating at temperatures exceeding 723 K. In the present contribution, preliminary results of an original processing route for such coatings is proposed, based on sequential application of the two elements by metallorganic chemical vapor deposition (MOCVD). This process presents significant advantages relatively to the usually used ones, namely relatively simple operation and reduced contamination of the films. Deposition of Pt and of Al was performed respectively with tri-methyl-methylcyclopentadienyl platinum (IV) at 573 K and with tri-isobutylaluminum at 623 K, on Ti6242 disks at 9330 Pa. To achieve simultaneous deposition on all sides of the substrates in view of subsequent isothermal and cyclic oxidation treatments, an original configuration of the deposition setup was realized, and deposition uniformity was optimized by fluid mechanic simulations using a CFD software. Microstructural characterization of the coatings reveals that, while aluminum is deposited in the form of filaments on platinum films, dense coatings can be obtained if iodine is adsorbed on the growing surface.