Diffusion aluminide coatings for TiAl intermetallic turbine blades

Alloys based on intermetallic phases of a Ti–Al system are materials that, thanks to their resistance characteristics, can be widely used in automotive and aerospace applications. The main restriction for the use of Ti–Al materials is their insufficient oxidation resistance above 850 °C. Oxidation parameters might be improved by aluminide coatings based on TiAl2 and TiAl3 phases, which could induce the creation of an Al2O3 scale in the oxidation process. This type of aluminide could be deposited on the surface of TiAl alloys by various methods such as pack cementation, plasma spraying or magnetron sputtering. This article presents a new method of aluminide coating deposition on TiAl intermetallic alloys: out of pack technology. The investigated coating was deposited on turbine blades made of a Ti45Al5Nb intermetallic alloy. The surface morphology, structure, phase and chemical composition have been investigated using XRD phase analysis, SEM and EDS. The phase analysis showed that TiAl3 and TiAl2 were the main components of the deposited coating. An isothermal oxidation test of the TiAl turbine blades was conducted as well. After 1000 h of testing at 950 °C, the scale formed on the surface of the uncoated blades underwent spallation. The scale on the turbine blade with deposited aluminide coatings was very thin and no spallation was observed.