Ti-Al-Cr-X Coatings for High Temperature Oxidation Protection of Gamma Titanium Aluminides for Elevated Temperatures

Kurzfassung

To extend the oxidation resistance of gamma titanium aluminides for applications above 750°C the formation of non-protective titanium oxide has to be prevented. The primary objective to improve the resistance of titanium aluminides against oxidation is the use of alumina forming coatings. The paper is focussed on the development of oxidation resistant metallic coatings on the basis of Ti-Al-Cr. Ti-Al-Cr and Ti-Al-Cr-X coatings with X=Ag,Hf,Y,Si were produced by magnetron sputtering techniques. The coated specimens were examined under cyclic conditions at 900°C and 950°C up to 1000 cycles, respectively. All coatings formed a thin alumina layer on top providing a diffusion barrier for oxygen at the beginning. But internal diffusion between substrate and coating led to a depletion of Laves phase which promotes the formation of alumina. The effect of cross diffusion between coating and substrate for the various coating chemistries will be discussed on the basis of post-oxidation SEM/EDX and oxidation kinetics analysis.