Oxidation Protective Coatings for γ-TiAl – Recent Trends

Abstract

Engine designers show continued interest in γ-TiAl based titanium aluminides as light–weight structural materials to be used at moderately elevated temperatures. Although alloy development has made significant progress in terms of mechanical properties and environmental resistance, protective coatings have been developed that help to extend the lifetime of these alloys significantly. The major challenge of coating development is to prevent the formation of fast growing titania. Furthermore, changes of coating chemistries at high temperatures have to be considered in order to avoid rapid degradation of the coatings due to interdiffusion between substrate and coating. The paper describes recent work of the authors on different coatings produced by means of magnetron sputter technique. Thin ceramic Ti-Al-Cr-Y-N layers tested at 900°C exhibited poor oxidation resistance. In contrast, intermetallic Ti-Al-Cr, Si-based and aluminum rich Ti-Al coatings were tested at exposure temperatures up to 950°C for 1000h resulting in reasonable and partially excellent oxidation behaviour.