On the influence of coating and oxidation on the mechanical properties of a γ-TiAl based alloy

The use of γ-TiAl based alloys in high-temperature applications requires an effective protection against oxidation and concomitant loss of ductility. Two coatings, Al2Au and Cr0.45Al0.53Y0.02N (CrAlYN), are tested for their oxidation protection in air and their influence on the mechanical properties of a Ti-47Al-2Cr-0.2Si alloy. Both coatings significantly improve the oxidation resistance of the investigated γ-TiAl. The plastic strain in the γ-TiAl outer fiber during four-point-bending tests at room temperature is reduced by the deposition with Al2Au and CrAlYN. After 168 h oxidation at 800 °C uncoated and Al2Au coated γ-TiAl samples crack without plastic deformation due to the oxide layers and interdiffusion zones formed. Contrary, a CrAlYN protected γ-TiAl four-point-bending specimen still exhibits a plastic strain of 0.12% after oxidation at 800 °C for 672 h, as a thin and dense oxide layer forms. We conclude that CrAlYN effectively retards oxidation and interdiffusion of γ-TiAl and hence the commonly observed deterioration of mechanical properties by oxidation and interdiffusion is significantly reduced.