Oxidation Resistance and Ductility of a Coated γ-TiAl Based Alloy

Abstract

The use of γ-TiAl based alloys in high temperature applications requires an effective protection against oxidation. Therefore, two coatings, Al2Au and Cr0.45Al0.53Y0.02N (CrAlYN), are tested for their oxidation protection and influence on the mechanical properties of a γ-TiAl based alloy (Ti-47Al-2Cr-0.2Si). Thermal exposure in air reveals that both coatings significantly improve the oxidation resistance. The specific mass gain after oxidation for 672 h at 800 °C is 0.12 mg/cm2 for CrAlYN coated and 0.79 mg/cm2 for Al2Au coated, but 8.9 mg/cm2 for the uncoated γ-TiAl. The plastic strain in the γ-TiAl outer fiber during four-point-bending tests is reduced from 0.52 % to 0.31 and 0.20 % by the deposition of Al2Au and CrAlYN, respectively. After oxidation at 800 °C for 168 h, uncoated and Al2Au coated γ-TiAl fail without plastic deformation due to the formed oxide layers and interdiffusion zones. Contrary, CrAlYN deposited γ-TiAl still exhibits plastic strain of 0.097 and 0.122 % after oxidation at 800 °C for 168 and 672 h. Based on these results it can be concluded that CrAlYN can effectively retard oxidation and interdiffusion of γ-TiAl. Hence, the commonly observed loss of mechanical properties by oxidation and interdiffusion can be avoided.