Long-term oxidation properties of Al–Ti–Cr two-phase alloys as coating materials for TiAl alloys

Abstract

Both Al–21Ti–23Cr (L12+Cr2Al) and Al–37Ti–12Cr (γ+TiAlCr) two-phase alloys have been accepted as the most appropriate coating materials in the Al–Ti–Cr alloy system to improve the high-temperature oxidation resistance of TiAl alloy, taking into consideration their oxidation resistance, resistance to thermal stress, and chemical compatibility with TiAl alloys. In this study, thermal stress analyses were performed on the basis of the thermal expansion coefficient and tensile and compressive strength of coating and substrate materials. Also the reaction properties between the alloys of interest in this paper and TiAl substrate were studied by bonding the two materials. This elucidates the long-term oxidation properties in L12-based and γ-based alloys. There was no significant difference in short-term oxidation resistance between the L12-based and γ-based alloys because both alloys could form a stable Al2O3 layer. However, although both alloys show similar resistance to thermal stress, it was confirmed that the L12-based two-phase alloy has much better oxidation properties than the γ-based two-phase alloy in long-term oxidation as it is considering the interface reaction properties with TiAl alloy.