Evaluation of Long-term Oxidation Properties of Al-21Ti-23Cr and Al-37Ti-12Cr Coating Materials for TiAl Alloy

摘要

Both Al-21Ti-23Cr(L1_2+Cr_2Al) and Al-37Ti-12Cr(gamma+TiAlCr) two-phase alloys have been accepted to be the most pertinent coating materials in Al-Ti-Cr alloy system to improve the high-temperature oxidation resistance of TiAl alloy taking into consideration of the oxidation properties, the resistance to thermal stress and the chemical compatibility. The cyclic oxidation tests at 1000 deg C and 1200 deg C were performed for the specimens coated with both materials of 10 mum thickness, and the breakaway oxidation could be observed although both bulk alloys could form a stable Al_2O_3 layer. And it was resulted from depleted Al content in the coating layer due to Al_2O_3 oxide growth and interdiffusion with substrate. Considering the decrease of Al content resulting from oxide growth, the Al-21Ti-23Cr coating with higher initial Al content was more effective for oxidation protection of TiAl alloy for long-term service. On the other hand, when the change of Al content due to the interdiffusion with substrate was considered, the Al-37Ti-12Cr coating with smaller compositional gradient with TiAl substrate was more effective than the Al21Ti-23Cr coating. However, it was confirmed through the cyclic oxidation tests at 1000 deg C and 1200 deg C that the initial Al content was more important for longer life-time of coating materials than the smaller compositional gradient with substrate. Therefore, the Al-21Ti-23Cr coating would be supposed to be more effective for long-term oxidation resistance of TiAl alloys.