The influence of Mn and Cr elements on the isothermal oxidation behavior of γ-TiAl alloys

This study systematically analyzed the thermal exposure behavior of two gamma titanium aluminide alloys (Ti-48Al-2Mn-2Nb and Ti-48Al-2Cr-2Nb) to investigate the effects of Mn and Cr elements on the oxidation resistance of the alloys at different temperatures of 750 °C, 850 °C, and 950 °C. At 750 °C and short thermal exposure times, Mn increases the α₂ transformation temperature and reduces the α₂ phase content, thereby hindering the diffusion of oxidation atmosphere and enhancing the oxidation resistance of the alloy. At increasing temperature, Mn tends to form oxidation products, disrupting the continuity of the oxidation layer and reducing the bonding strength, which has a detrimental effect on the oxidation resistance of the alloy. At low Cr contents, as the thermal exposure time increases, Cr exists in the form of Cr³⁺, increasing the concentration of oxygen vacancies and promoting the growth of TiO₂, thereby weakening the oxidation resistance of the alloy. At 750 °C, Ti-48Al-2Mn-2Nb exhibits better oxidation resistance; at 850 °C, the two alloys have similar oxidation resistance; and at 950 °C, the oxidation scale thickness increases dramatically, with Ti-48Al-2Mn-2Nb experiencing severe oxidation layer shedding, whereas Ti-48Al-2Cr-2Nb shows relatively good oxidation resistance.