γ-TiAl合金长期服役于高温环境中，其表面氧化和组织演变会影响合金部件的力学性能。因此，研究γ-TiAl合金在高温条件下的氧化行为至关重要。本工作研究了γ-TiAl铸造合金Ti-45Al-2Nb-2Mn-1B (45XD合金)和Ti-48Al-2Nb-2Cr (4822合金)在700 ℃空气中的长时等温氧化行为和组织演变。结果表明，4822合金的氧化增重和氧化膜增厚明显大于45XD合金。在0~2000 h内2种合金均表现出周期性氧化增重行为，即快速增长后缓慢增长交替进行，后期2者的氧化速率保持稳定。2种合金样品表面均形成了以表层TiO₂和Al₂O₃为主，靠近基体处为Ti/Al-N和富Nb/Mn(Cr)的分层氧化膜。45XD合金表面氧化产物细小致密，而4822合金表面氧化产物粗大疏松，内部存在微孔，且γ晶界处的大尺寸α₂相氧化严重，因此4822合金的抗高温氧化性能较差。受合金元素扩散的影响，45XD合金亚表层组织中的α₂片层发生分解：α₂→γ，在亚表层形成了一层富Al贫Ti的γ区；45XD合金内部组织中的α₂片层也部分转变为γ相，并且γ片层不断粗化。在4822合金内部组织中，γ晶粒内的α₂和晶界处的α₂ + β₀体积分数明显下降。

γ-TiAl alloys are a new generation of high-temperature lightweight materials characterized by low density, high specific modulus of elasticity, excellent high-temperature strength, and creep resistance, making them highly suitable for aviation, aerospace, and automotive engine applications. A typical application of the alloys is in the low-pressure turbine blades of aero-engines, such as GEnx and Trent XWB developed by the General Electric and Rolls-Royce, respectively. Their alloy compositions are Ti-48Al-2Cr-2Nb and Ti-45Al-2Nb-2Mn-1B (atomic fraction, %), respectively. γ-TiAl alloys are required for long-term service at 600-700 ^oC; however, they react readily with oxygen to form oxide scale when exposed in air at high temperatures, compromising service safety and reliability. Thus, understanding the long-term oxidation behavior of γ-TiAl alloys during service at high temperatures is imperative. In this study, the oxide scale and microstructural evolution of cast Ti-45Al-2Nb-2Mn-1B alloy (45XD alloy) and Ti-48Al-2Nb-2Cr alloy (4822 alloy) at 700 ^oC in air for 0-2000 h were investigated using SEM and TEM. The mass gain of both alloys was measured during oxidation, and their oxidation behaviors were compared. The 4822 alloy exhibited a notably higher mass gain than the 45XD alloy. Both alloys demonstrated periodic mass gain behavior during oxidation for 0-2000 h—alternating rapid and slow gains—with stabilization in the later stages. The oxide scales formed layered structures, primarily of TiO₂ and Al₂O₃, on the surface of both alloys; the scale of 45XD alloy was continuous and dense, whereas that of the 4822 alloy was porous. Additionally, the study revealed that α₂ lamellae in the subsurface of the 45XD alloy decomposed during oxidation, forming an Al-rich and Ti-lean γ zone on the subsurface. α₂ lamellae in the bulk microstructure of the 45XD alloy were also decomposed and transformed into γ phase. The 4822 alloy experienced a significant reduction in the volume fractions of α₂ in equiaxed γ grains and α₂ + β₀ at equiaxed γ grain boundaries.