采用第一性原理计算方法，计算了二元γ-TiAl基合金的广义层错能(GSFE)随成分的变化，获得了TiAl基合金中孪晶(TW)、普通位错(OD)、超晶格位错(SD_I和SD_II)等变形模式的形变势垒，分析了在外加应力作用下的变形模式选择，并讨论反位缺陷对二元γ-TiAl基合金塑性的影响。计算结果表明，Ti_Al反位缺陷能降低以超晶格内禀层错(SISF)为前缘分位错的TW变形模式的势垒，且扩大TW模式开动的剪切应力角度窗口，有利于改善TiAl基合金的塑性。Al_Ti反位缺陷则反之。Al_Ti反位缺陷降低了以复杂层错(CSF)为前缘分位错的OD和SD_II变形模式的滑移势垒(γ_EB)，而且扩大了它们开动的剪切应力角度窗口，可促进OD和SD_II的滑移。由于CSF的滑移势垒比SISF高，因此，相较于以SISF为前缘分位错的TW变形模式，OD及SD_II滑移对应的强度较高、塑性较差。计算结果较好地说明了Al_Ti反位缺陷对TiAl基合金塑性的改善没有Ti_Al反位缺陷明显的原因。

Microalloying is an effective approach to improve the mechanical properties of TiAl-based alloys which have been applied as high-temperature structure materials. The antisite defects may be regarded as special alloying elements. However, the detailed information about the effect of antisite defects on mechanical behavior (full slip and twinning), which may be described theoretically by generalized stacking fault energy (GSFE), of TiAl-based alloys are scarce. In this work, the composition dependent GSFEs of off-stoichiometric γ-TiAl were calculated by using the first-principles exact muffin-tin orbitals method in combination with coherent potential approximation. With the calculated GSFE, the energy barriers for various deformation modes including twin (TW), ordinary dislocation (OD), and superlattice dislocation (SD_I and SD_II) were determined. The selection of the deformation mode under external shear stress with various directions was analyzed. The effects of the Ti_Al and Al_Ti antisite defects on the mechanical properties of γ-TiAl were then discussed. The results showed that the Ti_Al antisite defect decreases the energy barrier for the TW deformation leading by the superlattice intrinsic stacking fault (SISF) partial dislocation and increases the angle window of the applied shear stress within which TW deformation may be activated. Therefore, Ti_Al antisite defect is expected to improve the plasticity of γ-TiAl. The effect of Al_Ti antisite defect is opposite. The Al_Ti antisite defect decreases the energy barriers for the OD and SD_II deformations leading by complex stacking fault (CSF) partial dislocation and increases their operating angle window, indicating that Al_Ti facilitates the slip of OD and SD_II. Considering that the energy barrier for CSF is much higher than that for SISF, the plasticity induced by OD and SD_II should be lower than that induced by TW. Calculations in this work explain the experimental finding that Ti_Al antisite defect improves the plasticity of γ-TiAl more significantly than Al_Ti antisite defect.