第一性原理研究反位缺陷對TiAl基合金力學行為的影響

第一性原理研究反位缺陷對TiAl基合金力學行為的影響The Impact of Antisite Defects on the Mechanical Properties of TiAl-Based Alloys: A First-Principles Study

本文采用第一性原理計算方法, 計算了二元γ-TiAl基合金的廣義層錯能 (GSFEs) 隨成分的變化, 獲得了TiAl基合金中孿晶(TW), 普通位錯(OD), 超晶格位錯(SD)等變形模式的形變勢壘, 分析了在外加應力作用下的變形模式選擇. 基于上述結(jié)果, 討論反位缺陷對二元γ-TiAl基合金塑性的影響. 計算結(jié)果表明, TiAl反位缺陷降低以超晶格內(nèi)稟層錯(SISF)為前緣分位錯的孿晶(TW)變形模式的勢壘, 且擴大TW模式開動的剪切應力角度窗口, 有利于改善TiAl的塑性. AlTi反位缺陷則反之. AlTi反位缺陷降低了以復雜層錯(CSF)為前緣分位錯的普通位錯(OD)和超晶格位錯(SDII)變形模式的滑移勢壘, 而且擴大了它們開動的剪切應力角度窗口, 可促進OD和SDII的滑移. 由于CSF的滑移勢壘較SISF高, 因此, 相較于以SISF為前緣分位錯的TW變形模式, OD及SDII滑移對應的強度較高, 塑性較差. 計算結(jié)果較好地說明了AlTi反位缺陷對TiAl塑性的改善沒有TiAl反位缺陷明顯.

The composition dependent generalized stacking fault energy (GSFE) 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) were determined. The selection of the deformation mode under external shear stress with various directions was analyzed. The effects of the TiAl and AlTi antisites on the mechanical properties of γ-TiAl were then discussed. We showed that the TiAl antisite 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, TiAl antisite is expected to improve the plasticity of γ-TiAl. The effect of AlTi antisite is opposite. The AlTi antisite decreases the energy barriers for the OD and SDII deformations leading by complex stacking fault (CSF) partial dislocation and increases their operating angle window, indicating that AlTi facilitates the slip of OD and SDII. Considering that the energy barrier for CSF is much higher than that for SISF, the plasticity induced by OD and SDII should be lower than that induced by TW. Our calculations explain the experimental finding that TiAl antisite improves the plasticity of γ-TiAl more significantly than AlTi antisite.

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