采用第一原理方法,计算了MoSi_2及其三元合金(Mo,M)Si_2(M=Nb、Tc、Ta、W)的电子结构,表面能(γ_s),不稳定层错能(γ_(us)),以及弹性常数.从"韧化参数"D-γ_s/γ_(us)以及弹性性质两个方面研究了合金化对MoSi_2韧性的影响.研究表明,MoSi_2(001)Si-|-Si具有较低的表面能,是最可能的解理面;带有方向性的强Mo4d-Si3p共价键是MoSi_2本征脆性的最主要原因.Nb、Tc、Ta合金化有利于增强MoSi_2的韧性;W则起到增脆作用.合金增韧的主要原因是弱M4d-Si3p键代替了方向性的强Mo4d-Si3p键.
With first-principles method, electronic structure, surface energy (γ_s), unstable stacking fault energy (γ_(us)), and the elastic parameters of MoSi_2 and (Mo, M)Si_2 (M= Nb, Tc, Ta, W) were obtained. By combining a "disembrittlement parameter" D=γ_s/γ_(us) and elastic properties, the influence of alloying elements on ductility was investigated. Ideal MoSi_2 crystal investigation shows that MoSi_2 (001) Si-|-Si plane with lower surface energy is preferred cleavage plane. Intrinsic hrittlement of MoSi_2 is caused by strong directional covalent Mo4d-Si3p bonding. Nb, Tc, and Ta alloying are found to be beneficial to the enhancement of ductility. In contrast, W alloying embrittles MoSi_2. Softening effect can be interpreted by the replacement of Mo4d-Si3p bonding by weaker and less directional M4d-Si3p bonding.
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