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利用基于第一原理的离散变分法研究了Fe-Mn-Si合金的电子结构与FCC相稳定性的关系.Si元素使Fe原子的d带空穴数减少,而Mn的影响较复杂.以此为基础,从电子浓度的角度解释了这两种元素对合金层错能的影响,并结合对合金结合能的计算结果——Si降低合金的结合能而Mn的作用相反,阐述了Mn降低而Si升高马氏体相变温度的物理原因.在不同方向上施加应力时,合金的电子结构发生变化,Fermi能级处的总态密度有明显提高.从Fermi能级附近的能谱变化可看出,应变使能隙减小,能级的简并性提高.在同一方向上施以不同的应变,中心原子的3d和4s轨道上的电子数减少,3d局域态密度变窄,且峰值增加.对比电子密度的变化,在应力方向上的成键轨道有减弱的趋势,而在垂直于应力的方向上出现增强,导致FCC结构的稳定性降低.这是外场(应力)作用下合金的马氏体相变温度提高的重要原因.
The relationship between the electronic structure of Fe-Mn-Si alloy and the stability of FCC phase was studied by the discrete variational method based on the first principle. The Si element reduced the d-band hole number of Fe atom and the influence of Mn was more complicated. Based on this, the influence of these two elements on the layer stacking fault energy is explained from the electron concentration perspective. Combined with the calculation results of the binding energy of the alloy - Si reduces the binding energy of the alloy and the effect of Mn is opposite, the reduction of Mn While Si increases the martensitic transformation temperature. When the stress is applied in different directions, the electronic structure of the alloy changes and the total density of states at the Fermi level increases obviously. From the change of the energy spectrum near the Fermi level It can be seen that the strain makes the energy gap decrease and the degeneracy of the energy level increases.During different strains in the same direction, the number of electrons on the 3d and 4s orbital of the central atom decreases and the density of 3d local state becomes narrower, And the peak value increases.Compared with the change of electron density, the bonding orbital in the direction of stress has a weaker tendency, and in the direction perpendicular to the stress increases, resulting in the decrease of the stability of the FCC structure.This is the effect of the external field (stress) Alloy martensitic transformation temperature is important to improve the original .