摘要:
基于密度泛函理论第一性原理方法,采用广义梯度近似下的PW91泛函形式,计算了合金元素Cr, Mo, Ni固溶于α-Fe(C)的电子结构,从晶格畸变、结合能、态密度、重叠布居及差分电荷密度等计算结果出发探讨了合金元素在α-Fe(C)中占位、键合性质及其合金化效应,结果表明： Cr优先占据铁素体晶胞顶角位置,而Mo, Ni 优先占据体心位置； Cr与晶胞的结合能最大,晶胞最稳定, Ni次之, Mo最低； Cr, Mo, Ni 在晶胞中都存在金属键、共价键和微弱离子键的共同作用,成键轨道主要是Cr3d与Fe3d, Mo4d与Fe3d, Ni3d与Fe3d, C2p的交互作用形成的； Cr与晶胞原子间的键合作用强,晶胞的稳定性好,对增强钢材的机械性能帮助较大, Ni的键合作用较弱,但还是能保持晶胞的稳定性, Mo虽然键合作用强,但反键作用也非常强,使晶胞的稳定性大大降低,对钢材的机械性能危害较大。
Abstract:
Variations of electronic properties of bulk α-Fe(C) due to the addition of Cr, Mo, Ni are studied using the first principles method, which is based on the density functional theory (DFT). Lattice distortion, cohesive energy, density of states, Mulliken charge population, overlap population and charge density differences are calculated by the generalized gradient approximation (GGA)-PW91, and the occupancy, bonding characters and alloying effect ofα-Fe(C) after mixing with alloy atoms are explained. Results show that Cr occupies perferentially the corner ofα-Fe(C) unit cell, but Mo and Ni occupy the body-center position of the cell perferentially. The mixing with Cr produces the biggest cohesive energe, and that with Ni and Mo in turn produces lower cohensive energy. There coexist the metallic bond, covalent bond, and weaker ionic bond in the unit cell. The bonding orbitals are created by Cr3d with Fe3d, Mo4d with Fe3d, and Ni3d with Fe3d and C2p; the bonding force between Cr and other atoms in the bulk is powerful, and the stability of cell is good, so it helps improve the mechanical strength of steels. The bonding force between Ni and other atoms in the bulk is weaker, but it can also maintain the stability of the cell. Though the bonding force between Mo and other atoms in the bulk is powerful, but the antibonding is so strong, that the statility of the cell reduced greatly. This is harmful to the mechanical strength of steels.
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