First principle study of occupancy, bonding characteristics and alloying effect of Zr, Nb, V in bulk α-Fe(C)

Abstract

The volume change rate, total energy, binding characteristics, state density, charge distribution number and mechanical properties of cells formed by solid solution of Zr, Nb and V in α-Fe(C) are calculated by using the first-principles method. Thus, the effect of Zr, Nb, V on α-Fe(C) are studied in this paper. The results show that V displaces Fe atoms which is at the apex angle of α-Fe (C) cells preferentially, while Zr and Nb displace Fe atoms at the body center of α-Fe(C) cells. Zr and Nb reduce the stability of ferrite, but Zr is more difficult to solidly solubilize in α-Fe(C) than Nb. Solid solution of V increases the binding energy of crystal cells, meanwhile the toughness of crystal cell is mainly improved. After solid is solubilized in ferrite, Zr and Nb atoms only form metal bonds with Fe atoms while V and Fe atoms form the metal bonds and Fe—V ionic bonds. The ionic bonds of Fe—V are stronger than metal bonds of Zr and Nb atoms with Fe atoms, which is the main factor of the cell increasing. Zr and Nb mainly improve the mechanical properties of steel material by means of dispersion strengthening. To some extent, V solid solution can improve the toughness of ferrite, which is the main reason for improving the mechanical properties.