Introduction
The energy of iron/ inclusion interface is
considered to play an important role in controlling nucleation
of phase transformation in steel. However, few experimental data
are available. A nearest neighbor broken bond (NNBB) model was
developed by Lee and Aaronson[1] to calculate coherent f.c.c./f.c.c.
interfacial energy. In this study, this method was extended to
evaluate the energy of austenite (g)/B1
type compound interphase boundary.
Description of NNBB method
B1 type compound (VN, VC, TiN, TiC, NbC, etc.) is composed by an f.c.c. lattice of substitutional atoms (denoted as M) and another f.c.c. lattice of interstitial atoms (denoted as I), with a lattice parameter close to g. g and B1 compound are reported to have cube-on-cube orientation relationship with a semi-coherent interface. By summing nearest neighbor bond energies across the interface, the chemical part of the energy of such an interface can be calculated expressed by the equation:
where ns is number of Fe atoms per unit area of interface. Zj and Zj' are the interfacial coordination numbers of Fe-M bonds and Fe-I bonds on the j'th plane from interface. eij is the enthalpy of an i-j bond, where i and j are Fe, M or I. Zj and Zj' are determined by a vector method, as illustrated in Fig.1.
Table 1 The interfacial coordination number
for Fe-M(Zj) and Fe-I (Z'j)
Result and Discussion
The interfacial coordination numbers
determined by vector method for some low index planes are shown
in Table 1. Figure 2 is the contour plot of constant for a cube-cube
oriented g/B1
interface within a unit stereographic triangle, which was calculated
assuming eFeI = 0. It can be seen that an interface
parallel to (111) has the largest interfacial energy in contrast
to ordinary f.c.c./ f.c.c. coherent boundaries[1].
Reference
# This paper published in
Current Advances in Materials and Process (Report of the Iron and Steel Institute of Japan (ISIJ) Meeting, Tokyo, 1998, Vol.11(3):584