Site Competition of Impurities and Grain Boundary Stability in Iron

摘要

Impurities such as H, P, S, B, etc., have a very low solubility in iron and,therefore, prefer to segregate at the grain boundaries (GBs). In order to analyze the energetics of impurities on the iron GB, the Linear Muffin Tin Orbitals (LMTO) calculations were performed on a simple 8-atom supercell emulating a typical (capped trigonal prism) GB environment. The so-called environment-sensitive embedding energies (EE) were calculated for H, B, C, N, 0, A1, Si, P, and S as a function of the electron charge density due to the host atoms at the impurity site. It was shown that, at the electron charge density typical of a GB, B and C have the lowest energy among the analyzed impurities and, thus, would compete with them for the site on the GB tending to push the other impurities off the GB. The above energies were then used in a modified Finnis-Sinclair embedded atom approach for calculating the equilibrium interplanar distances in the vicinity of a (111) 13 tilt GB plane, both for the clean GB and that with an impurity. These distances were found to be oscillating, returning to the equilibrium spacing between 1 1 1 lanes in bulk BCC iron by the 10th to 12th lane off the GB lane. Site competition, Impurities, Grain boundaries, Relaxation, Iron.