Site Competition of Impurities and Grain Boundary Stability in Iron
ARMY LAB COMMAND WATERTOWN MA MATERIAL TECHNOLOGY LAB
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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.
- Physical Chemistry
- Properties of Metals and Alloys