Effects of carbon on Fe-grain-boundary cohesion: First-principles determination
Abstract
The cohesive properties of the C/FeΣ3(111) grain boundary are investigated by means of the direct determination of the difference in binding energies of C in grain-boundary and free-surface environments. The atomic force approach based on the full-potential linearized augmented plane-wave method is used to optimize the atomic structure for the clean and C-segregated grain-boundary and free-surface systems. The ω phase structure obtained in a previous grain-boundary cluster calculation is found to be only a metastable state that is 0.72 eV/cell (0.81 J/m2) higher in energy than the distorted bcc ground state. The calculated binding-energy difference (i.e., ΔEb-ΔEs) is -0.61 eV/adatom, which is a theoretical demonstration that C is a cohesion enhancer in the Fe grain boundary. Comparisons with earlier results obtained for B, S, and P show that the number of hybridized p electrons and the resulting spatial anisotropy of bonding with the surrounding Fe atoms is the key factor determining the relative embrittling or cohesion enhancing behavior of a metalloid impurity.
- Publication:
-
Physical Review B
- Pub Date:
- March 1996
- DOI:
- 10.1103/PhysRevB.53.7504
- Bibcode:
- 1996PhRvB..53.7504W
- Keywords:
-
- 61.72.Mm;
- Grain and twin boundaries