Atomistic studies of grain boundary segregation in Fe-P and Fe-B alloys—II. Electronic structure and intergranular embrittlement

Abstract The local density of states (LDOS) of electrons at grain boundaries of iron with or without segregation (phosphorus or boron) was calculated. The grain boundary structures constructed by using empirical atomic pair potentials were used as the model systems. The hopping integrals were calculated by using the linear-muffin-tin orbitals and atomic sphere approximation. The atomic level of the individual atomic site near the grain boundary is determined so as to maintain the charge neutrality at each atomic site. Following results were obtained: 1. (1) In the grain boundaries of iron without impurities, the non-bonding orbitals are formed at the Fe-3d bands at the grain boundary, while LDOS's of the neighboring atoms have the bonding orbitals perpendicular to the boundary. 2. (2) When boron atoms segregate at the boundary, the non-bonding states of the iron atom disappear by forming the strong bonding orbital with the B-2p orbital, and the grain boundary is strengthened. 3. (3) In case of the phosphorus segregation, the non-bonding states are formed at LDOS's of Fe-3d electrons surrounding the Fe 9 P cluster, and the Fe-Fe bonds are weakened, although the Fe-P bonds in the Fe 9 P cluster are strengthened. 4. (4) The binding character is determined not only directly by the nature of impurity, but also indirectly by the structural change induced by the impurity segregation. Especially in the case of phosphorus segregation, the structural change reduces the bonding character of the host atoms.