Role of Vibrational Entropy in Impurity Segregation at Grain Boundaries in Bcc Iron

In this paper we study segregation of six sp−impurities to the Σ5(310)[001] grain boundary in bcc iron from first principles. First we evaluate segregation energy for interstitial and substitutional positions using the potential energy of a static lattice. Then we also evaluate Helmholtz free energy of harmonic phonons in order to check its effect at elevated temperatures. The results show that vibrational contribution to the crystal energy can be relatively high in some cases. However, the segregation preference of Al, Ga, In, Sn, Sb, and Te does not change with increasing temperature. Finally, based on calculations of the cleavage energy, we predict reduction of grain boundary cohesion due to the presence of segregated impurity atoms.