Speaker
Description
Recent progress in computational materials science provides a platform for calculations of various structures, states and processes (cf. e.g. [1]). However, there are still some limitations which enable us to obtain only simplified results not satisfying requirements for accurate description of real physical systems. For example, segregation of impurities at grain boundaries is usually studied from first principles. One of the main drawbacks of these methods is their limitation to 0 K temperature and neglecting the entropy terms [2]. The aim of this work is to include the temperature effect to energy balance via calculations of phonon spectra.
Simulation supercells for Σ5(310) grain boundary in bcc Fe were created within periodic boundary conditions and contained 60 atoms. Subsequently impurity atoms (Al, Si, P, S, Ga, Ge, As, Se, In, Sn, Sb, Te) were introduced to both the interstitial and the substitutional positions. The geometries were fully relaxed with the help of the Vienna Ab initio Simulation Package (VASP) [3], [4] implementing the density functional theory. The optimized cells were then subjected to atomic displacements applied by the phonopy software [5] (supercell method). Calculated force constants provided phonon spectra and Helmholtz free energy as a function of temperature. Preferred impurity segregation positions were determined. Finally, based on calculations of the cleavage energy, reduction of GB cohesion due to the presence of segregated impurity atoms was predicted.
References
[1] L.Q. Chen and Y. Gu, In: Physical Metallurgy, 5th ed., D.E. Laughlin, K. Hono eds., 2807 (Elsevier, Amsterdam, 2014).
[2] P. Lejček, M. Šob and V. Paidar, Prog. Mater. Sci. 87, 83 (2017).
[3] G. Kresse and J. Hafner, Phys. Rev. B 48, 13115 (1993).
[4] G. Kresse and J. Furthmüller, Phys. Rev. B 54, 11169 (1996).
[5] A. Togo and I. Tanaka, Scr. Mater. 108, 1 (2015).
