WEB Segregation of alloying elements and grain boundary reconstruction. Atomistic modellingWednesday (01.01.2020) 00:30 - 00:45 Part of:
Grain boundary (GB) segregation is an important phenomenon that affects many physical properties as well as microstructure of polycrystals, especially in ultrafine grained (UFG) materials. The segregations formation can change the phase equilibrium of alloys, thermal stability of microstructure and its deformation behavior. Thus, fundamental understanding of the mechanism of GB segregation formation and their effect on GB-controlled properties is necessary for effective control of structural state and mechanical behavior of polycrystalline materials.
We considered the segregation of solute atoms on GBs and its effect on GB structure in Al by using two approaches : first principles total energy calculations and the finite temperature large-scale atomistic modeling within hybrid MD/MC approach comprising molecular dynamics and Monte-Carlo simulations. We show that the character of chemical bonding is essential in the solute-GB interaction, and that formation of directed quasi-covalent bonds between Si and Zn solutes and neighboring Al atoms causes a significant reconstruction of the GB structure involving a GB shear-migration coupling [1,2]. For the solutes that are acceptors of electrons in the Al matrix and have a bigger atomic size (such as Mg), the preferred position is determined by the presence of extra volume at the GB and/or reduced number of the nearest neighbors. We studied the features of the segregation morphology of Mg and Zn directly by using ab initio calculations. Within MD/MC approach we found that GBs undergo significant structural reconstruction during segregation, which can involve the formation of single- or double-layer segregations, GB splitting, and coupled shear-migration depending on the details of interatomic interactions. The results obtained show the essential role of elements chemistry in segregation formation and explain the qualitative features in the morphology of GB segregation observed in Al-based alloys.
1. L.E. Karkina et al, Metals, 9, 1319 (2019)
2. L.E. Karkina et al, Comput. Mater. Sci., 112, 18 (2016)