Influence of Grain Boundary Character on Dopants Segregation in Nanocrystalline Aluminum

This work focuses on understanding the influence of grain boundary (GB) character on magnesium (Mg) dopants segregation in nanocrystalline (NC) aluminum (Al) using a hybrid Monte Carlo/molecular dynamics (MC/MD) framework. Studies are done to identify the dopant segregation behavior in symmetric (Sigma 3) and asymmetric Sigma 5, Sigma 7, Sigma 9, Sigma 11, Sigma 13 and Sigma 61 tilt GBs. The simulations reveal that GB segregation is apparently not random, instead, dopants prefer to segregate to specific sites in the GBs. It is found that tilt GBs exhibit periodic "V"-like cluster of atoms. The segregating Mg dopant atoms replace only those atoms at the foot of the "V"-clusters. The number of dopant atoms absorbed by a GB is directly correlated to the number of such sites in a GB. Dopant segregation to high angle GBs (HAGBs) is more preferential than to low angle GBs (LAGBs) and tilt boundaries (TBs), as more the "V"-atomic clusters are available in HAGBs. Dopants bring Sigma 5, Sigma 7, Sigma 9, Sigma 11, Sigma 13 and Sigma 61 GBs to lower energetic states, which increases the resistance of the NC material to deformation. The inability of Sigma 3 GB to accommodate dopants results in an excess of dopants in the bulk, which distorts the crystalline structure, thus reducing the resistance to deformation.