First-principles study on the segregation behavior of solute atoms at {101¯2} and {101¯1} twin boundaries of Mg

Abstract

Twin boundaries (TBs) are effective sinks for solutes to segregate, as they may drive the structural transformation and therefore tailor the properties of magnesium alloys. In this study, a systematic investigation on the TB segregation energy (Eseg) has been performed for the {101¯2} and {101¯1} TBs by first-principles calculations. The segregation of 19 solute atoms (X: Be, Si, Ge, Zn, Ga, Al, Ag, Sb, Ti, Cd, Sn, Li, Bi, Zr, In, Pb, Na, Ca, and Sr) has been considered at the TBs. The solute atoms smaller than Pb are prone to occupying the compression sites of TBs (exception: Ti and Zr for the {101¯1} twin), while the ones larger than Pb prefer to locate at the extension sites. Further inspections suggest that the segregation of solute atoms into preferable sites can be attributed to the combined effect of bond strengthening and alleviated lattice distortion in the vicinity of TBs. For both of the TBs, the Eseg decreases approximately linearly with an increase in the size deviations (equilibrium volume and atomic radius) between Mg and solute atoms, implying the increased propensity for segregation and the enhanced stability of twins. Considering the segregation potency and solubility, the strengthening effects of the 19 solute atoms on TBs are evaluated. Our calculated results may provide guidance for future design of novel Mg alloys based on TB strengthening.

Keywords

• Magnesium alloys
• First-principles calculation
• Segregation
• Twin boundary
• Strengthening