Electronic origin of the anomalous solid solution hardening of Y and Gd in Mg: A first-principles study

Abstract

Y and Gd demonstrate anomalous solid solution hardening efficiency, which cannot be understood using the elastic impuritydislocation interaction theory. We performed first-principles calculations to investigate the effect of different alloying elements such as Al, Zn, Y, and Gd on the chemical bonding of

First-principles calculations of the β′-Mg7Gd precipitate in Mg-Gd binary alloys

“…Thus, the brittle nature of β′-Mg 7 Gd can be correlated to its negative Cauchy pressures and thereby the angular character in its bonds. Similarly, the ductile nature of α-Mg can be related to its high Cauchy pressures (C 12 -C 66 = 5.2; C 13 -C 44 = 4.5, for hexagonal structures) [32,33], which suggest the metallic character in its bonds, as is already demonstrated by the corresponding electronic structure derived in a previous study [18]. We have also verified the bond characteristics of β′-Mg 7 Gd by calculating the electronic structure.…”

“…The calculated elastic properties of β′-Mg 7 Gd are summarized in Table 3, along with those of hexagonal Mg from a previous theoretical study [18]. The bulk modulus derived from the values of the elastic constants is in good agreement with that obtained from the Birch-Murnaghan's EOS (B 0 ).…”

“…This agreement suggests that the β′-Mg 7 Gd model is reasonable. For pure α-Mg, our calculated hcp lattice constants are a α = 3.19 Å and c α = 5.19 Å [18], which are consistent with the measured room temperature values of a α = 3.21 Å and c α = 5.21 Å [19] and other theoretical values of a α = 3.20 Å and c α = 5.18 Å [20,21]. From these data, the deduced theoretical lattice mismatches between β′-Mg 7 Gd and α-Mg are +3.6%, +2.2%, and -0.4%, respectively, along the three lattice directions a β′ , b β′ , and c β′ in Figure 1(a).…”

“…In summary, the structural, elastic and electronic properties of the recently identified β′-Mg 7 Gd precipitate in Mg-Gd binary alloys were investigated using first-principles Table 3 Calculated elastic constants C ij and macroscopic elastic parameters for β′-Mg 7 Gd precipitate and for hexagonal Mg from a previous theoretical study [18] (all except for ν and B/G in GPa) a) calculations based on density functional theory. The calculated equilibrium lattice constants of β′-Mg 7 Gd are in good agreement with experimental values.…”

First-principles study of solid solution strengthening in Mg–X (X=Al, Er) alloys

“…However, compared with Al, Fe and steel, the relatively poor mechanical properties and corrosion resistance of Mg alloys have seriously restricted their further application and development. Solid solution strengthening is one of the most effective methods to strengthen Mg alloys, because solute atoms can hinder the movement of dislocations owing to friction mechanisms, chemical interactions, short-range order and electrical interactions [2]. Although there are several studies on the solid solution strengthening effects of alloying elements on Mg alloys, the fundamental understanding of the solid solution strengthening mechanism at the atomic and electronic levels is still not clear.…”