Structural, electronic, and mechanical properties of Mg–Dy intermetallic phases studied by first-principles calculations

Abstract

Rare earth elements such as Dy, Gd and Y have been utilized in the fabrication of binary Mg alloys due to their beneficial effects on the formation of oxidation layers on the surface and intermetallics in the Mg matrix. These effects have been shown to enhance the corrosion resistance and mechanical properties of the alloys. Therefore, the study of Mg–Dy intermetallic phases is regarded as significantly important. These phases are considered to hold great potential effects on the properties of Mg–Dy alloys for various applications, thereby making their investigation essential in the academic and scientific domains. In this study, the energy, density of states, optical properties and elastic properties of the Mg₁Dy₁, Mg₂Dy, Mg₃Dy, and Mg₂₄Dy₅ intermetallic phases were calculated using first principles calculations. Based on the calculated formation enthalpy (derived from the energy) and density of states, it is suggested that the Mg₁Dy₁ phase exhibits greater stability compared to the other three Mg–Dy intermetallic phases. The calculated formation enthalpy results indicate that all four Mg–Dy phases are stable, while the band structure and density of states plots show metallic characteristics for these phases. The optical properties of the intermetallic phases were investigated, and the static dielectric constants for Mg₁Dy₁, Mg₂Dy, Mg₃Dy, and Mg₂₄Dy₅ were calculated to be 266.47 eV, 285.80 eV, 257.75 eV, and 373.98 eV, respectively. In addition, concerning the study of absorption spectra, the maximum values of the absorption coefficients for all four intermetallic phases occur within the energy range of 40–65 eV for incident light. Born-Huang's mechanical stability theory was employed to calculate the elastic constants of each Mg–Dy phase, and the bulk modulus (B), shear modulus (G), Young's modulus (E), Poisson's ratio (υ), and theoretical hardness (H_V) were derived. The results of the elastic modulus calculations indicate that the B, G, E, υ, H_V of the Mg₁Dy₁ phase are higher than those of the other Mg–Dy intermetallic phases. The Poisson's ratio (υ) and the ratio of bulk modulus to shear modulus (B/G) indicate that the Mg₂₄Dy₅ phase is ductile, while the other three phases are brittle. Finally, the universal anisotropy (A^U) is ranked as Mg₃Dy > Mg₁Dy₁ > Mg₂₄Dy₅ > Mg₂Dy, with the Mg₃Dy phase exhibiting the most pronounced elastic anisotropy.