Structural and mechanical properties of Mg₁₇Al₁₂and Mg₂₄Y₅from first-principles calculations

Abstract

Using density functional theory within GGA approximation, the structural and elastic properties of two important phases (Mg17Al12 and Mg24Y5) in Mg-based alloys have been studied. The obtained equilibrium structural parameters for both phases agree very well with experimental data. The calculated negative cohesive energy and formation energy show that both cubic precipitates have strong structural stability as well as good alloying ability. Three independent single-crystal elastic constants (C11, C12 and C44) at zero pressure as well as polycrystalline mechanical parameters such as bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio ν and anisotropy value A for both phases have been calculated. The mechanical properties of the cubic phases such as ductility and tenacity are further analysed and discussed.

Nanomechanical properties of Mg–Al intermetallic compounds produced by packed powder diffusion coating (PPDC) on the surface of AZ91E

“…These estimates exceed the estimate of the theoretical shear strength of 3.5-4.8 GPa for the β-phase, which is estimated as µ s /2π GPa, where the shear modulus of β phase, µ s , is taken to be in the range 22 to 30 GPa based on the first-principle calculations and experimental measurement [30][31][32]. These estimates indicate that the maximum shear stress beneath the indenter was equal to or exceeded the theoretical shear strength, which satisfied the stress condition for inducing the incipient plasticity.…”

“…For the β phase, first-principle method calculations [31] The experimental results obtained from nanoindentation mapping ( But the difference of measured modulus in those directions was insignificant compared with those from the theoretical evaluation. The cause of the small influence of orientation on the measured elastic modulus may be related to the complexity of crystal structure of the β phase, which reduces the difference in number of atomic bonds in different directions.…”

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

“…Table 3 indicates that the β′-Mg 7 Gd precipitate possesses a higher elastic stiffness than the surrounding α-Mg matrix, which contributes to the precipitation strengthening. Compared with β-Mg 17 Al 12 (E = 57.3 GPa [28]), which is the dominant strengthening precipitate in Mg-Al based alloys (for example, AZ91), β′-Mg 7 Gd is elastically stiffer and thus has a stronger strengthening effect than β-Mg 17 Al 12 . This finding is in accordance with experimental observations [29].…”

First principles prediction of structural and mechanical properties of the nanolaminate compound M4AlN3 (M = V, Nb, and Ta)

“…The ratio of shear modulus to bulk modulus (G/B) has been proposed by Pugh to roughly estimate brittle or ductile behavior of materials [31][32][33][34][35]. According to the Pugh criterion, G/B <0.57 means that ductile behavior is predicted; otherwise the material behaves in a brittle manner.…”