Thermodynamic stability of Mg–Y–Zn ternary alloys through first-principles

Abstract

In order to clarify thermodynamic stability of Mg-based long-period stacking ordered (LPSO) structure, we systematically study energetic preference for alloys on multiple stacking with different composition for random mixing of constituent elements, Mg, Y, and Zn based on special quasirandom structure (SQS). Through calculation of formation free energy of SQS, Mg-Y-Zn alloy exhibits phase separation into Mg-and Y-Zn rich phase, which is consistent with previous theoretical studies. Bulk modulus of SQSs for multiple compositions, stacking sequences, and atomic configurations ranges around 35 GPa, i.e., they do not show significant dependence of Mg concentration, which therefore means that the effects of phonon do not play significant role on LPSO phase stability. Introducing stacking fault to hcp stacking gains "negative" energy, which indicates profound relationship between introducing stacking faults and the formation of long-period stacking ordering.

Measurement of Thermal Expansion Coefficient of 18<i>R</i>-Synchronized Long-Period Stacking Ordered Magnesium Alloy

“…The nature of these properties has been intensively studied by both experimental and theoretical approaches. [1][2][3][4] However, many important physical constants of Mg alloys with LPSO phase are still unclear. This is because large single crystals of LPSO phase have so far been unobtainable.…”

First-principles Study on Formation of LPSO Structures for Ternary Alloys Revisited from Short-range Order

“…Our recent DFT-based studies 6,7 demonstrate the importance of considering the structural properties and energetics of disordered phases to address the stability of LPSO structure, where there found strong correlation between the SRO tendencies along nearest-neighbor (NN) coordination and whethere or not the ternary alloy can form LPSO structure, while the study did not address the above (i) and (ii). The present study addresses these points based on DFT calculations, finding the significant dependence of SRO on periodicity of stacking faults and physical quantity of constituent elements having strong correlation with the SRO tendencies.…”

Investigation on Thermodynamic Stability of 10H and 14H Long Period Stacking Ordered Phase in Mg-Zn-Y Alloy

“…Wang et al [11] calculated the charge density and deformation stacking fault density of different structures 10H, 14H, 18R and 24R, and analyzed the relationship between them. Tanaka et al [12] calculated the thermodynamic stability of 18R phase. The results show that the introduction of stacking faults in this structure will make its energy lower, indicating that the formation of LPSO phase is closely related to the introduction of stacking faults.…”