MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Thermodynamic Analysis of the Mg–RE–Zn (RE = Y, La) Ternary hcp Phase Using the Cluster Variation Method
Satoshi IikuboShuji HamamotoHiroshi Ohtani
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2013 Volume 54 Issue 5 Pages 636-640

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Abstract

In this study, thermodynamic properties of the Mg–RE–Zn (RE = Y, La) ternary hcp phase at finite temperature have been investigated by means of first-principles calculations combined with the cluster variation method (CVM). Free energy calculation, including the configurational entropy, shows that the Mg–Y–Zn ternary hcp phase has a tendency to phase separation. Conversely, the Mg–La–Zn ternary system does not exhibit such behavior even around room temperature. Furthermore, the calculated spinodal region extends to a broader composition range and the maximal spinodal temperature reaches above 1000 K for the Mg–Y–Zn system. Conversely, the spinodal region for the Mg–La–Zn system is a limited narrow region near the Mg-rich side, and the maximal spinodal temperature is 300 K. Formation enthalpies calculated on the basis of recent information from structure analyses do not show a definite difference in these two ternary systems. Therefore, we propose that the dominant factors in the formation of a novel long period stacking ordered structure include spinodal decomposition as well as structure transformation from 2H to other structures having periodic stacking faults.

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© 2013 The Japan Institute of Metals and Materials
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