First principles calculation on thermal stability of metastable precipitates in Mg–Gd binary alloys

Abstract

First principles thermodynamic models based on the cluster expansion formalism, lattice dynamic calculations and quantum mechanical total energy calculations are employed to compute the thermal stability of metastable hardening precipitations in hcp structure α-Mg–Gd binary alloys. It shows that vibrational entropy reverses the energetic preference and plays a critical role in hardening precipitation at different aging temperatures in Mg–Gd binary alloys. In addition to energetics, the analysis of bonding charge density reveals that the metastable β′ phase is responsible for the high strength during subsequent isothermal treatment. Our results are found to be in good agreement with experimental measurements and helpful in clarifying the metastable precipitation sequence in Mg–Gd binary alloys.

Keywords:

• Mg–Gd alloys
• First principles calculation
• Metastable precipitates
• Thermal stability

The authors gratefully acknowledge financial supports of the National Natural Science Foundation of China (grant no. 51001025), the Chinese Research Fund for the Doctoral Program of Higher Education (grant no. 200801451021) and the Fundamental Research Fund for the Central Universities (grant nos.N090405016 and N090502002).