First-principles Calculations Of The Thermodynamic Properties Of Rare Earths-aluminum And Rare Earths-magnesium Alloys

With the development of first-principles calculations independent of any empirical parameters,thermophysical properties of materials can be predicted which are important to set up a materials database.In order to accelerate materials design of Al- and Mg-base alloys to establish relative completed databases,thermodynamic and mechanical properties of some phases(including stable or metastable or hypothesized) in the Al-RE and Mg-RE systems were studied.Firstly,formation enthalpies of 558 intermetallic compounds in the Al-RE and Mg-RE binary systems were calculated by means of first-principles calculations.Thermodynamic stabilities of the studied phases are calculated and show good agreement with experiments. Moreover,lots of the potential phases were also predicted for the Mg-RE binary systems.Secondly,combining first-principle calculation with Debye model, mechanical properties,electronic structure and thermophysical properties of the B2-AlRE,C15-Al₂RE and Ll₂-Al₃RE were further predicted.The calculated lattice constants,elastic constants and Debye temperatures are coincident with the experimental data,and the calculated B/G ratios indicate that the B2-AlEu and B2-AlYb are brittle while other B2-AlRE are ductile,and the C15-Al₂RE and Ll₂-Al₃RE are all brittle.Thirdly,the mechanical properties,electronic structures and thermophysical properties of B2-MgRE have also been calculated.The calculated lattice constants agree with experimental data.Especially,the C' of B2-MgCe is in very good agreement with the experimental data. Although the calculated elastic constant of B2-MgTm differs from experimental data for about 25%,it is still acceptable.In addition,the B/G ratios were calculated indicating that the Mg-early RE compounds are slightly brittle and the others are slightly ductile.Lastly,with the help of first-principles calculations,Miedema's method and CALPHAD technique,the Mg-Eu binary system has been thermodynamically assessed.As a starting step,the Miedema's method and first-principles calculation are respectively used to determine the mixing enthalpy of liquid Mg-Eu alloys and formation enthalpies of intermetallic compounds.Then,using the CALPHAD technique,the Mg-Eu binary system has been described.Consequently,a set of self-consistent thermodynamic parameters have been obtained.