Effects Of La And Zr (or Cr,Fe) Co-doping On Structures And Properties Of γ-TiAl Based Alloys

As one of the most promising lightweight high-temperature materials for aerospace applications,γ-TiAl based alloys have excellent properties such as low density,high specific strength,high specific elastic modulus,high melting point and high temperature creeping resistance,and it arouses general concern.However,its poor ductility at room temperature set a boundary to its wide applications.In particular,as the main component,γ-TiAl’s room temperature plasticity is still a certain gap compared with the expected value.And,the alloying method has been proved to be an effective method.The study used the first-principles method based on the density functional theory and other physical theories,and selected La and Zr,La and Cr,La and Fe co-doped γ-TiAl alloys as the objects,calculated their total energy,average atomic energy,energy stability,elastic constants,mechanical stability,structural parameters,Mulliken populations,overlap population,charge density,charge difference density and chemical bond by using Materials Studio 6.0,to analyze the effects of co-doping elements to the γ-TiAl alloys’ ductility.The conclusions of this study are as follows: first,La and（or）Zr（or Cr,Fe）doping not only induces the change of lattice parameters（a,b,c）,but also induces the change of volume and density,and the density of the doped system is still small,which is only about half of the nickel based alloy.Second,the average atomic energy of doped γ-TiAl alloys is negative,which indicates that they possess energy stability.In addition to the special doping position of the double doped system do not have mechanical stability,other doped systems have mechanical stability.Third,the variation of the space group and the symmetry property of doped system lead to the error of the ductility’s judgment of γ-TiAl alloy based on axial ratio and elastic modulus ratio.Through analysis,the ductility of S₆₄（Ti₈Al₆La Zr）,S₆₅（Ti₈Al₆LaCr）and S₆₃（Ti₈Al₆LaFe）systems are significantly improved compared with pure γ-TiAl system.It is found that the electronic propertiy factors of their ductility can be improved: the orbital hybridization of p-d,the resistance of dislocation movement and the anisotropy weakened.