First-rpinciples Study On Structures And Properties Of TiAL With Rare Earth Element Doping

TiAl intermetallic compound has become the development goal of new aerospace materials for its low density,high specific strength,high elasticity modulus,oxidation resistance and creep-resistance at high temperature,however,the brittleness at room temperature seriously hampered its application and development.Alloying method can change mechanical performance and high temperature performance of intermetallic compounds.Doping appropriate amount rare earth in the TiAl intermetallic compound can improve the compressing ductility at room temperature.In this paper,the electronic structure,elastic nature and mechanical properties of rare earth-dopedTiAl intermetallic compound were calculatedThe TiAl crystal model and the TiAl models doped with La,Ce,Nd,Sm,Yb,respectively,were built by Visualizer module in Materials Studio,based on the first principles of density functional theory in this passage and the electronic structures and mechanical properties of them were calculated by CASTEP.The calculation results of the lattice constants and the bulk modulus of TiAl unit cell by CASTEP module are in a good agreement with experimental results,showing that the calculation parametres in this paper are reasonable.The TiAl state density figures indicates the main interactions between Ti atoms and Al atoms derive from the hybridization of 3d electron orbital in Ti atoms and 3p electron orbital in Al atoms.There are the hybridization between 3s electron orbital and 3p electron orbital in Al atoms,which result in a strong interactionamong Al atoms.The calculations of population demonstrate that Al-Al covalent bond effect and key direction aere stronger,and Metallic bondingsare weaker.The difference density map shows that the material is anisotropic.The calculation results demonstrates that the bulk modulus,shear modulus,Young modulus and Poisson's ratio from bottom of TiAl were 127.89Gpa,69.60Gpa,170.46Gpa,and 4.09,respectively,which indicated its hardness was low and was a brittle material.The structure and property calculation results of TiAl respectively doped with La,Ce,Nd,Sm,Yb Show La atoms,Ce atoms and Sm atoms trended to occupy the position of Al atoms,and Nd atoms and Yb atoms trended to occupy the position of Ti atoms;The doping of rare earth can make the lattice constants of models increased and axial ratio declined.The doping of La in TiAl led to the bonding between La and Ti,which would decrease its bonding direction,covalence and hardness,and rise up its ionicity and ductility,and doping of Nd was on the contrary compared to the La.The doping of Ce in TiAl would rise up its covalence,hardness and ductility.The doping of Sm atoms and Yb atoms can make the bonding direction of TiAl models,covalence and hardness increased,and ductility declined..The Ce doping had the best effect in all 5 rare elements.The covalent property of Ti-Ti and Al-Al bond for Ti₁₆Al₁₅Ce was more than Ti₁₆Al₁₅La.The metal of Ti-Ce bond is higher than that of Ti-La bondThe calculations result of TiAl supercell model by changing the doping Ce content demonstrate that doping Ce in TiAl can strengthen the internal orbital hybridization,covalence,bonding direction and hardness.There appeared ionic bonds between Ce atoms,Ti atoms and Al atoms,which led the increase of ionicity and ductility.The ductility and hardness had a rise with the growth of doping Ce content.It was found that there had a relatively high consistency by comparing the researchconsequence of the structure and performance of TiAl doping rare earth intermetallic compounds calculated by first principles and relevant literature achievements,come to same conclusion,which can provide a theoretical direction for the research and exploitation of TiAl intermetallic compounds.