First-principles Study Of Point Defects And Atomic Diffusion In Strenthening Phases Al₃Sc And Al₂Cu

Point defects and atomic diffusion are closely related to the preparation,heat treatment,and creep processes of materials.It is of great significance to study the micro-mechanism of atomic diffusion mediated by point defects,which contributes to the optimization design of materials and improvement of the material formation process.However,it is very difficult to study the point defects and atomic diffusion experimentally.The first-principles calculations are reliable enough and successfully predict the point defect structure and simulate the atomic diffusion process.The point defects and atomic diffusions in the strengthening phases Al3Sc and ?'-Al2Cu is deeply studied from first-principles calculations in this paper.The main contents are as follows:Firstly,point defects and atomic diffusion in pure and transition element(TM=Ti,Y,Zr or Hf)doped Al3Sc has been studied.The point defect formation energies are calucated,results show that under strong Al-rich condition VSc defect with lower formation energy is favorable over AlSc.Under strong Sc-rich condition,ScAl defect is preferential compared with VAl.And VAl defect is dominating in definite range near the stoichiometry.The energy profiles for dominating diffusion paths are obtained using climbing image nudged elastic band method.The energetic reults shows that Al atom diffusion through nearest-neighbor jump mechanism mediated by Al vacancy is the most favorable due to the lowest activation barrier,the other diffusion processes would make very small contribution due to the high activation barrier or unstable final state.The dominating Sc atom diffusion mechanisms are the Al-vacancy mediated nearest-neighbor jump under Al-rich condition and antistructure sublattice mechanism under Sc-rich condition.The 6-jump cycle and next nearest-neighbor jump are largely restricted with high activation barriers.Moreover,effect of typical transition element(Ti,Y,Zr or Hf)doping on atomic diffusion is further studied.The activation barriers for dominating diffusion mechanisms increase with increasing atom size mismatch in sequence of Zr<Hf<Ti<Y dopant.Seconedly,the first-principle calculations are employed to study the point defect and the atomic diffusion in ?'-Al2Cu phase.The formation energies of the point defects are calculated at 0 K.Under Al-rich conditions,the Alcu is the favorable over Vcu due to lower formation energy.Under Cu-rich conditions,the CuAl becomes preferential among the others.Based on the calculated phonon spectrum,the contribution of zero-point energies is computed.The results show that the zero-point energy has obvious effect on the formation of point defects,but the relative order of the point defects formation energies including the zero-point energies does not change.The atomic diffusion in 0' phase is futher investigated.The dominating diffusion mechanism for Al atom is the next-nearest neighbor jump mechanism,while the most favorable diffusion path for Cu atom is the antistructure sublattice mechanism.