Study On The Physical Properties,Point Defects And Atomic Diffusion In Intermetallics By A Modified Analytic EAM Model

Ordered intermetallics, such as FeA1, CoAl, NiA1 and TiAl alloy systems, are the candidates for high-temperature structural applications because of their high melting point, high specific strength, high specific stiffness, oxidation resistance, high temperature creep resistance and yield strength anomaly in high temperature. Numerous investigations of the mechanical properties in the ordered compounds were carried out in the past. Nevertheless, there is only little known about the formation and migration properties of atomic defects in these ordered compounds. The properties of atomic defects have a great influence on the mechanical properties, such as the creep resistance and the yield strength anomaly of FeA1. There are three levels of the material design theory: One is based on the thermodynamic theories, such as Miedema theory, another is based on the first-principles electric theories, the third is atomic theories. The EAM model is one of the typical atomic theories. Based on Johnson's analytic EAM model, Zhang has provided the modified analytic EAM (MAEAM) model by adding a modified term in the energy expression for modifying the non-spherical distribution of electrons and deviation from the linear superposition of atomic electronic density and by supposing a new pair potential function. The MAEAM has been widely used in the calculations of the thermodynamic properties, defects and diffusion properties of metals. In the present work, the properties of physical, point defects and diffusion of 7 ordered compounds in FeAI, CoAl, NiA1 and TiAl alloy systems are studied by using molecular dynamics method with MAEAM potentials. The conclusions are as follows: 1. Considering the effects of electronic factors and size factors of constituents in alloy, the parameter of f in electronic density distribution function is empirically defined. 2. The lattice constants of these ordered compounds are gained by molecular dynamics (MD) method with MAEAM potentials relaxation. The alloy formation energy and elastic constants of these ordered compounds are calculated. The point defects and atomic diffusion in the intermetallics are simulated by molecular dynamics method with MAEAM potentials. The point defect formation energies and atomic diffusion migration and activation energies are calculated in this work. 3. The equilibrium lattice constant values, the formation energies and the elastic constant values of ordered compounds are calculated in this work. The equilibrium lattice constant values are a little larger than those of the experimental data. 4. The single point defects are simulated by MD with the MAEAM potentials. The point defect formation energies are 1.053eV for Fe vacancy, 2.019eV for Al vacancy, 0.323eV for Fe antisite and 0.637eV for Al antisite in FeAI, respectively. The point defect formation energies are I .104eV for Fe vacancy, 1.472eV for Fe 1 vacancy, 2.011eV for Al vacancy, 0.354eV for Fe antisite, 0.154eV for Al antisite and 0.019eV for Al antisite in Fe3AI, respectively. The defect types are the antisite atoms on either sublattice for nonstoichiometry. The point defect formation energies are 1.197eV for Ni vacancy, 1.774eV for Al vacancy, 0.230eV for Ni antisite and 0.043eV for Al antisite in Ni3A1, respectively. The defect types are the antisite atoms on either sublattice for nonstoichiometry. The defect types are the antisite atoms on either sublattice for nonstoichiometry. The point defect formation energies are...