Construction And Application Of N-body Potential In Binary And Ternary Transition Metal Systems

Firstly, a brief review is presented concerning the types of interatomic potentials as well as their applications in materials science. Meanwhile, the main theoretical methods used in this thesis are also been introduced, i.e., n-body potential, ab initio calculation and molecular dynamics (MD) simulation.Secondly, two new n-body potential models are proposed based on the previous studies in this thesis, i.e., extended Finnis-Sinclair (FS) potential and long-range empirical potential (LREP). Extended FS potential has a simply analytic form and successfully overcomes two shortages of original FS potential, i.e., being too soft in short-range distance and limited scope of application. LREP overcomes the structural stability problem and the cutoff problem appearing in the previous short-range or long-range potentials. Both potentials are relevant in describing the atomic interactions in bcc, fcc metals and alloys.Thirdly, applied the methods of extended FS potential, MD simulation, ab initio calculation and molecular statics calculation, the formation and structural characteristic of metastable alloys in Ni-Nb and Ag-X (X=Mo, Nb, Ta, W) binary metal systems are studied in this thesis. The main results are as follows. (1) The glass-forming ranges of the five binary metal systems are predicted by MD simulations. (2) The asymmetric growing behavior has been revealed in the amorphization of Ni-Nb metallic multi-layered film. (3) The structural stability of metastable crystalline phases is predicted by ab initio calculations for three compositions of 3:1, 1:1 and 1:3 in Ag-Ta and Ag-W systems. (4) MD simulations reveal that moderate phase segregation exists in Ag-W amorphous phases.Fourthly, a scheme of construction of n-body potential assisted by ab initio calculation is proposed for ternary metal system in this thesis. Applied the methods of smoothed TB-SMA potential, LREP and MD simulation, the solid-state amorphization in Ni-Hf-Ti system and the liquid-solid phase transition in Ag-Cu-Ni has been studied, and the main results are as follows. (1) Applied MD simulations, the glass-forming region of Ni-Hf-Ti ternary system and the effects of Ni, Hf and Ti on the glass-forming ability of Ni-Hf-Ti ternary alloys are studied. (2) The effects of quenching speed rate and compositions on the crystallization and amorphization in Ag-Cu-Ni ternary alloys are studied by MD simulations, and it is found that the critical quenching speed rate of crystallization and amorphization is about 4×101 2K/s.(3) Through calculating the microchemical inhomogeneity of Ag-Cu-Ni ternary alloys, it is found that there exists a phase segregation in Ag-Cu-Ni alloys and the segregation degree is stronger with the decreasing of temperature during quenching and the decreasing of quenching speed rate.Finally, a scheme to calculate the formation enthalpy of binary and ternary metal systems through interatomic potential and molecular statics is proposed in this thesis. Under the proposed scheme, the formation enthalpies of 15 fcc-fcc binary metal systems and 4 fcc-fcc-fcc ternary metal systems are calculated, and the calculated results show a good agreement with those obtained by experiments or ab initio calculations. The calculated results also prove that the scheme proposed in this thesis is more accurate than the Miedema model for binary metal systems, the method of Johnson's and the extended Miedema model for ternary metal systems.