Construction Of N-body Interatomic Potential For The Cu-Al And Pd-Ti Systems And Its Application For Phase Stability Study

During the past decades, various nonequilibrium materials processing techniques have been developed and successfully employed to fabricate a great number of nonequilibrium materials with unique properties. Consequently, developing new materials theory to clarify the correlations among the microstructure, processing and property of the nonequilibrium materials has become an urgent demand with a great challenge. In response, researchers in the fields of materials and condensed matter physics have paid much effort to develop atomistic calculation or simulation methods based on quantum mechanics and/or interatomic potential (e.g. ab initio calculations or molecular dynamics simulations). Through these efforts, a solid foundation has been established to formulate new materials theories in a quantitative way.Generally, the reliability of molecular dynamics simulations depends on the interatomic potential adopted. For a binary metallic system, the n-body potential scheme is widely employed, which is usually constructed by fitting the physical properties of various intermetallic compounds in the alloy system. However, when turned to alloy systems without intermetallic compounds or with little physical property information, it is difficult to construct a realistic interatomic potential. Accordingly, we employ a new approach named the first-principle calculation aided construction of n-body potentials. The procedure consists two steps: firstly, the related physical properties of some possible non-equilibrium phases in the alloy system are obtained by the first-principle calculation; secondly, the obtained physical properties are then employed to fit the n-body potential.Following this idea, the Cu-Al and Pd-Ti systems were chosen to fit their respective n-body potentials. The derived potentials were proven to be able to reproduce those important physical properties, which are matched well with those obtained by the first-principle calculations or from experiments. Moreover, based on the constructed potentials, amorphous formation range and some other properties of the alloy phases were studied by molecular dynamics simulations and the results also agreed well with the experimental observations, lending support to the feasibility of the first-principle assisted potential construction approach.In the Cu-Al system, we calculate the energy of FCC solid solution, BCC solid solution and amorphous phase with the change of concentration of Al. It is found that the energy of solid solutions is always lower than that of amorphous phase, explaining why the amorphous phase is hardly obtained in the Cu-Al system. The results also show that for the Cu1-xAlx alloys, the energy of the BCC solid solutions becomes the lowest in the range of 0.32 < x < 0.72 among three phases studied here, in good agreement with the ball-milling experimental observation that the BCC solid solution was obtained in the composition range of 0.3 < x < 0.7. In another binary system, namely the Pd-Ti system, the energy sequence of FCC solid solution and amorphous phase was calculated in the whole composition range with concentration of Pd from 0 to 100 at.%. The results show that the glass formation range in PdxTi1-x is wihtin 0.21 < x < 0.70, in which the energy of amorphous phase is lower than its competitive partner. It is consistent with the experiment result that is in the range of 0.25 < x < 0.60.