Simulation Of Microstructure Evolution And Dynamic Properties Of Zr-cu Alloys During Rapid Solidification

Amorphous alloys have excellent physical and chemical properties, which are new type advanced materials with wide application prospect. In the last 20 years, Researching of Zr based amorphous alloys have made great progress, which have special properties of high strength, high toughness, anti-radiation, low temperature resistance, anti-atomic corrosion, which widely applied in nuclear industry, aerospace and other fields.The properties of Zr based amorphous alloys are based on special microstructure. In this paper, the Zr-Cu binary alloys are studied. The molecular dynamics simulation method is used to study the evolution law of atomic structure and the dynamic behavior of the amorphous alloys at the temperature of supercooled liquid, galss transition and amorphous solid. Specific contents are as follows:Using pair distribution function, coordination number, bond, bond angles, Voronoi polyhedra structure analysis method, we studied the evolution of the microstructure of Zr-Cu binary alloys during solidification process. Pair distribution function and coordination number analysis showed that it is different in the local structure of Cu and Zr around, and heteroatoms have strong interaction effect. The clusters show that the characteristics of the local five-fold symmetry enhanced in supercooled liquid than in melt, but the cluster’s linkablility is not strong. In the process of glass transition, the content of the cluster increases with the higher local five-fold symmetry and coordination numbers, the structure of the saturated bond are increased. The changes of the structure parameters have explained the relation between the microstructure and the glass transition.In this paper, the viscosity of the melt was calculated using the Green-Kubo formula. The influence of microstructure evolution on the viscosity is that the viscosity increased and the Voronoi entropy decreased during rapid solidification. The influence of different cooling conditions on viscosity is obvious, the increase in cooling rate or the decrease in pressure leads to a decrease in viscosity and an increase in the Voronoi entropy. The viscosity is the most sensitive to temperature, and the pressure and cooling rate have little effect. The relationship between the viscosity and temperature is confirmed Arrhenius ? ???/expRTEA in calculation. The relationship between viscosity and Voronoi entropy is in accordance with Adam-Gibbs formula: ? ?C??expTSCA, and the correlation between the thermodynamics and kinetics of the alloy in the process of glass transition is revealed. Further structural analysis shows that the main reason for the reduction of the Voronoi entropy is the system full of icosahedron clusters, which increases the stability and order degree of amorphous alloys and lead to the increase of the viscosity.The influence of microstructure evolution on the diffusion of Zr-Cu alloy during solidification was studied. It was found that the local five-fold symmetry increase with the increase of pressure and with the decreased of the cooling rate and temperature, especially near the temperature of Tg. The distribution of the local five-fold symmetry in space was not uniform. By calculating the mean square displacement of the atom, it was found that when the local five-fold symmetry less than 0.3 atomic diffusion increased, and which is slow between 1 and 0.7, so the stability of structure of local five-fold symmetry is verified. Using Einstein formula to calculate the self diffusion coefficient of the alloys found that the self diffusion coefficient decreases with the decrease of temperature or cooling rate, and with increase of pressure, especially near the temperature of Tg. The diffusion behavior is not uniform in space by the calculation of the non Gauss parameters. It is found that the decrease of the activation energy is the main reason for the increase of self diffusion coefficient. The diffusion coefficient and local five-fold symmetry in comfirmed D=Aexp(C/Td5), which reveals the intrinsic relation between the microstructure and the dynamics of the alloy during rapid solidification.