Immiscible Material Cu-Ta And Al-Pb Alloy Structure And Molecular Dynamics Simulation Of Nature

Immiscible alloys exhibit some extraordinary properties which are hardly observed in other materials, and the constituent elements in immiscible system are complementary in physical and chemical properties. The proper combination of the constituent elements will generate excellent performance. The study on the structure of immiscible materials is helpful for probing the physics, thus is essential for the potential applications of these materials. And it will be very important to the development of new materials. Molecular dynamics (Materials Explorer software) is employed to simulate the behaviors of the immiscible systems Cu-Ta and Al-Pb. A comparison study is performed between theoretical and experimental results. In this thesis the short-range ordering of Cu-Ta alloy is systematically studied. The structural evolution of short-range ordering with temperature and its relation with composition are investigated, as well as the dynamic, thermodynamic and mechanic properties. We reveal the nature of alloy’s properties from alloy structure. Further, the short-range ordering of liquid Al-Pb alloys is simulated in this paper, which will shed light on the understanding of structure of solid-state Al-Pb alloy. Additionally, the atom separation mechanism in Al-Pb alloy is explained on the atomic level.The influence of Cu-Ta amorphous alloy preparation methods on the structures and properties of alloys are studied in this paper. The results show that both the compactness and smoothness of the films are improved with increased sputtering power, and the content of Ta increased in the films. While the hardness and elastic modulus increase with sputtering power.The effect of Cu/Ta ratio on the film structure is studied. The results illustrate that the Cu-Ta alloy film structure can be modified by Ta content. Moreover, the entropy production of the alloy system reaches its maximum when the Cu and Ta ratio is close to1:1, which implies that Cu and Ta atoms are mixed homogeneously, and△G=△H-T△S is the lowest. This alloy is the most stable.The dependence of the hardness and elastic modulus of the Cu-Ta films on the Cu/Ta ratio is studied. The experimental results show that the hardness and elastic modulus of the film increase with the increase of Ta concentration. The simulated results show that the bonding energy of the alloy increases with the Ta content, therefore the hardness and elastic modulus of the films increase. The simulated results agree well with the experimental.The short-range order in CusoTaso is investigated. It is found that there are two types of short-range clusters in the alloy, one is centered by Ta atoms with an average coordination number of15.6; the other is centered by Cu atoms with the average coordination number of12.5. The partial pair correlation functions for Cu5oTa5o at300K are studied. The results show that the interaction of the unlike pairs is stronger than that of like pairs. The Voronoi polyhedron and the coordination number distribution in Cu50Ta50are simulated. The results show that the most abundant coordination numbers are12,13, indicating the dominance of icosahedral packing. The study of the structure of short-range order with temperature shows that the number of icosahedral and distorted icosahedral increased with temperature decreasing. This implies that glass-forming ability of Cu50Ta50alloy grows during cooling process. Diffusion of atoms with temperature in Cu50Ta50unveils that the atomic diffusion capacity turns smaller with decreased temperature. The atomic diffusion capacity reaches the lowest at300K. The alloy enters a steady state. The diffusion of Cu atoms is faster than that of Ta atoms.The dependence of the alloy structure on the alloy composition is studied. The bond length of Cu-Cu, Cu-Ta, Ta-Ta are investigated in Cu-Ta alloys through pair correlation functions. The results demonstrate that the bond length of Cu-Cu, Cu-Ta, Ta-Ta in the nearest neighbor shell decrease with increased Ta content, thus the atom stacks more closely. The short-range ordering with composition indicates that the structure is most stable when the Cu content was50%. The investigation on the dynamical properties of Cu-Ta alloy suggests that Cu50Ta50is most stable in the five alloys under study. Additionally, the study on the thermodynamics clearly shows that the maximal formation enthalpy and the minimal diffusion coefficient ars reached simultaneously when Ta content was50%.The influence of Pb content on Al-Pb alloy structure is studied. The partial pair correlation functions and chemical short-range order parameter of liquid Al-Pb alloy at2000K are simulated. The results show that the interaction of the like pairs is stronger than that of unlike pairs. The same kind of atom is easily to form clusters. The evolution of cluster structure in liquid Al-Pb alloy with composition is studied. It indicates that Al-Al and Pb-Pb clusters are easily to emerge and tend to be separated in liquid Al-Pb alloys. The study of clusters state and atoms distribution with time show that the size of Pb-Pb cluster turns bigger with time, and immiscible zone in the liquid alloy forms. The Al-Al and Pb-Pb atoms form clusters respectively, which lead to those elements aggregating separately in solid state. The study of atom diffusion in Al-Pb alloy indicates that both the diffusions of Al and Pb atoms deteriorate with increased Pb content. The diffusion of Al atom is faster than that of Pb atoms.