Study On Correlation Between Viscous-flow Activation Energy And Phase Diagram

Viscosity is a measure of the friction among atoms. The viscosity of molten metals and alloys is a structural sensitive property. A liquid's viscosity is of great interest to both the technology and theory of liquid metal behavior. The viscosity of liquid metals and alloys plays an important role in many phenomena relevant to both fundamental science and technological application.Solidification is the phase transition process from liquid state to solid state, which is important in the material preparation and formation. Investigations on phenomenon and law of solidification process have proved that heredity existed in transition from liquid state to solid state. The crystal structures of some elements or space configuration of the solid state persist in the liquid state. In this work, we studies correlation among activation energy of viscosity, phase diagrams and lattice parameters in solid state, which provides the theory and experimental data for the heredity in solidification.The dynamic viscosities for Cu-Sb, Cu-Te, and Bi-Sb alloy melts with different compositions have been measured by a torsional oscillation viscometer. The experimental results showed that the viscosities of different melts increase with decreasing temperature and fit well with Arrhenius equation. Moreover, the maximum values of the viscosity at the same superheated temperature are in the composition range of the intermetallic phases in Cu-Sb and Cu-Te systems. Bi-Sb systems show a monotonous composition dependence of the viscosities.Activation energy of viscous flow is obtained from temperature dependence of viscosities by means of a fitting to Arrhenius equation for liquid alloys of Cu-Sb, Cu-Te, Cu-Sn and Cu-Ag systems. We found that the changing trend of activation energy curves with concentration is similar to that of liquidus in the phase diagrams. Moreover, a maximum value of activation energy is in the composition range of the intermetallic phases:the maximum of activation energy is located at Sb-content of 25 at.%, which corresponds to the range ofβ-Cu-Sb intermetallic phase in the solid state in Cu-Sb system; the maximum of viscosities of Cu-Te system is located at a Te-content of 36.5 at.%, corresponding to the range of Cu2-xTe ((3-Cu-Te) in the solid state in Cu-Te system; the maximum of activation energy is located at Cu84.9Sn15.1 alloy, corresponding to the range ofβ-Cu-Sn of solid state in Cu-Sn system. And a minimum value of activation energy is located at the eutectic point in all systems. The correlation between activation energy and phase diagrams has been further discussed.Moreover, we further discuss the relationship between activation energy and lattice parameters in solid state. It is found that activation energy is direct proportional to cell volume in solid state for compound forming systems (Cu-Te, Cu-Si and Ag-Sb systems), while that is inversely proportional to cell volume in solid state for uniform grain system (Bi-Sb system).