Viscosity of liquid Co-Cu alloys

Abstract

The paper presents original experimental data on the kinematic viscosity of liquid Co-Cu alloys with Cu contents of 10, 20, 30, 40, 50, 60, 70, 80, and 90 at.%. The measurements were conducted during heating from the liquidus temperature, T_L, to 2000 K, followed by cooling of the melt to the stratification temperature, T**. The liquidus temperature, T_L, and the melt stratification temperature, T**, were determined based on viscosimetric experiments. A change in the viscous flow regime of the melt during heating was observed at a specific temperature, T*, for each composition. This change is described by variations in the parameters of the Arrhenius equation: the pre-exponential factor and the activation energy. The authors attribute the change in the viscous flow regime at T* to a liquid-liquid structural transition.

An analysis of the temperature dependences of the viscosity of Co-Cu melts with Cu contents of 30, 40, 60, and 80 at.% in the temperature range from T_L to T*, based on the theory of rate processes, indirectly indicates the presence of dispersed particles larger than 2 nm. These particles are enriched in one of the components, suspended in a medium of different composition, and separated by an interphase boundary. The concentration dependence of the viscosity of Co-u melts reveals pronounced minima at approximately 30 at.% and 70 at.% Cu, which can be explained by the two-phase structure of the metal before melting.