A. L. Bel’tyukov

An automated setup for determining the kinematic viscosity of metal melts

An automated setup for determining the kinematic viscosity of metal melts via the technique of damped torsional vibrations is described. A method for monitoring the onset of flapping vibrations of the suspension system of a viscosimeter in the course of an experiment during automatic detection of torsional vibrations is proposed. The experimental errors are assessed during determination of the viscosity via a numerical solution to the equation of motion. The effect of the values of the damping factor, the vibration period, and radius and height of the sample on the calculated viscosity error is analyzed.

Viscosity of Fe-Si melts with silicon content up to 45 at %

The temperature and concentration dependences of kinematic viscosity for melts of the Fe-Si system with the silicon content from 3 up to 45 at% have been investigated. Polytherms of the viscosity of molten alloys in the heating and cooling regimes coincide (hysteresis is absent) and are satisfactorily described by the Arrhenius equation. Concentration dependences of viscosity and activation energy for viscous flow are nonmonotonic with a minimum near 5% and a maximum near 25% of silicon.

Structural Transition in Liquid Cobalt

The temperature dependence of kinematic viscosity of liquid cobalt in the range 1490–1700°C and the influence of the degree of cobalt overheating on its overcooling were studied by viscometry and differential thermal analysis. It was found that liquid cobalt undergoes a structural transition near 1595°C, which manifests itself as a sharp change in the viscosity and the activation energy for viscous flow at this temperature and is accompanied by a considerable increase in crystallization ability.

Viscosity of glass forming Al86Ni8(La/Ce)6, Al86Ni6Co2Gd4(Y/Tb)2 melts

The temperature and time dependences of kinematic viscosity in Al86Ni8(La/Ce)6, Al86Ni6Co2Gd4(Y/Tb)2 melts over the range of liquidus up to 1300°C have been investigated. An irreversible non-monotonic change of the melts viscosity above the temperature of melting brought about by the destruction of their microheterogeneous state inherited from the multi-phase solid sample has been found out. It is shown that for the melts transition into the quasi-equilibrium state long isothermal holding is necessary. The relaxation time decreases with the increase of the melt temperature.

Effects of temperature and gas phase impurities on the composition of Co-B alloy surface layers

Layers formed on the surfaces of Co-B melts in vacuum and in a helium atmosphere with oxygen and carbon contamination are purified. It is established that films containing B2O3 and CoO oxides form on the melt surfaces, leading to abnormalities in the temperature dependences of viscosity. It is shown that increasing the boron content in the Co100−xBx alloys lowers the temperature of oxide disappearance. Raising the oxygen content stabilizes oxides, while carbon impurities block their formation.

Viscosity of hypereutectic aluminum-based iron-alloyed melts

We investigated the temperature dependences of the kinematic viscosity of liquid Al–Fe alloys with an iron content from 3.5 to 10 at %. We discovered a bifurcation of the viscosity polytherms obtained upon heating and subsequent cooling. We show that the value increase observed in the viscosity polytherm at melt heating near the liquidus temperature is caused by Al3Fe crystal sedimentation upon its passing the two-phase zone and by their subsequent melting.

Nonmonotonous relaxation processes in nonequilibrium nanoforming alloys of Al with transition and rare-earth metals

The temporal dependences of viscosity in Al87Ni8Y5, Al86Ni8Ce6, and Al86Ni8La6 melts were measured at various temperatures after the solid-liquid phase transition. A nonmonotonous change in viscosity with the passage of time was found, due to the destruction of the nonequilibrium microheterogeneous state of melts inherited from the initial multiphase melts. We propose a mechanism of nonmonotonous relaxation of nonequilibrium microheterogeneous melts within the dynamical theory of a molecular field, assuming the emergence of a hierarchy of different relaxation times in the system. A theoretical temporal dependence of viscosity of melts is proposed that is qualitatively consistent with the experimental data.

On possibility of a structural transition in the vicinity of the melting point in liquid copper

The temperature dependence of the kinematic viscosity of liquid copper has been studied by the method of torsional vibrations during heating and cooling within the temperature range 1080–1500°C. A reversible structural transition was discovered in the vicinity of 1170°C. This transition manifests itself in a jumpwise change of viscosity and the activation energy of viscous flow at this temperature.

Torsional vibration measurement of the viscosity of a metallic melt

The liquid Co91B9 alloy is used as an example to study the influence of boundary conditions at the upper melt boundary on the results of viscosity measurements using torsional vibrations. Specific features related to film effects and wetting phenomena are shown to appear in the temperature dependence of logarithmic decrement. To exclude the influence of these effects and phenomena, viscosity measurements should be performed under the experimental conditions where the melt to be studied is in closed volume and the internal crucible walls are fully wetted. The temperature dependence of the kinematic viscosity of the Co91B9 melt that is obtained under such experimental conditions has a monotonic character.

On particular measurements the viscosity of liquid cobalt by the method of torsional vibrations

Investigations on kinematic viscosity of liquid cobalt have been performed by the method of torsional vibrations, in which different boundary conditions on the upper boundary of the melt were used. A significant effect of the experimental conditions on the obtained results caused by the formation of the viscous film on the surface of the melt has been shown in this paper.