V. I. Lad’yanov

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.

Deformation-induced changes in the structure of fullerites C60/70 during their mechanical activation

Structural changes occurring during the mechanical activation of fullerites C60/70 have been investigated using X-ray diffraction, IR and UV spectroscopy, and scanning electron microscopy. The complete destruction modes of fullerite have been determined (3.5 h at the intensity of the mill of 4.3 W/g and 28 h at 2.2 W/g). The destruction of the crystal structure of fullerites is accompanied by the destruction of fullerene molecules. The residual solvent, which enters into the composition of C60/70, is retained during the entire time of mechanical activation. In this case, the low-frequency shift of absorption bands of toluene (729 → 725 cm−1), which is caused by the deformation of the solvent molecule in the composition of crystal solvates, has been observed. It has been shown that the deformation stability of graphite is substantially lower than in the case of fullerite.

C60-C70-C6H5CH3 crystal solvates: Structure and thermal stability

Differential scanning calorimetry (DSC) and X-ray diffraction were used to study the thermal stability and structure of C60-C70-C6H5CH3 crystal solvates synthesized at room temperature. The decomposition of the crystal solvates generates C60-C70 solid solutions with hexagonal close-packed (hcp) structure.

Effect of the state of a melt on the glass-forming ability, structure, and properties of a melt-quenched bulk amorphous nickel-based alloy

The glass-forming ability, viscosity, phase composition, and microhardness of a melt-quenched Ni64.4Fe4Cr4.9Mn2B16.2C0.5Si8 bulk amorphous alloy quenched from various melt temperatures at near-critical rates are studied. The melt-quenching temperature ensuring the maximum glass-forming ability and microhardness (HV= 13 GPa) of the alloy is found to be 1200–1230°C. The melt viscosity is shown to behave anomalously near the solidification temperature, and the related factors favoring this anomalous behavior are detected.

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 and nonequilibrium solidification of Co-P melts

The concentration dependences of the viscosity and solidification of Co-P melts containing from 16 to 25 at % P are studied by viscosimetry, differential thermal analysis, and metallography. A maximum near 20 at % P in the concentration dependence of the viscosity is observed for the first time. The maximum is associated with a composition short-range Co4P-type order present in this composition range. On cooling the melts at rates of 20–100 K/min in the concentration range from 18 to 22 at % P, a metastable phase with a composition close to the eutectic composition (20 at % P) can form. This metastable phase decomposes on cooling to form equilibrium phases (Co and Co2P).

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.