P. S. Popel

Microheterogeneity of liquid metallic solutions and its influence on the structure and properties of rapidly quenched alloys

Abstract The appearance of microdomains enriched with one of the components in metallic glasses is considered to be a result of microheterogeneity in the initial melts. The microheterogeneous state in liquid alloys is a long-lived metastable or non-equilibrium one with prolonged relaxation time. It is inherited from initial crystalline samples or formed during components mixing slightly above liquidus or immiscibility domain. The characteristic scale of the microheterogeneity is approximately 10–100 nm. Some new experimental data confirming these ideas are demonstrated and the possible structural changes of the melts due to temperature increase or other factors are discussed also. The influence of the melts structural state on the structure and properties of rapidly quenched crystalline and amorphous alloys is described.

The kinematic viscosity of liquid copper-aluminum alloys

The method of damped torsional vibrations of crucible with liquid under investigation is used for measuring the temperature dependences of kinematic viscosity ν of Cu100 − xAlx melts (x = 0–100 at.%) in the range of temperatures t between the liquidus and 1100–1450°C. Unlike the majority of such experiments, the measurements are performed both in the process of heating the sample after its melting and in the course of subsequent cooling. The branching of ν(t) curves corresponding to the foregoing modes is revealed below certain temperatures dependent on the composition of sample (viscosity hysteresis). The curves obtained under cooling have a simple exponential shape predicted by activation theories of viscous flow. The obtained temperature dependences are used for constructing isotherms of kinematic viscosity, on which maxima are observed in the vicinity of stoichiometric concentration of CuAl3 and composition of Cu-30 at.% Al. For the same compositions, extrema are observed on the concentration dependence of activation energy of viscous flow.

Heat treatment of iron based melts before quenching

Abstract Kinematic viscosity ν , magnetic susceptibility χ and surface tension σ of the Fe 85 B 15 and Fe 64 Co 21 B 15 liquid alloys were measured as functions of temperature. Pronounced anomalies on the ν ( T ) and σ ( T ) curves confirm the presence of structural transformations in the melts at the temperatures, which are specific for each composition. Three series of amorphous ribbons for each alloy composition were prepared using different modes of thermal treatment of the initial melt. Their properties were investigated. The results evidence the effect of the initial melt structure on those properties of the amorphous ribbons, which depend on the scale of microinhomogeneity. This correlation is discussed within the concept of metastable microheterogeneity of liquid metallic solutions.

Density of copper-aluminum alloys at temperatures up to 1400°c determined by the gamma-ray technique

The absolute method of penetrating gamma radiation has been used to measure temperature dependence of density for the Cu-Al alloys, which contain 0 to 100 at % of one of the components, in the temperature range between room temperature and 1300–1400°C. Based on the experimental values of density, the parameters of the linear approximation of its temperature dependence have been calculated. These parameters have been used then to calculate values of density at certain values of temperature and to plot density isotherms. Density jumps at melting for the specimens have also been determined.

An experimental investigation of the velocity of sound in molten lead and bismuth and in their reciprocal eutectic alloy at high temperatures

The pulse-phase method is used for measuring the velocity of sound in liquid lead and bismuth and in lead-bismuth eutectic in the range from the melting temperature to 1380 K. The purity of investigated metals is 9.99% by mass or better. The confidence error of experimental results does not exceed 0.3%. The experimental data are compared with those available from the literature.

Phase transitions and phase diagrams for liquid iron-based melts

Abstract Investigations of the magnetic susceptibility for Fe-B (up to 15 at.%) and Fe-C (up to 2.0 wt.%) alloys were carried out in a wide temperature range. Some anomalies on χ(T) curves were fixed and the kinetics of the crystallization versus melt structure was analyzed. The results are discussed in the suggestion that near liquidas we have two-structural melts: there exist microdomains enriched by the impurity element and the microareas of dilute solution of C(B) in Fe. For the latter, structural transformations similar to phase transitions in solids and connected with short-range order change could be realized. In the framework of local state representations of statistical mechanics, the necessary calculations were done and the lines of structural transformation in liquid phase were plotted.

Kinematic viscosity of liquid Al-Cu alloys

Temperature dependences of kinematic viscosity n of liquid Al100-x-Cux alloys (x = 0.0, 10.0, 17.1, 25.0, 32.2, 40.0 and 50.0 at.%) were measured. A technique based on registration of the period and the decrement of damping of rotating oscillations of a cylindrical crucible with a melt was used. Viscosity was calculated in low viscous liquids approximation. Measurements were carried out in vacuum in crucibles of BeO with a temperature step of 30°C and isothermal expositions of 10 to 15 minutes during both heating up to 1100-1250°C and subsequent cooling. We have discovered branching of heating and cooling curves v(T) (hysteresis of viscosity) below temperatures depending on the copper content: 950°C at 10 and 17.1 at.% Cu, 1050°C at 25 and 40 at.% Cu, 850°C at 32.2 at.% Cu. For samples with 10 and 17.1 at.% Cu the cooling curve returns to the heating one near 700°C. An abnormally high spreading of results at repeated decrement measurements was fixed at heating of the alloy containing 50 at.% Cu above 1000°C. During subsequent cooling the effect disappeared. Isotherms of kinematic viscosity have been fitted for several temperatures.

Density and ultrasound velocity in Ga-Bi melts

Density d temperature dependences of Ga-Bi melts with 0, 10.2, 16.2, 29.8, 42.0, 51.6, 61.5, 80.0 and 100 at.%Bi were measured using absolute gamma-absorption technique with accuracy of 0.2 to 1.5 % (depending on bismuth concentration). In addition, temperature dependences of ultrasound velocity Ds were determined for the samples with 11.0, 16.7, 29.8 and 100 at.% Bi. The accuracy in the acoustic measurements was higher than 0.3%. The special scanning equipment for the gamma-densitometer has allowed to measure density of co-existing phases below the separation cupola. The obtained values coincide with reference data within the declared accuracy. An anomalous behavior of ultrasound velocity (deviation of the Ds(T) from linear dependences) and significant increase of ultrasound attenuation were discovered for the samples with 16.7 and 29.8 at.% Bi at the temperatures of 70 to 100 K above the separation cupola. Using the experimental data, the thermal expansion coefficient, molar volume and adiabatic compressibility were calculated. All theses characteristics demonstrate linear behavior similar to ideal solutions.

Viscosity of aluminum–copper melts

The results of measuring the density of copper–aluminum melts obtained by Kurochkin et al. by the penetrating γ-ray technique are used to correct the results of viscosimetric experiments with melts of this system performed earlier by Konstantinova, who had no data on the density at that time and used the values of density obtained by a linear extrapolation between the densities of the pure components. This led to an error between the published values of viscosity, reaching 20% in some cases. The refined calculation results for the viscosity taking into account new data on the density of the copper–aluminum melts are recommended for use as reference data.

Nonergodicity in binary alloys

For binary liquids with limited miscibility of the components, we provide the corrections to the equation of state which arise from the nonergogic diffusivity. It is shown that these corrections result in lowering of critical miscibility point. In some cases, it may result in a bifurcation of miscibility curve: the mixtures near 50% concentration which are homogeneous at the microscopic level, occur to be too stable to provide a quasi - eutectic triple point. These features provide a new look on the phase diagrams of some binary systems. In present work, we discuss Ga-Pb, Fe-Cu, and Cu-Zr alloys. Our investigation corresponds their complex behavior in liquid state to the shapes of their phase diagrams.