L. V. Kamaeva

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.

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.

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).

Study of Viscosity of Fe-Cr Melts Containing 2 to 40 at % of Chromium

The temperature, time, and concentration dependences of viscosity ν of Fe-Cr melts containing 2 to 40 at % of chromium are studied. It is shown that the observed anomalies in viscosity polytherms in the first heating mode and the hysteresis of ν in subsequent cooling are due to the slow setting of thermodynamic and chemical equilibrium in the system of crucible-melt-atmosphere, which is shifted to higher temperatures with increasing oxygen content in the alloy. The minimum and maximum of viscosity are observed at 5 and 12 at % of Cr, respectively; they are caused by a concentration change in the binding energy between the atoms, which is determined by the geometric and compositional short-range order. The nonequilibrium state of the melts has no significant effect on the nature of their viscosity isotherms.

Viscosity and supercooling of Fe-Cr (≤40 at % Cr) melts

We have studied the composition dependences of the kinematic viscosity (ν) and supercooling (Δt) of Fe-Cr melts at chromium contents of up to 40 at %. The results indicate that there is a minimum in viscosity at 5 at % Cr, a maximum at 12 at % Cr, and a sharp rise in the crystallization tendency of the solid solution in this composition range. The Δt(x) and ν(x) data obtained can be understood in terms of the composition dependence of the bonding energy, which is governed by the geometric and chemical short-range order in the atomic arrangement. Using a probabilistic approach to evaluation of various short-range order configurations and the experimental viscosity and supercooling data at chromium contents of 2.5 and 30 at %, we have calculated Δt(x) and ν(x) up to 40 at % Cr.

Processes of the solidification of Ni-B alloys

The temperature and concentration conditions of metastable phase formation in a Ni-B system at melt cooling rates of 102 to 104 °C/s were investigated by X-ray structural analysis, metallography, and transmission electron microscopy. An increase in the cooling rate was shown to yield a decline in the concentration range of the metastable phase’s existence.

On the Tendency of the Co-, Ni-, and Fe-Based Melts to the Bulk Amorphization

In this article, the influence of the liquid phase state on the glass-forming ability and solidification processes of the Co65.5Fe6.5Si18B10, Ni64.4Fe4Cr4.9Mn2B16.2C0.5Si8, and Fe50Cr15Mo14C15B6 alloys was studied. It was shown that in conditions of quenching from the melt at ~103 K/s, the largest fraction of the amorphous phase is achieved by cooling from a narrow temperature range near 1573 K (1300 °C) for Co65.5Fe6.5Si18B10, 1503 K (1230 °C) for Ni64.4Fe4Cr4.9Mn2B16.2C0.5Si8, and 1653 K (1380 °C) for Fe50Cr15Mo14C15B6. It was found that at these temperatures, there are anomalies in the viscosity and undercooling polytherms caused by changes in short-range ordering in these melts. Overheating the Co65.5Fe6.5Si18B10, Ni64.4Fe4Cr4.9Mn2B16.2C0.5Si8, and Fe50Cr15Mo14C15B6 melts above these temperatures is accompanied by changing the nature of their crystallization. It was shown that the analysis of the temperature dependences of undercooling and kinematic viscosity can be used to determine the optimum temperatures of the melts quenching to achieve their best bulk amorphization.

On the viscosity of Fe79Cr21 melt of congruent composition

The temperature and time dependences of the Fe79Cr21 melt viscosity have been investigated by the method of damping torsional vibrations of a crucible with one or two face surfaces. Anomalies in the viscosity polytherms at certain temperatures have been found for the first time. The display of these anomalies is determined by the melt structure and the melt-crucible interaction.

Structural-peritectic transformations in Cr-C and Fe-P melts

Undercooling and the solidification processes of Fe-P and Cr-C melts with eutectic composition have been studied in this paper. It is shown that the equilibrium eutectics, α-Fe/Fe3P (for Fe83P17 melt) and α-Cr/Cr23C6 (for Cr86C14 melt), are formed at cooling the eutectic Fe-P and Cr-C liquid alloys from the melt temperatures lower than t* (t*= 1125°C for Fe83P17 and t*= 1610°C for Cr86C14) with the cooling rates interval from 20 to 100°C/min. The nonequilibrium eutectics, α-Fe/Fe2P (for Fe83P17) and α-Cr/Cr7C3 (for Cr86C14), are formed at cooling from the melt temperatures higher than t* and decomposed to equilibrium phases on further cooling.

Nonequilibrium solidification of Fe-P alloys

The specific features of solidification of Fe-P alloys in the concentration range 5–25 at % P have been studied by differential thermal analysis and X-ray diffraction. The equilibrium α-Fe + Fe3P eutectic is shown to form immediately from melt only for compositions with 17–19 at % P when a melt is superheated below temperatures of 1130–1160°C, at which the type of composition short-range ordering changes (Fe3P → Fe2P) under insignificant (∼50°C) supercooling conditions. A nonequilibrium α-Fe + Fe2P eutectic forms during cooling of the alloy at a large (∼200°C) supercooling.