The Effect of Nickel on the Viscosity of Iron-Based Multicomponent Melts

Yuri N. Starodubtsev,Viktor V. Konashkov,Vladimir S. Tsepelev

doi:10.3390/met11111724

Abstract

In this work, we investigated the temperature dependence of the kinematic viscosity of multicomponent Fe72.5−xNixCu1Nb2Mo1.5Si14B9 melts with a Ni content of up to 12.7 at. %. The peculiarities of the temperature dependence of Ni-containing melts were explained by the tendency of Ni atoms to surface segregation. Ni atoms are concentrated near the interfaces of the liquid and solid phases in the mushy zone at the stage of melting and restrain the melting of the solid phase. With increasing Ni content, the Arrhenius type of viscous flow begins at a higher temperature. Ni atoms are concentrated at the periphery of clusters, increasing their size and decreasing their mobility. The movement of Ni-containing clusters increases the activation energy and decreases the kinematic viscosity. The change in the activation energy at a temperature of about 1700 K was associated with a liquid-liquid structure transition (LLST). This structural transition is reversible since it is observed both at the heating and cooling stages. The increase in kinematic viscosity at temperatures above 1900 K was associated with the decomposition of high-temperature clusters based on cementite and silicon oxides.

Highlights

The viscosity is associated with the movement of liquid particles relative to each other, and it depends on the diffusion mobility of these particles
Since the temperature dependence of the diffusion coefficient is expressed by the Arrhenius equation [1], the viscosity can be represented in the form [2]: ν where ν is the kinematic viscosity (m2·s−1), ν0 is the pre-exponential factor with the dimension of the kinematic viscosity, Ea is the activation energy of the viscous flow (J·mol−1), R is the gas constant (J·K−1·mol−1), T is the absolute temperature (K)
We investigated the temperature dependences of the kinematic viscosity of the multicomponent Fe72.5−xNixCu1Nb2Mo1.5Si14B9 melt with a Ni content of up to 12.7 at. %

Summary

Introduction

The viscosity is associated with the movement of liquid particles (atoms, molecules, clusters) relative to each other, and it depends on the diffusion mobility of these particles. Since the temperature dependence of the diffusion coefficient is expressed by the Arrhenius equation [1], the viscosity can be represented in the form [2]: ν = ν0e Ea RT (1). From relation (1) it follows that the viscosity decreases with increasing temperature at the constant activation energy Ea. The activation energy depends on the size and interaction of the particles participating in the viscous flow, and the transition of individual particles to a new state occurs after the particle reaches the activated state. The change in the activation energy on the temperature dependence of the viscosity is associated with a change in melt structure, and this phenomena is interpreted as a liquid-liquid structure transition (LLST) [3,4,5,6,7,8,9,10,11]

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Discussion

Conclusion