Kinetics of the microstructure formation in a rapid solidified immiscible alloy

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Abstract

A model is presented to describe the microstructure evolution during a liquid–liquid decomposition when cooling an alloy rapidly in the miscibility gap. The model was first verified by comparing with the experiments and then applied to investigate the microstructure formation in a rapid solidified Cu–Co alloy. The results indicate that the size of the minority phase particles is dominated by the nucleation behavior of the minority phase droplets (MPDs) during the liquid–liquid decomposition. Both the Brownian coagulations of the MPDs and the diffusional interaction between the MPDs affect the nucleation of the MPDs. The later has a relatively stronger effect.

Introduction

Many alloys show a phase diagram characterized by the appearance of a miscibility gap in the liquid state. Such an alloy decomposes into two liquids when cooled into the miscibility gap. Many efforts have been made to use the demixing phenomenon for the production of the finely dispersed metal–metal composite materials. It has been indicated that the rapid solidification technique has great potential in the manufacturing of the immiscible alloys with a well dispersed microstructure [1], [2], [3], [4], [5], [6]. There is an increasing interest in synthesizing the composites of immiscible alloys containing micro or even sub-micro particles by using the nonequilibrium processing technique [1], [7]. This paper will develop a model to describe the microstructure evolution in a rapidly solidified immiscible alloy.

Section snippets

Formulations

The microstructure evolution during a rapid cooling of an immiscible alloy in the miscibility gap is dominated by the concurrent actions of the nucleation, the diffusional growth and the Brownian coagulations of the minority phase droplets (MPDs). We describe the microstructure development by using a MPD size distribution function f(R, t). f(R, t)dR gives the droplet number per unit volume in a radius range between R and R + dR at time t. f(R, t) satisfies Eq. (1) during the liquid–liquid

Verification of the model

Kolbe et al. carried out rapid solidification experiments with Cu84Co16 alloy under the drop tube conditions [12]. They measured the apparent (2d) average radius of the Co-rich particles in the section plane of the powders of different diameters. Their result is shown in Fig. 2 as a function of the powder diameter. The microstructure formation in the Cu84Co16 powders were calculated according to the practical experimental conditions. The details of the calculation and the thermodynamic

Conclusions

A model is presented to describe the microstructure evolution in a rapidly solidified miscibility alloy. Calculations are carried out for Cu–Co alloy. The numerical results demonstrate that the final size of the minority phase particles is dominated by the nucleation behavior rather than the coarsening due to the Brownian coagulation and the Ostwald ripening of the minority phase droplets (MPDs) after the nucleation period. The calculations also demonstrate that both the Brownian coagulations

Acknowledgements

This work is financially supported by the National Natural Science Foundation of China (Grant Nos. 50671111, 50771097, 50620130095, 50704032) and the Natural Science Foundation of Liaoning province (20050047).

References (13)

  • J. An et al.

    Tribol. Int.

    (2003)
  • X.Y. Lu et al.

    Mat. Sci. Eng. A

    (2004)
  • J.Z. Zhao

    Scripta Mater.

    (2006)
  • J. He et al.

    Acta Mater.

    (2006)
  • M. Zhu et al.

    Wear

    (2000)
  • K.E.J. Lehtinen et al.

    J. Colloid Interf. Sci.

    (2001)
There are more references available in the full text version of this article.

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