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The influence of buoyant forces and volume fraction of particles on the particle pushing/entrapment transition during directional solidification of Al/SiC and Al/graphite composites

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Abstract

Directional solidification experiments in a Bridgman-type furnace were used to study particle behavior at the liquid/solid interface in aluminum metal matrix composites. Graphite or siliconcarbide particles were first dispersed in aluminum-base alloysvia a mechanically stirred vortex. Then, 100-mm-diameter and 120-mm-long samples were cast in steel dies and used for directional solidification. The processing variables controlled were the direction and velocity of solidification and the temperature gradient at the interface. The material variables monitored were the interface energy, the liquid/particle density difference, the particle/liquid thermal conductivity ratio, and the volume fraction of particles. These properties were changed by selecting combinations of particles (graphite or silicon carbide) and alloys (Al-Cu, Al-Mg, Al-Ni). A model which considers process thermodynamics, process kinetics (including the role of buoyant forces), and thermophysical properties was developed. Based on solidification direction and velocity, and on materials properties, four types of behavior were predicted. Sessile drop experiments were also used to determine some of the interface energies required in calculation with the proposed model. Experimental results compared favorably with model predictions.

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Abbreviations

d 0 :

interatomic distance

f p :

volume fraction of particles

g :

acceleration due to gravity

k p :

thermal conductivity of particle

k L :

thermal conductivity of liquid

n :

coefficient, function of type of repulsive forces acting between particle and solid

r :

radius of particle

F :

force acting on particle

F d :

drag force

F r :

repulsive force

K :

constant in Neumann’s equation

V :

growth velocity

V cr :

critical growth velocity

η :

viscosity of melt

η r :

relative viscosity

gDρ :

density difference between the particle and the liquid

ρ L :

density of liquid

ρ p :

density of particle

σ SL :

surface energy between solid and liquid

σ LV :

surface energy between liquid and vapor

σ PL :

surface energy between particle and liquid

σ PS :

surface energy between particle and solid

σ PV :

surface energy between particle and vapor

θ :

wetting angle

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Authors and Affiliations

  1. Solidification Laboratory, Department of Metallurgical and Materials Engineering, The University of Alabama, 35487-0202, Tuscaloosa, AL

    Doru M. Stefanescu (University Research Professor), Avijit Moitra (Graduate Research Assistant) & A. Sedat Kacar (Graduate Research Assistant)

  2. I.I.T. Kharagpur, India

    Brij K. Dhindaw (Professor)

Authors
  1. Doru M. Stefanescu
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  2. Avijit Moitra
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  3. A. Sedat Kacar
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  4. Brij K. Dhindaw
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Additional information

BRU K. DHINDAW Visiting Scholar with the Solidification Laboratory at the time this work was performed.

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Stefanescu, D.M., Moitra, A., Kacar, A.S. et al. The influence of buoyant forces and volume fraction of particles on the particle pushing/entrapment transition during directional solidification of Al/SiC and Al/graphite composites. Metall Trans A 21, 231–239 (1990). https://doi.org/10.1007/BF02656440

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  • DOI: https://doi.org/10.1007/BF02656440

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