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Metallurgical Transactions A

, Volume 21, Issue 1, pp 231–239 | Cite as

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

  • Doru M. Stefanescu
  • Avijit Moitra
  • A. Sedat Kacar
  • Brij K. Dhindaw
Solidification

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.

Keywords

Metallurgical Transaction Buoyant Force Critical Velocity Planar Interface Gravity Vector 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Nomenclature

d0

interatomic distance

fp

volume fraction of particles

g

acceleration due to gravity

kp

thermal conductivity of particle

kL

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

Fd

drag force

Fr

repulsive force

K

constant in Neumann’s equation

V

growth velocity

Vcr

critical growth velocity

η

viscosity of melt

ηr

relative viscosity

gDρ

density difference between the particle and the liquid

ρL

density of liquid

ρp

density of particle

σSL

surface energy between solid and liquid

σLV

surface energy between liquid and vapor

σPL

surface energy between particle and liquid

σPS

surface energy between particle and solid

σPV

surface energy between particle and vapor

θ

wetting angle

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Copyright information

© The Metallurgical of Society of AIME 1990

Authors and Affiliations

  • Doru M. Stefanescu
    • 1
  • Avijit Moitra
    • 1
  • A. Sedat Kacar
    • 1
  • Brij K. Dhindaw
    • 2
  1. 1.Solidification Laboratory, Department of Metallurgical and Materials EngineeringThe University of AlabamaTuscaloosa
  2. 2.I.I.T. KharagpurIndia

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