Modeling the infiltration kinetics of molten aluminum into porous titanium carbide
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I.
INTRODUCTION
COMPOSITE materials have found increasing applications in recent years, primarily as a result of the vast range of properties attainable through the combination of two or more different materials tailor made for specific needs. Metal/ceramic composites are even more attractive because they have improved properties over conventional materials and are relatively simple to fabricate. The various forming techniques for particulate ceramic/metal composites include slurry casting, tL21 powder metallurgyt3m and melt infiltration; tS,6,Tj however, novel methods such as spray deposition CSl and in situ particulate formation t9j are currently emerging. Melt infiltration is a process whereby molten metal penetrates the pore channels of a porous ceramic compact. It offers the advantage of producing material with a high ceramic content and near-net-shape fabrication. The metal may be assisted by an external force, as is the case with squeeze casting, [7A~ or may be driven by a capillary pressure that develops when the molten metal wets the ceramic phase. The rate of infiltration of liquids in porous media has been of interest to various sectors of engineering, most notably that of agriculture and civil engineering, which is primarily concerned with the movement of water in soils and sand. tll,~2] This led to more fundamental scientific studies such as that of the motion of liquids in a capillary tube. Such an approach was taken by DANIEL MUSCAT, formerly Graduate Student, Department of Metallurgical Engineering, McGill University, is Lecturer, Department of Metallurgy and Materials Engineering, University of Malta, Msida, Malta. ROBIN A.L. DREW, Professor, is with the Department of Metallurgical Engineering, McGill University, Montreal, PQ, H3A 2A7 Canada. Manuscript submitted July 14, 1993. METALLURGICALAND MATERIALS TRANSACTIONSA
Washbum in 1921, [131 who looked at the penetration of various liquids into cylindrical capillaries. He then expanded this and treated a porous body as an assemblage of very fine cylindrical capillaries. Washburn looked at the problem by considering the flow in a capillary to follow Poiseuille's law, t~aj which states that
dV
7rr4dp -
-
-
dt
[ 1 ]
8 ~71
where dV is the volume of liquid which in time dt flows through a length, l, of a capillary having a radius, r, 7/ being the viscosity of the liquid and dp the total effective pressure acting to force the liquid along the capillary. So, by considering
dV = ~'r2dl
[21
and if, according to Kelvin's law, tl51
dp =
2Try cos 0
[31
r
3% being the surface tension and 0 the wetting angle, the expression may be written in terms of a velocity:
dl
rylv COS 0 -
-
dt
[41
-
4 ~ll
After integration, the expression becomes the length of infiltration as a function of time, where air resistance and gravity effects are neglected:
lz
=
(rytvC~ \
t
[5]
2,1
Washburn used Hg, water, and other liquids to show the VOLUME 25A, NOVEMBER 1994--2357
validity of this equation, which is still in use today in commercial porosimetry
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