Ni-W
Liquid Phase Sintering
T
A
B
A powder + B powder
L
Tsint
A+B
LPS as flow through packed beds-
the chemical engineering approach
The space between particles-the interconnected porosity-are pipes. These pipes have an effective radius (hydraulic radius) given as
Example
2R
Example (continued)
Now determine the hydraulic radius
Example (continued)
See Gaskell 2.6 and the Die Cast Mold Filling Example
Example (continued)
Liquid
Polycrystalline
particle
Grain boundary ‘wetting’ breaks the polycrystalline particle into single crystal particles in the initial stages of liquid phase sintering. These single crystal particles then spheroidize and coarsen.
Youngs’ Equation
Represent the surface tensions of a multi-phase junction as vectors drawn parallel to the respective surfaces
The surface energies for the for the solid/liquid, the solid/vapor and the liquid/vapor interfaces are γsl, γsv, γlv. The vectors representing these surface energies must balance at the three phase triple junction. This equation representing this balance is known as ‘Youngs’ equation”
γsl
γsv
γlv
θ
Large γsl, non-wetting θ Large
Large γsv, wetting θ small
Grain A
Grain B
Liquid
γBL
γAL
γAB
θB
θA
Grain boundary wetting during LPS occurs when θA and θB approach zero.