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Ni-W

Liquid Phase Sintering. Ni-W. A+B. L. T sint. T. B. A. A powder + B powder. 2R. a. 2r. LPS as flow through packed beds- the chemical engineering approach.

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Ni-W

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  1. Liquid Phase Sintering Ni-W A+B L Tsint T B A A powder + B powder

  2. 2R a 2r 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

  3. 2R a 2r Example 2R

  4. Example (continued) Now determine the hydraulic radius

  5. Example (continued) See Gaskell 2.6 and the Die Cast Mold Filling Example

  6. Example (continued)

  7. Polycrystalline particle Liquid 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.

  8. γlv γsv θ γsl 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”

  9. γlv γsv θ γsl γlv θ γsv γsl Large γsl, non-wetting θ Large Large γsv, wetting θ small

  10. Grain boundary wetting during LPS occurs when θA and θB approach zero. Grain B γBL θB Liquid γAB θA γAL Grain A

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