2. Consider Two Spherical Particles Undergoing Sintering with Neck Formation. What Is The

1. We consider the flow of fluid through the powder pack as flow through channels or ‘pipes’. This is known as ‘tube bundle theory’. In tube bundle theory, the effective ‘pipe’ radius is known as the hydraulic radius, Rh. Compare Rh to the diameter of an octahedral site and a tetrahedral site in an FCC powder pack with particles of 70 um diameter.

2. Consider two spherical particles undergoing sintering with neck formation. What is the difference in pressure on the atoms between point a and point b if r1=0.1 um, r2=0.025 um and r3=0.25 um. The surface energy is 1 J/m^2.

3. This assignment will require you to examine the experimental data shown below (next page) in terms of a simple model for sintering

Using the idealized geometry below, an expression for the rate of change in sintered density as a function of ancillary parameters has been proposed

Figure 2

(a) Use the pressure/temperature dependent density data to determine the activation energy, Q, and pre exponential term, Do, for the diffusion coefficient D where

Assume G=50 um and no CIP (0 compaction pressure on the data plot) and gsv=1 J/m^2.

(b) Use the answer from (a) to determine the value of G at the CIP pressure of 400 MPa.

(c) Using the diffusion coefficient determined in (a) and G=50 um, compare the kinetics of densification from part (a) with a HIP process where Pa=300 MPa

Please note that you will have to calculate the atomic volume of Ni.