Solid state sintering Flashcards

1
Q

How do you calculate shrinkage?

A

~ assume a part is made up of cube elements
~ assume the sintered part is theoretically dense

~ Ai = green body dimension
~ Af = sintered dimension
~ Fp = volume fraction pores in the green body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Fp =

A

~ Vi - Vf / Vt = 1 - Vf/Vi = 1 - Af^3/Ai^3

~ Vi - Vf: volume taken up by pores
~ Vt: total volume

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is Xl?

A

~ Xl = linear shrinkage fraction

~ Xl = Ai-Af/Ai
~ Ai-Af: change in length
~ Ai: original length

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is Fp knowing that Af = Ai(1-Xl)?

A

~ Fp = 1 - Ai^3(1-Xl)^3 / Ai^3

~ Fp = 1-(1-Xl)^3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the final Xl equation?

A

~ because 1 - Xl = (1 - Fp)^1/3

~ Xl = 1 - Fs^1/3
~ Fs = fraction solid in the green body = 1 - Fp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the driving force for sintering?

A

~ the elimination of solid-vapor interfaces (many un-sataisfied bonds), replacing them with solid-solid interfaces (grain boundary, fewer unsatisfied bonds)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the average particle size for a good sinter?

A

~ avg particle size of 0.5-1 μm

~ green relative densities generally sinter well

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What occurs during the initial stages of sintering?

A

~ atoms show net migration to points of particle contact, filling them in to form early grain boundaries in the form of necks

~ atoms supplied by surface diffusion or evaporation condensation if the solid has a high vapor pressure

~ atoms diffusing to this neck location satisfy more dangling surface bonds-surface atoms are more stable at this location

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What occurs during the intermediate stage of sintering?

A

~ most macroscopic shrinkage

~ atomic source is predominately from interior sources: grain boundaries and particle interiors

~ GB diffusion dominates because of high conc. of vacancies from lattice mismatch

~ bulk diffusion has an increasing role with increasing temp because of an exponential increase in vacancy concentration

~ gaps between particles sinter to near-cylinders. these are interconnected and the network extends to the part surface: open porosity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What happens during the final stage of solid state sintering?

A

~ starts at 90% relative density

~ cylindrical pores close off to isolated spherical pores along 3-grain intersection curves and at four grain intersection points

How well did you know this?
1
Not at all
2
3
4
5
Perfectly