Sintering Flashcards
Define sintering
The densification of a particulate ceramic compact.
Removal of pores between particles, shrinkage, and bonding of
particles.
What is the criteria required for sintering?
Presence of material transport mechanism
• Diffusion
• Viscous flow
Source of energy to activate and sustain the transport
• Heat
• Energy gradients
between particlesThere are __________ stages of sinterig
3
The ___________ have the greatest impact on the total densification of a ceramic.
peak temperature and time
During this stage of sintering neck formation starts to form at contact points.
Stage 1
The pore channels get pinched off and are no longer continous in this stage of sintering.
Stage 3
In this sintering mechanism one component melts and wets the narrow channels between the particles.
liquid-phase sintering
The formation of continous pore channels occurs during this stage of sintering.
Stage 2
What is the sintering case that will result in the strongest ceramic components
pure densification
In this sintering mechanism material is transported from curved surfaces to contact regions due to differences in partial pressure
vapor-phase sintering
Design of furnace
Furnace is key to achieve proper sintering
Four key furnace parameters
- Temperature capability
- Temperature control
- Temperature uniformity
- Atmosphere control
Time and temperature cycles incorporate…
the rate of heating,
peak temperature, soak time, and rate of cooling.
__________ affect mechanical integrity.
Heating and cool rates
How is mechanical integrity affected?
- Too rapid and can induce thermal shock
- If binders or other organic additives were utilized during shaping operation, heating too quickly can result in crack formation due to rapid burn-off.
Controls for Conventional
Sintering
Atmosphere
Time & Temperature Cycles
Design of Furnace
Sintering Problems
Warpage Overfirring Burn-Off of Binders Decomposition Reactions Polymorphic Transformations
Modified Densification Process
These processes extend conventional sintering by
simultaneously applying temperature and pressure.
Infiltration
Great for near shape highly complex geometries.
Types of Modified Densification Process
- Hot Pressing
- Hot Isostatic Pressing
- Spark Plasma Sintering
Warpage
Results from…
Inadequate support during sintering
Density variations
• To differentiate the two, warpage due to sagging will not show differences in
thickness; warpage due to density will be clear in microstructure.
Overfirring causes
- Can cause warpage, reactions with furnace, bloating
- Easy to detect
- Can also cause excessive grain growth
- More difficult to detect, may require microstructural analysis.
- Recall; the larger the grains, the lower the strength.
