Information on Diffusion Coatings by Pack and above the pack.
Pack coatings typically are external only and result from burying the component in a powder mix. Gas phase or above the pack techniques do NOT require contact between the part and the powder mix. Instead, a gas is generated.
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Gas Phase / CVD Aluminizing
CrAl is used to activate AlF3. Coatings can be both Internal as well as External. |
Typical Schematics for pack and Above the Pack
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Low Temperature / High Activity vs High Temperature / Low Activity
There are subtle differences but for a LTHA coatings, diffusion of aluminide is all inward while for a HTLA, Nickel diffuses outward and typically the coating is about 35% inward and 65% outward. |
The above CVD system uses a molten aluminum pool.
The molten pool dissasociates the AlCl3 to the more reactive and unstable mono chlorides. |
Simple CVD Schematic
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Flow Tubes are used to bring the coating gases into the part.
The gas tubes can be designed to input a more or less correct amount of gas into each pathway. |
Process Basics
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