Gordon England Surface Engineering Forum



Re: level of oxidation in NiCrAlY coatings


Posted by Gordon England on November 21, 2003 at 15:11:57:

In Reply to: level of oxidation in NiCrAlY coatings posted by Adam Pawlowski on November 21, 2003 at 14:21:38:

: Hello Mr. Gordon
: I would like to ask about NiCrAlY plasma sprayed coatings as a bond coat for TBC coating. I need to produce coatings with low level of oxidation. What are the main parameters which affect oxide content and what is the relation between powder size range and oxide content in the coating.
: Regards
: Adam Pawlowski


Hi Adam

I assume you are referring to atmospheric plasma spray (APS) and not vacuum or low pressure plasma spray (VPS of LPPS)as the latter is essentially oxide free.

APS will produce oxides in the coating. The only way to stop this is to exclude the air from the spray stream. Powder size will influence the total oxide content of the coating, the coarser the powder, the lower the oxide content (surface area effect). The downside is the coarser the powder, the higher the porosity content of the coating. Parameter settings such as current, primary and secondary plasma gas flows, spray distance, powder feed rate and injection etc. are important and need to be carefully optimised to produce a coating that is neither "under reacted" (low oxide, porous, many unmelted particles and poorly bonded)or "over reacted" (high oxide, possibly dense). If oxide content is still too high after optimisation, an inert gas shroud may reduce oxidation further.

If VPS is not an option or just to expensive then I would suggest HVOF or HVAF coating methods to produce denser and slightly cleaner coatings than APS.


Hope this helps.

Regards Gordon


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