Thermo chemical cleaning .

[traytown]

We are tyring to clean surface oxides from nickel nased superalloys using thermochemical cleaning ovens using cf4.
We are struggling to remove fully the oxide films using a 1000c fro 1 hour cycle . Any ideas?

 

[CoryPad]

Basic solutions like ammonium hydroxide can remove nickel oxide. Dow Actronal 440 (II) is an acidic product for nickel oxide removal.

 

[traytown]

sorry should have been more expansive, this is normally cracks in engine run aerofoils that we are thermochemically cleaning in preparation for brazing

 

[btrueblood]

Carbon tetrafluoride? Yikes. I'd be willing to bet that you need some %age of the atmosphere as water to help drive the reaction, but am by no means certain.

 

[traytown]

Hi trueblood,

no water just hydrogen and cf4 and argon purge,
the parts are coming off wing and the cracked aerofoils are littered with okide clusters on the surface of the cracks

 

[btrueblood]

OK, the H2 is doing the same thing as the water (allows formation of hydrofluoric acid to etch the oxide surface). How clean (what O2 residual) is the argon, and is it running the whole time or only at the beginning and end of the cycle? Past those questions I'm stumped. I assume you are worried about repeating the cycle or extending its duration for fear of doing damage to the uncracked surfaces?

 

[traytown]

The argon is 99.9% pure, it runs pre and post run, the reality is if we repeat/extend the cycle time or temp we cause tantalum/chromium carbide precipitation and this fails for that reason whilst still not removing the oxides from the cracked surfaces.

 

[WKTaylor]

The best cleaning practices are probably abrasive, followed by chemical. The abrasive loosens/detaches/erodes a high % of the contaminates; then the agressive [highly dangerous acids] can be used. But this would be my best guess.

This materials cleaning problem is best suited for the materials "other" forum... Suggest posting your question there:

http://www.eng-tips.com/threadminder.cfm?pid=367

Regards, Wil Taylor

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