oxide cluster in NiCrAl plasma coating

[Zhiguo]

hello all,

I am suffering from oxide cluster problem in plasma spray NiCr-6%Al coating.
I tried kinds of methodes (decrease heat input, increase powder feed rate, add airjet and so on) to decrease the oxide cluster. But failed each time.
Gun: F4-MB; Powder: Amdry 960; Nozzle: 6mm;
Ar: 35, 40, 55 NLPM; H2: 5, 7, 9NLPM;
Current: 550, 575, 600, 625A;

Sometimes the metallographic result is good on oxide except several big oxide clusters.
I am really puzzled. Is it because the powder? The powder I used has been stored 5 years.

[Ramin]

could you send one of its microstructure pictures?
let me know about the percentage of oxide in microstructure,
put the powder on oven and mix again,
what is the distance of spraying?

[Zhiguo]

(12-15-2012 08:22 AM)Ramin Wrote:  could you send one of its microstructure pictures?
let me know about the percentage of oxide in microstructure,
put the powder on oven and mix again,
what is the distance of spraying?

I tried several distance. 130, 140, 160mm.
The powder is always kept in the oven and I also mixed the powder before fill it in the pot.
I am not sure is it because of the powder has been stored for 5 years? so there is some change in the composition?

I tried to insert a imagine but failed. I am not sure is it because the poor internet in the office. I will try it again when i back home.[/php]

[Gordon]

Hi Zhiguo

If you have problems uploading your images, email them to me and I will insert them for you.

Is the powder a composite or alloy product?

[Zhiguo]

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(12-19-2012 06:45 PM)Gordon Wrote:  Hi Zhiguo

If you have problems uploading your images, email them to me and I will insert them for you.

Is the powder a composite or alloy product?

it should be composite.