About Thermal Barrier Coating Porosity

[Amanda]

Hi, All~
Long time no see!
I have some questions need your professional help on TBC porosity of plasma spraying.
Now our lab evaluate the metallograph of TBC Class C TOP coat on porosity according to specification.
I wonder how many types of porosity are there on Class C top coat?
My question is, are some faveolate powder blocks seems normal in this kind of coat? is that a kind of porosity? We mount the speciman, resin is also immerging in this kind of hollows. and as I know, the normal porosity is stacked by melt powders which is hollow and a little bit larger.

Sincerely appreciate any help and comments~

Thanks&regards.

Amanda

[mehongbo]

Amando,
It is always diffucult to discuss micrstructure without photo. Generally porosity either comes from spray process, which is the true porosity, and comes from polishing pull-out. Most of the time these pull-outs are either large hollows or linear and usually being found in interpass area. Don't understand what "powder blocks" mean . If you mean unmelt powder, then you should call yr spec. find out the allowance. Definitely too much unmelt indicates bad coating.

Hong

Hi, All~
Long time no see!
I have some questions need your professional help on TBC porosity of plasma spraying.
Now our lab evaluate the metallograph of TBC Class C TOP coat on porosity according to specification.
I wonder how many types of porosity are there on Class C top coat?
My question is, are some faveolate powder blocks seems normal in this kind of coat? is that a kind of porosity? We mount the speciman, resin is also immerging in this kind of hollows. and as I know, the normal porosity is stacked by melt powders which is hollow and a little bit larger.

Sincerely appreciate any help and comments~

Thanks&regards.

Amanda

[Amanda]

Hello, Hong,

Thanks for your response~
For "faveolate powder blocks" I meant some melt powders is faveolate, not unmelt powder block!
I know the true porosity and pullout you mentioned, but not know what the faveolate hollow is, it's different from the two types of porosity..so confused..
I'm thinking over to upload some pics for your reference later~
Anyway, thanks a lot for your response!

[quote='mehongbo' pid='3285' dateline='1239306277']
Amando,
It is always diffucult to discuss micrstructure without photo. Generally porosity either comes from spray process, which is the true porosity, and comes from polishing pull-out. Most of the time these pull-outs are either large hollows or linear and usually being found in interpass area. Don't understand what "powder blocks" mean . If you mean unmelt powder, then you should call yr spec. find out the allowance. Definitely too much unmelt indicates bad coating.

Hong

[quote='Amanda' pid='3282' dateline='1239244731']

[Gordon]

Hi Amanda

Sorry, I'm not sure I understand your inquiry. Please, no need for apology for English language, many native English people don't communicate as well as you Uploading a few images may certainly help.

I wonder how many types of porosity are there on Class C top coat?

Porosity is empty spaces or voids within coating. Not sure about types. I suppose they could be categorized into size or shape or maybe from how they originated/formed. Basically, porosity forms from

* Incomplete filling of space when particle splats and deforms
* voids generated through contraction stresses on cooling (including cracks, micro-cracks and particle interface separation)
* voids already present in powder particles (particular reference to hollow sphere TBC powders)