YSZ Patching

[Max K]

Hello everybody!

I have low top coat (YSZ Metco 204NS-G powder) spots on a sprayed part that I want to patch. Is there a time frame during which I can do it after a part was coated and removed from a booth? Do I need to roughen a surface to do it? What would be general concerns of doing patching?

Thank you.

[kschewe]

I assume there is a bond coat. You can lightly blast off the ceramic and spray the ceramic back on. Depending on the application you might be able to grit blast lightly the areas that need to be repaired and do touch up.
concerns will be contamination, part has to be clean and not exposed to oils for example that would contaminate the bond coat resulting in problems like delamination.

[Max K]

I assume there is a bond coat. You can lightly blast off the ceramic and spray the ceramic back on. Depending on the application you might be able to grit blast lightly the areas that need to be repaired and do touch up.
concerns will be contamination, part has to be clean and not exposed to oils for example that would contaminate the bond coat resulting in problems like delamination.

Kschewe,

Thanks for your tips. I conducted small experiment. I sprayed a test piece, and left it in shop environment for 24 hours. Then I sprayed on top of coated test without grit blasting but using preheat option (gun heat without powder). Mounted test piece in epoxy. Under microscope there were no indications or a line where you can tell that a separate layer of coating was sprayed.

[sreenuvundela]

Hi,

I never suggest any type of patch work in thermal spray, from my knowledge the term patch will be used where coating chipped off from the substrate on some location. There will not be any mechanical bonding between old coating and new coating where patch work done.

It is always better to carry patch work as early as possible after coating operation and it is better to clean and roughen the surface where patch work to be done.


There are lot of issues you have to consider during patch work like

1. Thickness of the patch (it should not be higher thicknesses because total coating may peel off).

2. Contamination & Oxidation problems for metals.

3. Temperature raise in that particular area where patch work to be done.

Your experiment is very similar to increase coating thickness rather than patch work, we can always carry coating to increase the thickness with out any problem but we have to take necessary care so that the coating surface should not contaminate by dust or atmosphere etc.


Regards

SREENIVAS

[derek]

I kind of disagree with SREENIVAS.

If the surface of TBC was not polished and surface is clean, you can patch TBC on small area. I did same test with microstructure and tensile test, all pass our Spec.

Yes, if the part was laying on floor too long time let say more than 48 hours and the surface was contaminated, you can't patch TBC.

Believe it or not, lot of coating shop doing it. You don't want strip all TBC and coat it again because small area coating thickness is thin. Especially when you found out, you already coat 20 parts.