Chromium Carbide crack

[novakmichal86]

Hi!

I have a problem with chromium carbide. I use HVOF Tafa JP 5000. And sometimes when I apply chromium carbide coating then I have problem with cracks.

Could you recommend me what I can do, please?
Could you advise me some good bondcoat?
What is good temperature before and after spraying?

Now, I want to try apply coating without any bondcoat.

Thank you for your help!

Michal

[Gordon]

Hi Michal

to the Surface Engineering Forum.

When you say a problem with cracking, is this on the coated part or the test pieces required for quality control? If on the part, are cracks found in the as-sprayed condition or after finishing? Are you using Praxair recommended parameters and powders? What thickness per gun pass are you applying the coating?

I would not use a bond coat apart from when you need a very thick build-up.

"What is good temperature before and after spraying?" I would try to keep within 100 and 200 degrees C.

[novakmichal86]

Hi Michal

to the Surface Engineering Forum.

When you say a problem with cracking, is this on the coated part or the test pieces required for quality control? If on the part, are cracks found in the as-sprayed condition or after finishing? Are you using Praxair recommended parameters and powders? What thickness per gun pass are you applying the coating?

I would not use a bond coat apart from when you need a very thick build-up.

"What is good temperature before and after spraying?" I would try to keep within 100 and 200 degrees C.

Hi Gordon,

It was on the coated part and I found this cracks after grinding. Yes, I always use exact parameters from Praxair. But I use firstly bondcoat 1275 and then chromium carbide 1375. The thickness is 0.2mm. Now, I want to try make coating without bondcoat.

Ok, I know this temperature. Also, we mix powder before spraying, but somewhere I read some information that I should heat also powder before spraying. Is it right? How I can do it?

[KevGarty]

Hi Michal,

What is the base material of the part ? If its stainless make sure you give it a good preheat before coating as stainless can be a bit of a pain for expanding.

If the coating cools at a different rate to the base material it can crack. Almost like crazy paving

If it was me I would pre-heat it to around 70-80° then start coating. When your coating go with what Gordon said.

Also when Grinding make sure you don't take heavy cuts.

Ensure you have a good profile etc after blasting and you should be fine.

As far as heating the powder goes it certainly wouldn't do it any harm
Applying 0.2mm doesn't require bond coat

Good Luck !

[kschewe]

Good advice here. You should be able to spray 1375vf to 1mm with no cracking. Are you grit blasting or glass beading the substrate? Make sure the grinders are using a diamond wheel with small cuts .0005" or less