Repair Ni-Cr coating

[vevecaz]

Dear all,
First, excuse me for my bad english.
I have a local problem on a Ni80-Cr20 coating, made with JP5000.
I think there is some porosity on the steel weld joint on this part and the coating is bad in this area.
How can I repair this ?

[MichiganMan]

When you say the coating is bad what do you mean? (i.e. is it delaminating, discontinuous, just too porous?)

What are you tying to accomplish by the coating (i.e. corrosion resistance, erosion resistance)?

Without the answers to the above all I can say is that a failure at a weld seam is often indicative of poor surface preparation. What was done to get the piece ready for spray? The remedy depends on all of these factors.

[vevecaz]

The problem is that the NiCr don't stick locally on the weld joint. I think there is porosity in the steel
and we don't have good surface preparation (dirt in porosity i think).
How repair this? I think we have to make a new part.

[MichiganMan]

You may very well be best off to make a new part, but more information is needed to say for sure. If the weld was not a clean radius before the preparation and spraying (but the weld was structurally sound), then yes you probably trapped contaminates in the pores, or just tried to bridge over gaps. Either could cause your failure. If the cost of making a new part is prohibitive and you have effective means available, then you may try to carefully grind down to the weld, remedy the poor surface preparation and reapply. This may be near impossible to do if you have tight tolerances on the part and depending on the part it may be less costly to start over than to try to fix this.

[k09]

Hi Vevecaz & MichiganMan,

when you mentioned that the coating doesnot stick or adhere at the weld joints, I feel it could probably be due to improper Surface Preparation.

After Grit Blasting, visually, were there any signs of inadequate surface roughness at the weld area? There is a possibility that the weld material is somewhat harder that the adjoining base material and therfore would require change in blasting pressure or grit mesh size to gain adequate roughness.

before removing the weld or redoing it all over again, you can surely give this a try.

Regards

K09