Blistering problem in Chromium Carbide Coating -- Reg

[sreenuvundela]

Friends,

Attached photos are taken during removal of the defective chromium carbide coating - Nikelchrome coating.

Blistering observed at customer end after storage of 2 to 3 months. When we removed this defective coating by grinding process, we observed lot of rust on the base material. the substrate material is low alloy steel and which have the tendency of rusting, because of this problem only we carried 150 microns Ni-Cr bond coat before carrying the Chromium carbide coating.

Kindly share your thoughts/views to know the exact reason for blistering.

All the process parameters are well maintained.

This problem occurred in 20 components in time span of 3 to 4 months.


Regards,

SREENIVAS

[Gordon]

Hi Sreenivas

The environment has penetrated the coating and caused corrosion of the substrate. I would guess that the storage conditions were damp or of high humidity.

How was the coating applied?
How thick was the coating?
Was the coating sealed?
Was the coating stored in the as-spray condition or after finishing?

[sreenuvundela]

Dear Gordon,

How was the coating applied?
The said coating contains top coat and bond coat. Bond coat applied with 80Ni-20Cr powder with the help of Detonation spray process and top coat applied with 75Cr3C2 -25NiCr powder with the help of HVOF spray process (H.C.Starck make).

How thick was the coating?
Bond coat thickness is 100 to 150 microns and top coat thickness is 150 to 200 microns. The total coating thickness will be 300 to 350 microns.

Was the coating sealed?
No sealent applied. Customer will not permit to apply sealent.

Was the coating stored in the as-spray condition or after finishing?

The coated component stored at customer end after finishing. the component wrapped with paper after proper cleaning with the help of acetone, bubble sheet also wrapped on paper and finally wrapped rubber sheet on bubble sheet. Total three layers of protection given for the coating.

The customer complaints that blistering observed after removal of the packing on the component.

Kindly suggest where we are going wrong.


Regards,

SREENIVAS

[loriolo]

Hi Sreenivas
Please keep in mind that thermal spray proceses are porous coatings, if you have a cathodic material as base material, of coarse you will have corrosion on it, so or you seal the coatings, otherwise you must change this coating with a non porous one, as spray and fuse...

[shantanu]

Friends,

Attached photos are taken during removal of the defective chromium carbide coating - Nikelchrome coating.

Blistering observed at customer end after storage of 2 to 3 months. When we removed this defective coating by grinding process, we observed lot of rust on the base material. the substrate material is low alloy steel and which have the tendency of rusting, because of this problem only we carried 150 microns Ni-Cr bond coat before carrying the Chromium carbide coating.

Kindly share your thoughts/views to know the exact reason for blistering.

All the process parameters are well maintained.

This problem occurred in 20 components in time span of 3 to 4 months.


Regards,

SREENIVAS

Advise you to apply a sealer, even a simple lacquer on the ground Cr3C2 surface prior to packing if you have any hint that the material may not be put it use almost immediately after coating and grinding.
We just supplied a Cr3C2 coated roll to a customer after stocking it in our works for 4 months after completion of work, but the surface was free from any corrosion or oxide layer due to application of a lacquer prior to bubble paper and wood slab packing.

Shantanu