delamination of spray - fuse coating

[Arturas]

Hello,
Maybe someone can help, explain the reason of delamination, splating ( between layer) sprayed and fused NiCrBSi +WC coating deposited on "guide roll" diameter 70mm. Delamination goes not from the substrate. Thickness of coating about 0.5mm. Many years we have no problems there and I don't understant where is the reason. At the begining I thouht that maybe due to impact of too cold armature. But after more rolls failured I just don't know the real reason.
Thanks for help

[Stephen Booth]

Hi Arturas, greetings from Indonesia. Delamination between layers of a NiCrBSi WC fused coating. My guess would be operator error. I expect the coating was sprayed and fused in two discrete layers. An oxide buildup between the layers, caused the delamination.

Is it possible that it was operator error?

If not, any other parameters have changed, powder, torches, RPM, mesh size, ....?

[Arturas]

Hi Arturas, greetings from Indonesia. Delamination between layers of a NiCrBSi WC fused coating. My guess would be operator error. I expect the coating was sprayed and fused in two discrete layers. An oxide buildup between the layers, caused the delamination.

Is it possible that it was operator error?

If not, any other parameters have changed, powder, torches, RPM, mesh size, ....?

Spraying of coating was performed in 10 pases, thickness as I mentioned about 0.5-0.6mm. After fusing was performed with oxy-acetylen torch. So we do in such way all the time. But the coating really is britle. Maybe to much carbide there are in a matrix?

[landemarre]

Hello,
Maybe someone can help, explain the reason of delamination, splating ( between layer) sprayed and fused NiCrBSi +WC coating deposited on "guide roll" diameter 70mm. Delamination goes not from the substrate. Thickness of coating about 0.5mm. Many years we have no problems there and I don't understant where is the reason. At the begining I thouht that maybe due to impact of too cold armature. But after more rolls failured I just don't know the real reason.
Thanks for help

Hello

Does your problem come with a new batch powder?
Perhaps try change of batch.

[Arturas]

Hello,
Maybe someone can help, explain the reason of delamination, splating ( between layer) sprayed and fused NiCrBSi +WC coating deposited on "guide roll" diameter 70mm. Delamination goes not from the substrate. Thickness of coating about 0.5mm. Many years we have no problems there and I don't understant where is the reason. At the begining I thouht that maybe due to impact of too cold armature. But after more rolls failured I just don't know the real reason.
Thanks for help

Hello

Does your problem come with a new batch powder?
Perhaps try change of batch.

Yes , one of the reason, it can be related with powder. But what wrong could be with them?

[landemarre]

Hello,
Maybe someone can help, explain the reason of delamination, splating ( between layer) sprayed and fused NiCrBSi +WC coating deposited on "guide roll" diameter 70mm. Delamination goes not from the substrate. Thickness of coating about 0.5mm. Many years we have no problems there and I don't understant where is the reason. At the begining I thouht that maybe due to impact of too cold armature. But after more rolls failured I just don't know the real reason.
Thanks for help

Hello

Does your problem come with a new batch powder?
Perhaps try change of batch.

Yes , one of the reason, it can be related with powder. But what wrong could be with them?

Problems of composition (mass proportion, change of WC supplier) or fabrication (spray drying problems, labelling problems ...), really a lot of problems!

Which powder do you use? I'm interesting on this sort of powder for a client, this does not seem very current.

Regards

[Arturas]

Hello,
Maybe someone can help, explain the reason of delamination, splating ( between layer) sprayed and fused NiCrBSi +WC coating deposited on "guide roll" diameter 70mm. Delamination goes not from the substrate. Thickness of coating about 0.5mm. Many years we have no problems there and I don't understant where is the reason. At the begining I thouht that maybe due to impact of too cold armature. But after more rolls failured I just don't know the real reason.
Thanks for help

Hello

Does your problem come with a new batch powder?
Perhaps try change of batch.

Yes , one of the reason, it can be related with powder. But what wrong could be with them?

Problems of composition (mass proportion, change of WC supplier) or fabrication (spray drying problems, labelling problems ...), really a lot of problems!

Which powder do you use? I'm interesting on this sort of powder for a client, this does not seem very current.

Regards

Now I compared this "guide roll" with another which we did several years ago. I hited both of them with sharp hammer. After a lot of stroke directly to coating delamination do not occur on both , only we can see not very deep hollow, but after I started tohit rolls from sides began delamination of coating between layers on that one we are talking about and that which was done several years ago show himself normaly no spalling. So maybe sameone can explain? That is very important for me. Thanks

[Gordon]

Hi Arturas

Very difficult to say what is causing your problem. Is this effecting many parts or just a few? I would suggest taking a section from the effected part (assuming you can spare the cost of scrapping it) and get some metallography done, hopefully this should provide some ideas of what is going wrong.

[drramc]

Hi,
If you can conduct the dry sand abrasion test as per ASTM G65,praticeA,then probably I can zero down with your problem.I spent long years in manufacturing these and other thermal spray powders and have helped solving so many of customers problem.This alloy has been successfully used for critical applications by PTA process
ram chattopadhyay

[Arturas]

Hi,
I do some metallographic photos of this delaminated rolls and those which work perfect.
The biggest different is carbide form and quantity.
Number 3 work perfect, number 1 delaminate

[Gordon]

Hi Arturas

Is the powder used in the good and bad examples meant to be the same? If so, I'd suspect your powder supplier/manufacturer has big quality issues. If you are using a different powder product, then I would change back to the original.

Have your operators noticed any change in the way the coating is fusing? like needing higher temperature to get to fusing point, different "shine" or "fluidity" at fusing point or just comments like easier or harder to fuse etc..

The coating metallography is very different between samples and suggests to me that the powders are quite different in nature and or composition. I would doubt that these differences would be caused just from changes in spray or fusing technique.