Inco 718 complete delamination!!

[TurbineWorks]

Hi,

We are currently spraying an Inco 718 parent material part using Praxair Ni-202-1 powder. The Internal Diameter we are spraying is around 6" through a sulzer metco A3000 unit. We have cleaned and gritted the part with 60-80 grit getting surface finish of around 120 microns which to our manual is well within spec. However we have had complete delamination of the coating 3 times now.
I have checked all airlines for moisture content and parameters used are correct. We are holding the part in a rather large fixture as it spins. Could it be possible that we aren't achieveing a good enough pre-heat temp prior to spray and that the part is cooling quicker than the powder applied therefore it is not adhering??
I noticed in an earlier thread you advised a cooler spray stream to achieve less brittle coating results. Could this be another reason behind our delamination?

Regards,

Matt

[Gordon]

Hi Matt

to the Surface Engineering Forum.

I suspect this may be a temperature control or coating thickness issue, though it could be down to other issues.

What coating thickness are you aiming for?
Pre-heat temperature and coating/part temperature during spraying?
Speeds and feeds?
Devices for cooling, ventilation and removal of over-spray dust?

[TurbineWorks]

Gordon,

Many thanks for your reply.
The coating thickness we are aiming for is around 0.030" to 0.050". I believe this particular powder has a good reputation for thickness build up.
Pre-heat temp is around 200 Deg C and temperature directly after spraying is around 250 Deg C. I am not sure of speeds and feeds i will get this info.
We have 2 air coolers blowing on the outside of the part which is located within a vented room. As for extraction the part is a shaft which sits on a baseplate which has a small (50mm) hole at the bottom. I don't believe they have any device to extract the dust when spraying. I will get them to run it with portable extraction attached to bottom to remove over-spray dust.

Regards,

Matt

[Gordon]

Hi Matt

Not sure what the thickness limitation is for this material plasma sprayed, but 0.050" on an internal diameter could be pushing it.

Pre-heat temp around 200 Deg C sound good, but is this a thoroughly evenly soaked temperature or perhaps less even obtained by a couple of passes of the gun?

Control of substrate temperature again sounds good, but I would try to concentrate or localise cooling on the hotter parts of the coating, rather than the outside of the substrate. Heat removal from freshly laid coating will be far more effective than removing heat after its soaked through the part. Ideally, a situation where the outside of the part maintains the initial preheat temperature at a constant value throughout the process, without the need of any extra cooling on the outside.

I suspect you are limited on selection of speeds and feeds by your handling equipment. If your coating deposit per pass is heavy, this certainly will not help the situation. If you can't reduce deposit thickness per pass by adjusting speeds and feeds, consider taking a little more time to spray the part using lower spray rate parameters.

Hope that helps and good luck

[TurbineWorks]

Gordon,

Success!!!

We lowered the current from 500 to 400 and sped up the turntable from a paltry 40 RPM to 150 RPM and air cooled the part whilst spraying maintaining a temp of around 130-150 Deg C and the process has been successful.

Many tanks for your assistance on this

Best Regards,

Matt

[Gordon]

Well done Matt cool (pun intended)