Plasma Sprayed Metco 443 NS microstructure issue

[CSiang]

Hi Guys,

Hope to get your input on this issue.
For the past 1 year, on and off we are seeing some weird big oxides in the Metco 443 coating, which according to our observation, it usually occurred when the batch of powder contained around 3wt% or more of powder at -325mesh size. We feedback to Metco regarding this, which they simply said this issue was mainly due to turbulence and dust. But well, we do not really see this issue happen when the powder contained around 2wt% of -325mesh particle or less....so I am not sure what is the real cause.

We are using Metco 9MB gun, consoles are 9MC or Multicoat (we have 3 systems in total), powder feeder is 9MP.
Below is the parameter we use, unit for airflow is SCFH.

Ar = 90 SCFH, H2 = 28 SCFH, Carrier, N2 = 12 SCFH, current = 550A, Nozzle = GH, SOD = 5.5 inch, surface speed = ~200ft/min, step size = 4 mm.

Microstructure image link below:

https://ibb.co/TrLX2Qs

https://ibb.co/ZmtGK3N



Hope you guys are able to help me on this.


Thanks,
CS

[Gordon]

Hi CSiang,

Check your powder port and possibly nozzle face for fouling after spraying for a while. More fines in your powder will make this problem worse. Reducing the powder feed rate may help.

[CSiang]

Hi Gordon,

Thanks for your reply.
While reducing the powder feed rate, do I need to reduce the power by reducing H2 or current to prevent over-melting?
What is the rational behind that reducing powder feed rate may help? Is it to reduce the possibility of powder accumulation at the powder port tip & nozzle face?

At the moment my feed rate is already at 6lb/hr...seems low.


Thanks,
CS

[Gordon]

Hi CSiang,

I would leave the feed rate alone as that is low to normal for that type of powder. I've seen this problem with very high spray rate parameters.

Check your powder port for build-up, if staying clean then problem lies else where.

[CSiang]

Noted, thanks Gordon.

[kooias]

You mentioned that you had already contacted Metco about this problem, but their response attributed it mainly to turbulence and dust. However, given your specific observations, it is clear that you are not sure of the true cause. Sometimes you shouldn't give up everything and play, I also found Astral casino bonus code https://casinosanalyzer.com/casino-bonus...astral.com and now all I need is good company. To better understand the situation, could you provide more information? It would be helpful to know more about the operating conditions and the specific steps you take in the coating process. Also, have you made any recent changes to the process parameters? Gathering this information can help in identifying any potential contributing factors to the formation of large oxides.