sample polishing question WC Co

[Chico]

Is it safe to say that I could use the same Polishing technique for Metco 73F plasma , Metco 72F plasma and Metco 73F HVOF?

My 72F coating has lots of porosity in excess of 5%.

[Chico]

Here are the parameters I am using to spray 72F. My Results too much porosity.
How can i reduce the porosity?

Metco 7mc console
9MB gun w/ GP nozzle
Powder Port #3
Argon 100 PSI 160FMR
Helium 100 PSI 40FMR
500 Amps 83volts
No cooling air jets
9MP powder feeder
powder shaft C
carrier PSI 60 20scfh
feed rate 8lbs/hr
3inch stand off

[Gordon]

Hi Chico

There are alternative parameter sets which may give denser high quality coatings. These should be available through Sulzer Metco.

Quote:My Results too much porosity.
How can i reduce the porosity?

Little point to trying to improve spraying parameters if testing is not showing true picture. So first thing to establish/verify is the quality/reliability of your testing. I've seen many coatings rejected because of excessive porosity, many of these perfectly good coatings, just poor testing and poor interpretation of results. I will stress this can happen the other way round as well, as it is also possible to make coatings look denser than they actually are

Quote:My 72F coating has lots of porosity in excess of 5%.

Yes this is too high if true. Are you impregnating coatings with epoxy resin before metallographic preparation? If not try it. If the majority of the porosity sites are identified as filled with resin, then you can be confident that at least these are true porosity and not pluck-out.

[Chico]

Gordon, Thank you for your response.
Our lab is using hot mount and polishing them with the same method as 73F plasma and 73F HVOF. Both 73F HVOF and 73F plasma look good. Should the polish be the same for 72F?? I have sprayed 25 coupons each time change one variable including every metco parameter available. All coupon results porosity over 8% and more.