Good evening? or morning? or day
Does anybody have experience in plasma, (not HVOF) coating of WC-17%Co?
We obtain very brittle coating: the cross- section shows transverse cracks, originated from thermal stresses, I think. At the same time microhardness results are about 700HV, that is below the Spec. requirements: 800-1000 HV
We use the METCO powder 73FNS-1, spray distance- 80 mm, gases helium and hydrogen, deposition rate 20 mkm per pass, total thickness about 250 mkm.
Thank you, volf

Hi volf

Really need more information to help you. What plasma gun and parameters used?

Deposition rate 20 mkm (assume that's 20 micrometres per pass) I doubt will be the cause of all of your problems, but possibly a contributory one. I would reduce thickness per pass to something like 5 micrometres if possible.

helium/hydrogen plasma gases???? is this right?

Gordon Wrote:helium/hydrogen plasma gases???? is this right?

is the use of H/He in this app. used to increase the plasma gas velocity?

To max out the plasma gas velocity, would you typically choose H/He combination? Also, would that be the typical gas choice when spraying carbide??

I have seen where amerpit 526 (wc-c0 83/17) is best used or "designed" for kerosene guns. So I would assume that you would try and max out the plasma velocity if using a plasma gun. Correct?

thanks

Hi Intel55

I have not come across the use of helium/hydrogen (primary/secondary) parameters before, though I suppose its use is possible. I suspect Volf is really referring to Argon/Helium and Argon/Hydrogen.

The higher quality plasma spray carbide coatings usually employ Argon/Helium high energy parameters and as you say this is to achieve higher velocity (not higher particle temperatures).

hi every body
I hope i can be helpful even my bad english
in my experience in plasma transfer arc ,we used to mix helium and argon for welding stellite
and in coating carbide (-45 + 15 )we use always azote but sometimes we use argon to have better coating .
size of guns too must concord with the size of the powder used ,if there are different longers of nozzles ,may be that means we have to choose right one

Hi Hvofhamid

Quote:we use always azote but sometimes we use argon to have better coating

Azote being the same as nitrogen, had me wondering for a while

I suggest Volf used to Argon/Hydrogen gas.spraying gun is F4-MB, it's so easy to the microhardness results meet 800-1000 HV,Ar:70 slpm,H2:2.5 slpm,current:700A,Powder carrier Gas:5.0 [slpm];Powder feed rate:45g/min