WC-17Co plasma coating

[volf]

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

[Gordon]

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?

[Intel55]

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

[Gordon]

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).

[hvofhamid]

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

[Gordon]

Hi Hvofhamid

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

[zhoudesign]

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