03-15-2007, 05:27 PM,
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volf
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WC-17Co plasma coating
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
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03-16-2007, 01:57 PM,
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Gordon
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RE: WC-17Co plasma coating
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?
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09-21-2007, 04:37 PM,
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Intel55
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RE: WC-17Co plasma coating
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
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09-23-2007, 01:55 AM,
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Gordon
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RE: WC-17Co plasma coating
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).
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09-24-2007, 02:19 PM,
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Gordon
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RE: WC-17Co plasma coating
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
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09-30-2007, 03:06 PM,
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zhoudesign
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RE: WC-17Co plasma coating
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
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05-25-2023, 09:42 AM,
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RE: WC-17Co plasma coating
Hi Zhao Yun,
Vertical cracks in a sprayed coating is an indication of critical tensile stresses in the coating. One measure you can take against this is to preheat the steel substrate to around 200°C. Another measure is the thickness reduction of monolayer, which you can achieve by increasing the speed (number of revolutions) of the component.
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05-25-2023, 02:14 PM,
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RE: WC-17Co plasma coating
(05-25-2023, 10:41 AM)Zhao Yun Wrote: (05-25-2023, 09:42 AM)Vadim Verlotski Wrote: Hi Zhao Yun,
Vertical cracks in a sprayed coating is an indication of critical tensile stresses in the coating. One measure you can take against this is to preheat the steel substrate to around 200°C. Another measure is the thickness reduction of monolayer, which you can achieve by increasing the speed (number of revolutions) of the component.
Thanks, Vadim Verlotski.
The critical tensile stresses comes from two aspects I think:
- temperature of the coating is too high;
- the coefficient of thermal expansion varies greatly;
For the 1st one, optimize the cooling system or the spraying parameters;
For the 2nd one, preheating works;
Do you think so? And from you experience do you think the flame's trembling or quivering a little bit is normal or not?
I'll try the two measures you mentioned.
I'm sure that preheating and faster component rotation when coating will solve your problem, I've seen it in practice several times.
As far as unstable flame is concerned, it can have several causes and it does not necessarily have to be related to the cracking of the layer. The most common cause of an unstable flame is wear of the anode (nozzle) and cathode.
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