Porosity problem with Metco 71 FNS-2
02-13-2008, 09:45 AM,
#1
Porosity problem with Metco 71 FNS-2
Hi All,

I have a Porosity problem with Metco 71 FNS-2, Tungsten Carbide powder when it is sprayed on a 10mm diameter Titanium rod.

FYI, i have tried 2 parameters to spray on flat test coupons and the parameters are:-

a. Distance: 100mm
Ar 80 NLPM
H2 4 NLPM
Amp 410
Powder feedrate: 120g/min
Result: ~10% porosity

b. Distance: 100mm
Ar 84 NLPM
H2 4.2 NLPM
Amp 400
Powder feedrate: 62
Result: ~19% porosity

Using the above parameters, when i spray on rotating titanium rod rotating at 270rpm, and traverse speed of 3mm/sec (using step program which is the same for flat test coupon), the porosity turn worse to more than 25% porosity.

Questions:-

1. Does anyone has some good parameters that you can share?
2. Does traverse speed of the gun and rotating speed of the part has any contribution to the unacceptable porosity?
3. Does the rod size of 10mm contribute to the porosity?
4. Is it common that as we increase the powder feedrate, the coating actually get denser for Metco 71 FNS-2?

Thanks all.

Aigole08
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02-15-2008, 02:41 AM,
#2
RE: Causes to Porosity Defect on Porous TBC Coating
Hi Aigole08

Sign0016 to the Surface Engineering Forum.

First thing I noticed was that your part rotation and traverse speed are very low for a 10 mm diameter. Try and get the highest rotation speed your equipment will handle and set your traverse speed to give about 3 mm per revolution. Though this probably does not explain your porosity problem.

What plasma equipment are you using?

I would advise initially to use the equipment/powder supplier recommended parameters. If you are then still getting very poor porosity levels, I would suspect that your metallography procedures are at fault and not the coating.
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02-25-2008, 03:16 AM,
#3
RE: Causes to Porosity Defect on Porous TBC Coating
Dear Gordon,

Thanks for the quick advice.

I am using Sulzer Metco 9MB gun.

I have used the same parameters to spray on flat coupon and the result turn out to be acceptable. However, using the same parameters spraying on the rotating titanium rod, the results are different. That is why I am wondering is it due to the size of the rod.
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02-25-2008, 07:04 AM,
#4
RE: Causes to Porosity Defect on Porous TBC Coating
Could you blame this to overspray trapped in the coating?
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02-25-2008, 02:18 PM,
#5
RE: Porosity problem with Metco 71 FNS-2
Hi ycwbycwb

Quote:Could you blame this to overspray trapped in the coating?
Possibly, but I doubt this is the cause in this case.

Hi Aigole08

Quote:Dear Gordon,

Thanks for the quick advice.

I am using Sulzer Metco 9MB gun.

I have used the same parameters to spray on flat coupon and the result turn out to be acceptable. However, using the same parameters spraying on the rotating titanium rod, the results are different. That is why I am wondering is it due to the size of the rod.

To some extent. The 9MB plasma gun suffers from "target point deviation" where the spray stream is kicked slightly off the gun axis due the side ways powder injection. Normally, this is not a problem, but with a small target point as in this case, it is very important to line up the actual spray stream with the centre point or axis of the part and not rely on the gun axis for aiming. Hope that makes sense Happy0193 Anyway, a possible cause for your problem.
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02-25-2008, 03:30 PM, (This post was last modified: 02-25-2008, 03:37 PM by erick212.)
#6
RE: Porosity problem with Metco 71 FNS-2
Here is a study I did a while ago on this coating.

Thickness- General rule, decreased with increasing standoff. Not enough to warrent a parameter change. No other real trend or affector

Porosity- Decreased with decreasing standoff. Also decreased(slightly) with an increase in amperage level. Also decreased with an increase in primary agron flow. Became more wide varied(wider spread) with an increase in voltage. Biggest factor was standoff.

Globules - Increased with increased voltage. Also increased(lesser extent) with increased stand off. Voltage was the biggest factor

Cracks- Decreased with increased stand off. Also increased with a higher primary flow.

Oxides- Increaded with decreasing amerage. Also increased with a decrease in primary flow.

Best compromise is as follows.

Moderate standoff- reduces cracking and porosity (~2.75 - 3.25")
Lower aperage - slight porosity and oxide increase offset the signifigant crack increase @ higher primary flows (~540-560a)
Lower voltage-reduces globules and cracking (~57-65v)
Higher primary flow- decrease porosity, oxide, and cracking (~120-150scfh)
Feedrate- ~ 40-45g/min
Nozzle- GE
Powder port- #2
Traverse speed ~ .31seconds/inch
Rotation speed ~ 1950rpm
Trav and rotation were based just off my head for a 10mm rod.
Also you do not want to lay this coating down any thicker than .00025/pass

The condition of the gun is very important and also make sure your powder stream is injecting into the heart of the flame(no powder flame kick) I hope this helps a little, Now I was not able to give you exact paramerters but this should be a good start point. This is a very tricky coating, good luck.

Erick
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02-25-2008, 05:06 PM,
#7
RE: Porosity problem with Metco 71 FNS-2
Hi Aigole08

Some good post above, but if you are not very experienced with this coating, I fear we could be leading you up the garden path with too much information Happy0193

My advice: Restart from basics.

Start with Sulzer Metco recommended parameters. Consider these as starting point parameters, although they should give a good standard of coating meeting typical properties of density, hardness etc. (equipment calibrated and in good working order). If you can not achieve these coating properties, it will be pointless modifying basic parameters as the problem will be elsewhere.

Use higher speeds and feeds as mentioned before.

Make sure spray stream rather than gun axis is aimed at axis of rod.

If you still have major problem with porosity, I would suspect that metallographic preparation procedure is at fault and not the coating.
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02-28-2008, 04:48 AM,
#8
RE: Porosity problem with Metco 71 FNS-2
Dear Gordon and All,

This is very helpful indeed. I will try out all the recommendation and update you guys. Cheers Smile

Regards,
Aigole08
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02-29-2008, 03:36 AM, (This post was last modified: 02-29-2008, 03:40 AM by Alexangel1226.)
#9
RE: Porosity problem with Metco 71 FNS-2
Aigole,

Great advice from all, I may not be able to help much as I am not exactly spraying the same type of powder in our shop. We are spraying the Metco-72F-NS(Tungsten carbide 12% cobalt aggregate) Not sure if these 2 powder are the same?

btw, are you able to share the microstructure picture of your coating? for the one sprayed on flat specimen which is acceptable and the one sprayed on the ti rod? You may send the pics to Gordon, and get his help to post on the forum.

that will help much in visualizing the "prob" as it may not be a real issue at all.

Thanks.

Regards,
alexangel1226
Reply
03-03-2008, 01:31 PM,
#10
RE: Porosity problem with Metco 71 FNS-2
Hi Alex

Quote:We are spraying the Metco-72F-NS(Tungsten carbide 12% cobalt aggregate) Not sure if these 2 powder are the same?

They are pretty much the same chemically (88/12 WC/Co), but produce quite different coatings. Metco 71 variants are cast and crushed powders while Metco 72 variants are sintered and crushed powders. The cast version tends to have many intermediate phases between WC and Co, while the sintered is pretty much just WC in a relatively pure Co matrix. The sintered 72F forms coatings (when sprayed right Happy0193) that produce much more abrasion resistant and ductile coatings than the cast 71 type forms.
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