Sintering process for nickel wire mesh

[Lyrl]

I work at a commercial heat treater with vacuum furnace equipment. We had a local manufacturer contact us to ask if we could sinter together nickel wire mesh sheets (product as described in this paper).

The manufacturer's current supplier sinters stainless steel sheets for him, but they have a customer requesting mesh made of nickel alloy 200, and their current supplier will not work with that material.

We have no experience with sintering wire mesh. The manufacturer also had no idea what the sintering process would look like. Does anyone know of any references with general information on times, temperature, and atmosphere requirements for this kind of sintering?

 

[WKTaylor]

Find vendors capable of making AMS7724 Alloy Sheet and Strip, Sintered Wire Mesh, Corrosion and Heat Resistant 30Fe - 1.5Mn - 21Cr - 20Ni - 20Co - 3.0Mo - 2.5W - 1.0(Cb + Ta) - 0.15N Porous - UNS R30100

Regards, Wil Taylor

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[EdStainless]

We used to sinter Ni200 mesh.
First the mesh must be rolled flat.
Then you stack layers of them onto a very solid base plate (coated with Al2O3 to prevent sticking).
Then you set a heavy flat steel plate on the top to hole them all in contact.
We always sintered in hydrogen with a dew point -80F.
Then after we sintered them we would cold roll it in order to get the density that we wanted.

This is just as easy as sintering stainless, not sure why the current guys wouldn't do it.

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P.E. Metallurgy, Plymouth Tube

 

[Lyrl]

Hi Ed - Thank you for the process description, it looks like we would need some specialized fixturing if this customer wanted to work with us, and they would need to do any rolling themselves. Our vacuum furnaces usually run around 50 microns of pressure, which is roughly equivalent to hydrogen with a dew point of -60; not quite as dry as your process, but perhaps close enough to work.

Would you be willing to share what times and temperatures you used?

 

[EdStainless]

I think that you would need some Hydrogen at the beginning of the cycle in order to strip surface oxides.
After that Vac should work, but I not sure if 50u is low enough.
The fixtures were just steel plates that were ground flat. We used the lowest C steel that we could find.
I don't remember the temp exactly. We were doing it in a continuous furnace. We heated high in the first zone (1700F?) then dropped to a lower temp (1500F?). The total time was 30-60 min. We were trying to limit grain growth.
You should double check the vapor pressure of Ni. You want to vaporize a little (it helps it stick together when it condenses) but you don't want to boil off too much.


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P.E. Metallurgy, Plymouth Tube

 

[Lyrl]

Thank you for the time and temperature estimates. I am guessing both the top and bottom plates had the Al2O3 coating? How was the coating applied (would be nice if it were simple like painting it on)?

Thanks for the tip on vapor pressure, I will look that up.

We had an issue with (lack of) reduction of chromium oxides a few years back, and confirmed independently what this page (

https://vacaero.com/information-res...reducing-metal-oxides-in-brazing-part-1.html)

says:

Although this chart was initially developed using a hydrogen atmosphere, subsequent testing revealed that... perhaps due to the high partial pressure of water vapor in a vacuum furnace, these oxide dissociation curves also applied to a continuously pumped vacuum furnace as well

. As long as we keep our vacuum pressure under control, we can reduce the chromium oxide off stainless steel and successfully carburize it, no hydrogen needed.

 

[MagBen]

50 microns is not a good vacuum, you 'd better to decrease to <5 micron, and more importantly, leak-free. You may also not to go higher than 1600F for pure Nickel.

 

[EdStainless]

We mixed an alumina slurry with alcohol and sprayed it on.
I agree with Ben, you need to be under 10u in order to have any chance.

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P.E. Metallurgy, Plymouth Tube