Test alloy for high temp casting

[Yggdrasil]

Hi.
I know this is slight on the side of what we do here.

But here it comes:

Do anyone here have recommendations for alloys one can use to test high temp casting?

I was thinking to use steel which I can just dump after.
And maybe then ramp it up to more expensive alloys after.

I have an induction furnace for which I'm building vacuum chamber, crucible system and so on for.
So it would be nice to be able test different designs with cheap alloys underways.

Edit, added paragraph.

I have checked around a bit, and so far it looks like Stainless is a place to start.

 

[stella polaris]

Tin? It have a quite high boiling point. But you better control the temperature not to reach that point or you oven will become a tin can.

ps i would not recommend to use standard tin soldier forms when pouring 2000+ degrees tin. 8)

 

[Yggdrasil]

I was hooked on high melting point and overlooked the boiling point.
Still it is a bit on the light side, lead on the other hand may be a better choice, but lower temp.
I'll check this side a bit further, thanks Jens

Edit, added text

 

[nickvc]

Try brass it’s cheap and casts well as a starting alloy, maybe then silver.

 

[butcher]

Why high melting point metals?
Why not low melting point alloys?
why not experiment:
Making low melting solders that do not require a torch, that can be used with a match to solder metals or wires together.
Making fusible links safety links that melt if a fire starts in a room (the link melts and breaks apart) these links used on fire doors or where a device needs to close to block airflow.
Fusible plugs used in boilers or other pressure vessels.
Bushings (like bearings) to reduce friction between moving parts...

Bismuth is a lot of fun, you can melt it in anything that gets hot enough to almost boil water, like on an automatic coffee pot warmer.

 

[g_axelsson]

I wouldn't recommend brass for melting and casting in a vacuum chamber at high temperature. It would distill off zinc at a quite low temperature.

Stainless steel is something that I would test. Different alloys could have quite different properties so I guess that you have to experiment a bit. The choice of crucible could also matter, for example iron could dissolve carbon, creating a lower melting alloy as cast iron.

Göran

 

[stella polaris]

I was hooked on high melting point and overlooked the boiling point.
Still it is a bit on the light side, lead on the other hand may be a better choice, but lower temp.
I'll check this side a bit further, thanks Jens

Edit, added text

Silver have some more weight and is a PM. But its boiling point is not very far from melting point of Rh ( I guess that is what u will practice to cast). Copper i think you should try. I have never ever casted Rh or have any knowledge about it but iron/SS might behave diffrently. I suggest you try out many different metals and alloys in order to get some range of feeling before trying out the expensive stuff.

 

[Lou]

Hi.
I know this is slight on the side of what we do here.

But here it comes:

Do anyone here have recommendations for alloys one can use to test high temp casting?

I was thinking to use steel which I can just dump after.
And maybe then ramp it up to more expensive alloys after.

I have an induction furnace for which I'm building vacuum chamber, crucible system and so on for.
So it would be nice to be able test different designs with cheap alloys underways.

Edit, added paragraph.

I have checked around a bit, and so far it looks like Stainless is a place to start.

What is it you’re actually trying to do??

 

[Yggdrasil]

Hi Lou.
In time I will cast Rhodium into a ring, I believe we have already covered that part before.

But I need to test the capacity and structural integrity of both suceptor and vacuum/pressure system.
Investment design will also be tested in the same go.

For the time beeing I plan to use a graphite suceptor
and Yttrium stabilized Zirconia crucibles.
What has to be determined is amongst other things,
the position of the investment flask with
respect to the coil.

Due to the narrow window of melt versus investment capacity, it is important to minimize travel for the melt
to counteract freezing and premature solidifying.

I am also playing with the Idea to fabricate custom coils to improve magnetic charasteristics, if neccessary.

Any input is of course welcome.

 

[Lou]

You might talk to Dan Dement of Stone Oak Jewelers. He once made me a rhodium ring.

 

[Yggdrasil]

Thanks Lou.
You have already relayed that information
some time ago :wink:
He has however retired and so far has not
been back to the forum to read his PM.
I may try to contact him by Stone Oak Jewelers though.

For the test alloy/metal it is strictly not necessary.

Based on the info I was given I have devised a plan.

A two stage test, first with superheated Tin,
which will strain flask/investment design
due to long liquid phase/low viscosity
investment contact.
Then stainless steel 200 C above melting to test high viscosity strain on the flask/investment design.

At least I will use that as a general plan for now :wink:

 

[stella polaris]

Yggdrasil, just a question about melting in Vacum

Will the boiling point of a molten metal become lower i vacum just like liquids?

 

[Yggdrasil]

Hi Nortern Star :wink:

I really don't know yet.
That is one of the reasons I'm asking in this eminent
forum even if slight off topic.

So far I have not found any reference regarding significant change of melting tempetature of metals
in vacuum.
Honestly that path has not been searched yet.
Platinum and gold are regularly melted and cast in vacuum induction furnaces.

Lou!
I have now sent a mail directly to "Stone Oak Jewelers"
Even if Dan has retired they may still be in contact
with him.
Do you have/wish to share a picture of that ring?
If not in public, then maybe in PM?

 

[stella polaris]

Hi Nortern Star :wink:

I really don't know yet.
That is one of the reasons I'm asking in this eminent
forum even if slight off topic.

So far I have not found any reference regarding significant change of melting tempetature of metals
in vacuum.
Honestly that path has not been searched yet.
Platinum and gold are regularly melted and cast in vacuum induction fu

I am not worried about melting point. But after I gave you the suggestion about tin I started to think. You do not want to reach boiling point. It will mess up your setting, putting metal all over. A melted metal, in Vacuum, should get a lower boiling point due to lack of pressure. The closer its heated to normal boiling point, under vacuum, the larger risk for entering a lower boiling point as i see it. Have tried to find info about it but failed so far. But i think it should be checked up before you run a trial with tin. You will be close to normal boiling point if heat it up to 2000+.

As Göran pointed out with brass and the zinc the very same can occur with other metals in alloys, if their boiling point is lower or close to the temperature you heat the melt to. Seems safer to start trial with pure metals having high boiling point til you know how vacuum affect boiling point.

 

[Yggdrasil]

That is true Jens.
But in pure metals like pure Tin, I do not expect the vacuum to be that much of a factor,
at least not 400+ C factor :wink:
In Stainless I think the alloy is mostly comprised of high MP metals so an overtemp of 250 C should be within a safe envelope, I hope....

Anyways it is still months away so I have ample time
for the research yet, and that is why I start early,
so I can get opinions and or search
other sources of information.

 

[g_axelsson]

Yes, molten metals in vacuum does evaporate a bit (it also happens when we melt metal in a melting dish). It's the principle behind vacuum evaporators used to put thin layers of metal on various stuff. It all comes down to partial pressure and it vary with temperature. You have to look at phase diagrams of the metals you are going to melt to see how the pressure vary with temperature.

https://en.wikipedia.org/wiki/Triple_point

https://www.researchgate.net/figure/Equilibrium-vapor-pressure-of-metals-at-different-temperatures_fig1_226061334

In vacuum evaporators a trick to avoid cleaning off deposited metal all over the place is to cover interior parts in aluminium foil. Only parts in direct view from the melt is getting the deposit.

Göran

 

[Yggdrasil]

Hi all.
Thanks a lot for the inputs.

I really have to start my studies before I'm asking questions on the forum :wink: :roll:

But then again it pushed me to some study on the fly.
I found amongst a lot of other information,
an interesting document from
"Research Laboratories, Johnson Matthey & Co Limited"
Called "The Vapour pressures of Platinum metals".

Here it becomes apperant that most if not all
Platinum metals start to sublimate long before
melting in high vacuum.

Rhodium should not be subjected to less than 0.01 Torr
as far as I can read from this and other information.
Given the target of a melt temperature of 2100 - 2200 C.
Or maybe the sublimation rate may be disregarded
for the short time needed to reach a pouring
temperature of 2100 C ?

Tin can not be used as I planned in high Vacuum.
Though that is not that important.

The main purpose of the vacuum is to avoid
turbulence and gas resistance during the
metal rushing into the void of the flask.

 

[Lou]

I’d just have Dan make them. The Rh is very hard on the standard jewelers tooling. Otherwise it’s like whiter platinum that takes a helluva polish.

Here’s a few photos.

First one was in 2012. The other is some evap pellets with other ring and scrap.

 

[Yggdrasil]

Thanks for sharing.
Very nice color and shine.
The good thing when things are hard to polish,
the polish will most likely last long as well

How is it mechanically?
Brittle or is it formable?

I saw a comment in an article which described Rhodium
as malleable, but it is supposed to have a hardness
of 6.1 (can't remember which scale) but due to the number I'll guess Mohs.
Well I'll break out the hammer and try when I get home.
If it is malleable I won't need to solder Rh/Pt prongs
to it ;-)

 

[Lou]

Rh is very fibrous when drawn but it’s brittle as cast.

Ir is better suited to a ring.