# Test alloy for high temp casting



## Yggdrasil (Mar 27, 2021)

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.
*


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## stella polaris (Mar 27, 2021)

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)


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## Yggdrasil (Mar 27, 2021)

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


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## nickvc (Mar 27, 2021)

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


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## butcher (Mar 27, 2021)

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.


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## g_axelsson (Mar 27, 2021)

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


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## stella polaris (Mar 27, 2021)

Yggdrasil said:


> 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.


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## Lou (Mar 27, 2021)

Yggdrasil said:


> Hi.
> I know this is slight on the side of what we do here.
> 
> But here it comes:
> ...



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


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## Yggdrasil (Mar 27, 2021)

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.


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## Lou (Mar 28, 2021)

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


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## Yggdrasil (Mar 28, 2021)

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:


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## stella polaris (Mar 29, 2021)

Yggdrasil, just a question about melting in Vacum

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


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## Yggdrasil (Mar 29, 2021)

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?


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## stella polaris (Mar 29, 2021)

Yggdrasil said:


> Hi Nortern Star :wink:
> 
> I really don't know yet.
> That is one of the reasons I'm asking in this eminent
> ...



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.


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## Yggdrasil (Mar 29, 2021)

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.


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## g_axelsson (Mar 29, 2021)

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


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## Yggdrasil (Mar 30, 2021)

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.


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## Lou (Mar 30, 2021)

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.


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## Yggdrasil (Mar 30, 2021)

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 ;-)


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## Lou (Mar 30, 2021)

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

Ir is better suited to a ring.


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## Yggdrasil (Mar 30, 2021)

Thanks Lou.
I am dedicated to Rh on good and bad terms :wink: 

Would not annealing after casting alleviate the
brittleness?
It is considered malleable in most litterature, which indicate that it can be "beaten" into shape at least once,
at least that is how I understand the term.


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## Yggdrasil (Mar 31, 2021)

After reading around I have found it neccessary to 
revise my plan. 

It seems vacuum melting could lead to losses 
of tenths of grams depending of time, surface 
and vacuum.

It seems that the most sound approach will be to
melt under a mild pressure with argon or similar and 
then pour/evacuate to a secondary chamber 
with vacuum.

I have seen this design in casting furnaces so it 
should dooable.

It is strange how things evolve. 
I started with some ideas about how to do things.
And had become quite confident over time that it 
would be that simple, then I asked a few not well
founded questions.

Then people ask back and hints to well known facts and laws of nature and it all change.

Thanks folks, this is what makes this forum so great
:mrgreen: :lol:


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## stella polaris (Mar 31, 2021)

Yggdrasil said:


> After reading around I have found it neccessary to
> revise my plan.



No plan survives reality... A known fact..


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## Yggdrasil (Mar 31, 2021)

That is where plan B +++ and contingencies come into
effect. This time though, the evaporation/sublimation
issues had completely bypassed my mind  
Due to the forum I'm on track again


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## Lou (Apr 1, 2021)

Yggdrasil said:


> Thanks Lou.
> I am dedicated to Rh on good and bad terms :wink:
> 
> Would not annealing after casting alleviate the
> ...



You can try and anneal it and it will probably help. Malleable though? Ehhh...I'd say more ductile than malleable and there's a lot of tricks into making it into wire (by the way, the wire itself is almost fibrous in structure). I can smash a button of Rh with a hammer into smithereens. It's not as bad as Ru or Os in the brittleness department but it isn't great.

Why don't you just cast an 80 % Pt 20 % Rh alloy? Very white, much cheaper, great alloy, nice and hard...


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## kurtak (Apr 1, 2021)

Interesting thread - out of my knowledge base (so can't really contribute) but interesting none the less --- thanks for posting :G 

Kurt


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## Yggdrasil (Apr 1, 2021)

Thanks Lou.
I was contemplating to solder the prongs on to the ring and use 30/70 Pt/Rh alloy.

And you are right they use some tricks to pull Rhodium thread, I have found that one way was to embed a 
Rhodium rod 3mm into a Nickel tube and then pull it 
before the Nickel is dissolved in HCl.

They would not go to these lenghts if it was easy, 
but then pulling a thread means repeated stress in the same area over time. Tapping a localized piece a few times into a defined position/form is a completely other ballgame, I guess.......

Interesting to see the Rhodium ring still inside the investment, nice luster and color too  

Kurt.
This forum is rewarding in many ways, and it is nice to see that other people enjoys the threads too 
I for one has found ideas and educational information all over the forum.
Your posts are always informative, among the posts of
many other esteemed members.
So I thank you all for that


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## stella polaris (Apr 5, 2021)

Its off topic but it seems interesting. 
Should it not be possible to use vaccum and heat, to purify pm from metals with low boiling temp? (or vice verse) If pm losses could be hold low it would be a quite clean way of refining.


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## Lou (Apr 5, 2021)

Sure.

A lot of refining comes from the process of evaporation during say, floating zone electron beam remelting (a refining procedure).

On metals with appreciable vapor pressures, like iridium, losses can get...expensive!

I have personally fire refined Pt alloys many times. You can slag off a lot of crap with melting the Pt and running oxygen through it.


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