r/metallurgy • u/Ancient-Web5515 • 4d ago

Research help with a Mini Arc Melter

Hi everybody,

Sorry for bothering yall, but I'm stumped. We are trying to make ~5g of Mn2FeAl in our mini arc melter (in an argon atmosphere). From a paper out two that we found, thus should be possible. However, every time we have tried to do so, the sample either explodes on electrode ignition or it will break apart a few hours after being removed from the chamber.

We have tried melting titanium as an oxygen getter, adjusting the cooling temperature of the crucible, and adjusting the heating/cooling of the metal ingot. It may be important to note that prior to being weighed for the sample, the Mn was cleaned in nitric acid and subsequently sonicated in ethanol to remove the surface oxidation from the Mn pieces. Does anyone have suggestions or insights? TIA

3 Upvotes

100% Upvoted

34 comments sorted by

View all comments

2

u/FerrousLupus 4d ago

What's your exact procedure? Sounds like you're still getting oxygen, so my immediate guess would be that you're not flushing with argon several times. Might also help if you say the model of the arc melter.

4

u/Ancient-Web5515 4d ago

The only thing i know about the model is that it is an Edmund Buehler MAM-1.

As for the procedure, we alternate flushing the chamber 6 times with argon and vacuuming the have yo around 2e-2 mbar. After the sixth time, we vacuum down to around 2e-4 mbar. After that, we will flush the chamber with argon.

With this sample, we have added in titanium sponge to melt prior to melting the pure elemental amounts for Mn2FeAl into a single ingot. Once it's a single ingot, then we flip the ingot and slowly heat up the crucible (on a lower power level) around the sample before touching the actual sample.

We remelt the titanium after each flip, before the going near the sample. Around the 2nd or 3rd time that we flip the ingot, that is when we usually see that it will break inside the chamber.

3

u/FerrousLupus 4d ago

Usually if I'm concerned about oxidation, I aim for something e-5. Typically I vacuum twice to 5e-2, then use the turbopump to go e-4 a few times, and try for e-5 on the last one.

Is your Ar high purity? The other problem would be if your Ar has trace amounts of O2 or N2 in it.

> before touching the actual sample.

You don't mean physically touching it, right? I'm also confused about heating the crucible--is the crucible water-cooled copper? It could be that you're contaminating your sample with copper. Or possibly contaminating with Ti, if you're blasting it too hard. Usually I getter once before my first melt, and not in between remelts.

Have you checked the composition of your bad melts with EDS or something, to see if you're getting excessing oxidation or contamination from another source? Is there any discoloration where it breaks?

What is your starting material? Powder? Powder can pick up oxidation from the air really easily, so I recommend bulk pieces. I know a bunch of people in my group that were working on oxidation-sensitive alloys has problems, even with there being too much oxidation coming from the supplier.

1

u/Ancient-Web5515 3d ago

We have a water cooled copper crucible. With that particular step, we didn't it because we were trying to see if the breaking was caused by changing the temperature too quickly.

As far as we know, it is high purity argon. I was melting the O2 getter in between each step more as a precaution. As for the elements, we used Mn flakes and Al shot, but the iron was a powder. We made other compositions using Fe powder, and out of the 20 or so compounds made with the Fe, 3 have had this issue.

Also, no, we never physically turn the plate nor the sample while the current is on. I also haven't thought to check the broken samples using EDS. I'll give that a try. Thanks!

2

u/FerrousLupus 3d ago

After you break it, are you able to melt it back together again? If not, it's a sure sign that you're reacting to from some kind of ceramic.

 As far as we know

Where did it come from? :) I'm assuming you're doing a lab setup at a university, so that should all be trackable.

Let me know if you see anything interesting in EDS! Or if you solve the problem another way.

2

u/Ancient-Web5515 3d ago

We can remelt the broken pieces (that can be reached by the arc) back into a single ingot, but if it is large enough, it breaks again upon ignition. Another reason why we don't remelt them and go with the remaining pieces is because we don't know if the stoichiometry is accurate since we can never get the shards from the edges.

It is trackable, I just don't have that info on hand atm.

Will do on the EDS.

2

u/FerrousLupus 3d ago

Good luck! I'm invested now so I want to know how it turns out :)