Hello Dear Sarabjeet Singh Sidhu,

There are many papers about the sintering of Cu-Zn-Al SMA alloys, e.g. you can read F.C.Lovey papers.

Good luck

The result you report is not astonishing. First work under a protective atmosphere, best use Argon with a few percent hydrogen. This reduces copper or avoids formation of copper oxide. To accelerate sintering go above the melting point of Zinc, meaning use a temperature of about 450° to 500°C (you then do what is called liquid phase sintering; being much more rapid than solid state sintering). Liquid Zinc should dissolve rapidly Al and diffuse into copper forming the CuZnAl alloys (the dissolution might be inhibited initially, since typically all Al-powders have an oxide or oxide-hydroxide film on the surface. There is no way to avoid that; just wait. Initially compression of the powder is always a good thing. By the way: what is the total composition. Where is you alloy in the phase diagram? What is the liquidus temperature? What is the particle size (very smal particles might induces some problems...)?

If I understand correctly, initially you mixed Cu-powder, Zn-powder and Al-power physically. That means after mixing, each of the particles is in its elemental form and not in the alloy form.

Metal Powders mentioned above with fine particle sizes are susceptible to easy oxidation, if they are not in an inert atmosphere, as suggested by Lorenz.

Yes you need inert atmosphere for the sintering process. It is compulsary. The cheapest n easiest is to use argon gas in a tube furnace. But before that special control must be taken during powder mixing process because you dont want to introduce oxides n contamination, specially when you use ball mill

is  the sintering process carried out in absence of oxygen?

Apart from the suggestions made above, I would prefer to buy an alloyed powder corresponding to your required composition Cu-Zn-Al alloy and compress it under an inert atmosphere.

Please define burning. scaling, blackening and oxidation? blistering/ sweating? 

-very pertinently the above replies are great.

I worked extensively on Al based Al Cu alloy systems in 1973-1980, including Zn as a phase, and always considered the choice of sintering temperature consulting Binary ( even Ternary) phase diagrams. Dis you consult these?

The Powder Metallurgy is gr8 from many angles. So stoichiometry and the way of alloying are vital.

Sure send me the treatments employed and we can deliberate on what's the best course for your problem

Prof. P Thareja, CE (I), F.I.E

BE (Met Engg, PU); ME (1974, IIT-R); Ph.D (PU)

Certified Six Sigma Black Belt

Certified Auditor & Tutor ISO 9000 & ISO 14000

Qualified LA ISO TS 16949,Supplier auditor Tier-III

Director Principal

Rayat Institute of Engineering & Information Technology

Railmajra ( Nr Ropar) , SBS Nagar, 144 533

You should try doing vacuum (at least 10^-5 mbar, which is not the best but it should not get burned) and then full fill the furnance with argon to avoid your problem.

Also as Sarat Panigrahy tell you, it is better to buy a premixed alloy becouse it's very hard to handle the mixed powder without loosing the mixture. I'm working with a CuAlNi alloy and I have that problem, I made some tests And I discovered that at the surface I had 68% of Al instead of 14% (I was trying to prepare a Cu-14Al-4Ni alloy). I think that I lost all the mixture when I made the green compact.  

In the other hand there are some papers that reports that with mechanical alloying you can resolve this problem, but you need a very good milling machine to do that and it happens after 34 hours in many cases. But I think that it should be very hard to do it that way.

Best regards 

Gonzalo

Why are you working with powders ? You could conventionally cast the alloy and then by hot forming (extrusion is working well wizth this kind of alloys) you can refine the structure. If you need a predetermined transition temperature you have to be careful. Extrusion will shift it by a few degrees. Regards Alberto

What is the alloy composition ? is aluminium the bulk constituent with smaller percentage of Cu and Zn. What is the size of the aluminium powder? One can consider making a suitable aluminium colloid by first removing the oxides. The aluminium is then coated in %age by weight with Zn using a zincate solution of ZnO + NaOH and subsequently with electroless Cu. This is then dried into a powder and sintered using under hot isostatic pressure.

Hi Saarabjeet

Many good suggestions before. Let me add some new suggestions:

1) If you suppose your precursor powders can be partially oxidized because of shelf standing, you can etch your powders  with a slight chemical attack (a different etching solution for each metal).

2) If you dont have Ar you can try N2 atmosphere (not oxidant as said above)

3) You can also avoid powders, instead use pellets and let sufficient time for homogenization (the larger the pellets, the longer the homogenization time ).

4) if you are not sure of your gas quality, you can use an O2 getter. As getter you can use hot Cu powder for example.