>
> > > Uli wrote:
> > > >
> > > > Hello,
> > > >
> > > > I am trying to find an explanation for a strange effect I experienced
> > > > with a unknown alloy.
> > > >
> > > > The material looks like a bit like aluminium is brittle like cast iron
> > > > and was sold to me from a scrapyard as titanium. On one piece there
> > > > was written TiAl15.
At a guess, from a metal scrap ( sometimes ) trader, I would suggest that what you have there is 85 % Ti, 15 % Al. That can be the way that alloy pieces are marked .
> > >
> > > > The material is easy to cut with a saw, the small sponges burn white
> > > > and give a bunch of sparks.
> > > >
> > > > The strange effect starts when one side of aa small piece (30x30x4mm)
> > > > was heated in a propane flame. It heats up until orange glow without
> > > > melting. On the surface some little drops of molten material appear
> > > > like mercury. Then it starts to heat up by itself and glows bright
> > > > orange through the whole piece eve where it was not heated by the
> > > > flame ! It expands visibly about 10%.
> > > >
> > > > Later, cooled down again it is even more brittle but harder and even
> > > > scratches glass. The surface of the broken material is much darker
> > > > than the unheated one. The surface shows yellow oxides.
> > > >
> > > > Can anybody give me a hint about what I got here ???
> > > >
> > > > Your answers are greately appreciated.
> > >
> > > If it is an isostatic press of Al and Ti powders, you are triggering a
> > > remarkably exothermic solid flame to synthesize intermetallic titanium
> > > aluminide. The globules are molten aluminum before the mass gets hot
> > > enough to react. The extreme hardness of the product is supportive.
> > > This is only a scientific wild ass guess, mind you.
> > >
> > > Section the starting a "alloy," maybe etch in a littl HCl or lye, and
> > > look at it under a metallograph or microscrope. Is it a compacted > > > powder?
> > >
> > > Note that titanium burns in air, nitrogen, carbon dioxide, and water. > >
> > Al,
> >
> > thank you, this sounds very competent and plausible for me. It really
> > fits to my observations. Do you know an application for such a > > material ?
> >
> > I could imagine to make parts out of it and to transform it later to
> > titanium aluminide. But why should I do that ?
>
> Google
> "titanium aluminide" 1760 hits
>
> Titanium and nickel aluminides are low density candidates to replace
> nickel superalloys to ~900 C service. NASA was/is all ga-ga over them
> (re Regan's China Clipper scramjet).
I was asked recently by one reader of this group ( Hi there !!! you know who you are :-) ) if we could prepare or help to supply scandium aluminide for a similar purpose. The comment was, when I asked why , " I guess titanium aluminide isn't expensive enough. " Al3Sc does seem to have some interesting properties....like being very light and melting at 1,450 o C or so.
I also asked a contact at a very large Aluminum company whether they had ever thought about using Al3Sc instead of the Al Sc 2 % master alloy for all those bike frames and baseball bats. Yes, was the answer, but when we tested it it just sat there in the middle of the melt waving at us. Perhaps a slightly anthropomorphic image.
If anyone knows any information about what Al3Sc could be usefully used for would be welcome. I guess from Uncle Al's comments nothing structural. Our program for a new scandium extraction plant gets closer and closer and it looks like we can drive volumes up and prices down most efectively.....now all we need are sufficient new uses.
Google on " scandium aluminide " returns no results. Which will probably change when this post gets spidered.
Tim Worstall
However, aluminides are overall
brittle and undergo catastrophic ductile failure. You obviously want
> an initiation tab to avoid damaging the final part, a survivable can
> to keep it in shape and without surface oxidation during
> transformation, and all the engineering calculations to get from
> preform to properly dimensioned product given the density change. >
> Solid flame near-net synthesis from compacted powders is very nice for
> fabricating intractable materials like aluminides, titanium carbide,
> etc. However, producing mission-critical parts without flaws can be > very difficult.