Re: What Is Alloy?

nick c <nchen711@xxxxxxxxxxxxx> wrote in
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Agent Smith wrote:
nick c <nchen711@xxxxxxxxxxxxx> wrote in
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Agent Smith wrote:
nick c <nchen711@xxxxxxxxxxxxxxx> wrote in
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Agent Smith wrote:
Does anybody know the name (or names) of the famous alloy from
which high- end racing components are made? :] Whenever I see
it referred to in books and articles, it is just called "alloy,"
but apparently there's a whole branch of engineering that's
embodied in that single word, and writers gloss over the whole
subject when they say that.

Alloys are chosen or created with the intention to reliably fit
the function that engineers planned for in design. My guess is the
word alloy is used as representing a variety of alloys suitable
for a given design/application. Example: valves in a high
performance engine, be the valve stems hollow or solid, may be
made from 6-4 titanium (heat treated to 160KSI), while domed
piston heads may be made from 6061 aluminum; piston head pins may
be made from 7075 aluminum, assembled on connecting rods which may
be forged from 6-6 titanium (heat treated to 180KSI). Various
stainless steel and/or titanium parts may be made from sintered
stainless steel or titanium, where loads are low, below the limits
of sintered material yield. Then there's ceramics ...... (shrug)

I supposed you've already done an Internet search? I'll guess
again and say if you've done a search, you may have found alloys
having proprietary designations.
Until you said "7075," I didn't have a keyword to search for, but I
googled it last night, and now I've got the details. I would have
thought that it was alloyed with nickel, but it turns out to be
zinc.
Compared to steel, 20+ KSI yield stresses are pretty pathetic, but
I
guess that it's sufficient for the loads a component is likely to
experience in bicycling. I wonder who Campagnolo's suppliers are,
for that stuff, and who forges it.

Nickel is not a good alloying agent with aluminum.

Do you know why? :]

I wrote a reply and then canceled the reply because the reply was
about titanium. Why I misread aluminum to mean titanium is beyond me.
Sorry, about that.

Now, about nickel being blended with aluminum.

The only thing that readily comes to mind is poor grain structure.

I can think of several ways to interpret that statement, enough that I
can't pull my thoughts together into a sufficiently coherent form to
write down anything intelligible. When I was in material science, I
never was very good at it, but I have an excellent excuse, because it's
an unbelievably complex branch of science.

If you want, you can answer for titanium, because a few months ago I was
reading up on super-allows, and the conclusion I came to was that, to
out-perform high grade steels, nickel is used as the starting metal, and
iron is often completely left out of the mixture. However, nickel
alloys perfectly well with all the usual ingredients in high grade
steels, ie. chrome, moly, manganese, etc, making it quite surprising
that neither aluminum nor titanium is allowed. Not to mention that
those are two materials are crucial to a *lot* of important
applications.

IMO, surface energy is the critical issue for understanding this,
because alloying won't happen unless the two metals can "dissolve" into
each other. If they form large droplets of separate, pure phases,
before cooling, then the result isn't even an alloy at all. That is a
surface energy question, and surface energy is very closely related to
the chemical potential. Chemical potential is the master controller for
everything that happens everywhere, in all branches of chemistry, of
which metallurgy is one. Since chemical potentials are (theoretically)
tabulated quantities, you can generally start any analysis by just look
at those numbers to get a feel for what will and won't make a good
alloy, without having to mess around with experiments.

Of course, in real life, it's never that simple, because theoretical
models are always so highly simplified that they never describe reality.
In the end, you still have to go to the oven and cook up your samples,
to find out what really happens. In fact, I think that's how the
chemical potentials are measured.

However, such analyses are great for pencil-and-paper guys like me, and
even scientists have enough math anxiety that when they hear "chemical
potential," they run for the hills. That gives me the edge because I'm
not afraid of chemical thermodynamics, but am actually looking for an
excuse to teach it to myself. ?:]

I
did a search to see if there was an existing aluminum alloy with
nickel and didn't find an actual alloy but did find research being
done; such as:

http://adsabs.harvard.edu/abs/2004AIPC..706..593M
.

Relevant Pages

  • Re: What Is Alloy?
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