Working with Metals: Exotics and Composites
By Matt Carlson /autoMedia.com
Understanding the Different Materials in a Resto Project - Children don't
dream of being general aviation pilots with nice sensible Cessnas. They want
to fly screaming fighter jets that tear gaping holes in the sky, and touch the
edge of space. And when the military builds the most sophisticated attack
plane out of exotic materials, adult children naturally attempt to produce
their own fighter jet, at least one for the ground, by using those same
materials in their cars. Is this just a silly dream, to put these high tech
parts in cars? Or is there a real advantage to using ultra-modern parts in
your old restoration project?
First of all, let's be clear on our definition of an exotic material. For
something to be exotic, it has to be rare, or at least unusual in its class.
We will concentrate here on exotic metals but also will make mention of some
exotic non-metals as well.
One of the first metals that may come to mind when you think of exotics is
titanium. Titanium is not derived from iron, so it is considered non-ferrous.
The qualities of this material are really quite amazing. It is very resistant
to corrosion, whether by chemicals, and saltwater. Even more impressive is
that it has the highest strength-to-weight ratio of any known metal at normal
room temperature. This means that a rod of titanium that is 12 inches long and
weighs one pound will be stronger than any other piece of metal with the same
dimensions. It is almost as lightweight as aluminum, but can withstand much
higher loads than most kinds of steel.
So should everything be made of titanium? Well, it could, but not many of us
would be able to afford it. The processes used to manufacture raw titanium are
very time consuming and expensive. Reaching more than 3,000 degrees Fahrenheit
is required to liquefy titanium, and at that point it likes to absorb
hydrogen, oxygen and nitrogen gases. These gases are all very common in the
air that we breathe, so titanium must be kept in an airtight environment when
it is made. If this sounds a little complicated, then we can move on to the
fact that after it is made it is still quite difficult to machine when
compared with steel or aluminum.
Where might you find titanium used? Besides the treads of Soviet tanks and the
engines of fighter aircraft, there is a growing trend in the use of titanium
in making the intake and exhaust valves of commercially available engines.
Really though, this is most common in racing applications.
Since the valves are much lighter in weight than stainless steel, the engines
can run higher RPMs without danger of encountering valve float. (Valve float
occurs when a valve moves so fast that its momentum causes it to continue
opening even when it should be closing.) A reduction in weight helps to keep
this from happening.