From: ulrich@canberra (Nathan Ulrich)
Subject: Titanium
Reply-To: ulrich@canberra.whoi.edu
Organization: Woods Hole Oceanographic Institution
Date: Fri, 22 Jan 93 02:55:03 GMT

Jim Delwiche writes
> As I understand it, a large percentage of the world's titanium is
> found in Russia.  So much of it, in fact, that our old friends the
> USSR used titanium to make the hulls of their nuclear subs, which gave
> them a significant strategic advantage.  Now that Russia is undergoing
> a transformation to a market economy, this Russian titanium is
> starting to make it's way into the west.  Titanium bicycle frames,
> which used to be in the hyper-exotic category, are becoming much more
> affordable.  Perhaps titanium will become common in racing (or even
> street) engines soon.
> 
> Jim

Actually, we don't really depend upon the former USSR for titanium ore (that  
wouldn't make much sense in a strategic sense, would it?).  Titanium is one of  
the most common elements in the earth's crust, and it is expensive mainly  
because it is difficult to refine.  We apparently don't build military  
submarine hulls from titanium because we can't weld the hulls well enough to  
satisfy the safety requirements of the US Navy.  The Soviets have better  
titanium welding techniques (and a very large inert gas welding chamber) and  
are not nearly as concerned with safety for the sub crew.  Our manned  
submersible Alvin has a 2 meter diameter personnel sphere welded from two  
hemispheres of titanium alloy, and can withstand external pressures in excess  
of 10,000 psi (corresponding to a water depth of 6000 meters).

Liquid titanium is such a good solvent that refining must be done in a vacuum  
electric-arc furnace, and to increase purity, it is usually melted two or three  
times before being cast into production ingots.  This is understandably  
expensive, both because of the requirement for a very good vacuum and because  
of the energy cost.  Similarly, titanium welds must be shielded by an inert  
gas.

However, welding of commercially-pure titanium (not very strong but extremely  
corrosion-resistant) isn't that difficult, and heat-exchangers and chemical  
processing equipment are commonly produced from CP titanium.  In fact, it is  
quite easy to obtain CP titanium fasteners, but they aren't nearly as strong as  
steel fasteners, and I commonly see prices of $2 - $5 per bolt.

The most commonly-used alloy of titanium is 6Al-4V, which combines very high  
strength (as good as high-strength alloy steels) with light weight (about 60%  
that of steel) and with excellent corrosion resistance.  This alloy is somewhat  
more difficult to weld.  It is difficult to machine both because of its  
hardness and because of its tendency to work-harden at the cutting surface.  At  
slow speeds and heavy feeds it is not too bad, about like some of the stainless  
steels, and I've turned parts for my racecar out of scraps of 6-4 titanium--and  
I'm by no means an expert machinist.

Titanium is easy to obtain in many sizes of bar, rod, and sheet, though getting  
exactly the size and shape you need is sometimes difficult.  6-4 titanium cost  
about $27.50/kg the last time I checked, which is about 5 times the cost of  
aluminum and about 10 or 20 times the cost of steel.  I usually figure it will  
cost about twice as much to machine or weld titanium as aluminum when I'm  
working up budget estimates.

The main reason that titanium-framed bikes are becoming less expensive is that  
they are taking advantage of economies of scale and producing large quantities  
of tubing in the appropriate sizes.  I also understand that they are getting  
good deals from welders and suppliers now that aerospace business prospects are  
bleak.

I suspect that the cost of titanium will continue to be strongly tied to the  
cost of energy.  If energy becomes cheap, so will titanium (and so will a lot  
of other things).  The parts of a racecar that can be fabricated from tube  
forms similar to bike frames could enjoy reduced costs, however....

--
Nathan Ulrich
Deep Submergence Laboratory
Woods Hole Oceanographic Institution
ulrich@canberra.whoi.edu
Newsgroups: rec.autos.sport