No showcase of metal wonders would be complete without inclusion of the exotic übermetal, titanium. It maintains its exotic reputation despite being ninety three times more abundant than copper in the Earth's crust. Bikes, golf clubs, watches, eyeglasses, tent stakes, jewelry, even buildings (the Guggenheim in Bilboa, Spain, pictured below) try to cash in on titanium's mystique. Even the computer this website is being created with uses titanium for not entirely structural reasons.

In the US, 70% of all titanium is produced in the form of the exceptionally strong and tough 6Al-4V alloy (Titanium + 6% Aluminum + 4% Vanadium). It attains a strength of roughly 160,000 psi, making it about three times stronger than pure Titanium. Titanium's density is a little over half the density of steels (4.4 vs 8 g/cc) so a steel would need to have a strength of 290,000 psi to match the strength-to-weight ratio of Titanium. Only a handful of the most exotic steels can meet this standard and then, only after rigorous, technically demanding physical processing and heat treatments. The flip side of this is that the steels can be worked in a much lower strength condition while 6/4 Titanium is always quite strong and hard to form. As a result 6/4 Ti parts are always expensive. For instance you can get the slightly lower strength alloy 3Al-2V in 9mm tubing with a .6mm wall thickness for about $10/foot. Double that for 6/4 Ti even though 3/2 Ti is still about 130,000 to 140,000 psi strong.

Titanium's strength plus its corrosion resistance and weldability place it squarely into its own class. Titanium is resistant to corrosion by seawater, hot acid, body fluids, and a wide variety of industrial chemicals. It's often used in demanding applications from hip implants to entire submarines to the plumbing in caustic chemical manufacturing plants. Corrosion probably played THE justifying role in its selection for the above mentioned museum. Being a seaport, Bilboa has a far more corrosive environment than mere stainless steel can cope with. Pure titanium is a shoo-in compared to a nickel superalloy that could also handle the climate.

Titanium welds have nearly 100% of the strength of the untouched material. This unusual property allows complicated lightweight structures to be efficiently and reliably fabricated. The 6/4 titanium alloy was specifically developed by the US Army to optimize this property. Here's the patent, #2,906,654 (may require this plug-in). Notice the filing date was 1954 and the granted date was 1959. In the five years it took to process the patent (intentionally stalled by being placed under a secrecy order) there was quite a fuss owing to no less than three organizations, Armour Research and the Rem-Cru and Crucible Corporations, claiming ownership and demanding royalties for the alloy. The Air Force must have been highly unamused at this grab for intellectual property. In 1954 alone it used five and a half MILLION pounds of the stuff–a huge production that predated all the other patent claims.

The material used for BOMApen endcaps is fully pedigreed military and aerospace material. Each batch comes with certification of alloy content and strength. The current batch of endcap material, Timet lot #R7761, lists the following content percentages of elements other than titanium (given as a range found within the alloy lot):
Aluminum: 6.339 - 6.36%
Vanadium: 3.905 - 3.98%
Oxygen: .176 - .184% (for titanium, an extremely important element to control)
Iron: .15 - .17%
Nitrogen: .01 - .014%
Carbon: .006 - .013%
Other unnamed elements: each less than .1%, maximum total of all: .4%
Strength data: Yield strength: 148,000psi; Ultimate tensile strength: 160,000psi; Elongation: 14%; Reduction of area: 45.8% (These last two values say just how ductile the titanium was. They indicate that the alloy failed very gracefully–stretching and deforming rather than just busting with no warning. This is what engineers mean by a tough material and it's an absolutely essential property for materials that are depended on for safety.) Standards met by this batch of endcap material include Mil-T-9047G, AM 2, and AMS 4928N.