"Iron Man" Gold-Titanium Alloy Found

Fact has once more caught up to fiction in a remarkable way, as Rice University scientists announce the development of a gold-titanium alloy with quadruple the hardness of titanium alone.

If you've caught any of the Iron Man movies, you will immediately recognize this as the (no longer) fictional gold-titanium alloy that Tony Stark invented to build his Iron Man armors. However, this new alloy is not destined for use in flying, powered exoskeletons (at least, not yet!). Instead, it will be used to revolutionize the field of medical implants and prosthetics.

Titanium is the most commonly used metal used to repair the body, be it in screws and plates to hold bones together, hip replacements, or anchoring prosthetic limbs to the body. Titanium (and gold) are non-toxic, bio-compatible, and resistant to corrosion inside the body. Titanium also has the rare property of "osseointegration," which allows bone to firmly grow over and attach itself to the implant, securing it to the body. This is especially important in load-bearing implants, such as knee replacements and the stubs for leg prosthetics.

Rice University's Morosan Lab arc melter used to form the "Iron Man" gold-titanium alloy.

The secret behind this alloy, know as "β Ti3Au" (beta titanium 3 gold), is the temperature used during the melting process. The Rice University scientific team used an arc melter to repeatedly melt and re-melt a mass of three parts titanium, one part gold at ultra-high temperature until its composition was uniform. This procedure took the alloy from its usual "alpha" configuration to the "beta" one, which features a very compact, cubic crystalline structure with a high valence electron density.

Dr. Emilia Morosan, lead scientist in the Rice University lab that bears her name, notes that even though this alloy is the hardest bio-compatible intermetallic compound known to man,  "[It] is not difficult to make, and it's not a new material."

In the best traditions of great scientific advances, the discovery of the hardness properties of beta Ti3Au was an accident.  The team was conducting experiments on making magnetic substances from nonmagnetic materials. Testing various ratios of titanium to gold in these experiments led to beta Ti3Au being discovered. The alloy has probably been made by accident before (all it requires is a far hotter melting process than normal), but Morosan's team is the first to obverse and document its unique properties.

Morosan noted, "One of the things that we do when we make a new compound is try to grind it into powder for X-ray purposes. This helps with identifying the composition, the purity, the crystal structure and other structural properties. “When we tried to grind up titanium-gold (beta ti3Au), we couldn’t,” she recalled. “I even bought a diamond (coated) mortar and pestle, and we still couldn’t grind it up.”

In addition to being four times stronger than pure titanium (which is pretty strong to begin with), beta Ti3Au has a coefficient of friction that is four times less than titanium. This means that wear is greatly reduced, compared to existing implant devices. Normal replacement joints have to be replaced surgically ever 10 years or so. Implants made of Ti3Au should last much longer before needing replacement. The alloy will also adhere to ceramics, which results in lighter and cheaper medical components.

In true Tony Stark fashion, Dr. Morosan and her team are conducting more tests on Ti3Au, exploring whether treating the alloy with chemicals will make it even harder. Now, where are those folks who were working on miniature reactors?

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