In Brief
Scientists from Rice University have discovered a titanium alloy that's better than titanium at being a medical implant, and it is four times harder than titanium and a vast majority of steels.

The Gold Standard

When it comes to bone replacements, the go-to material is still titanium. Hard, wear-resistant, and compatible to the body, titanium looks like the best alternative to actual bone, maybe even better. Who knew that you could improve the ‘gold standard’ by just adding actual gold?

Rice University physicists have discovered that an alloy of titanium and gold is three to four times harder than steel, and may actually be better as a material for replacement body parts. The study, published in Science Advances, described the properties of an alloy of the two metals, a 3-to-1 mixture of titanium and gold, called Titanium-3. They found the alloy to be four times harder than titanium.

When they checked the biocompatibility and wear rate of the alloy, the researchers knew that it would rank high, since its parent metals are already biocompatible and used in medical implants. Surprisingly, Titanium-3 performed well over their expectations, actually being more biocompatible and wear resistant than pure titanium.

Hard Chemistry

These unexpected properties stem from the structure of Titanium-3. The researchers previously did not know a harder version of the alloy comes out when higher temperatures are used. High temperatures create an almost purely crystalline form of the beta version of the alloy.

The structure of Titanium-3 Credit: E. Morosan/Rice University

According to the study’s abstract, the alloy’s hardness can be attributed “to the elevated valence electron density, the reduced bond length, and the pseudogap formation. Understanding the origin of hardness in this intermetallic compound provides an avenue toward designing superior biocompatible, hard materials.”

In contrast, making the alloy at lower temperatures arranges the atoms to another structure, the alpha version. This version is as hard as regular titanium, and is most likely the previously documented form of Titanium-3.