New Biocompatible Alloy is Four Times Harder than Pure Titanium

A new biocompatible alloy has been developed, and it’s about 3-4 times harder than most steels and pure titanium.

Crystal structure of beta-Ti₃Au (blue – titanium, red – gold). Image credit: Rice University.

Titanium is the leading material for artificial knee and hip joints because it’s strong, wear-resistant and nontoxic.

The new alloy, a 3-to-1 mixture of titanium and gold (Ti₃Au), has even better properties.

“It is about 3-4 times harder than most steels. And it’s four times harder than pure titanium, which is what’s currently being used in most dental implants and replacement joints,” said Prof. Emilia Morosan of Rice University in Houston, TX, senior author on a study in the journal Science Advances that describes the properties of the new material.

According to Prof. Morosan and co-authors, making Ti₃Au at ‘high temperatures’ produces an almost pure crystalline form of the beta version of Ti₃Au (β-Ti₃Au) – the crystal structure that’s four times harder than titanium.

At lower temperatures, the atoms tend to arrange in another cubic structure – α-Ti₃Au. This structure is about as hard as regular titanium.

“The fourfold increase in the hardness of Ti₃Au compared to other Ti–Au alloys and compounds can be attributed to the elevated valence electron density, the reduced bond length, and the pseudogap formation,” the scientists said.

Because titanium and gold by themselves are among the most biocompatible metals and are often used in medical implants, they believed β-Ti₃Au would be comparable.

In fact, tests by the team determined that the new alloy was even more biocompatible than pure titanium.

The story proved much the same for wear resistance: β-Ti₃Au also outperformed pure titanium.

Prof. Morosan and her colleagues are planning to conduct follow-up tests to further investigate the crystal structure of β-Ti₃Au and to see if chemical dopants might improve its hardness even further.

_____

Eteri Svanidze et al. 2016. High hardness in the biocompatible intermetallic compound β-Ti₃Au. Science Advances 2 (7): e1600319; doi: 10.1126/sciadv.1600319