New titanium alloy is four times stronger than steel

By adding gold to titanium, Rice University researchers report in the latest edition of the journal Science Advances that they have discovered an alloy that is several times stronger than steel, but which is still wear-resistant and non-toxic enough to be used in artificial knees and hips.

According to BBC News, Emilia Morosan, a professor of nanomaterials engineering at Rice, and her colleagues claim that the titanium-gold (Ti-Au) alloy is the hardest known metallic substance compatible with living tissues and is four times stronger than pure titanium, the material which is now used in the majority of dental implants and replacement joints.

“This began from my core research,” Morosan explained in a statement. “We published a study not long ago on titanium-gold, a 1-to-1 ratio compound that was a magnetic material made from nonmagnetic elements. 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.”

However, when they developed the new alloy – a compound of three parts titanium and one part gold called beta-Ti3Au – they were unable to grind it, even when using a diamond-coated mortar and pestle. Follow up tests and comparisons to other titanium-gold compounds revealed that this new allow was at least three times harder than most steels, and comparable to other engineering alloys, according to the study authors.

Substance also more biocompatible, wear-resistant than regular titanium

The breakthrough could be good news for joint replacement patients, as in most cases, hip and knee implants need to be replaced once every 10 years or so because of wear and tear, said BBC News. Beta-Ti3Au could lead to the development of longer-lasting medical implants.

According to Morosan, the compound is “not difficult to make.” Its atoms are densely packed in what is known as a cubic crystalline structure long associated with hardness, and while the Rice-led team is not even certain that they were the first team to develop a purse sample of the alloy’s ultrahard beta form, they are the first to document the compound’s incredible properties.

In addition to measuring its hardness, the researchers gauged the biocompatibility and the wear resistance of beta-Ti3Au. Those tests revealed that the alloy was even more biocompatible than pure titanium, and it also exceeded its unaltered counterpart in measures of wear resistance. The material could also be used in the drilling and sporting goods industry, they added.

So what exactly is it that makes this alloy so much stronger, more biocompatible and better at resisting wear and tear than other types of titanium? As the researchers explained in the abstract of their study, its traits “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.”

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Image credit: Volker Steger

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