Researchers at Rice University, Houston, report that they have developed a titanium-gold-intermetallic (Ti3Au) said to be four times harder than titanium. The team, led by physics Prof. Emilia Morosan, measured the hardness in conjunction with colleagues at Texas A&M University’s Turbomachinery Laboratory and at the National High Magnetic Field Laboratory at Florida State University.
Because titanium and gold by themselves are among the most biocompatible metals and are often used in medical implants, the team believed Ti3Au would be comparable. In fact, tests by colleagues at the University of Texas MD Anderson Cancer Center in Houston determined that the compound was even more biocompatible than pure titanium, and its wear resistance is also higher.
According to Prof. Morosan, “This compound is not difficult to make, and it’s not a new material.”
In fact, the atomic structure of the material — its atoms are tightly packed in a “cubic” crystalline structure that’s often associated with hardness — was previously known. It’s not even clear that Prof. Morosan and former graduate student Eteri Svanidze, the study’s lead co-author, were the first to make a pure sample of the ultrahard “beta” form of the compound. But due to a couple of lucky breaks, they and their co-authors are the first to document the material’s remarkable properties.
“This began from my core research,” says Prof. Emilia Morosan,. “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.
“When we tried to grind up Ti3Au, we couldn’t,” she recalled. “I even bought a diamond (coated) mortar and pestle, and we still couldn’t grind it up.”
Prof. Morosan and grad student Eteri Svanidze decided to do follow-up tests to determine exactly how hard the compound was, and while they were at it, they also decided to measure the hardness of the other compositions of titanium and gold that they had used as comparisons in the original study.
What the team didn’t know at the time was that making the compound at a relatively high temperature produces an almost pure crystalline form of the beta version of the alloy — the crystal structure that’s four times harder than titanium. At lower temperatures, the atoms tend to arrange in another cubic structure — the alpha form . The alpha structure is about as hard as regular titanium. It appears that labs that had previously measured the hardness of Ti3Au had measured samples that largely consisted of the alpha arrangement of atoms.
Read the full-length article, “High hardness in the biocompatible intermetallic compound β-Ti3Au,“ in Science Advanced.
http://news.rice.edu/2016/07/20/titanium-gold-new-gold-standard-for-artificial-joints/
