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Hard Titanium-Gold Alloy Ideal for Artificial Joints

Pat Waurzyniak
By Patrick Waurzyniak Contributing Editor, SME Media
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Crystal structure of beta titanium-3 gold. Image courtesy Rice University

Researchers at Rice University (Houston) have discovered a titanium-gold (TiAu3) alloy that is harder than most steels and may be an optimal choice for use in orthopedic joint replacement surgery.

Prized by orthopedic surgeons for knee and hip replacements, titanium offers a strong, wear-resistant and nontoxic choice for implants. But an unexpected discovery by Rice University physicists shows that the standard for artificial joints can be improved with the addition of gold.

“It is about three to four times harder than most steels,” said Emilia Morosan, the lead scientist on a new study published in Science Advances that describes the properties of a 3-to-1 mixture of titanium and gold with a specific atomic structure that imparts hardness. “It’s four times harder than pure titanium, which is what’s currently being used in most dental implants and replacement joints.”

The paper, “High hardness in the biocompatible intermetallic compound ß-Ti3Au,” is available at: http://advances.sciencemag.org/content/2/7/e1600319.

A physicist who specializes in the design and synthesis of compounds with exotic electronic and magnetic properties, Morosan said the new study is “a first for me in a number of ways. This compound is not difficult to make, and it’s not a new material.” 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. While it’s not clear Morosan and former graduate student Eteri Svanidze, the study’s lead co-author, were the first to make a pure sample of the ultra-hard “beta” form of the compound, they and their co-authors are the first to document the material’s properties.

Morosan, professor of physics and astronomy, of chemistry and of materials science and nanoengineering at Rice, said the discovery began from her core research. “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,” Morosan said. “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, we couldn’t,” she recalled. “I even bought a diamond [coated] mortar and pestle, and we still couldn’t grind it up.”

Follow-up tests showed how hard the compound was, and the team also measured the hardness of the other compositions of titanium and gold that they had used as comparisons in the original study. One of the extra compounds was a mixture of three parts titanium and one part gold that had been prepared at high temperature. What the team didn’t know at the time was that making TiA3 at 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 of TiAu3 and the alpha structure is about as hard as regular titanium. The team measured the hardness of the beta form of the crystal in conjunction with colleagues at Texas A&M University’s Turbomachinery Laboratory and at the National High Magnetic Field Laboratory at Florida State University. Morosan and Svanidze also performed other comparisons with titanium.

Two key measures for biomedical implants are biocompatibility and wear resistance. Because titanium and gold by themselves are among the most biocompatible metals and are often used in medical implants, the researchers team believed TiAu3 would be comparable. Tests by colleagues at the University of Texas MD Anderson Cancer Center in Houston showed that the new alloy was even more biocompatible than pure titanium, and the results were same for wear resistance.

Morosan said she has no plans to become a materials scientist or dramatically alter her lab’s focus, but she said her group is planning to conduct follow-up tests to further investigate the crystal structure of beta titanium-3-gold and to see if chemical dopants might improve its hardness even further.

Co-authors of the study include Pulickel Ajayan, Sruthi Radhakrishnan and Chandra Sekhar Tiwary, of Rice; Tiglet Besara, Yan Xin, Ke Han and Theo Siegrist, of Florida State; Fevzi Ozaydin and Hong Liang, of Texas A&M; and Sendurai Mani of MD Anderson. The research was supported by the National Science Foundation, the Department of Energy, Texas A&M’s Turbomachinery Laboratory and the Florida State University Research Foundation.

DOE Awards 13 HPC Projects

The Department of Energy (DOE) announced $3.8 million in funding for 13 projects to use high-performance computing resources at the department’s national laboratories to improve manufacturing. The collaborations in the High Performance Computing for Manufacturing (HPC4Mfg) program will help manufacturers to address key problems in US manufacturing through application of modeling, simulation and data analysis to the manufacturing of materials. The program’s intent is to aid manufacturing decision-making, optimize processes and design, improve quality, predict performance and failure, quicken or eliminate testing, and shorten the time for adoption of new technologies.

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A simulation of pressure applied to felt used to absorb water in a paper drying process is one of the projects that received DOE funding. Image courtesy of David Trebotich/Lawrence Berkeley National Laboratory.

Led by the Lawrence Livermore National Laboratory (LLNL; Livermore, CA), with Lawrence Berkeley National Laboratory (LBNL; Berkeley, CA) and Oak Ridge National Laboratory (ORNL; Oak Ridge, TN) as strong partners, the HPC4Mfg program brings together world-class supercomputers and scientific expertise at the national labs with US manufacturers to address technical problems related to energy and manufacturing. The effort also advances the Obama administration’s National Strategic Computing Initiative, started in July 2015, which calls for public-private partnerships to increase the adoption of high-performance computing.

The program previously funded 16 projects ranging from improving turbine blades for aircraft engines to reducing heat loss in electronics to improving fiberglass production. Partners range from small to large companies, industry consortia and institutes. “We’re excited about this second round of projects because companies are bringing forward challenges that we can help address, which result in advancing innovation in US manufacturing and increasing our economic competitiveness,” said LLNL mathematician Peg Folta, director of the HPC4Mfg Program.

The 13 new projects include LLNL partnering with GE Global Research (Niskayuna, New York) to study how to mitigate defects when 3D printing metal parts; General Motors Co. (Detroit) and EPRI of California will partner with ORNL to improve welding techniques for automobile manufacturing and power plant builds; Alzeta Corp. (Santa Clara, CA) is partnering with LBNL to reduce emissions from semiconductor processing that could potentially harm the ozone layer; and Actasys Inc. (Watervliet, NY) is partnering with ORNL to decrease the fuel consumption of tractor trailer trucks by actively modifying their aerodynamics to reduce drag.

Other new projects funded by HPC4Mfg include: Shiloh Industries of Ohio will partner with ORNL to study phase change cooling of tooling to speed up casting processes; Rolls-Royce Corp. of Indiana will partner with ORNL to improve silicon carbide composites; ORNL will partner with Agenda 2020 Technology Alliance, a consortium focused on the paper industry to design better catalysts for lignin breakdown; and PPG of Pennsylvania will partner with LBNL to decrease the time needed to paint automobiles. Carbon Inc. of California will partner with LBNL to increase the speed of polymer additively manufactured components; the American Chemical Society Green Chemistry Institute will partner with LBNL to develop lower energy mechanisms of chemical separation using membranes; Sepion Technologies of California will partner with LBNL to make new membranes to increase the lifetime of Li-S batteries; Applied Materials Inc. of California will partner with LLNL to enable the manufacture of higher quality, more efficient LEDs for lighting; and Harper International Corp. of New York will partner with ORNL to reduce the cost of carbon fibers.

Tech Front welcomes your manufacturing research-related news releases: Please email them to Tech Front editor Patrick Waurzyniak at pwaurzyniak@sme.org.

This article was first published in the October 2016 edition of Manufacturing Engineering magazine.

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