Could Super Steel Give Ortho Implants a Big Boost?

University of California, San Diego researchers invented a steel alloy that can withstand extreme pressure without bending, nicking, or breaking.

Researchers have fabricated possibly the strongest type of steel ever made.

The new steel alloy won’t nick or break unless subjected to extreme amounts of pressure—more than 12.5 giga-Pascals or about 125,000 atmospheres, according to Olivia Graeve, a professor of mechanical engineering at the Jacobs School of Engineering at the University of California, San Diego. Graeve led the design and fabrication effort for the steel, whose unique atomic structure differentiates it from other metal alloys.

"Atoms organize themselves into these beautiful crystal structures. That means that the atoms are situated in very specific, repeatable locations,” Graeve explained. “This material is not like that. The arrangement of the atoms is completely random.”

Researchers at the University of Southern California took the material that Graeve’s team made and tested it, along with an alloy made from a different set of metal powders. At lower pressures, they saw little difference between the materials’ elasticity. When they subjected both to extreme pressure, the super-steel, named SAM2X5-630, was the clear winner, according to Veronica Eliasson, associate professor of aerospace and mechanical engineering at USC.

“Sometimes you’ve got to bring out the big guns to actually hit it hard and then you actually see, wow, there is a difference,” Eliasson said.

The research was supported by the Defense Threat Reduction Agency. The new alloy could have a wide range of applications, from drill bits, to body armor for soldiers, to meteor-resistant casings, according to a statement from UC San Diego. That list could expand to include medical devices, these researchers said.

“I think in the long run this is probably a good candidate,” Eliasson said. “It seems to be fairly good when it’s impacted or subject to stress. Why not look into it?”

Graeve said the new alloy has potential as a coating and on its own. She wondered if it could be used to make hip implants.

“Both stainless steel and titanium are used for those applications (with) the capacity to resist deterioration or corrosion in the body,” Graeve said. “I would imagine that this could have the same capabilities."

“I have not tested it, but it sounds very reasonable,” she added. “This material has very high wear resistance.”

Such toughness to wear and tear could be especially attractive, given the checkered history of medical devices such as all-metal hip implants. First introduced in the late 1990s, all-metal hip implants were thought to be stronger than other types of implants with the exception of those made of ceramic, which are hard yet brittle. It turned out, though, that the implants had serious issues, wearing down and releasing chromium and cobalt ions. These ions can seep into local tissue near the site of an implant, potentially destroying bone and muscle. If these ions manage to enter a patient’s circulatory system, they can injure the kidneys, liver, spleen, and lymph nodes before elimination from the body through urine.

To create the super-strong steel, Graeve said she and her team mixed metal powders in a graphite mold, pressurized them at 100 megaPascals, or 1000 atmospheres, and exposed to a powerful current of 10,000 A at 1165 °F (630 °C) during a process called spark plasma sintering.

The researchers believe that the steel owes its super strength to the randomness with which atoms are organized. It has small crystalline regions, only a few nanometers in size with only hints of structure, Graeve explained.

The research team, also from the California Institute of Technology, describe the material’s fabrication and testing in a recent issue of Nature Scientific Reports.

They worked on the project for 3-½ years, completing the project last fall. They have moved on, but would like to pursue it further, according to Eliasson.

“The last set of results was so good, someone needs to take it up and someone needs to play around with it a little more,” she said. “Hopefully that is us.”