Sandia material scientists have created a platinum-gold alloy believed to be the most wear-resistant metal in the world. It’s 100 times more durable than high-strength steel, making it the first alloy to get into the same class as diamond sand sapphires, nature’s most wear-resistant materials. During development, the team also uncovered a fundamental modification that can be made to some alloys that imparts a tremendous increase in performance.
Although metals are typically thought of as strong, when they repeatedly rub against other metals, like in an engine, they wear down, deform, and corrode unless they have a protective barrier, like additives in motor oil. In electronics, moving metal-to-metal contacts receive similar protections with outer layers of gold or other precious metal alloys. But these coatings are expensive. And eventually they wear out as connections press and slide across each other day after day, year after year, sometimes millions (or even billions) of times. These effects are exacerbated with smaller connections because the less material you start with, the less wear-and-tear a connection can endure before it no longer works.
The ultradurable Sandia coating could save the electronics industry more than $100 million a year in materials alone, and make electronics of all sizes and across many industries more cost-effective, long-lasting, and dependable, from aerospace systems and wind turbines to microelectronics for cell phones and radar systems. A hypothetical (and unrealistic) example which shows the new alloy’s wear resistance is that if you put a a set of alloy tires on a car, they would lose only a single layer of atoms after skidding a mile.
The Sandia discovery flies in the face of accepted wisdom on friction. It says that a metal’s ability to withstand friction is based on how hard it is. The Sandia team proposed a new theory that says wear is related to how metals react to heat—not their hardness—and they handpicked metals, proportions, and a fabrication process that could prove their theory.
“Many traditional alloys were developed to increase the strength of a material by reducing grain size,” says John Curry, a postdoctoral appointee at Sandia. “Even still, in the presence of extreme stresses and temperatures, many alloys coarsen or soften, especially under fatigue. We saw that with our platinum-gold alloy the mechanical and thermal stability is excellent, and we did not see much change to the microstructure over immensely long periods of cyclic stress during sliding.”
The new alloy looks and feels like ordinary platinum—silver-white and a little heavier than pure gold. Most important, it’s no harder than other platinum-gold alloys, but it resists heat much better and is a hundred times more wear resistant.
Discovering the new alloy was a happy accident. One day, while measuring wear on the platinum-gold alloy, an unexpected black film started forming on top. The team recognized it: diamond-like carbon, one of the world’s best man-made coatings, slick as graphite and hard as diamond. Their creation was making its own lubricant, and a good one at that. Diamond-like carbon usually requires special conditions to manufacture, and yet the alloy synthesized it spontaneously.
“We believe the stability and inherent resistance to wear lets carbon-containing molecules from the environment to stick and degrade during sliding to ultimately form diamond-like carbon,” Curry says. “Industry has other methods of doing this, but they typically involve vacuum chambers with high temperature carbon plasmas of carbon. It can get very expensive.”
The phenomenon could be harnessed to further enhance the already impressive performance of the metal and lead to a simpler, more cost-effective way to mass-produce premium lubricants.
