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.How wear resistant is it? Remember, we're talking about an expensive alloy that will be used by the gram (or milligram), so the example is a little absurd, but vivid. They say if you put tires made of this alloy on a car, they would lose only a single layer of atoms after skidding a mile.
“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.”
But the story gets better for applications where the metal would be in moving parts, due to a feature in its surface chemistry.
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.While industry strives to reduce the use of precious metals in electronics to keep costs down, switches and other electrical contacts often get a thin coating (microns thick) of gold or silver. 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.
“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 ultradurable coating could save the electronics industry more than $100 million a year in materials alone, Nic Argibay says, 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.To hop over to the Sandia Labs story:
“These wear-resistant materials could potentially provide reliability benefits for a range of devices we have explored,” said Chris Nordquist, a Sandia engineer not involved in the study. “The opportunities for integration and improvement would be device-specific, but this material would provide another tool for addressing current reliability limitations of metal microelectronic components.”Unlike some of the stuff I've reported (cough, cough), this one looks like it could well be commercially successful. How successful probably comes down to calculated cost/benefit ratios for the switch makers and other electronics companies.
Sandia National Laboratories researchers Michael Chandross, left, and Nic Argibay show a computer simulation used to predict the unprecedented wear resistance of their platinum-gold alloy, and an environmental tribometer used to demonstrate it. Photo by Randy Montoya.