Most Wear-Resistant Metal
Alloy in the World Engineered at Sandia National Laboratories
ALBUQUERQUE, N.M. —- August 16, 2018 -- If you’re ever
unlucky enough to have a car with metal tires, you might consider a set made
from a new alloy engineered at Sandia National Laboratories. You could skid —
not drive, skid — around the Earth’s equator 500 times before wearing out the
tread.
Sandia’s materials science team has engineered 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, or combination of metals, in the same class as diamond and sapphire,
nature’s most wear-resistant materials. Sandia’s team recently reported their
findings in Advanced Materials. “We showed there’s a fundamental change you can
make to some alloys that will impart this tremendous increase in performance
over a broad range of real, practical metals,” said materials scientist Nic
Argibay, an author on the paper.
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, too, as
connections press and slide across each other day after day, year after year,
sometimes millions, even billions of times. These effects are exacerbated the
smaller the connections are, because the less material you start with, the less
wear and tear a connection can endure before it no longer works.
With Sandia’s platinum-gold coating, only a single layer of
atoms would be lost after a mile of skidding on the hypothetical tires. The
ultradurable coating could save the electronics industry more than $100 million
a year in materials alone, 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.
“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.”
New metal puts an old
theory to rest
You might be wondering how metallurgists for thousands of
years somehow missed this. In truth, the combination of 90 percent platinum
with 10 percent gold isn’t new at all.
But the engineering is new. Argibay and coauthor Michael
Chandross masterminded the design and the new 21st century wisdom behind it.
Conventional wisdom says 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,” said John Curry, a postdoctoral
appointee at Sandia and first author on the paper. “Even still, in the presence
of extreme stresses and temperatures many alloys will 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.”
Now they have proof they can hold in their hands. It 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’s
much better at resisting heat and a hundred times more wear resistant.
The team’s approach is a modern one that depended on
computational tools. Argibay and Chandross’ theory arose from simulations that
calculated how individual atoms were affecting the large-scale properties of a
material, a connection that’s rarely obvious from observations alone. Researchers
in many scientific fields use computational tools to take much of the guesswork
out of research and development.
“We’re getting down to fundamental atomic mechanisms and
microstructure and tying all these things together to understand why you get
good performance or why you get bad performance, and then engineering an alloy
that gives you good performance,” Chandross said.
A slick surprise
Still, there will always be surprises in science. In a
separate paper published in Carbon, the Sandia team describes the results of a
remarkable accident. One day, while measuring wear on their platinum-gold, an
unexpected black film started forming on top. They 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
allows carbon-containing molecules from the environment to stick and degrade
during sliding to ultimately form diamond-like carbon,” Curry said. “Industry
has other methods of doing this, but they typically involve vacuum chambers
with high temperature plasmas of carbon species. It can get very expensive.”
The phenomenon could be harnessed to further enhance the
already impressive performance of the metal, and it could also potentially lead
to a simpler, more cost-effective way to mass-produce premium lubricant.
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