In complex alloys,
chemical disorder results from a greater variety of elements than found
in traditional
alloys. Traces here indicate electronic states in a complex alloy; smeared
traces
reduced electrical
and thermal conductivity. Image credit: Oak Ridge National Laboratory,
U.S. Dept. of
Energy. Image by G. Malcolm Stocks
(October 30, 2015) Designing
alloys to withstand extreme environments is a fundamental challenge for
materials scientists. Energy from radiation can create imperfections in alloys,
so researchers in an Energy Frontier Research Center led by the Department of
Energy’s Oak Ridge National Laboratory are investigating ways to design
structural materials that develop fewer, smaller flaws under irradiation. The
key, they report in the journal Nature Communications, is exploiting the
complexity that is present when alloys are made with equal amounts of up to
four different metallic elements.
“Chemical complexity gives us a way to modify paths for
energy dissipation and defect evolution,” said first author Yanwen Zhang, who
directs an Energy Frontier Research Center, called “Energy Dissipation to
Defect Evolution,” or “EDDE,” funded by the U.S. Department of Energy Office of
Science. The growing center is nearly 15 months old and brings together more
than two dozen researchers with experimental and modeling expertise. EDDE has
partners at Oak Ridge, Los Alamos and Lawrence Livermore national laboratories
and the universities of Michigan, Wisconsin–Madison and Tennessee–Knoxville.
Radiation can harm spacecraft, nuclear power plants and
high-energy accelerators. Nuclear reactions produce energetic particles—ions
and neutrons—that can damage materials as their energy disperses, causing the
formation of flaws that evolve over time. Advanced structural materials that
can withstand radiation are a critical national need for nuclear reactor
applications. Today, nuclear reactors provide one-fifth of U.S. electricity.
Next-generation reactors will be expected to serve over longer lifetimes and
withstand higher irradiation levels.
In a reactor, thousands of atoms can be set in motion by one
energetic particle that displaces them from sites in a crystal lattice. While
most of the displaced atoms return to lattice sites as the energy is
dissipated, some do not. Irradiation can damage structural materials made of
well-ordered atoms packed in a lattice—even obliterating its crystallinity.
Existing knowledge of radiation effects on structural materials is mostly about
reactor-core components. Over the life of a typical light water reactor, all
atoms in the structural components can be displaced on average 20 times, and
accumulated damage may threaten material performance. To prepare for new
reactor concepts, scientists will have to design next-generation nuclear
materials to withstand atoms displaced more than 200 times—a true “grand
challenge.”