Magnetics Business & Technology - July/August 2021 - 4

EDITOR'S CHOICE
Findings Offer 'Recipe' for Fine Tuning Alloys for
High-Temperature Use
Superalloys that withstand
extremely high
temperatures could
soon be tuned even
more finely for specific
properties such as
mechanical strength, as
a result of new findings
recently published.
A phenomenon related
to the invar effect -
which enables magnetic
materials such as
nickel-iron (Ni-Fe) alloys
to keep from expanding
with increasing temperature
- was reported to
have been discovered in
paramagnetic, or weakly
Volume 20, Issue 4
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A piece of alloy is stress tested in Levente Vitos' lab at KTH.
(photo: courtesy of Levente Vitos)
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Scott Webster
magnetized, high-temperature alloys.
Levente Vitos, Professor at KTH Royal Institute of Technology in Stockholm, says the
breakthrough research, which includes a general theory explaining the new invar effect,
promises to advance the design of high-temperature alloys with exceptional mechanical
stability. The article was published in the Proceedings of the National Academy of Sciences
of the United States of America. Led by Vitos, the research team was comprised of
KTH researchers Zhihua Dong, Wei Li and Stephan Schönecker.
Short for " invariant, " invar plasticity enables magnetically-disordered Ni-Fe alloys to show
practically invariant deformation behavior over a wide temperature range - making them
ideal for turbines and other mechanical uses in extremely high temperatures.
The invar effect, however, has never been fully understood, and Vitos says that these new
findings help explain the peculiar high-temperature properties of special alloys used in jet
engines, such as nickel-based superalloys.
Invar has two known effects: thermal expansion and elasticity (the ability to spring back
after bending, for instance). Because both of these effects are linked with the interplay between
temperature and magnetic order, they are considered to be specific to magneticallyordered
alloys.
Using first-principles quantum mechanical modeling, the researchers identified how invariant
plasticity also occurs in non-magnetic alloys, when a structural balance exists at the
atomic level between cubic and hexagonal close-packed structures.
The new discovery emerges from a long-term collaboration with industry to find alternatives
to carcinogenic cobalt in hard metals, such as cutting tools. Vitos says this finding broadens
the palette of invar phenomena and material compositions, with clear implications for
new applications.
" Our findings create a new platform for tailoring high-temperature properties of technologically
relevant materials towards plastic stability at elevated temperatures, " he says.
The research was supported by the Swedish Research Council (VR), the Swedish Foundation
for Strategic Research (SSF), and the Swedish Foundation for International Cooperation
in Research and Higher Education (STINT).
Administration
Marsha Grillo
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