TY - JOUR

T1 - Direct Formation of Hard-Magnetic Tetrataenite in Bulk Alloy Castings

AU - Ivanov, Yurii P.

AU - Sarac, Baran

AU - Ketov, Sergey V.

AU - Eckert, Jürgen

AU - Greer, A. Lindsay

N1 - Publisher Copyright: © 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.

PY - 2023/1/4

Y1 - 2023/1/4

N2 - Currently, predominant high-performance permanent magnets contain rare-earth elements. In the search for rare-earth-free alternates, body-centered tetragonal Fe–Ni is notable. The ordering to form this phase from the usual cubic close-packed Fe-Ni is understood to be possible only below a critical temperature, commonly accepted to be 593 K. The ordering is first demonstrated by using neutron irradiation to accelerate atomic diffusion. The tetragonal phase, designated as the mineral tetrataenite, is found in Fe-based meteorites, its formation attributed to ultra-slow cooling. Despite many attempts with diverse approaches, bulk synthesis of tetrataenite has not been reported. Here it is shown that with appropriate alloy compositions, bulk synthesis of tetrataenite is possible, even in conventional casting at cooling rates 11‒15 orders of magnitude higher than in meteorites. The barrier to obtaining tetrataenite (slow ordering from cubic close-packed to body-centered tetragonal) is circumvented, opening a processing window for potential rare-earth-free permanent magnets. The formation of tetrataenite on industrially practicable timescales also throws into question the interpretation of its formation in meteorites and their associated cooling rates.

AB - Currently, predominant high-performance permanent magnets contain rare-earth elements. In the search for rare-earth-free alternates, body-centered tetragonal Fe–Ni is notable. The ordering to form this phase from the usual cubic close-packed Fe-Ni is understood to be possible only below a critical temperature, commonly accepted to be 593 K. The ordering is first demonstrated by using neutron irradiation to accelerate atomic diffusion. The tetragonal phase, designated as the mineral tetrataenite, is found in Fe-based meteorites, its formation attributed to ultra-slow cooling. Despite many attempts with diverse approaches, bulk synthesis of tetrataenite has not been reported. Here it is shown that with appropriate alloy compositions, bulk synthesis of tetrataenite is possible, even in conventional casting at cooling rates 11‒15 orders of magnitude higher than in meteorites. The barrier to obtaining tetrataenite (slow ordering from cubic close-packed to body-centered tetragonal) is circumvented, opening a processing window for potential rare-earth-free permanent magnets. The formation of tetrataenite on industrially practicable timescales also throws into question the interpretation of its formation in meteorites and their associated cooling rates.

KW - meteorite

KW - order-disorder

KW - rare-earth-free permanent magnet

KW - tetrataenite

UR - http://www.scopus.com/inward/record.url?scp=85141391811&partnerID=8YFLogxK

U2 - 10.1002/advs.202204315

DO - 10.1002/advs.202204315

M3 - Article

AN - SCOPUS:85141391811

VL - 10.2023

JO - Advanced science

JF - Advanced science

SN - 2198-3844

IS - 1

M1 - 2204315

ER -