November, 2022
Materials containing rare-earth elements dominate the market for high-performance permanent magnets, and there is much interest in finding alternatives. Among the most promising of these is an iron-nickel phase first reported 60 years ago to form under neutron irradiation. Later, the same phase was found in small amounts within meteorites, and given the mineral name tetrataenite. The formation of tetrataenite in meteorites is attributed to their ultraslow cooling ̶ a few degrees per millennium. Trying diverse and difficult processing routes, the search has been on to find a production route for tetrataenite with a practicable timescale.
Collaboration between the Microstructural Kinetics Group, led by Lindsay Greer, and researchers in Leoben, Austria, has led to the demonstration that tetrataenite can be obtained in simple castings, when the composition is appropriately tweaked. This surprising result (successful synthesis without irradiation or waiting for millennia, or any complex processing) offers a possible route to good permanent magnets without rare earths. It also challenges the conventional understanding of tetrataenite formation in meteorites.
Figure: Castings containing large volume fractions of tetrataenite.
Yurii P. Ivanov, Baran Sarac, Sergey V. Ketov, Jürgen Eckert, A. Lindsay Greer, "Direct formation of hard-magnetic tetrataenite in bulk alloy castings", Advanced Science (2022) 2204315
https://doi.org/10.1002/advs.202204315
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