Researchers have made improved cheap and heavy rare-earth-free Nd-Fe-B magnets that are in high demand for electric vehicles and may make them more affordable. More than 90% of electric cars use brushless direct current (BLDC) motors made from neodymium iron-boron (Nd-Fe-B) rare earth magnets. Since its discovery by Sagawa in 1984, Nd-Fe-B magnet has been one of the most sought-after permanent magnetic materials for many applications due to its exceptional combination of magnetic properties.
Nd-Fe-B magnets used in EVs operate at high temperatures of 150-200oC and must exhibit high resistance to demagnetization, an ability that pure Nd-Fe-B magnets do not have. The metal dysprosium (Dy) is therefore added as an alloy to improve resistance to demagnetization. Around the world, researchers are trying to increase the coercivity (resistance to demagnetization) of Nd-Fe-B magnets without adding expensive Dy. A
strategy adopted by the research community to increase the coercivity is to enrich the region between the grains of the Nd-Fe-B magnet with “non-magnetic” elements through appropriate thermal treatments (grain boundary diffusion). Recently, scientists from the Center for Automotive Energy Materials at the International Advanced Research Center for Powder Metallurgy and New Materials (ARCI), an autonomous research and development center of the Department of Science and Technology (DST), Govt. of India, have increased the coercivity of a niobium (Nb)-containing Nd-Fe-B melt-spun strip by a grain boundary diffusion process (GBDP) using a low-melting alloy Nd70Cu30, which acts as a source for a “non-magnetic element.
They report limited grain growth during grain boundary diffusion due to Nb precipitation, which facilitates copper (Cu) enrichment at grain boundaries, contributing to increased demagnetization resistance of Nd-Fe-B powders. The coercivity value of 1 T at 150oC critical for automotive applications achieved in this research published in Materials Research Letter could be a useful strategy for developing Dy-free magnets for EV applications.
ARCI has embarked on setting up a pilot plant for the production of Nd-Fe-B magnets in the shape of a near net through a major project funded by the Scientific and Technical Research Board (SERB) in line with the Atmanirbhar Bharat Mission of the Government of India and the above strategy will be explored for magnets produced in semi-operational plant. The new strategy could also be used for the commercial production of Nd-Fe-B magnets in India, reducing imports to meet the major requirements of the automotive sector.
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