Prospects for Non-Rare Earth Permanent Magnets for Traction Motors and Generators

Abstract

With the advent of high-flux density permanent magnets based on rare earth elements such as neodymium (Nd) in the 1980s, permanent magnet-based electric machines had a clear performance and cost advantage over induction machines when weight and size were factors such as in hybrid electric vehicles and wind turbines. However, the advantages of the permanent magnet-based electric machines may be overshadowed by supply constraints and high prices of their key constituents, rare earth elements, which have seen nearly a 10-fold increase in price in the last 5 years and the imposition of export limits by the major producing country, China, since 2010. We outline the challenges, prospects, and pitfalls for several potential alloys that could replace Nd-based permanent magnets with more abundant and less strategically important elements.

Coercivity and nanostructure of melt-spun Ti-Fe-Co-B-based alloys

“…[1][2][3] The magnets, which typically contain Fe, Co, Ni, Al, and various additives, have very good overall permanent-magnet properties but suffer from modest coercivities, which are limited to the shape-anisotropy contribution. [4][5][6] Several non-traditional ways to improve alnico magnets have been proposed.…”

“…Figure 2 shows XRD patterns of the three samples. Ribbons I and II consist of tetragonal Ti 3 (Fe, Co) 5 B 2 and Fe-Co-rich bcc phases, whereas the ribbons of Sample III contain the tetragonal 3:5:2, bcc, and NiAl-rich L2 1 In order to identify the magnetic phases in the ribbons, we have measured the magnetization as a function of temperature. Figure 3 indicates two ferromagnetic-to-paramagnetic phase transitions.…”

Preparation and Magnetic Properties of MnBi Alloy and its Hybridization with NdFeB

“…The price of rare-earth elements has increased sharply (e.g., for NdPr alloys, the price was increased by 565% in 2011 in comparison to that in 2010 [1]); therefore, the development of rare-earth-free permanent magnets is becoming more important, and MnBi-based magnets have received renewed research interest [2][3][4][5].…”

Novel mechanisms for solid-state processing and grain growth with microstructure alignment in alnico-8 based permanent magnets

“…However, when motor operational conditions increase to 180 • C, they result in a strong reduction of magnetic properties, e.g., energy product (BHmax), in Nd-based 2-14-1, making non-RE PM materials like alnico attractive. [6][7][8] Alnico is an established magnet alloy family consisting primarily of Al, Ni, Co, and Fe, along with Cu and Ti, with a unique spinodal nanostructure that can yield significant shape anisotropy-based coercivity. 9 Alnico also is notable for high saturation magnetization, and high-temperature performance with small magnetic remanence temperature coefficient (-0.025%/ • C) and positive coercivity temperature coefficient (+0.01%/ • C), as well as resistance to corrosion effects.…”

“…9 Alnico also is notable for high saturation magnetization, and high-temperature performance with small magnetic remanence temperature coefficient (-0.025%/ • C) and positive coercivity temperature coefficient (+0.01%/ • C), as well as resistance to corrosion effects. 7 However, alnico typically has insufficient coercivity and a poor hysteresis loop shape for use in traction drive motors. Yet, theoretically, the upper limit for alnico coercivity and BHmax are far higher than have been observed.…”