Effect of temperature and vacuum on the magnetic properties and compositional changes in high temperature Sm–Co magnets

Abstract

Electric propulsion systems for space exploration require materials and components that can perform reliably under a vacuum of 10−5 Torr and at temperatures of over 400 °C. Scanning electron microscopy analysis shows that when Sm–Co magnets are exposed to temperatures up to 550 °C for up to 240 h in a vacuum of 10−5 Torr, the surface alteration is morphologically similar to oxidation in air. However, the scale of the affected region is much smaller and consists of about 1–2 μm of a top outermost Sm-depleted oxide layer and about 10–20 μm of a more complex layer in which the constituent atoms redistribute with oxygen penetration. No excessive Sm depletion was observed in the second layer. For all Sm–Co magnet samples, the maximum energy product decreased by less than 10% even at temperatures of 100 °C above their specified maximum operating temperature TM. The residual induction of the magnets with TM=550 °C decreased by 8.5% after baking at 700 °C under vacuum for 240 h.

On high-temperature oxidation and protection of 2:17-type SmCo-based magnets

“…Besides physical reasons (e.g., microstructural defects), chemical variation within the magnets by surface oxidation has been recently proposed to be a decisive (if not an exclusive) factor leading to the collapse of their cellular precipitations structure. Oxidation of the 2:17-type magnets has been investigated by some authors (Chen et al, , 2001Kardelky et al, 2004;Kardelky, (110) Gebert, Gutfleisch, Hoffmann, & Schultz, 2005;Liu & Walmer, 2005;Liu, Marinescu, Vora, Wu, & Harmer, 2009;Mao et al, 2014;Pauw et al, 1997;Pragnell, Williams, & Evans, 2008;Pragnell, Evans, & Williams, 2009;Wang, Zheng, An, Zhang, & Jiang, 2013;Yang et al, 2012Yang et al, , 2013a. The unacceptable coercivity loss may be prevented by adding appropriate surface coatings that can effectively offer oxidation protection to the magnets.…”

Initial Irreversible Losses and Enhanced High‐Temperature Performance of Rare‐Earth Permanent Magnets

“…Effects due to oxidation or rare earth volatilization fall in this category. The irredeemable losses of Sm‐Co magnets due to oxidation and Sm volatilization in a demagnetized layer may be reduced by surface coating …”

Effect of B addition on the microstructure and magnetic properties of melt-spun Sm12Co60−xFe19Cu6Zr3Bx (0≤x≤3) ribbons

“…Until now, powder metallurgy is the most commonly used process to produce Sm 2 Co 17 -type permanent magnets [2][3][4][5][6][7][8]. Recently, a significant interest has been developed to understand the coercivity mechanism, high temperature stability, microstructure and domain structure of isotropic permanent magnets produced using meltspinning technique [9][10][11][12][13][14].…”