Exploring Ho substituted Y-Fe-B nanocrystalline alloys and hot worked magnets

Abstract

Aiming to balance the utilization of rare earth (RE) resources and develop Y-Fe-B based permanent magnets, Ho is employed as strategic substitution for enhancing the magnetic properties and thermal stability of nanocrystalline Y-Fe-B alloys. Ho substituting Y can enhance the coercivity of Y-Fe-B alloys while maintaining their excellent thermal stability. 30 at.% Ho substitution leads to an abnormal increase of remanence J _r and (Y _0.7 Ho _0.3 ) _2 Fe _14 B alloy exhibits good magnetic properties with remanence J _r = 0.73 T, intrinsic coercivity H _cj = 303 kA m ^−1 , and maximum energy product ( BH ) _max = 66 kJ m ^−3 . High thermal stability with temperature coefficient of remanence α = −0.124%/K and temperature coefficient of coercivity β = −0.245%/K were obtained between 300–400 K. The results for RE-rich (Y _1−x Ho _x ) _2.5 Fe _14 B alloys also show that the magnetic properties change with Ho content are similar to those of (Y _1−x Ho _x ) _2 Fe _14 B alloys, but the coercivity is higher. In addition, nanocrystalline (Y _0.5 Ho _0.5 ) _2.5 Fe _14 B magnets were prepared by hot-pressing and hot deformation process. Due to the lack of low melting point RE-rich phase, this alloy is difficult to be densified and deformed. The formation of high temperature RE _2 O _3 and RE _6 Fe _23 phases and the lack of continuously distributed RE-rich grain boundary phase are responsible for the poor texture of hot deformed magnet. The hot deformed magnet has the magnetic properties of J _r = 0.50 T, H _cj = 739 kA m ^−1 , and ( BH ) _max = 40 kJ m ^−3 together with high thermal stability. The micro-analysis demonstrated the chemical segregation of Y and Ho elements. Higher proportion of Ho than Y existed in main phase and grain boundary phase indicate excess Y were precipitated as Y-rich oxides.

Keywords

• melt-spun Y-Ho-Fe-B alloys
• nanocrystalline magnets
• magnetic properties
• thermal stability
• rare earth permanent magnets