Enhanced thermal stability of nanocrystalline melt-spun Nd-Pr-Fe-B alloys by Gd substitution

Thermal demagnetization of Nd-Fe-B permanent magnets at elevated temperature presents a noteworthy challenge. Current research endeavors are concentrated on enhancing the thermal stability of Nd-Fe-B magnets. This study investigates the use of the cost-effective element Gd as a substitute for Nd in nanocrystalline melt-spun [(Nd0.8Pr0.2)1-xGdx]14.3Fe76.9B5.9M2.9 (M = Co, Cu, Al and Ga) (wt.%; x = 0-0.6) alloys. Although Gd substitution is not conducive to the magnetic properties of the alloys at room temperature, the Gd-substituted alloys exhibit excellent high-temperature performance. The Curie temperature (Tc) of the RE2Fe14B phase increases from 582 K to 643 K, with increasing Gd substitution from 0 to 0.6. The alpha and fi coefficients for Gd-free (x = 0) alloy are -0.120 %/K and -0.468 %/K, respectively. By Gd substitution, they respectively increase to -0.068 %/K and -0.295 %/K for x = 0.6 alloy, which are superior to that of reported nanocrystalline Nd-Fe-B alloys and commercially sintered Nd-Fe-B magnets. Microstructural analysis revealed that Gd substitution promotes grain refinement. Furthermore, it was observed that Gd is uniformly distributed across both the grain boundary and main grains. Overall, this study offers a cost-effective and straightforward approach for enhancing the thermal stability of Nd-Fe-B magnets.