Mechanism Analysis of Coercivity Enhancement of Hot Deformed Nd-Fe-B Magnets by ${\rm DyF}_{3}$ Diffusion

Isotropic and anisotropic Nd-Fe-B magnets with 2 wt% DyF₃ addition are successfully prepared. With the addition of 2 wt% , the coercivity of the hot-pressed magnets increases from 20.52 kOe to 23.13 kOe by increasing the hot-pressed temperature. BSEM results show that most of the DyF₃ additions exist in triple junctions and on the surface of ribbons even though the hot-pressed temperature is as high as 983 K. The coercivity of the die-upset magnets increases from 15.18 kOe to 19.14 kOe when 2 wt% DyF₃ added. The BSEM results of the hot-deformed magnets show that the content of the DyF₃ between ribbons in the die-upset magnets is reduced which indicates that most DyF₃ decomposes into Dy and F elements. The Dy atoms penetrate into the Nd₂Fe₁₄B phases and (Nd, Dy)₂Fe₁₄B phases are formed. The improvement of coercivity of the die-upset magnets is caused by the higher magnetocrystalline anisotropy of (Nd, Dy)₂Fe₁₄B.