Enhancing the magnetic properties of Pr2Fe14B/α-Fe melt-spun ribbons by long-term natural air ageing

Abstract

Nanocomposite Pr_9.5Fe_84-xB_6.5Ti_x (x = 1, 2, 3, 4) permanent magnetic alloys were fabricated by the melt spinning technique at a wheel speed of 21 ms⁻¹. The magnetic properties, microstructure, and coercivity mechanism were studied before and after three years of aging in air at room temperature. XRD analysis indicated that the as-spun ribbon contains α-Fe soft, Pr₂Fe₁₄B hard phase, an amorphous phase, and the aging process enhances the crystalline peaks of α-Fe and Pr₂Fe₁₄B phases. The peaks shifting of XRD to lower angles in the aged sample evidence the lattice constant expansion and the stress relaxation. The relaxation in stress induced crystallinity in the aged sample. TEM results showed that the grain size increased in the aged samples, while amorphous content reduced. DSC analysis revealed exothermic peaks near 200 °C for the fresh samples which indicates transformation of amorphous into 2:14:1 and α-Fe while aged samples does not show any heat changes up to 200 °C. The long-term air aging process has a significant effect on the magnetic properties, which increase the value of (BH)_max by 184 % increment in the ribbon with x = 4. Initial curves revealed that the coercivity mechanism of the ribbons varies with the content of Ti and aging. The coercivity mechanism with x = 1,2,3 was mainly controlled by the mixture of nucleation of domain and pinning of domain wall movement in both aged and fresh ribbons. In the x = 4 ribbon, the freshly spun sample showed a mixture of nucleation and pinning, while aged samples exhibited a dominant pinning mechanism.