Pre-deformation assisted fabrication of bulk Nd2Fe14B/α-Fe nanocomposites with high energy density

Abstract

For Nd2Fe14B/α-Fe nanocomposite magnets, which exhibit great superiority in theoretical energy products, it is a great challenge to obtain controlled nano-scale microstructural features while eliminating the harmful metastable phases due to the general metastable fabrication methods. Here, we report a strategy to control the nano-scale features and simultaneously eliminate metastable phases for Nd2Fe14B/α-Fe nanocomposites through low-temperature pre-deformation of amorphous alloys combined with subsequent thermal annealing. The resultant bulk Nd2Fe14B/α-Fe nanostructure exhibits desired ultrafine grain sizes, ∼20 nm for soft-magnetic α-Fe phase with a high fraction of Vα-Fe ≈ 30 wt% and ∼33 nm for hard-magnetic Nd2Fe14B phase. The desired microstructure results in a larger coercivity (Hci = 4.1 kOe) and higher saturation magnetization (Ms = 1.51 T) compared to those (Hci = 3.3 kOe and Ms = 1.35 T) of the counterpart without pre-deformation, contributing to a high energy density of 26.3 MGOe. This energy density is 200% larger than that of the counterpart without pre-deformation and far beyond that (around 20 MGOe) of previously reported bulk Nd2Fe14B/α-Fe nanocomposites with Vα-Fe ≥ 20 wt%. The superior property stems from the purposely introduced low-temperature pre-deformation that changed the structure and local chemistry of the amorphous alloy, facilitating the decomposition of harmful metastable phases and the formation of Nd2Fe14B phase during annealing processes, which lowers the temperature, from 750 to 700 °C for producing the Nd2Fe14B/α-Fe nanostructure and thus yields ultrafine nanograins. These results demonstrate an effective means to prepare high-performance bulk Nd2Fe14B/α-Fe nanocomposite magnets.

Keywords

• Permanent magnetic materials
• Nd-Fe-B magnets
• Bulk nanocomposite magnets
• Pre-deformation
• High energy density
• Metastable phases