Microstructural Modification of Melt-Spun Ribbons by SPS and HP Process

Abstract

High-performance Nd-Fe-B permanent magnets are indispensable for applications such as electric vehicle traction motors, wind power generators, hard disk drives, and magnetic sensors. However, the limited supply and unstable price of neodymium have prompted alternative strategies, among which partial substitution with abundant rare-earth elements such as cerium (Ce) has attracted considerable attention. Despite its abundance, Ce substitution often reduces coercivity due to the intrinsically low magnetic anisotropy of the Ce2Fei4B phase. To mitigate this drawback, the melt-spinning technique has emerged as a promising approach. By rapidly solidifying the alloy melt at cooling rates above 105-106 K/s, nanocrystalline or amorphous Nd-Ce-Fe-B ribbons are produced, with grain sizes close to the single-domain size of the NtLFewB phase (〜300 nm). Such fine grains effectively suppress reverse domain nucleation and enhance coercivity. In this study, Nd-Ce-Fe-B melt-spun ribbons were fabricated under various process parameters to control crystallinity and grain size. Following ribbon fabrication, the samples were consolidated into isotropic magnets via low-temperature spark plasma sintering (SPS) and hot press (HP). This process preserved the fine-grained microstructure by suppressing grain growth while achieving high densification. To identify the relation between grain structure and magnetic performance, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were conducted on the melt-spun ribbons. BH-tracer measurements were also performed on the sintered magnets derived from them. The findings of this work provide valuable insights into optimizing processing conditions for high-performance nanostructured Nd-Ce-Fe-B magnets with reduced neodymium content and improved thermal stability.