Nanocrystalline Fe84Nb7B9 alloys prepared by mechanical alloying and ultra-high-pressure consolidation

Nanocrystalline soft magnetic alloys such as Nanoperm have attracted a great deal of attention over the past 10 years. In the present paper, the mechanical alloying process followed by ultra-high-pressure consolidation was used to produce nanocrystalline Nanoperm (Fe84Nb7B9) alloy. An elemental powder mixture of Fe84Nb7B9 (in at.%) was milled in a planetary ball mills. The structural evaluation of the powder during alloying was studied with the use of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the average grain size of the milled powder was about 5.5 nm after milling for 35 h and it accorded with the relation: D = Kt−0.6, where D is the average grain sizes, t the milling time, and K is a coefficient. Subsequently, the milled powder was consolidated under a high pressure (5.5 GPa). The XRD investigations of the consolidated samples revealed that after consolidating, the bulk samples remained nanocrystalline with grain size about 8–10 nm and there is no phase change during consolidating. The relative density of the bulk sample was about 98.3%. The spontaneous magnetization Ms and coercivity Hc of the bulk sample was 155 emu/g and 360 A/m, respectively. The high coercivity is mainly due to the internal strain and anti-size defects developed during mechanical alloying and consolidation. In addition, the coercivity Hc decreased to 120 A/m after annealing at 350 °C for 30 min. On the basis of the results of the present study, the mechanical alloying technique accompanied by ultra-high-pressure consolidation can provide powerful tools for the fabrication of nanocrystalline materials.