Crystallization behavior in two-phase PrFeB mechanically milled powder

In this research, PrFeB-based mechanically milled powders are studied with emphasis on the microstructure peculiarities, phase transformations and their relation with the magnetic properties. X-ray diffraction data of Pr₉Fe₈₅B₆ and Pr₉DyFe₇₆Co₈SiB₅ powders milled for 4 h reveal a structure free of long range crystallographic ordering. Annealing at 400°C (27 h), 500°C (30 min), and 680°C (150 min) is done for the mechanically milled powders. Results show that a well-defined nanophase structure is developed by annealing above 500°C. HRTEM micrographs in as-milled powder reveal the presence of bcc (Fe, Co) phase with an average grain size of about 10-15 nm, and an amorphous phase. Annealing the powder at temperatures as high as 400°C still does not release the internal stress caused by the energetic collision of the powder particles during milling. The microstructure becomes free of internal stresses and completely crystallizes at 650°C.