Structure evolution of Y₂O₃ nanoparticle/Fe composite during mechanical milling and annealing

Fe-25 wt% Y₂O₃ composite powders have been fabricated by mechanical milling (MM) Fe powders of 100 μm in diameter and Y₂O₃ nanoparticles in an argon atmosphere for the milling periods of 4, 8, 12, 24, 36, and 48 h, respectively. The features of these powders were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe micro analyzer (EPMA) and transmission electron microscopy (TEM). The experimental results showed that the mean particle size and crystalline size of MM powders decreased with the milling time increasing. All the elements distributed homogenously inside the powders after 48 h of MM. The lattice constant of the matrix α-Fe kept constant with the milling time, and no solid solution took place during MM process. After 8 h of MM, the α-Fe in each powder became nanocrystalline. After 48 h of MM, Y₂O₃ changes from nanostructure into amorphous structure, and the crystalline size of α-Fe further decreased to 10 nm. The Y₂O₃ in the powders mechanically milled for 48 h kept the amorphous structure after being annealed at 400 °C, and starts to crystallize when the powders are annealed at 600 °C. The amorphous Y₂O₃ contains a small amount of Fe, and crystalline FeYO₃ appears at 800 °C.