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.