Electron-microscopy investigations of microstructure in Fe-Nd alloys

The microstructure of hyper- and hypoeutectic as-cast and heat treated Fe-Nd alloys is investigated by using optical and high-resolution electron microscopy technique. The mixture of b-Nd and nanocrystalline regions Ax phase with size 10-50 nm are observed within amorphous-like areas. This areas constitute the fine globular eutectic with alternate crystalline Nd areas. Information from HREM images and SAED patterns indicates an ordering of Ax phase by type AB (L1.0 structure) or AB3 (L1.2 structure). The Ax phase is found the same as the well known highly anisotropic A1 phase in Fe-Nd and Nd-Fe-B alloys. The source of high coercivity of Fe-Nd alloys and a hypothetic scheme of the metastable Fe-Nd diagram, which explain the formation of metastable phases are suggested. (orig.)