Transmission electron microscopy study on the superstructure and the precipitation of γ -Fe4N in initially homogeneous ε-iron nitride powders

Annealed and quenched ε-Fe2−3N powders with an initially homogeneous composition of Fe3N1.0 were studied by transmission electron microscopy (TEM). TEM specimens were successfully prepared from the powder using a sandwiching technique. The superstructure in ε-powders was identified as ε -Fe3N type (space group P6322), and no other type of superstructure was observed. γ -Fe4N nitride precipitated from ε powders as individual grains during the annealing process, which is different from the typical fine lamellar structure observed in bulk iron-nitride samples. The observed orientation relationships between γ and ε grains are also different from that reported in the lamellar structure of bulk iron-nitride samples. This suggests that in the powder investigated by us there is no one specific orientation of the precipitated γ grains with respect to the parent ε grains. C 2006 Springer Science + Business Media, Inc.