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

Annealed and quenched epsilon-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 epsilon-powders was identified as epsilon'-Fe3N type (space group P6(3)22), and no other type of superstructure was observed. gamma'-Fe4N nitride precipitated from epsilon 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 gamma' and epsilon 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 gamma' grains with respect to the parent epsilon grains. (c) 2006 Springer Science + Business Media, Inc.