Microstructural study of long-range-ordered phase delta'-TiN 0.5 by transmission electron microscopy

The microstructure of the long-range-ordered delta'-TiN x phase was studied using transmission electron microscopy. The ordered phase presented a fine lamellar structure. The lamellar structure was formed by two of the three equivalent orientation variant plates. The crystallographic characteristics of the lamellar structure were discussed in terms of the crystal symmetry changes from disordered delta-TiN0.5 to ordered delta'-TiN0.5. The interfaces between domain plates are always parallel to{011}M planes of the matrix, but there are only two possible equivalent orientations for any domain pair. During ordering transformation, the transformed products grow along the normal directions of the plates by combination of the two plates which form a domain pair, and this gives rise to the final lamellar structure in the delta'-TiN0.5 phase. This lamellar structure may considerably reduce the elastic energy accumulated in the matrix around the precipitates during the transformation.