Abstract:Lamellar structure in long range ordered δ′-TiN _0.5 phase was analyzed by transmission electron microscopy (TEM), and the crystallographic properties of the lamellar structure were discussed in terms of the crystal symmetry changes before and after transformation. It was shown that the lamellar structure is formed, at least locally, by plate pairs of any two of the three equivalent orientation variants. The interfaces between domain plates are always parallel to {011} M planes of the matrix, but there are only two possibleequivalent orientations for any domain pair. During ordering transformation, the transformed products grow along the normal directions of the plates by way of combination of the two plates which form a domain pair, and this gives rise to the final lamellar structure in δ′-TiN _0.5 phase. Such lamellar structure may considerably reduce the elastic energy accumulated in the matrix around the precipitates during transformation.

Key words: lamellar structure δ′-TiN _0.5 long range ordering transformation