A study of defect sub-structures in the Fe–Cr sigma phase by means of transmission electron microscopy

Abstract

A number of defect sub-structures have been observed directly by means of transmission electron microscopy in thin foils of the Fe–Cr σ phase prepared from the bulk material. These defects for the most part consist of faults lying on (100) and (010) planes and which have been identified as sequence faults. Certain modifications of this basic configuration however do exist and have been considered in detail. No glissile dislocations have ever been observed, although sessile Frank partial dislocations which act as termini for sequence faults have been seen. This behaviour has been tentatively associated with the difficulty that Kronberg's zonal dislocations may encounter in moving through the ordered Fe–Cr σ phase structure. All of the sub-structures observed in the σ phase are postulated to arise during the course of its transformation from the ferrite phase.