Positron annihilation study of defects in martensite transformation of FeMn alloy

It has been observed that a small number of repetitions of the transformation by thermal cycling enhanced the formation of ϵ‐Martensite whereas a large number of repetitions of transformation decreased the amount of ϵ‐Martensite formed. PAT analysis and electron microscope show that a few repetitions of the transformation produced less defects, including vacancies and dislocations, whereas a large number of repetitions of transformation produced progressively more defects. The PAT analysis also shows that these accumulated defetcs are mainly dislocations, which form a network of dislocations or a Lomer‐Cottrell dislocation net. A small number of dislocations enhanced the nucleation of ϵ‐Martensite whereas a large number of dislocations prevented the nucleation. So the dislocations‐produced by cycling transformation thermally — has a great effect on the ϵ‐formation.