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 (Positron Annihilation Technology) 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 defects 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 the thermal cycle of transformation has a great effect on the ε-formation. (author)