Positron annihilation study of hardening in Fe-Cu alloy during low temperature aging

Yamashita, Takako*; Katsuyama, Jinya  ; Sato, Kaoru*; Mizuno, Masataka*; Araki, Hideki*; Shirai, Yasuharu*

The hardness of Fe-Cu alloys is known to increase by the precipitation of Cu clusters during thermal aging. However, the mechanism of Cu precipitation has not been clarified yet. In this study, the positron lifetime and coincidence Doppler broadening techniques have been used to investigate the recovery behavior of lattice defects such as vacancies, vacancy clusters and dislocations as well as the diffusion behavior of Cu atoms of cold rolled and thermally-aged Fe-Cu alloys. Both vacancies and dislocations caused by cold rolling were reduced through the thermally aging process. Some dislocations remained even after aging at 550C, although the vacancies almost disappeared after aging at 300C. Cu clusters precipitate mainly on the dislocations, where is the sinks of the vacancies, caused by the diffusion of Cu atom and vacancies.