Deformation-enhanced Cu precipitation in Fe-Cu alloy studied by positron annihilation spectroscopy

The formation of Cu precipitates in Fe-1.0 wt % Cu alloy specimens enhanced by deformation has been studied by positron annihilation technique, coincidence Doppler broadening, and the positron lifetime method. In the alloy specimens quenched and 20% rolled at room temperature, the formation of Cu-vacancy clusters was observed, which evidenced the enhanced diffusion of Cu atoms by deformation-induced excess vacancies mobile at room temperature. By annealing up to 400°C following the deformation, vacancies and vacancy clusters were dissociated from these Cu-vacancy clusters, and ultrafine Cu precipitates coherent with the Fe matrix were formed. The increase of the hardness was also observed and was attributed to the precipitation.