Positron annihilation study of open volume defects and Cr segregation in deformed CoCrFeMnNi alloy

Abstract

The effects of thermal annealing on the evolution of vacancy-type defects and Cr segregation in deformed CoCrFeMnNi alloys were investigated using positron annihilation spectroscopy (PAS) and scanning electron microscopy with energy dispersive spectroscopy. On microstructure observation, Cr atoms tended to segregate at the grain boundaries in the CoCrFeMnNi alloy after severe plastic deformation, and after thermal annealing, the size of the Cr segregation phase gradually decreased in the range of 300–800 K, eventually dissolving in the matrix at 1300 K. Positron annihilation spectroscopy results showed that divacancy defects were formed in the deformed samples, indicating that the movement of excess vacancies caused by deformation at room temperature increases the diffusion of Cr atoms and causes Cr segregation. The quenched alloy was annealed at 600–800 K to form vacancy clusters, and with an increase in temperature, the vacancies gradually recovered and were completed at approximately 1300 K.