Positron lifetime investigation of Ni–W and Cu–Cr–Zr alloys after severe plastic deformation and annealing

Positron annihilation lifetime spectroscopy was used to investigate the microstructure of commercial Cu–Cr–Zr and Ni–W ultrafine-grained alloys processed by severe plastic deformation namely equal channel angular pressing, accumulative roll bonding and groove pressing and annealing at 600, 900 and 1000°C. All the lifetime spectra bear the same trends and were a sum of three exponential decay components. The dominant vacancy/dislocations component lifetime changed considerably and dropped after high temperature annealing. Positron lifetime spectroscopy results correlated well with microhardness measurements. The results suggest the presence of three stages in Cu–Cr–Zr and Ni–W industrial alloys which were attributed to dislocations storage through severe plastic deformation, recovery-recrystallization and grain growth. Graphical abstract