Strain hardening and jump-like deformation of ultra-fine grained polycrystals of Al-Li solid solution at temperature 0.5 K

The effect of microstructure formed by severe plastic deformation (SPD) and annealing on strain hardening and jump-like deformation of Al-Li alloy is studied. It is shown that SPD processed polycrystals in the course of tension at 0.5 K retain considerable strain hardening rate and possess high strength and ductility. At the same time the SPD stimulates the unstable (jump-like) flow of polycrystal caused by dislocation dynamic which is revealed as stress jumps in tension curve. The average jumps amplitude increases with deformation, whereas the amplitude distribution corresponds to the collective motion of dislocation avalanches of predominantly scale. After a high-temperature annealing the jump-like deformation mode is partially suppressed whereas the jumps amplitude distribution is described by power law. The observed correlation between the mean coefficient of strain hardening and the average stress jump amplitude imply the common dislocation-dynamic nature of strain hardening and jump-like deformation at low temperatures. The detected peculiarities of low-temperature plastic deformation are considered due to grain size and dislocation density changes during SPD processing and annealing.