Staged work hardening of polycrystalline titanium at low temperatures and its relation to substructure evolution

Tensile test diagrams of commercial-grade polycrystalline titanium foil are obtained in the temperature range 10–373 K, and the corresponding work hardening curves are plotted as stress versus plastic deformation, σ(εp). It is shown that the hardening curves consist of two (at low temperatures) or three (at high temperatures) fragments or stages, which are approximated by the equation σ=const+hεpn with constant rheological parameters n and h within each stage, and the empirical values of these parameters are determined over the investigated temperature range. The behavior of the hardening curves is compared with the features of the substructure evolution of the polycrystalline titanium at different stages of the plastic deformation, which are revealed by methods of electron and optical microscopy. The presence of correlations between the individual stages of the hardening and the structural states formed in the samples in the process of deformation is established. The effectiveness of the different types of substructures—ensembles of randomly distributed dislocations, reorientation bands, and twins—in the hardening of polycrystalline titanium is discussed.