Temperature-induced twinning mechanism transformation and strain hardening behavior of pure rhenium in compression

This work investigates the activation twinning mechanism at different temperatures and its role on the strain hardening in rhenium. The microstructure of compression at 200 °C to 1000 °C was analyzed using electron back scattered diffraction (EBSD). Only {11 2 ¯ 1} twins were activated during compression at 200 °C. {10 1 ¯ 2} twins were observed during compression at 400 °C, and its number increased with increasing temperature. The strain hardening rate (SHR) could be classified into multiple plastic deformation stages governed by twin-induced geometrical hardening and softening, and grain boundary strengthening. The preferentially activated {11 2 ¯ 1} twin variants usually conform to Schmidt law and contribute to grain refinement and grain boundary strengthening, inducing localized geometrical hardening. In contrast, the subsequently activated {10 1 ¯ 2} twin variants released the local high stresses and decreased SHR, in contrast to the regularity of other HCP metals. Whether the selective behavior of the {10 1 ¯ 2} twin variants conform to Schmidt law were dependent on the local stress. A large number of {10 1 ¯ 2} twins with negative Schmidt factors were activated to accommodate stress compatibility at grain boundaries and {11 2 ¯ 1} twin boundaries. As the deformation temperature increases, it was more likely to activate {10 2 ¯ 2} twins with negative Schmidt factor at grain boundaries and {11 2 ¯ 1} twin grain boundaries to accommodate local stress compatibility.