Abnormal twin-twin interaction by {112¯2} twinning in [0001]-oriented micropillar of pure titanium at cryogenic temperature

Abstract

Uniaxial compression tests were performed on [0001]-oriented micropillars of pure titanium at cryogenic temperature (T = 205 K). The interaction between {$11\overline{2}2$} twin variants activated in the micropillar was investigated by transmission Kikuchi diffraction (TKD) in scanning electron microscope (SEM) and precession electron diffraction (PED) in transmission electron microscope (TEM). Critical resolved shear stress (CRSS) for {$11\overline{2}2$} twinning was estimated to be 471 $\pm$ 40 MPa. The sudden stress-drops were induced by twinning, and the subsequent stress-strain response was dependent on the twin-twin interaction. The interaction between nano-size twins resulted in the formation of abnormal twin-twin boundaries (TTBs), thereby suppressed the twin growth and reduced the twinning-induced stress-drop. The complicated twin structures led to the strain-hardening after the stress-drop.