Atomic scale observation of FCC phase formed symmetrically in {\(10\overline{1 }2\)} < \(\overline{1 }011\)> twin in Zircaloy-4 subjected to cyclic deformation

The formation mechanism of FCC phase on prismatic-basal (PB) interfaces in { \(10\overline{1 }2\) $10\overline{1}2$ } <  \(\overline{1 }011\) $\overline{1}011$ > twin in Zircaloy-4 under cyclic deformation at the strain level of 1.0% was systematically investigated by using transmission electron microscopy. Results showed that { \(10\overline{1 }2\) $10\overline{1}2$ } <  \(\overline{1 }011\) $\overline{1}011$ > twin was presented in α-Zr grain and PB interfaces can be introduced into the twin boundaries. Under cyclic stresses, the emission of 1/3[ \(0\overline{1 }10\) $0\overline{1}10$ ] and 1/3 \([01\overline{1 }0]\) $[01\overline{1}0]$ Shockley partial dislocations would be initiated on the PB interfaces of the twin and slipped symmetrically on every other ( \(0001\) $0001$ ) planes of the twin, resulting in the HCP → FCC phase transformation. Moreover, when the shear stresses were large enough, 1/6 <  \(\overline{1 }\overline{1 }2\) $\overline{1}\overline{1}2$ > Shockley partial dislocations were activated during cyclic deformation and the formation of { \(111\) $111$ } SFs in FCC phase was presented.