Stacking faults and growth twins in long-period stacking ordered structures in a near-equilibrium Mg97Zn1Y2 alloy

We investigated the structure, symmetry, and distribution of stacking faults and growth twins in 18R and 14H long-period stacking ordered (LPSO) structures in a near-equilibrium Mg97Zn1Y2 (at.%) alloy by transmission electron microscopy. The stacking faults and growth twins here result from the insertion of the n-Mg components in the LPSO structure, and some of them possess inversion centers or mirror symmetry. The stacking faults and growth twins in 18R LPSO depend on whether the sum of inserted Mg layers of all n-Mg components in defects is even number or odd number, respectively, while only stacking faults appear in 14H LPSO. The gliding of Shockley partial dislocation pairs induces the transformation of stacking faults and motion of twin boundary. Statistically, the periodical arrangement of stacking faults in 18R or 14H LPSO structures results in the formation of superstructures, such as 62L, 86L, 152L, and 235L. •The structure, symmetry, and distribution of SFs and growth twins in LPSO structures in a Mg-Zn-Y alloy was characterized.•Shockley partial dislocation pairs play a crucial role in the transformation between SFs and the motion of twin boundaries.•Superstructures formed via the statistically periodical distribution of stacking faults in 18R or 14H LPSO structures.