X.H. Shao

Interplay between deformation twins and basal stacking faults enriched with Zn/Y in Mg97Zn1Y2 alloy

Basal stacking faults (SFs) enriched with Zn/Y are identified in an Mg97Zn1Y2 alloy, and the interaction between SFs and {} deformation twins (DTs) is characterized at the atomic scale by means of high-resolution transmission electron microscopy. Such an interaction results in deviations of twin angle from its theoretical value and twin boundary (TB) from its () habit plane. In addition, the DT-SF reaction not only leads to the TB with terraces along basal planes, but also makes the TB broaden with severe distortion. The role of long-period stacking ordered lamellae in propagation of DTs is also clarified based on the atomic-scale high-resolution images.

New polytypes of LPSO structures in an Mg–Co–Y alloy

Abstract The magnesium alloys containing long-period stacking ordered (LPSO) structures exhibit excellent mechanical properties. Each LPSO structure is known to contain either AB′C′A or AB′C building block and feature its own stacking sequences. By atomic-scale high-angle annular dark field scanning transmission electron microscopy, we find the co-existence of AB′C′A and AB′C building block in a single LPSO structure of the as-cast Mg92Co2Y6 (at.%) alloy, leading to the formation of six new polytypes of the LPSO structures determined as 29H, 51R, 60H, 72R, 102R and 192R. The lattice parameter of each LPSO structure is derived as and (n presents the number of basal layers in a unit cell). The stacking sequences and the space groups of these newly identified LPSO structures are proposed based on the electron diffraction and atomic-scale aberration-corrected high-resolution images. A random distribution of Co/Y elements in the basal planes of AB′C′A and AB′C structural units is also observed and discussed.

Unravelling the local ring-like atomic pattern of twin boundary in an Mg-Zn-Y alloy

ABSTRACT Understanding the interactions between deformation twins and plate-like phases in magnesium alloys is one of the key issues to tailor the microstructure of magnesium alloys for better mechanical properties. The {102} twin boundary with the local ring-like atomic pattern in magnesium alloy, accompanied by the interaction between deformation twin and solute atoms, has been investigated using aberration-corrected scanning transmission electron microscopy. We found that these boundaries featured local overlapping morphology near the intersection between deformation twins and stacking faults (SFs) enriched with solute atoms. The overlapping morphology is proposed to be induced by the asynchronous shuffling of the SFs and matrix during the twinning. The local ring-like atomic patterns shown here imply that the shearable specific SFs in magnesium alloys will increase twinning energy and resultantly hinder twinning propagation.

New polytypes of long-period stacking ordered structures in a near-equilibrium Mg97Zn1Y2 alloy

Abstract By atomic-scale high-angle annular dark-field scanning transmission electron microscopy, the long-period stacking ordered (LPSO) structures in a near-equilibrium Mg97Zn1Y2 (at.%) alloy have been characterised. In addition to 18R and 14H, new polytypes of LPSO structures are analysed and determined as 60R, 78R, 26H, 96R, 38H, 40H, 108H and 246R. All of these LPSO structures feature AB′C′A building blocks with two Mg layers and three Mg layers sandwiched between them. The Bravais lattices and space groups of new polytypes of LPSO structures were easily determined via the newly introduced method. A structural relationship between the LPSOs is proposed.