Complex polytypes of LPSO structures in an Mg₉₂Co₂Y₆ alloy

Magnesium alloys strengthened by long-period stacking ordered (LPSO) phases have received considerable attention due to their outstanding mechanical properties and unique structural characteristics. The structures of new poly-types of LPSO phases within a Mg₉₂Co₂Y₆ alloy were studied via energy dispersive X-ray spectroscopy (EDX) and atomic resolution high-angle annular dark-field scanning transmission electron microscopy. The results of the study revealed that the 444 R LPSO phase exhibited a rhombohedral structure with the R3m space group. Its lattice parameters were found to be a = 0.321 nm and c = 115.4 nm in hexagonal coordinate. Repeated structure containing 148 layers were observed at the middle of 444 R, while various stacking faults were observed at the left and right part of 444 R structure. The EDX analysis also verified that the fluctuation of the Co/Y element in 444 R and 15 R is smaller than that in 18 R. In addition to the 444 R phases, other new types of LPSO phases, including 26 H and 10 H, were also found within the alloy, and their structures were examined.