Forming asymmetric tilt interfaces on the distorted 10(1)over-bar1 twin boundaries near fracture in Mg-RE based alloys

SH Lv and W Sun and YL Zhu and P Chen and X Qiu and Q Yang, JOURNAL OF ALLOYS AND COMPOUNDS, 1047, 184935 (2025).

DOI: 10.1016/j.jallcom.2025.184935

Generally, symmetric interfaces act as the boundaries of twins. However, a similar to 48 degrees/82 degrees asymmetric tilt interface dominated the boundaries of the distorted 101 twin plates near fracture in Mg-RE based alloys. Their atomic structures were revealed using aberration- corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). An array of misfit dislocations can be observed on these boundaries, but their Burger vectors, b(6/8), seems to be zero. Indeed, these boundaries are consisted of many jaggedly distributed similar to 48 degrees/82 degrees asymmetric tilt interfaces, which are deviated by similar to 5 degrees from the 1011M or 1011T plane, and in some cases, ultra-short distorted 1011 twin boundary (TB) debris could be discovered between similar to 48 degrees/82 degrees asymmetry tilt interfaces. Therefore, the similar to 48 degrees/82 degrees asymmetric tilt interfaces can be deduced to be transformed from the 101 1 coherent TB (CTB). Based on analyzing energy barriers for nucleating a new facet interface from the initial flat boundary, the formation of the 48 degrees/82 degrees and 37 degrees/93 degrees asymmetric tilt interfaces would not lead to, at least, an increase on the distortional filed energy, while only forming the former could decrease the interfacial energy. Therefore, generating 48 degrees/82 degrees asymmetric tilt interfaces from the 1011 CTB is more energetically favorable compared with other singular interfaces under the 1014 orientation. This work provides not only a detailed explanation for the formation of the oft-reported similar asymmetric tilt grain boundaries in various Mg alloys, but also a new insight in understanding the evolutions of 1011 twins near fracture of Mg alloys.

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