Formation Process of Long-Period Stacking-Ordered Structures in Mg₉₇Zn₁Y₂ Alloy Comprising HCP and Cubic Phases Fabricated by High-Pressure High-Temperature Annealing

• Main Authors: Atsuki Yokota, Masafumi Matsushita, Naruhito Geshi, Daiki Yamasaki, Toru Shinmei, Michiaki Yamasaki, Yoshihito Kawamura
• Format: Article
• Language: English
• Published: MDPI AG 2021-06-01
• Series: Metals
• Subjects: Mg–Zn–Y ternary alloys; long-period stacking-ordered structure; high-pressure treatment; X-ray diffraction; transmission electron microscopy
• Online Access: https://www.mdpi.com/2075-4701/11/7/1031

As-cast Mg₉₇Zn₁Y₂ alloy consists of α-Mg matrix and 18R-type long-period stacking-ordered (LPSO) structures. We observed that the alloy undergoes a phase transformation to D0₃ superlattices and α-Mg matrix due to high-pressure high-temperature (HPHT) annealing at 3 GPa and above 773 K. Further, the alloy recovered after HPHT annealing, consisting of the α-Mg matrix and D0₃ superlattices, transformed into 18R-type LPSO structures during further annealing at ambient pressure. An fcc structure with a lattice parameter of 1.42 nm, which was twice that of D0₃, emerged in both the collapse process of the 18R-type LPSO structure under high-pressure, and the formation process of the 18R-type LPSO structure at ambient pressure. This fcc phase was an intermediate structure between 18R-type LPSO and D0₃. From the electron diffraction results, it is considered that 18R-type LPSO is continuously present with 2H including stacking faults, which almost corresponded with previous studies.