title: Microstructure study of a severely plastically deformed Mg-Zn-Y alloy by application of low angle annular dark field diffraction contrast imaging.
abstract: Microstructural investigation of extremely strained samples, such as severely plastically deformed (SPD) materials, by using conventional transmission electron microscopy techniques is very challenging due to strong image contrast resulting from the high defect density. In this study, low angle annular dark field (LAADF) imaging mode of scanning transmission electron microscope (STEM) has been applied to study the microstructure of a Mg-3Zn-0.5Y (at%) alloy processed by high pressure torsion (HPT). LAADF imaging advantages for observation of twinning, grain fragmentation, nucleation of recrystallized grains and precipitation on second phase particles in the alloy processed by HPT are highlighted. By using STEM-LAADF imaging with a range of incident angles, various microstructural features have been imaged, such as nanoscale subgrain structure and recrystallization nucleation even from the thicker region of the highly strained matrix. It is shown that nucleation of recrystallized grains starts at a strain level of revolution [Formula: see text] (earlier than detected by conventional bright field imaging). Occurrence of recrystallization of grains by nucleating heterogeneously on quasicrystalline particles is also confirmed. Minimizing all strain effects by LAADF imaging facilitated grain size measurement of [Formula: see text] nm in fully recrystallized HPT specimen after [Formula: see text].
authors.affiliation: Structural Materials Unit, National Institute for Materials Science , Sengen 1-2-1, Tsukuba , 305-0047 Japan .
authors.forename: Dudekula Althaf
authors.initials: DA
authors.lastname: Basha
authors.affiliation: Erich Schmid Institute of Materials Science, Austrian Academy of Sciences , Austria .
authors.forename: Julian M
authors.initials: JM
authors.lastname: Rosalie
authors.affiliation: Structural Materials Unit, National Institute for Materials Science , Sengen 1-2-1, Tsukuba , 305-0047 Japan .
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Somekawa
authors.affiliation: Structural Materials Unit, National Institute for Materials Science, Sengen 1-2-1, Tsukuba, 305-0047Japan.; Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8577Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Miyawaki
authors.affiliation: Structural Materials Unit, National Institute for Materials Science , Sengen 1-2-1, Tsukuba , 305-0047 Japan .
authors.forename: Alok
authors.initials: A
authors.lastname: Singh
authors.affiliation: Structural Materials Unit, National Institute for Materials Science, Sengen 1-2-1, Tsukuba, 305-0047Japan.; Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8577Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Tsuchiya
keywords: 10 Engineering and structural materials; 106 Metallic materials; 503TEM, STEM, SEM; LAADF; STEM; diffraction contrast; high pressure torsion (HPT); recrystallization; severe plastic deformation (SPD)