2024年5月31日、NIMSにて、National Taiwan UniversityのProf. Jer-Ren Yangによるご講演が第154回構材ゼミとして開催されました。
Prof. Jer-Ren Yang (National Taiwan University)
BIO|Prof. Jer-Ren Yang
日時：2024年5月31日(金曜日)16:00-17:00
会場：先進構造材料研究棟 5階カンファレンスルーム
開催者：井誠一郎
（NIMS構造材料研究センター材料評価分野 微細組織解析グループ）
Abstract：
The exploration of hierarchical nanotwin structures (annealing nanotwins and deformation nanotwins)
in FCC-based high-entropy and medium-entropy alloys to achieve the excellent combination of strength and ductility.
Jer-Ren Yang
Distinguished Professor
Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan.
In FCC-based high-entropy alloys (HEAs) and medium-entropy alloys (MEAs), the presence of deformation nanotwins, formed within annealed-grain structures during severe plastic deformation, has been identified as a significant contributor to the strengthening. The lower stacking fault energies of the alloys favorably causes a change in the deformation mechanism from dislocation-slip to twinning. This presentation aims to elucidate the roles of annealing nanotwins and deformation nanotwins in an FCC-based HEA (Fe22Co22Ni20Cr22Mn14) and two MEAs (Fe27Co24Ni23Cr26 and CoNiCrSi0.3) concerning strength and ductility. Firstly, the exploration of the different-sized annealing twins in the range from sub-nanometer and nanometer to micrometer in the annealed specimens of HEA and MEAs will be illustrated. Subsequently, the deformed structures and their mechanical properties of the annealed samples subjected to the ultra-high strain rate compressive deformation (9 × 103 s −1) using a split Hopkinson pressure bar system at cryogenic temperatures will be reported and discussed.
In summary, abundant lamellar annealing nanotwins, already present within the grains of as-annealed FCC-based high- and medium-entropy alloy samples, segment the matrix grains into narrower strips, being an efficient source of grain refinement. These pre-existing annealing nanotwins and the slender matrix strips undergo further segmentation by newly-formed deformation nanotwins during severe deformation. The hierarchical nanotwin structures observed in both HEAs and MEAs hold promise for resolving the strength–ductility trade-off challenge.