In situ SEM nanoindentation characterization of quasi-isotropic and anisotropic three phase eutectic grains

Wissuchek F., Doğan G., KAPLAN D., Yürük A. E., ŞEREFOĞLU KAYA M., Misra A.

Materials Characterization, cilt.240, 2026 (SCI-Expanded, Scopus)

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 240
  • Basım Tarihi: 2026
  • Doi Numarası: 10.1016/j.matchar.2026.116783
  • Dergi Adı: Materials Characterization
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Chemical Abstracts Core, Chimica, Compendex, INSPEC, Academic Search Ultimate (EBSCO), Engineering Source (EBSCO)
  • Anahtar Kelimeler: Directional solidification, Eutectic microstructure, Nanoindentation, Phase boundary energy anisotropy, Pile-up
  • Marmara Üniversitesi Adresli: Evet

Özet

This study investigates the relationship between phase morphology, microstructure, and hardness in a three-phase In-Bi-Sn eutectic alloy exhibiting non-uniform pile-up during nanoindentation. The alloy at the ternary eutectic point was solidified using rotating directional solidification (RDS), producing concentric quasi-isotropic and anisotropic grains. The anisotropic grain, called Laminated Matrix with Rods (LMR), has three unique microstructural states as a function of rotation angle. Two of the states are classified as 2D and one as 3D based on the phase continuity through the thickness of the sample. Hardness measurements were conducted in both grains using nanoindentation, while in situ and post mortem SEM imaging enabled phase-level characterization and direct measurement of projected contact areas. Results showed differences in hardness among the constituent phases, namely β(In), In2Bi, and γ(Sn), and among the microstructural states, with the 3D LMR state exhibiting hardness 15% higher than any of the 2D states. Non-uniform pile-up was observed around indents spanning multiple phases, driven by the large disparity in hardness and the propensity for the soft β(In) phase to extrude from the microstructure. The pile-up and plastic zone morphology were strongly governed by the spatial arrangement and connectivity of the phases.