Direct observations of multi-cyclic nanoindentation-induced phase transformations in single-crystal Ge

Koji Kosai, Jiwang Yan

Research output: Contribution to journalArticle

Abstract

Multi-cyclic nanoindentation experiments with various holding loads were carried out on single-crystal Ge to investigate pressure-induced phase transformation behaviors. Cross-sectional transmission electron microscopic observation and laser micro-Raman spectroscopy of the indents revealed various phase transformation behaviors at different holding loads. Distinctive phase transformation behaviors were observed under various loading and unloading conditions. With a low holding load, a broad phase transformed region containing r8-Ge phase and dislocations was generated. A middle holding load promoted twinning but limited phase transformations. On the other hand, a densely transformed region containing dc-Ge, a-Ge, r8-Ge and st12-Ge was widely formed at a high holding load. In addition, the calculation results of the average contact pressure in the last unloading step verified the occurrence of these phase transformations. By integrating these results, a path diagram for phase transformations of single-crystal Ge during multi-cyclic nanoindentation was established, which is useful for understanding the subsurface damage formation in mechanical processing of the material.

Original languageEnglish
Article number075065
JournalMaterials Research Express
Volume6
Issue number7
DOIs
Publication statusPublished - 2019 Apr 24

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Keywords

  • cyclic load
  • mechanical processing
  • microstructural change
  • nanoindentation
  • phase transformation
  • single-crystal germanium
  • subsurface damage

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Surfaces, Coatings and Films
  • Polymers and Plastics
  • Metals and Alloys

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