Bendable bulk metallic glass: Effects of a thin, adhesive, strong, and ductile coating

Jinn P. Chu, J. E. Greene, Jason S.C. Jang, J. C. Huang, Yu Lin Shen, Peter K. Liaw, Yoshihiko Yokoyama, Akihisa Inoue, T. G. Nieh

Research output: Contribution to journalArticle

55 Citations (Scopus)

Abstract

We demonstrate, for the first time, that a thin, strong, ductile, and adhesive coating renders bulk metallic glasses (BMGs) bendable. The bending ductility of 3 mm thick BMGs, Zr 50Cu 30Al 10Ni 10 in this case, can be dramatically enhanced from ∼0% to ∼13.7% by the deposition of a thin bilayer film on the tensile side of the BMG sample. The bilayer, consisting of a 25 nm thick Ti adhesive layer with a 200 nm thick metallic glass (MG) overlayer, exhibits the required synergistic combination of good adhesion, high strength, and ductility compared with other single-layer films examined (Ti, TiN, and MG). Cross-sectional scanning and transmission electron microscopy, together with finite element modeling, reveal that the bilayer coating absorbs deformation while allowing more homogeneous formation of a high density of smaller shear bands at the bilayer/BMG interface. The bilayer coating, in turn, covers surface weak points and minimizes the formation of localized shear bands which lead to catastrophic failure under bending. As a result, the average shear-band spacing in bilayer-coated BMGs is small, 54 μm, and approximately equal to that found in bendable, 450 μm thick, MG ribbons. Thus, coated BMGs can accommodate large strains and overcome the MG size effect, without sacrificing their extraordinary mechanical properties. Our results for both coated and uncoated BMGs, as well as previously reported results for uncoated metallic glasses, with thicknesses ranging from ribbons to thin plates to bulk, are well described by a simple power law relationship between plastic strain to failure and shear band spacing. This scaling law may be useful in guiding future experiments toward producing more flexible BMGs.

Original languageEnglish
Pages (from-to)3226-3238
Number of pages13
JournalActa Materialia
Volume60
Issue number6-7
DOIs
Publication statusPublished - 2012 Apr 1

Keywords

  • Bending test
  • Coating
  • Metallic glasses
  • Shear bands

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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    Chu, J. P., Greene, J. E., Jang, J. S. C., Huang, J. C., Shen, Y. L., Liaw, P. K., Yokoyama, Y., Inoue, A., & Nieh, T. G. (2012). Bendable bulk metallic glass: Effects of a thin, adhesive, strong, and ductile coating. Acta Materialia, 60(6-7), 3226-3238. https://doi.org/10.1016/j.actamat.2012.02.037