Title

Metastable phase transformation and deformation twinning induced hardening-stiffening mechanism in compression of silicon nanoparticles

Abstract

The compressive mechanical responses of silicon nanoparticles with respect to crystallographic orientations are investigated by atomistic simulations. Superelastic and abrupt hardening-stiffening behaviors are revealed in [110]-, [111]- and [112]-oriented nanoparticles. The obtained hardness values of these particles are in good agreement with the experimental results. In particular, [111]-oriented particle is extremely hard since its hardness (~33.7 GPa) is almost three times greater than that of the bulk silicon (~12 GPa). To understand the underlying deformation mechanisms, metastable phase transformation is detected in these particles. Deformation twinning of the metastable phase accounts for the early hardening-stiffening behavior observed in [110]-oriented particle. The twin phase then coalescences and undergoes compression to resist further deformation, and leads to the subsequent re-hardening and re-stiffening events. The same metastable phase is also detected to form in [111]- and [112]-oriented particles. The compression of such metastable phase is responsible for their hardening-stiffening behavior. In contrast, the crystal lattice of diamond cubic silicon is merely elastically deformed when compressing along [100] direction. Throughout the simulations, no perfect tetragonal β-tin silicon phase formed due to the deconfinement status of nanoparticle comparing to the bulk silicon. A size effect on hardness of silicon nanoparticles, i.e., "smaller is harder" is also revealed.

Department(s)

Materials Science and Engineering

Comments

The authors are grateful for computer time allocation provided by the Extreme Science and Engineering Discovery Environment (XSEDE), aw ard number TG-DMR140008.

Keywords and Phrases

Atomistic simulation; Deformation twinning; Hardening mechanism; Metastable phase transformation; Silicon nanoparticle; Stiffening mechanism

International Standard Serial Number (ISSN)

1359-6454

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2018 Acta Materialia Inc, All rights reserved.

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