Metastable phase transformation and deformation twinning induced hardening-stiffening mechanism in compression of silicon nanoparticles
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 -, - and -oriented nanoparticles. The obtained hardness values of these particles are in good agreement with the experimental results. In particular, -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 -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 - and -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  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.
Y. Hong et al., "Metastable phase transformation and deformation twinning induced hardening-stiffening mechanism in compression of silicon nanoparticles," Acta Materialia, vol. 145, pp. 8-18, Acta Materialia Inc, Feb 2018.
The definitive version is available at https://doi.org/10.1016/j.actamat.2017.11.034
Materials Science and Engineering
Keywords and Phrases
Atomistic simulation; Deformation twinning; Hardening mechanism; Metastable phase transformation; Silicon nanoparticle; Stiffening mechanism
International Standard Serial Number (ISSN)
Article - Journal
© 2018 Acta Materialia Inc, All rights reserved.