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Shear-Transformation Zone Activation during Loading and Unloading in Nanoindentation of Metallic Glasses

  • Using molecular dynamics simulation, we study nanoindentation in large samples of Cu–Zr glass at various temperatures between zero and the glass transition temperature. We find that besides the elastic modulus, the yielding point also strongly (by around 50%) decreases with increasing temperature; this behavior is in qualitative agreement with predictions of the cooperative shear model. Shear-transformation zones (STZs) show up in increasing sizes at low temperatures, leading to shear-band activity. Cluster analysis of the STZs exhibits a power-law behavior in the statistics of STZ sizes. We find strong plastic activity also during the unloading phase; it shows up both in the deactivation of previous plastic zones and the appearance of new zones, leading to the observation of pop-outs. The statistics of STZs occurring during unloading show that they operate in a similar nature as the STZs found during loading. For both cases, loading and unloading, we find the statistics of STZs to be related to directed percolation. Material hardness shows a weak strain-rate dependence, confirming previously reported experimental findings; the number of pop-ins is reduced at slower indentation rate. Analysis of the dependence of our simulation results on the quench rate applied during preparation of the glass shows only a minor effect on the properties of STZs.
Author:Karina E. Avila, Stefan Küchemann, Iyad Alhafez, Herbert M. UrbassekORCiD
URN (permanent link):urn:nbn:de:hbz:386-kluedo-58171
Parent Title (English):Materials
Document Type:Article
Language of publication:English
Publication Date:2019/05/07
Year of Publication:2019
Publishing Institute:Technische Universität Kaiserslautern
Date of the Publication (Server):2019/12/17
Issue:2019, 12 (9)
Number of page:17
Faculties / Organisational entities:Fachbereich Physik
DDC-Cassification:5 Naturwissenschaften und Mathematik / 530 Physik
Licence (German):Zweitveröffentlichung