Lithiation-induced tensile stress and surface cracking in silicon thin film anode for rechargeable lithium battery J. Appl. Phys. 112, 093507 (2012) Mechanical and thermal behaviors of nitrogen-doped Zr-Cu-Al-Ag-Ta--An alternative class of thin film metallic glass Appl. Phys. Lett. 101, 181902 (2012) Effect of relative humidity on crack propagation in barrier films for flexible electronics J. Appl. Phys. 112, 083520 (2012) Torsion fracture of carbon nanocoils J. Appl. Phys. 112, 084311 (2012) Additional information on J. Appl. Phys. Thin film metallic-glasses (TFMGs) are a promising structural material for fabricating the next generation of micro-and nano-devices; however, a comprehensive study is still lacking today for understanding their mechanical behaviors. In this article, we present a systematic study on the Zr 53 Cu 29 Al 12 Ni 6 TFMGs with varying thicknesses. Other than the intrinsic factor of structural amorphousness, our study pinpoints other extrinsic variables that could affect the hardness and yield strength of the TFMGs. Furthermore, the experimental results from microcompression show that the plastic flow in the TFMG-based micropillars exhibit strong sample size-and-shape dependence, which manifests as a smooth plastic deformation transition from the inhomogeneous to homogeneous mode when the TFMG-based micropillars with a submicron-scale film thickness are deformed into the shape of a low aspect ratio. V C 2012 American Institute of Physics.

In this letter, the anelastic deformation of a Zr-based metallic glass ͑MG͒ at ambient temperature is revealed through spherical nanoindentation. A general rheological model, which is linked with the atomic structure of MGs, is proposed to explain the observed anelasticity. The experimental and theoretical results clearly indicate the existence of structural inhomogeneity intrinsic to MGs, which causes the anelastic deformation upon mechanical loading under high loading rates before shear banding. The outcome of the current research provides an important insight into the property-structure relation of MGs.Since the advent of metallic glasses ͑MGs͒ in the 1960s, understanding their inelastic deformation at ambient temperature has been the issue of intense research efforts. [1][2][3][4][5][6][7][8][9] Over the past decades, a variety of deformation models have been proposed to rationalize the observed deformation phenomena in MGs, 1-4,9 which were almost built on the same notion that MGs possess intrinsic structural inhomogeneity at the atomic scale which governs their overall mechanical properties. [1][2][3][4]9 Despite the wide use of these models, however, it is still obscure how the inelastic deformation occurs in the apparent elastic deformation regime. The answer to this question is not trivial and related to the atomic packing in MGs, which is a challenging issue even today for materials scientists to resolve. 10,11 In view of these, studying the subcritical inelastic deformation events that carry structural "fingerprints" may help us decode the nature of atomic packing in MGs.To unveil the preyielding inelastic deformation mechanism, a spherical nanoindentation approach is proposed in this study. A Zr-based MG sample, which has the chemical composition of Zr 55 Pd 10 Cu 20 Ni 5 Al 10 ͑in at. %͒, was selected as the model material. Prior to the nanoindentation, the amorphous nature of the MG was confirmed using x-ray diffraction analyses ͑not shown here͒ and the sample surface was mechanically polished to a mirror finish. The nanoindentation experiments were subsequently performed with the low-load NanoIndenter system ͑Hysitron Inc., Minneapolis, MN͒ with a 5-m spherical nanoindenter, which possesses the resolutions of ϳ1 nm in displacement and ϳ1 N in load. Owing to its ultrafast data acquisition rate ͑ϳ10 000 points per second͒, unusually high loading rates can be programmed and applied during nanoindentation. With the built-in nanodynamic mechanical analysis ͑nanoDMA͒ module, the damping factor of the whole system was characterized to be around ϳ0.014 kg s −1 before nanoindentation. Such a machine damping factor will result in an 'artificial' viscosity of about ϳ0.05 MPa s when deforming the material with a microscopic dimension, which, however, is negligibly small and would not affect the experimental results as can be seen later.As shown in Fig. 1͑a͒, a trapezoidlike loading profile was programmed for the nanoindentation experiments, which consists of three segments, namely, loading, holding and unloadi...

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