Exploring size effect phenomena in Zr65Ni35 thin film metallic glasses
(2013) 20th International Symposium on Metastable, Amorphous and Nanostructured Materials — Location: Torino (Italy) (30.June.2013)
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- Bulk metallic glasses (BMGs) are known for their superior mechanical properties with respect to their crystalline counterparts owing to a high hardness and yield strength close to the theoretical limit, as well as to a large elastic deformation (around 2%) [1]. Nevertheless, the shear band instability that occurs during plastic deformation of BMGs leads to a macroscopic brittle behaviour, thus significantly undercutting structural applications [1]. Facing this issue, research is moving toward thin film metallic glasses (TFMGs) in order to investigate size-effects: namely a brittle-to-ductile transition below a thickness threshold [2]. Most size-effects studies are dealing with compression test of FIB-milled micro-pillars, reporting a correlation between the reduced size and several mechanical properties [3]. However, most of these results are inconsistent. Here, we present a detailed study of size-effects occurring in Zr65Ni35 TFMGs deposited by DC magnetron sputtering with thickness ranging from 900 nm down to 100 nm. A composite sputtering target – in which pure grade Ni slices are inserted in a Zr high purity matrix – has been designed to tune the composition. The structural investigation of Zr65Ni35 TFMGs has been carried out by x-ray diffraction (XRD) and transmission electron microscopy (TEM) showing the absence of crystalline phase. The effect of thickness on the mechanical behaviour of Zr65Ni35 TFMGs has been investigated by nanoindentation and Brillouin spectroscopy, and the TFMGs fracture surface after rupture test by scanning electron microscope (SEM). While nanoindentation and Brillouin spectroscopy show limited variations of the hardness and elastic modulus as a function of the thickness, the fracture surface analysis shows a dramatic change for thickness below 500 nm wherein the characteristic vein pattern is no more present. This transition – observed for the first time for TFMGs – has been thoroughly analysed with respect to crack propagation in metallic glasses. Based on the obtained results, we provide an effective analysis of size-effects for Zr65Ni35 TFMGs.
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Ghidelli, M., Volland, A., Blandin, J.-J., Pardoen, T., Raskin, J.-P., Mompiou, F., Djemia, P., & Gravier, S. (2013). Exploring size effect phenomena in Zr65Ni35 thin film metallic glasses. 20th International Symposium on Metastable, Amorphous and Nanostructured Materials, Torino (Italy). https://hdl.handle.net/2078.5/231728