Nanoindentation creep behavior of Cu–Zr metallic glass films

Abstract

The size-dependent hardness, strain-rate sensitivity (SRS) and shear transformation zone (STZ) volume of co-sputtered Cu-Zr metallic glass films with film thickness h spanning from 1000 to 3000 nm were systematically investigated by nanoindentation creep tests at room temperature. Experimental results manifested an exceptional decrease in hardness and a monotonic increment in SRS (or a monotonic decline in STZ volume) with reducing h. The deformation mechanism could be rationalized in light of more free volume combined with smaller STZs in thinner films, which likely trigger the strain-softening behavior. Moreover, STZs and deformation-induced devitrification promote the homogeneous-like plastic flow. IMPACT STATEMENTEmploying nanoindentation creep tests revealed size-dependent hardness and strain-rate sensitivity in metallic glass films, enabling comprehensive understanding of the deformation mechanism based on atomic-scale shear transformation zone theory. ARTICLE HISTORY

High-Temperature Nano-Indentation Creep of Reduced Activity High Entropy Alloys Based on 4-5-6 Elemental Palette

“…The decrease of n value with increasing temperature is due to the enhancement of dislocation movement and more thermal recovery at a higher temperature compared to their generation [17]. A similar trend was reported for other alloys [28,37]. The significantly larger drop in stress exponent with increasing temperature for HEAs may be due to less dislocation movement in their highly distorted lattice structure at room temperature leading to a high n value.…”

On the origin of softening in the plastic deformation of metallic glasses

“…These results prove that nanoindentation is an effective technique in revealing the creep mechanisms of engineering materials (Gan and Tomar, 2010;Su et al, 2013;Zhang et al, 2017b). As nanoindentation creep is performed immediately following a loading stage during which the maximum creep load is reached at different loading rates, the loading rate-dependent creep behaviors of various materials are systematically characterized to understand their plasticity mechanisms (Lee et al, 2016;Liu et al, 2015;Tehrani et al, 2011;Wang et al, 2010Wang et al, , 2018b. Enlightened by the nanoindentation creep technique, since the deformation in the creep stage of normal nanoindentation with different loading rates adopted in the loading stage is believed to stem from the "delayed plasticity" from the loading stage of nanoindentation (Klaumünzer et al, 2011;Schuh and Nieh, 2003), revealing the origin and the dynamics of the deformation in the creep stage of nanoindentation with different loading rates adopted in the loading stage should also bring out new understandings on the plasticity mechanisms of engineering materials.…”

“…What's more, as mentioned above, the creep stage of nanoindentation characterizes the "delayed plasticity" of materials being plastically deformed underneath the indenter, and thus depends intimately on the softened deforming state of the MGs in the loading stage, providing a critical resort to examining "quasi in-situ" the softening effect in the plastic deformation of MGs, unlike the post-mortem tests having been done previously (Pan et al, 2018). For the complicated stress state under the indenter and utilizing the absence of dilatation in crystalline structures, a systematic study on the MGs before and after crystallization is necessary to thoroughly understand the plastic deformation of MGs in nanoindentation (Burgess and Ferry, 2009;Castellero et al, 2008;Kramer et al, 2018;Wang et al, 2018b;Yang et al, 2016b).…”

Nanoindentation Investigation on the Size-Dependent Creep Behavior in a Zr-Cu-Ag-Al Bulk Metallic Glass

“…As with most nanoindentation creep experiments, creep behaviors were detected in plastic regions by adopting a three-sided pyramidal, namely a Berkovich indenter. Wang et al performed creep tests in Cu-Zr films with thicknesses from 1000 to 3000 nm [18], while Ma et al investigated creep behaviors in 500-1500 nm Cu-Zr-Al films [19]. Creep features in Ni-Nb thin films and ribbons were also compared by Ma [20].…”