Nanoindentation study of size effect on shear transformation zone size in a Ni–Nb metallic glass

A B S T R A C TUniaxial tension and compression experiments were performed on a typical Zr 52.5 Cu 17.9 Ni 14.6 Al 10 Ti 5 (Vit 105) bulk metallic glass over a wide range of strain rates at room temperature. It is found that the strain rate effect of the yielding strength will change from insensitive to negative with increasing strain rate above a critical value. This phenomenon can be quantitatively described by a modified cooperative-shear model of shear transformation zones that takes the adiabatic temperature rise into account. The model predicts well the present and other experimental data.

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“…However, the work of Pan et al [14] showed a positive rate sensitivity. Similar inconsistent results have been also reported [15][16][17].…”

Section: Introductionsupporting

confidence: 83%

Effect of strain rate on yielding strength of a Zr-based bulk metallic glass

Jiang

Yang

et al. 2017

Materials Science and Engineering: A

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“…For example, Xue et al [12] reported a positive strain rate dependence of the hardness and ascribed this correlation to the stronger strain rate softening effect under lower strain rates. There are also analogous inconsistent results, but the underlying mechanism has been rarely shed light on [13][14][15][16][17]. In addition, Bhattacharyya et al [6] demonstrated a lower strain rate sensitivity of the hardness under a higher peak-load, but the results of Ma et al [17,18] showed a much more positive rate sensitivity when the peak-load increased by 1 order of magnitude.…”

Section: Introductionmentioning

confidence: 98%

“…There are also analogous inconsistent results, but the underlying mechanism has been rarely shed light on [13][14][15][16][17]. In addition, Bhattacharyya et al [6] demonstrated a lower strain rate sensitivity of the hardness under a higher peak-load, but the results of Ma et al [17,18] showed a much more positive rate sensitivity when the peak-load increased by 1 order of magnitude. Moreover, Jang et al [19] reported a continuous reduction of hardness with increasing peak-load or indentation size, i.e., an indentation size effect (ISE).…”

mentioning

confidence: 98%

Testing effects on hardness of a Zr-based metallic glass under nanoindentation

Jiang

et al. 2017

Scripta Materialia

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A series of nanoindentation tests were performed on a Zr-based bulk metallic glass at different peak-loads and strain rates. It is observed that the strain rate sensitivity index gradually decreases from positive to almost zero with increasing peak-load. Furthermore, at a fixed strain rate, the indentation hardness firstly shows a dramatic reduction and then becomes stable with increasing peak-load. These observations can be well understood in the framework of the activation and the accumulation of free volume via shear transformation zones. The current work may provide a practical way to tailor the hardness of the metallic glass.© 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords:Metallic glass Nanoindentation Strain rate Indentation size effect Metallic glasses have been long regarded as potential structural materials due to their ultra-high strength and hardness [1,2]. Therefore, a number of researchers have paid much attention to the factors that will influence the hardness of metallic glass [3][4][5]. For instance, it is demonstrated that the increase of loading rate corresponded to a decrease of hardness and the underlying mechanism was attributed to the free volume relaxation induced hardening that was more dramatic under lower strain rates [6]. However, the free volume dynamics includes not only the relaxation induced annihilation, but also stress driven creation [7][8][9]. It is believed that the free volume creation could lead to a softening effect on the hardness of metallic glasses [10,11]. Therefore, both hardening and softening effects of strain rates on the hardness is possible. For example, Xue et al. [12] reported a positive strain rate dependence of the hardness and ascribed this correlation to the stronger strain rate softening effect under lower strain rates. There are also analogous inconsistent results, but the underlying mechanism has been rarely shed light on [13][14][15][16][17]. In addition, Bhattacharyya et al. [6] demonstrated a lower strain rate sensitivity of the hardness under a higher peak-load, but the results of Ma et al. [17,18] showed a much more positive rate sensitivity when the peak-load increased by 1 order of magnitude. Moreover, Jang et al. [19] reported a continuous reduction of hardness with increasing peak-load or indentation size, i.e., an indentation size effect (ISE). On the contrary, Wang et al. [20] recently demonstrated that the ISE would disappear when the indentation size is larger than a critical value.Evidently, the dependence of hardness on the testing conditions (strain rate and peak-load) under nanoindentation is still under debate. Further exploration is required to gain more insights into these issues. In the current work, a series of nanoindentation tests were performed on a Zr-based metallic glass under different peak-loads and strain rates. A positive dependence of hardness on the strain rate is found. Meanwhile, both the strain rate sensitivity index and the indentation hardness firstly decrease and then become stabl...

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“…Wang et al investigated creep behaviors of Cu-Zr films with thickness from 1000 to 3000 nm [18]. Ma et al reported thickness effects on the creep deformation in Cu-Zr-Al and Ni-Nb metallic glassy films [19,20]. According to previous results, metallic glasses with smaller dimensions exhibit more pronounced creep deformation under both elastic and plastic holdings.…”

Section: Introductionmentioning

confidence: 99%

Revealing Nanoindentation Size-Dependent Creep Behavior in a La-Based Metallic Glassy Film

Song

Zhang

2019

Nanomaterials

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We systematically studied nanoindentation size effect on creep deformation in a La-based metallic glassy film, including holding depth effect and indenter size effect. Creep displacement was mainly dependent on both holding strain and deformation volume beneath indenter. Under elastic holding, creep strain was merely holding strain-dependent. While for plastic holding, creep strain was greatly enhanced by adopting smaller indenter and/or decreasing holding depth at the same holding strain. A strong nanoindentation size effect on creep resistance was validated. Strain rate sensitivities (SRS) were calculated, which were obviously higher at elastic regions than at plastic holdings. The relationship between SRS value and creep mechanism in metallic glass was discussed. Author Contributions: Data curation, Y.S.; formal analysis, Y.S.; investigation, Y.M.; supervision, T.Z.; writing-original draft, Y.M.

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Nanoindentation study of size effect on shear transformation zone size in a Ni–Nb metallic glass

Cited by 53 publications

References 39 publications

Effect of strain rate on yielding strength of a Zr-based bulk metallic glass

Effect of strain rate on yielding strength of a Zr-based bulk metallic glass

Testing effects on hardness of a Zr-based metallic glass under nanoindentation

Revealing Nanoindentation Size-Dependent Creep Behavior in a La-Based Metallic Glassy Film

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