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

Avila, Karina E.; Küchemann, Stefan; Alhafez, Iyad Alabd; Urbassek, Herbert M.

doi:10.3390/ma12091477

Cited by 26 publications

(17 citation statements)

References 51 publications

(94 reference statements)

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“…Also, the active zone increases with temperature, suggesting more localized plastic events for low temperatures. This effect is well known and has been reported in nanoindentation studies [8,31,45] and other loading experiments [46][47][48]. From the top view snapshots, a very noticeable activity can be observed at the surface of the sample with increasing temperature, with no shear-band formation at the surface at any of the studied temperatures.…”

Section: Active Zonessupporting

confidence: 76%

“…A crystalline mixture was first heated to a temperature above the melting point, T = 2000 K, for a time period of 500 ps and then cooled to the final temperature with a quenching rate of 0.01 K/ps to obtain the metallic glass. We note that we studied previously the effect of the quenching rate on the plastic properties of the glass and found that the quenching rate adopted here is sufficiently slow to obtain reliable results on the glass plasticity [31]. The glass transition temperature T g for this particular composition and potential is around 1000 K for a quenching rate of 1 K/ps [32]; for the quenching rate adopted here there would be a slight change of T g toward a lower temperature, but not below 800 K. Here, we simulated samples at 5 different temperatures.…”

Section: Methodsmentioning

confidence: 88%

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Nanoscratching of metallic glasses – An atomistic study

Avila

Küchemann

Alhafez

et al. 2019

Tribology International

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Tribological properties of materials play an important role in engineering applications. Up to now, a number of experimental studies have identified correlations between tribological parameters and the mechanical response. Using molecular dynamics simulations, we study abrasive wear behavior via nanoscratching of a Cu 64.5 Zr 35.5 metallic glass. The evolution of the normal and transverse forces and hardness values follows the behavior well known for crystalline substrates. In particular, the generation of the frontal pileup weakens the response of the material to the scratching tip and leads to a decrease of the transverse hardness as compared to the normal hardness. However, metallic glasses soften with increasing temperature, particularly above the glass transition temperature thus showing a higher tendency to structurally relax an applied stress. This plastic response is analyzed focusing on local regions of atoms which underwent strong von-Mises strains, since these are the basis of shear-transformation zones and shear bands. The volume occupied by these atoms increases with temperature, but large increases are only observed above the glass transition temperature. We quantify the generation of plasticity by the concept of plastic efficiency, which relates the generation of plastic volume inside the sample with the formation of external damage, viz. the scratch groove. In comparison to nanoindentation, the generation rate of the plastic volume during nanoscratching is significantly temperature dependent making the glass inside more damage-tolerant at lower temperature but more damage-susceptible at elevated temperatures.

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Section: Active Zonessupporting

confidence: 76%

Section: Methodsmentioning

confidence: 88%

Nanoscratching of metallic glasses – An atomistic study

Avila

Küchemann

Alhafez

et al. 2019

Tribology International

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“…Additionally, we correlate the core densities with the indentation hardness values determined for the same samples in Ref. 18. These results are shown in the inset of Fig.…”

mentioning

confidence: 72%

“…Plastic-zone size factor f as a function of temperature. Inset: Hardness[18] as a function of the core plastic density, ρ max .…”

mentioning

confidence: 99%

Stucture and size of the plastic zone formed during nanoindentation of a metallic glass

Avila

Küchemann

Urbassek

2019

Journal of Non-Crystalline Solids

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Using molecular dynamics simulation, we study the plastic zone created during nanoindentation of a large CuZr glass system. The plastic zone consists of a core region, in which virtually every atom undergoes plastic rearrangement, and a tail, where the density distribution of the plastically active atoms decays to zero. Compared to crystalline substrates, the plastic zone in metallic glasses is significantly smaller than in crystals. The so-called plastic-zone size factor, which relates the radius of the plastic zone to the contact radius of the indenter with the substrate, assumes values around 1, while in crystals -depending on the crystal structure -values of 2-3 are common. The small plastic zone in metallic glasses is caused by the essentially homogeneous deformation in the amorphous matrix, while in crystals heterogeneous dislocations prevail, whose growth leads to a marked extension of the plastic zone.

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“…The resulting avalanche of sessile STZ activations may lead to localised flow in the form of shear bands, which may ultimately lead to material failure. Extensive numerical [130][131][132][133][134][135] and some indirect experimental [136][137][138] evidence exists for the inelastic deformation of metallic and polymeric glasses at T/T g < 1 (and at moderate strain rates) to be governed by STZ dynamics.…”

Section: Mesoscale Modelling Via Shear Transformation Zone (Stz) Dynamentioning

confidence: 99%

Nanomechanics serving polymer-based composite research

Pardoen¹,

Klavzer²,

Gayot³

et al. 2021

Comptes Rendus. Physique

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Tremendous progress in nanomechanical testing and modelling has been made during the last two decades. This progress emerged from different areas of materials science dealing with the mechanical behaviour of thin films and coatings, polymer blends, nanomaterials or microstructure constituents as well as from the rapidly growing field of MEMS. Nanomechanical test methods include, among others, nanoindentation, in-situ testing in a scanning or transmission electron microscope coupled with digital image correlation, atomic force microscopy with new advanced dynamic modes, micropillar compression or splitting, on-chip testing, or notched microbeam bending. These methods, when combined, reveal the elastic, plastic, creep, and fracture properties at the micro-and even the nanoscale. Modelling techniques including atomistic simulations and several coarse graining methods have been enriched to a level that allows treating complex size, interface or surface effects in a realistic way. Interestingly, the transfer of this paradigm to advanced long fibre-reinforced polymer composites has not been as intense compared to other fields. Here, we show that these methods put together can offer new perspectives for an improved characterisation of the response at the elementary fibre-matrix level, involving the interfaces and interphases. Yet, there are still many open issues left to resolve. In addition, this is the length scale, typically below 10 micrometres, * Corresponding author.

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

Cited by 26 publications

References 51 publications

Nanoscratching of metallic glasses – An atomistic study

Nanoscratching of metallic glasses – An atomistic study

Stucture and size of the plastic zone formed during nanoindentation of a metallic glass

Nanomechanics serving polymer-based composite research

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