Plasticity Of Glasses Research Articles

Plasticity improvement of an Fe-based bulk metallic glass by geometric confinement

In this paper, the effect of nickel coating on the plasticity of a brittle Fe-based bulk metallic glass (BMG) was investigated. By electrodepositing a nickel coating onto an Fe 75Mo 5P 10C 8.3B 1.7 BMG, the plasticity of the BMG is shown to increase dramatically from ~ 0.5% to ~ 5.0%. Without reducing the strength of the BMG, the findings demonstrate that the electrodeposited nickel is an effective way to improve prominently brittle BMGs. The increased compressive plastic strain is believed to be attributed to the nucleation, intersection and bifurcation of multiple shear bands due to the exterior impedance of the surrounding coating.

Enhancement of plasticity and toughness in monolithic Zr-based bulk metallic glass by heterogeneous microstructure

A significant enhancement of plasticity and toughness was achieved by increasing Zr content but decreasing Cu content in the Zr–Cu–Ni–Al–Ta bulk metallic glass system. It was found that higher Zr content induces strong icosahedral medium-range order clusters in amorphous phase which, in turn, cause heterogeneous distribution of free volume and eventually lead to the enhancement of plasticity and toughness of the monolithic bulk metallic glasses.

Enhanced plastic deformation in a metallic glass induced by notches

It is shown that the compressive plasticity of a metallic glass, namely Zr52.5Ni14.6Al10Cu17.9Ti5, can be improved by the introduction of two symmetrical notches. The enhanced plasticity may be ascribed to a blocking effect of the propagation of shear bands caused by large stress gradients around the notches. In contrast to ceramic specimens with similar notches, the plasticity enhancement of metallic glass induced by notches can provide a new approach to understanding its unique mechanism of deformation.

The effect of annealing on the mechanical properties of a ZrAlNiCu metallic glass

In this paper, the effects of annealing and nanocrystallization on the mechanical properties of a Zr 55Al 10Ni 5Cu 30 metallic glass have been studied. It has been shown that the high volume fractioned nanocrystals facilitate the formation of shear bands and thus decrease the yield stress. At the same time, the nanocrystals also facilitate the formation of interfacial voids during compression, resulting in substantial decrease in the plasticity of the metallic glass.

Deformation behavior and enhanced plasticity of Ti-based metallic glasses with notches

The plasticity of Ti-based metallic glasses with different aspect ratios can be improved by introducing two semicircular notches on the edges of the samples, owing to the interactions of shear bands (SBs) under conventional compression tests. The interaction of SBs can be ascribed to the easy initiation of SBs around the notches due to the large stress gradient, and the consequent blocking effect of notches on the propagation of shear bands. Additionally, the current findings provide a new way to understand the physical nature for the plastic deformation behavior of some brittle metallic glasses and supply an effective approach to enhance the plasticity to some extent.

Effect of frame stiffness on the deformation behavior of bulk metallic glass

It has been shown that the stability of shear banding and plasticity of bulk metallic glasses (BMGs) can be strongly influenced by the machine stiffness. Here, we demonstrated that the practice of adding a frame parallel to the sample is quantitatively equivalent to increasing the machine stiffness by the frame stiffness. A series of carefully designed experiments were conducted to verify such an effect, showing controllably enhanced plasticity of BMG samples.

Shear stability of metallic glasses

The effect of sample size on the shear deformation and compressive plasticity of different metallic glasses were investigated. The experimental results showed that the deformation and fracture behaviors of samples prepared from chemically identical Zr-, Ti-, Fe-, or Mg-based metallic glass ingots were strongly dependent on the sample size and machine stiffness, and a super-high compressive plasticity was achieved in the Zr-based metallic glasses with sample size of 1.0 mm in width. It is also found that the sample size can significantly influence the density of elastic energy dissipated in the shear band: with sample size decreasing and machine stiffness increasing, the density of the elastic energy dissipated in the shear band of metallic glasses is prominently decreased, thus the shear deformation turns to be more stable, resulting in the improvement of plasticity in ductile metallic glasses and the transition from fragmentation fracture to shear fracture in brittle metallic glasses. This finding is important for the potential applications of the present metallic glasses and for designing new metallic glasses with better mechanical properties.

Plasticity of Ductile Metallic Glasses: A Self-Organized Critical State

We report a close correlation between the dynamic behavior of serrated flow and the plasticity in metallic glasses (MGs) and show that the plastic deformation of ductile MGs can evolve into a self-organized critical state characterized by the power-law distribution of shear avalanches. A stick-slip model considering the interaction of multiple shear bands is presented to reveal complex scale-free intermittent shear-band motions in ductile MGs and quantitatively reproduce the experimental observations. Our studies have implications for understanding the precise plastic deformation mechanism of MGs.

Plastic deformability of metallic glass by artificial macroscopic notches

Abstract This paper reports that the plasticity of Zr-based metallic glass can be improved by creating two symmetrical semi-circular notches. Unlike the experimental findings of the samples without notches, a steady shear deformation can be created by the large-scale stress gradient around the two symmetrical notches and the plasticity of metallic glass can be enhanced to a high value of ∼10% under compression tests. The improved plasticity may be due to the easy initiation of shear bands around the notches, and the consequent blocking effect of notches on the propagation of shear bands, similar to the dislocation mechanism in crystalline materials. To reveal the particular plastic deformation behavior of metallic glass, Ti3SiC2 ceramic and high-strength steel specimens with two symmetrical semi-circular notches were also conducted under compressive loadings; however, no enhancement in plasticity was found. It is suggested that creating a stress gradient is a particular strategy for designing metallic glasses in order to improve their plasticity.

Anisotropic plasticity and chain orientation in polymer glasses

AbstractThe anisotropic mechanical response of oriented polymer glasses is studied through simulations with a coarse‐grained model. Systems are first oriented by uniaxial compression or tension along an axis. Then the mechanical response to subsequent deformation along the same axis or along a perpendicular axis is measured. As in experiments, the flow stress and strain hardening modulus are both larger when deformation increases the degree of molecular orientation produced by prestrain, and smaller when deformation reduces the degree of orientation. All stress curves for parallel prestrains collapse when plotted against either the total integrated strain or the degree of molecular orientation. Stress curves for perpendicular prestrains can also be collapsed. The stress depends on the degree of strain or molecular orientation along the final deformation axis and is independent of the degree of orientation in the perpendicular plane. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1473–1482, 2010

Short-range-order effects on intrinsic plasticity of metallic glasses

Through a systematical analysis of the elastic moduli for 137 metallic glasses (MGs) and 56 polycrystalline metals, we use a simple model developed by Knuyt et al. [J. Phys. F: Met. Phys. 16 (1986) p.1989; Phil. Mag. B 64 (1991) p.299] based on a Gaussian distribution for the first-neighbor distance to reveal the short-range-order (SRO) structural conditions for plasticity of MGs. It is found that the SRO structure with dense atomic packing, large packing dispersion and a significant anharmonicity of atomic interaction within an MG is favorable for its global plasticity. Although these conditions seem paradoxical, their perfect matching is believed to be a key for designing large plastic bulk MGs not only in compression but also in tension.

Density change upon crystallization of amorphous Zr–Cu–Al thin films

Systematic deflection measurements with micro-cantilevers and a combinatorial-deposition method have been used to investigate the density change upon crystallization of amorphous Zr–Cu–Al thin films. It is found that, in general, the density change decreases from Cu-/Al-rich compositions to Zr-rich compositions, and the previously reported good glass-forming compositions are found to correspond to global minima of the density change inside respective local eutectic systems. Furthermore, we propose that the general trend of density change as a function of alloy compositions discovered in this work may have implications for the macroscopic plasticity of metallic glasses.

Effect of manipulating atomic scale heterogeneity on plasticity in Mg-based bulk metallic glasses

This paper investigates the effect of manipulating atomic scale heterogeneity on plasticity in Mg-based bulk metallic glasses (BMGs). First, we show that tailoring combinations of bonding energy among constituent elements in Mg-based BMGs results in local structural and/or chemical heterogeneity, which can influence the formation and propagation of the shear bands during deformation. Secondly, we show that by controlling cooling rate during vitrification, it is possible to modulate heterogeneity and thereby influence the viscous flow in supercooled liquid region, which is closely related to mechanical properties in BMGs. These findings suggest that optimization of heterogeneity by controlling the cooling rate as well as tailoring combinations of constituent elements could enhance plasticity in various BMGs.

Unusual compressive plasticity of a centimeter-diameter Zr-based bulk metallic glass with high Zr content

The thermal stability, melting behavior, and glass-forming ability of Zr 70Al 8Cu 22− x Ni x ( x = 3–19 at.%) metallic glasses were investigated. Fully glassy sample with largest critical diameter of 10 mm was obtained for alloy with x = 8.5 in the alloy series, which corresponds to a deep eutectic, largest supercooled liquid region, and largest γ value. Room temperature compression test revealed that the monolithic Zr 70Al 8Cu 13.5Ni 8.5 bulk metallic glass exhibits a high yield strength of 1570 MPa, a Young's modulus of 80 GPa, and a super large plastic strain more than 70%.

Enhancement of plasticity of Fe-based bulk metallic glass by Ni substitution for Fe

Bulk metallic glasses (BMGs) (Fe 1− x Ni x ) 71Mo 5P 12C 10B 2 ( x = 0, 0.1 and 0.2) with a diameter of 3 mm were synthesized by copper mold casting. The effect of Ni substitution for Fe on the structure, thermal and mechanical properties has been studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and compressive testing. It was found that the substitution of Ni for Fe enhances the glass forming ability, and improves the plasticity of Fe 71Mo 5P 12C 10B 2 BMG as indicated by the increase in the plastic strain from 3.1% ( x = 0) to 5.2% ( x = 0.2). The improvement of the plasticity is discussed in term of the reduction of glass transition temperature and the supercooled liquid region due to the substitution of Ni for Fe.

Improved plasticity of bulk metallic glasses upon cold rolling

The intrinsic plasticity of Zr 44 Ti 11 Cu 9.8 Ni 10.2 Be 25 and Zr 55 Ti 5 Al 10 Cu 20 Ni 10 bulk metallic glasses (BMGs) are improved from 0.5% up to 15% plastic strain due to the introduction of microstructural inhomogeneities upon cold rolling at room temperature. This approach shows an easy way to overcome the intrinsic brittleness of the BMGs by modifying their physical properties, which enables easy nucleation and branching of multiple shear bands upon unconstrained loading during the compression test.

Response to “Comment on ‘Mechanical heterogeneity and mechanism of plasticity in metallic glasses’ ” [Appl. Phys. Lett. 96, 026101 (2010)

Response to “Comment on ‘Mechanical heterogeneity and mechanism of plasticity in metallic glasses’ ” [Appl. Phys. Lett. 96, 026101 (2010)

Characteristic length scales governing plasticity/brittleness of bulk metallic glasses at ambient temperature

In this letter, we propose a unified theory for the size-dependent plasticity of bulk metallic glasses (BMGs) at room temperature. Based on the principle of energy balance and the shear-banding kinetics, two characteristic length scales are derived. One is a sample-geometry dependent variable related to the elastic energy released to drive shear-band propagation and the other is a material-dependent constant related to the internal resistance to brittle fracture. It is shown that this unified theory is effective in explaining many unusual deformation and fracture behaviors of BMGs.

Size dependent plasticity of a Zr-based bulk metallic glass during room temperature compression

The plastic deformation of Zr 65Cu 17.5Ni 10Al 7.5 bulk metallic glass with different diameters (Ø 1–4 mm) but the same initial atomic-scale structure was investigated through compression at room temperature. It was found that the plastic strain increases with decreasing sample dimension, and this tendency becomes more prominent when the diameter of the specimen decreases to 1 mm, indicating a size dependent plasticity. Correspondingly, the morphology of sheared surface also shows size dependence. The fracture surface is characterized by typical vein-like patterns for the sample with large diameter, but for the small size sample, the sheared surface exhibits regular spaced striations. The origin of shear-banding instability that is responsible for the size dependent plasticity is discussed in terms of the adiabatic heating and the free volume model.

Compressive plasticity and toughness of a Ti-based bulk metallic glass

The effects of changes in sample dimensions on the compressive plasticity and fracture toughness/energy have been determined for Ti 40Zr 25Cu 12Ni 3Be 20 bulk metallic glass (BMG). Changes in sample dimensions alone produced widely different values for compressive plasticity. While these were correlated with changes to the measured Poisson’s ratio for samples of the same composition cast into different sample sizes, significant effects of testing conditions apart from the Poisson’s ratio on the measured compressive plasticity are also demonstrated. Fracture toughness testing on the same material/size that exhibited zero compressive plasticity produced both notch and fatigue pre-cracked toughness in excess of 100 MPa m 1/2, while a size effect on the magnitude of toughness was similarly demonstrated. Discussions on the source(s) of the size effect on toughness are provided in addition to demonstrating that exceptional toughness can be obtained in this BMG which exhibits essentially zero compressive plasticity under certain test conditions. The apparent critical Poisson’s ratio for plasticity/toughness is thus different in these very different types of tests.