scholarly journals Probe Embryonic Damage Evolution in Bulk Metallic Glasses under Plate-impact Loading

2018 ◽  
Vol 183 ◽  
pp. 03013
Author(s):  
Zhong Ling ◽  
Xin Huang ◽  
Lanhong Dai
Keyword(s):  
Metallic Glass ◽  
Metallic Glasses ◽  
Volume Content ◽  
Impact Loading ◽  
Damage Evolution ◽  
Ductile Damage ◽  
Plate Impact ◽  
Shear Transformation ◽  
Stress Environment ◽  
Shear Transformation Zones

Microdamage in very short stress durations of spallation process in Zr-based bulk metallic glass (Zr-BMG) samples were captured by a specially designed plate impact technique. With stress durations vary, microdamage “frozen” in Zr-BMG samples exhibited different damage levels. Based on the morphology and stress environment of the microdamage, a compound microdamage evolution mode is applied to characterize the spallation evolution in Zr-BMGs. Especially the spallation in BMGs originates from cavitation instabilities in the weak regions with higher free volume content, which results in formation of ductile damage zones. The activation of shear transformation zones (STZs) or tension transformation zones (TTZs) between these ductile damage zones finally leads to detached spallation.

Stimulation of shear-transformation zones in metallic glasses by cryogenic thermal cycling

2020 ◽  
Vol 548 ◽  
pp. 120299 ◽  
Author(s):  
C.M. Meylan ◽  
F. Papparotto ◽  
S. Nachum ◽  
J. Orava ◽  
M. Miglierini ◽  
...  
Keyword(s):  
Thermal Cycling ◽  
Metallic Glasses ◽  
Shear Transformation ◽  
Shear Transformation Zones ◽  
Stimulation Of

scholarly journals Atomic-scale viscoplasticity mechanisms revealed in high ductility metallic glass films

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Hosni Idrissi ◽  
Matteo Ghidelli ◽  
Armand Béché ◽  
Stuart Turner ◽  
Sébastien Gravier ◽  
...  
Keyword(s):  
Metallic Glass ◽  
Metallic Glasses ◽  
Shear Banding ◽  
Atomic Scale ◽  
Microscopy Imaging ◽  
Rate Dependent ◽  
Imaging And Spectroscopy ◽  
Shear Transformation Zones ◽  
The Impact ◽  
Glass Films

Abstract The fundamental plasticity mechanisms in thin freestanding Zr65Ni35 metallic glass films are investigated in order to unravel the origin of an outstanding strength/ductility balance. The deformation process is homogenous until fracture with no evidence of catastrophic shear banding. The creep/relaxation behaviour of the films was characterized by on-chip tensile testing, revealing an activation volume in the range 100–200 Å3. Advanced high-resolution transmission electron microscopy imaging and spectroscopy exhibit a very fine glassy nanostructure with well-defined dense Ni-rich clusters embedded in Zr-rich clusters of lower atomic density and a ~2–3 nm characteristic length scale. Nanobeam electron diffraction analysis reveals that the accumulation of plastic deformation at room-temperature correlates with monotonously increasing disruption of the local atomic order. These results provide experimental evidences of the dynamics of shear transformation zones activation in metallic glasses. The impact of the nanoscale structural heterogeneities on the mechanical properties including the rate dependent behaviour is discussed, shedding new light on the governing plasticity mechanisms in metallic glasses with initially heterogeneous atomic arrangement.

scholarly journals Effect of Hydrogen Charging on Pop-in Behavior of a Zr-Based Metallic Glass

Metals ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 22 ◽  
Author(s):  
Lin Tian ◽  
Dominik Tönnies ◽  
Moritz Hirsbrunner ◽  
Tim Sievert ◽  
Zhiwei Shan ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Metallic Glass ◽  
Spatial Correlation ◽  
Hydrogen Content ◽  
Amorphous Structure ◽  
Homogeneous Deformation ◽  
Hydrogen Charging ◽  
Shear Transformation ◽  
Shear Transformation Zones ◽  
Clear Increase

In this work, structural and mechanical properties of hydrogen-charged metallic glass are studied to evaluate the effect of hydrogen on early plasticity. Hydrogen is introduced into samples of a Zr-based (Vit 105) metallic glass using electrochemical charging. Nanoindentation tests reveal a clear increase in modulus and hardness as well as in the load of the first pop-in with increasing hydrogen content. At the same time, the probability of a pop-in occurring decreases, indicating that hydrogen hinders the onset of plastic instabilities while allowing local homogeneous deformation. The hydrogen-induced stiffening and hardening is rationalized by hydrogen stabilization of shear transformation zones (STZs) in the amorphous structure, while the improved ductility is attributed to the change in the spatial correlation of the STZs.

scholarly journals Effect of Annealing on Strain Rate Sensitivity of Metallic Glass under Nanoindentation

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1063
Author(s):  
Mingcan Li
Keyword(s):  
Mechanical Properties ◽  
Metallic Glass ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Annealing Time ◽  
Isothermal Annealing ◽  
Rate Sensitivity ◽  
Underlying Mechanism ◽  
Shear Transformation ◽  
Shear Transformation Zones

The influence of isothermal annealing on the strain rate sensitivity (SRS) of a Zr-based bulk metallic glass (BMG) was investigated by nanoindentation. A more positive SRS is observed with a decrease in the content of the free volume (FV) of the sample. Furthermore, the SRS becomes nearly constant with increasing annealing time when the FV is annealed out. By taking into consideration the FV-assisted activation and combination of the shear transformation zones (STZs), the underlying mechanism is well understood. The current work may offer useful insights into the correlation between the microstructure and mechanical properties of BMGs.

scholarly journals Controlling shear band instability by nanoscale heterogeneities in metallic nanoglasses

2021 ◽  
Author(s):  
Sree Harsha Nandam ◽  
Ruth Schwaiger ◽  
Aaron Kobler ◽  
Christian Kübel ◽  
Chaomin Wang ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Yield Strength ◽  
Shear Band ◽  
Metallic Glasses ◽  
Strain Localization ◽  
Catastrophic Failure ◽  
Compression Tests ◽  
Medium Range ◽  
Shear Transformation ◽  
Shear Transformation Zones

Abstract Strain localization during plastic deformation drastically reduces the shear band stability in metallic glasses, ultimately leading to catastrophic failure. Therefore, improving the plasticity of metallic glasses has been a long-standing goal for several decades. In this regard, nanoglass, a novel type of metallic glass, has been proposed to exhibit differences in short and medium range order at the interfacial regions, which could promote the formation of shear transformation zones. In the present work, by introducing heterogeneities at the nanoscale, both crystalline and amorphous, significant improvements in plasticity are realized in micro-compression tests. Both amorphous and crystalline dispersions resulted in smaller strain bursts during plastic deformation. The yield strength is found to increase significantly in Cu–Zr nanoglasses compared to the corresponding conventional metallic glasses. The reasons for the mechanical behavior and the importance of nanoscale dispersions to tailor the properties is discussed in detail. Graphic Abstract

The Thermal Shear-Transformation-Zone Theory: Homogeneous Flow and Superplasticity in Bulk Metallic Glasses

2003 ◽  
Vol 806 ◽  
Author(s):  
Michael L. Falk ◽  
James S. Langer ◽  
Leonid Pechenik
Keyword(s):  
Metallic Glass ◽  
Yield Stress ◽  
Metallic Glasses ◽  
Strain Rates ◽  
Superplastic Behavior ◽  
Transformation Zone ◽  
Transient Stress ◽  
Shear Transformation ◽  
Shear Transformation Zone ◽  
System Approaches

ABSTRACTWe present an extended version of our earlier shear-transformation-zone theory of amorphous plasticity that takes into account thermally assisted molecular rearrangements. As in the previous low-temperature theory a transition is predicted between jammed and flowing states at a well defined yield stress. In the new theory the jammed state below the yield stress exhibits thermally assisted creep. The theory accounts for the experimentally observed strain-rate dependence of the viscosity of a bulk metallic glass. In particular it models the onset of superplastic behavior at high strain rates as the system approaches the yield stress. The theory also captures many of the details of the transient stress-strrain response of the metallic glass at temperatures near the glass transition.

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