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.

Mechanism of Chip Segmentation in Orthogonal Cutting of Zr-Based Bulk Metallic Glass

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Naresh Kumar Maroju ◽  
Xiaoliang Jin
Keyword(s):  
Shear Stress ◽  
Large Strain ◽  
Orthogonal Cutting ◽  
Amorphous Structure ◽  
Experimental Result ◽  
Thermomechanical Model ◽  
Stress Variation ◽  
Highly Sensitive ◽  
Shear Transformation ◽  
Shear Transformation Zones

Abstract Bulk metallic glasses (BMGs) are a series of metal alloys with an amorphous structure. The deformation of BMGs occurs in localized regions and is highly sensitive to the applied stress, strain rate, and temperature. This paper presents a coupled thermomechanical model to analyze the chip segmentation mechanism due to material shear localization in orthogonal cutting of Zr-BMG. The shear stress variation in the primary shear zone is modeled considering the tool-chip friction and large strain of the material. The constitutive property of BMG corresponding to the inhomogeneous deformation through shear transformation zones is modeled. The oscillations of shear stress, temperature, and free volume are simulated based on the cutting conditions. The predicted chip segmentation frequency is compared with the experimental result under different cutting speeds and uncut chip thicknesses. The developed model provides the fundamental mechanism of material deformation and chip formation in cutting Zr-BMG with an amorphous structure.

scholarly journals HYDROGEN CHARGING OF FUEL CLADDING METHODOLOGY

2016 ◽  
Vol 4 ◽  
pp. 38
Author(s):  
Jakub Krejčí ◽  
Jitka Kabátová ◽  
Jan Kočí ◽  
Zuzana Weishauptová ◽  
Věra Vrtílková
Keyword(s):  
Mechanical Properties ◽  
Hydrogen Content ◽  
Normal Operation ◽  
Fuel Cladding ◽  
Oxidation Test ◽  
Hydrogen Charging

Hydrogen content is a very important parameter for mechanical properties of fuel cladding, especially after LOCA transients. Therefore, it is necessary to take into account the amount of hydrogen absorbed in the fuel cladding during normal operation (before a hypothetical LOCA). The required value of hydrogen content is possible to reach by a long-term pre-oxidation test or a much shorter hydrogen charging experiment. The methodology of hydrogen charging developed in UJP is described in this contribution. Results of experiments aiming to prepare samples with uniform hydrides and samples with a rim-layer and other hydrides are shown.

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.

Atomistic study of the mechanical properties of metallic-glass nanowires

2011 ◽  
Vol 1297 ◽  
Author(s):  
K. Koshiyama ◽  
K. Shintani
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Tensile Strength ◽  
Metallic Glass ◽  
Tensile Strain ◽  
Amorphous Structure ◽  
Structure Change ◽  
Atomistic Study ◽  
B2 Structure ◽  
Dynamics Method

ABSTRACTMelt-growth simulations based on the molecular-dynamics method for both the Cu-Zr and Ni-Al crystalline nanowires of B2 structure are performed to produce metallic-glass nanowires of amorphous structure. Next, tensile deformations of these nanowires are simulated at various temperatures. For the sake of comparison, Cu-Zr and Ni-Al crystalline nanowires of B2 structure are also elongated. It is revealed that the tensile strength of the metallic-glass nanowires is third or fourth of the tensile strength of the crystalline nanowires. Increasing tensile strain, the Cu-Zr crystalline nanowires of B2 structure change their structure twice, whereas the metallic-glass nanowires only decrease their thicknesses locally, and necking takes place.

Probing the size- and constituent-mediated mechanical properties and deformation behavior in crystalline/amorphous nanolaminates

Nanoscale ◽  
2018 ◽  
Vol 10 (46) ◽  
pp. 21827-21841 ◽  
Author(s):  
Y. Q. Wang ◽  
K. Wu ◽  
J. Y. Zhang ◽  
G. Liu ◽  
J. Sun
Keyword(s):  
Mechanical Properties ◽  
Deformation Behavior ◽  
Shear Transformation ◽  
Shear Transformation Zones ◽  
Tunable Mechanical Properties

The tunable mechanical properties and deformation behavior in crystalline/amorphous nanolaminates are revealed to be through cooperation between dislocations and shear transformation zones.

scholarly journals Influence of grain size and composition, topology and excess free volume on the deformation behavior of Cu–Zr nanoglasses

2015 ◽  
Vol 6 ◽  
pp. 537-545 ◽  
Author(s):  
Daniel Şopu ◽  
Karsten Albe
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Free Volume ◽  
Deformation Behavior ◽  
Alloy Composition ◽  
Topological Order ◽  
Shear Transformation ◽  
Shear Transformation Zones ◽  
Dynamics Simulations ◽  
Topological Disorder

The influence of grain size and composition on the mechanical properties of Cu–Zr nanoglasses (NGs) is investigated by molecular dynamics simulations using two model glasses of different alloy composition, namely Cu64Zr36 (Cu-rich) and Cu36Zr64 (Zr-rich). When the grain size is increased, or the fraction of interfaces in these NGs is decreased, we find a transition from a homogeneous to an inhomogeneous plastic deformation, because the softer interfaces are promoting the formation shear transformation zones. In case of the Cu-rich system, shear localization at the interfaces is most pronounced, since both the topological order and free volume content of the interfaces are very different from the bulk phase. After thermal treatment the redistribution of free volume leads to a more homogenous deformation behavior. The deformation behavior of the softer Zr-rich nanoglass, in contrast, is only weakly affected by the presence of glass–glass interfaces, since the interfaces don’t show topological disorder. Our results provide clear evidence that the mechanical properties of metallic NGs can be systematically tuned by controlling the size and the chemical composition of the glassy nanograins.

Investigation of Local Shear Transformation in a Metallic Glass by Means of High Amplitude Internal Friction Measurements

2012 ◽  
Vol 184 ◽  
pp. 411-415
Author(s):  
A. Nakamura ◽  
Yasushi Kamimura ◽  
Keiichi Edagawa ◽  
Shin Takeuchi
Keyword(s):  
Internal Friction ◽  
Metallic Glass ◽  
High Amplitude ◽  
Broad Peak ◽  
Flip Flop ◽  
Bias Stress ◽  
Local Shear ◽  
Shear Transformation ◽  
Shear Transformation Zones ◽  
Friction Measurements

In order to investigate flip-flop transitions of shear transformation zones (STZs) which are believed to be the elementary deformation sites in metallic glasses, internal friction measurements have been conducted for a commercial bulk metallic glass of a Zr-based alloy (Johnson alloy). Since the STZ is an asymmetrical two-level system, it is necessary to measure the internal friction at a high amplitude or under a bias stress condition to detect the transitions. Measurements have been made at temperatures between 130 K and 573 K at frequencies between 0.1 Hz to 10 Hz. The results showed that quite a broad peak appears between 200 K and 500 K in high amplitude internal friction measurements. The broad peak, observed for the first time in metallic glass, is interpreted to be due to flip-flop transitions of STZs having a broad spectrum, 0.5∼1.2 eV, of the activation enthalpy.

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