Defect Analyses of Deformed Zr-Cu-Ni-Al Bulk Metallic Glasses

2009 ◽  
Vol 283-286 ◽  
pp. 453-457
Author(s):  
Jung Hoon Yoo ◽  
Dae Hwang Yoo ◽  
Jung Hwa Seo ◽  
Ji Ling Dong ◽  
Young Sang Na ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Plastic Deformation ◽  
Metallic Glasses ◽  
Shear Bands ◽  
Bulk Metallic Glasses ◽  
Electron Holography ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Localized Plastic Deformation

In Zr-Cu-Ni-Al bulk metallic glasses where there are no dislocations, localized plastic deformation in shear bands occurs largely by the formation and migration of defects such as voids, micropores, shear bands and local variations in composition. Thus, the investigation on defects is critical for the understanding and improvement of plastic deformation in metallic glasses. In this study, microstructures and nano defects in the Zr-Cu-Ni-Al BMGs are characterized by variety of techniques, such as X-ray diffractometry, high resolution transmission electron microscopy, scanning transmission electron microscopy and electron holography.

Three-Dimensional Imaging of Shear Band Produced by ECAP Process in Al-Ag Alloy

2006 ◽  
Vol 503-504 ◽  
pp. 603-608
Author(s):  
Koji Inoke ◽  
Kenji Kaneko ◽  
Z. Horita
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Tomography ◽  
Shear Bands ◽  
Three Dimensional ◽  
Angular Pressing ◽  
Ecap Process ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
The Matrix

A significant change in microstructure occurs during the application of severe plastic deformation (SPD) such as by equal-channel angular pressing (ECAP). In this study, intense plastic strain was imposed on an Al-10.8wt%Ag alloy by the ECAP process. The amount of strain was controlled by the numbers of passes. After 1 pass of ECAP, shear bands became visible within the matrix. With increasing numbers of ECAP passes, the fraction of shear bands was increased. In this study, the change in microstructures was examined by three-dimensional electron tomography (3D-ET) in transmission electron microscopy (TEM) or scanning transmission electron microscopy (STEM). With this 3D-ET method, it was possible to conduct a precise analysis of the sizes, widths and distributions of the shear bands produced by the ECAP process. It is demonstrated that the 3D-ET method is promising to understand mechanisms of microstructural refinement using the ECAP process.

Plasticity at Crack Tips in Zr-Based Bulk Metallic Glasses

2000 ◽  
Vol 644 ◽  
Author(s):  
Jing Li ◽  
Xiaofeng Gu ◽  
Li-Qian Xing ◽  
Ken Livi ◽  
T. C. Hufnagel
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Plastic Deformation ◽  
Metallic Glasses ◽  
Fourier Transforms ◽  
Structural Information ◽  
Dark Field ◽  
Atomic Scale ◽  
Partial Explanation ◽  
Transmission Electron

AbstractWe have examined the structure of plastic deformation zones ahead of the tips of microcracks in Zr-based bulk metallic glass Zr57Ti5Cu20Ni8Al10. We have used an axially aligned dark field transmission electron microscopy technique, with the objective aperture placed to form images using electrons from several different areas of the diffraction patterns. We also compared Fourier transforms of the high resolution transmission electron microscopy images of deformed and undeformed regions to extract additional structural information. The plastic zones produce enhanced low-angle scattering of electrons and an apparent broadening of the amorphous halo, suggesting increased disorder and the presence of voids in the deformed zones. These results are consistent with an increased degree of atomic-scale disorder and enhanced free volume in highly deformed regions, which may provide a partial explanation of the manner in which plastic deformation occurs in metallic glasses.

Elastic Properties of Three Bulk Metallic Glasses. Evolution Versus Temperature in the Glass Transition Region and Influence of Crystallisation.

2000 ◽  
Vol 644 ◽  
Author(s):  
B. Van De Moortele ◽  
J.M. Pelletier ◽  
J.L. Soubeyroux ◽  
I.R. Lu
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Glass Transition ◽  
Metallic Glasses ◽  
Bulk Metallic Glasses ◽  
X Ray Diffraction ◽  
Mechanical Spectroscopy ◽  
Crystalline Materials ◽  
X Ray ◽  
Transmission Electron

AbstractThree bulk metallic glasses, with different resistance against crystallisation, were investigated using DSC experiments, X-ray diffraction, transmission electron microscopy and mechanical spectroscopy. Like in other non-crystalline materials, the elastic modulus exhibits a large decrease above the glass transition temperature. In materials with a large supercooled region (Pd-Ni-Cu-P for instance), this decrease can reach three decades, leading to an attractive glass forming ability. In contrast, in bulk metallic glasses in which onset of crystallisation occurs very rapidly above Tg, this decrease is on less than one decade. A correlation is made with the microstructure evolution revealed by X-Ray diffraction and transmission electron microscopy.

Structure of Shear Bands in Zirconium-Based Metallic Glasses Observed by Transmission Electron Microscopy

2002 ◽  
Vol 754 ◽  
Author(s):  
Xiaofeng Gu ◽  
Kenneth J. T. Livi ◽  
Todd C. Hufnagel
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Metallic Glasses ◽  
Defect Structure ◽  
Shear Bands ◽  
Tem Analysis ◽  
Transmission Electron ◽  
Before And After ◽  
High Resolution Tem ◽  
Band Spacing

ABSTRACTWe have used transmission electron microscopy (TEM) to investigate the structure of shear bands produced by bending electron-transparent Zr52.5Cu17.9Ni14.6Al10Ti5 metallic glass specimens. Shear bands were located by comparing the structure of the specimens before and after deformation. The shear band spacing is influenced by the structure of the specimen; portions of the specimen with a significant population of nanocrystals show a smaller separation between shear bands. Quantitative high resolution TEM analysis based on ratio technique has been used to explore the defect structure in shear bands. High density and void-like defects with size of about 1 nm were found in shear bands formed in both amorphous and nanocrystalline areas. A simple model was proposed to explain the formation of these defects.

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