16th Magnetic Materials Center Seminar
May 25, 2006, 9:00 am
7th floor seminar room, Sengen
Mechanical properties of BMGs: effect of preparation and heat treatment
G. Kumar
Inhomogeneous deformation in bulk metallic glasses (BMGs) is governed by formation of localized shear bands resulting in virtually no tensile ductility at room temperature. Whereas the compression tests showed the appearance of a large plastic strain in some of the BMGs. However, these results of compression tests are of stochastic nature, showing a large variation from a piece to another as well as a strong composition dependence. Because of featureless microstructure of BMGs, it is difficult to control their mechanical properties alike crystalline materials. Recent claims seem to indicate that the deformation processes (initiation, multiplication, and propagation of shear bands) in some BMGs can be controlled by preparation conditions or appropriate heat treatment. In present work, we are extending these hypothesis to other well-known BMGs (vit1, vit105, vit106 etc.) in order to understand their general applicability. In this presentation I will discuss the outcome of my recent experiments and further scope in this context.

New Zr-based bulk metallic glasses with improved mechanical properties
K. Mondal
Recent research thrust in the field of bulk metallic glasses is to design an alloy with a better glass forming ability in terms of critical thickness and improved mechanical properties. In this work, series of quaternary, quinary and six-component Zr-based bulk glass forming compositions have been developed by using the empirical formula [(ABeutectic)80(CDeutectic)20]. Most of the alloys are very good glass formers with a reduced glass forming temperature (Trg) in the range of 0.60-0.65 and high thermal stability (Tx-Tg) in the range of 60-100 K. The compositions can be easily cast into amorphous rods of 5 mm diameter. The as-cast specimens show a large compressive strain before failure in the range of 5-10 % along with a high strength of about 2 GPa. I will present the results of mechanical properties and microstructural analysis from the aforementioned bulk metallic glasses.

Intuitive understanding of Fourier transform and HRTEM imaging
T. Ohkubo
Recently, new TEM, FEI TECNAI G2 F30 S-TWIN, was installed. We can do many kinds of work by this TEM. As a analytical TEM, EDS, EELS elemental mapping and HAADF-STEM are available. And, it is useful for magnetic domain observation by Lorenz and electron holography techniques. Furthermore, we can easily take high-resolution TEM (HRTEM) images. All these information can be taken from same region. This is a big merit of this TEM. In order to explain something from the HRTEM image, you need to understand the basis of imaging theory. Although the dynamical diffraction theory for thick specimen is a little complicate, weak phase object approximation for thin specimen is not so difficult. To help you to understand this, I will explain the basis, especially phase contrast transfer function, by intuitive method rather than equations. For the HRTEM imaging, Fourier transform is very important. Therefore, I will also explain 1D and 2D Fourier transform by showing some examples.