Effect of Preparation Method on TEM Specimen

Abstract

We have investigated the amorphous phase of bulk metallic glass Zr 41.25 We have examined the influences of TEM specimen preparation techniques on the microstructural evolution of the BMG.The Differential Scanning Calorimetry measurements were performed with a Perkin-Elmer Pyris 1 DSC. TEM observations were conducted on a Philips CM300 and a Philips EM430 machines both operating at 300 kV. One group of specimens were mechanical thinned and polished and then dimpled to a thickness of less than 15 um. This was followed by ion milling at an incident angle of 5 0 for approximately 9 h to electron transparency at room temperature using a Gatan 691 Precision Ion Polishing System. Another group of specimens were prepared by dispersing finely ground BMG powders onto holey carbon film supported by a microgrid. The toughness of BMG material prevented crushing of solid pieces using a mortar and pestle, instead powder was produced by grinding on a new sheet of diamond lapping film. The abrasive particles contaminating the powder were easily distinguished (and therefore avoided) in the TEM based on their different appearance and chemical composition.Representative TEM observations of the Zr 41.25 Ti 13.75 Ni 10 Cu 12.5 Be 22.5 BMG prepared by grinding are shown in Fig. 1a and b. At high magnification, the TEM image exhibits a maze-like pattern at the sub-nanomatre scale as shown in Fig. 1a. Fig. 1b shows a corresponding SAED pattern with two diffraction rings. All these features are consistent with an inherent amorphous character of the BMG. The ion milled BMG shows a quite different character (see Fig. 1c) -some patterns of thickness variation (presumed due to preferred etching) now dominate the TEM image. Also, the corresponding SAED pattern shows more weak diffraction rings appear at higher diffraction angles (see Fig. 1d), indicating early stages of the nanocrystallization [7].To further characterize the structure of the ion milled BMG, DSC analysis was carried out to monitor the crystallization process. Fig. 2 shows the DSC traces of the BMG prepared by ion milling. The ion