Quantitative energy filtered transmission electron microscopy (EFTEM) of metallic glasses

In some Al-rare earth-transition metal (Al-RE-TM) glasses, nucleation processes are featured with nucleation rates orders of magnitude higher than predicted by classical nucleation theory. Kinetics of nucleation in these metallic glasses is poorly understood, partly due to the difficulties in direct characterization of chemical fluctuation at the nanometric scale. The objective of this thesis is to advance quantitative techniques using Energy Filtered Transmission Electron Microscopy (EFTEM) to the study of local chemical fluctuations associated with the nucleation phenomena in metallic glasses.; The thesis focuses on the methodology for using the energy loss spectrum in a transmission electron microscope to monitor compositional fluctuations in a multicomponent amorphous system. Metallic glass sample Al₈₈Gd ₆La₂Ni₄ was used as testbed to examine their chemistry distribution. Elemental maps and EFTEM image series were used as the multi-variate database. By applying histogram analysis and Principal Component Analysis (PCA) on this multivariate database, detailed compositional distribution information was able to be extracted from the database. The computational procedures for conducting a principal component analysis are described, which result in the establishment of a “chemical image” showing possible fluctuations and clustering of chemistry within the microstructure. A series of images are shown that exhibit length scales of compositional gradients which are qualitatively consistent with suggestions made in the literature for the same composition of metallic glass.; The implications of the thesis procedure extend beyond the specific research testbed of crystallization of metallic glasses used in this thesis. This work extends the field of quantitative energy filtered transmission electron microscopy (EFTEM), with a protocol established for the use of EFTEM in the study of the spatial distributions in chemistry in amorphous materials.