Fundamental investigations of hydrogen embrittlement by using electron microscopy

Abstract

The scope of this thesis was to explore the applications of electron microscopy in the field of hydrogen embrittlement (HE). The fundamental understanding of HE is still lacking and requires some advanced approaches to improve it. Electron energy-loss spectroscopy (EELS) was tested as a potentially viable technique for indirect hydrogen detection at nano-scale with transmission electron microscope (TEM). Hydrogen trapped at the grain boundaries or dislocations changes electronic structure of local iron atoms in pure Fe specimens as predicted by density functional theory (DFT). Such alterations could in principle be observed by EELS experiments, however they were not successful presumably due to knock out damage by the high dose electron beam, and high background signal because of low concentration of hydrogen. In addition, dislocation structures were studied in post-mortem specimens fractured in hydrogen, air and nitrogen gases. Scanning electron microscopy and scanning TEM have shown plasticity and dislocation organization variations in different atmospheres, which implied that hydrogen alters dislocation motion.