Disputation: Domas Birenis
Doctoral candidate Domas Birenis at the Department Of Physics, Faculty of Mathematics and Natural Sciences, is defending the thesis
“Fundamental investigations of hydrogen embrittlement by using electron microscopy”
for the degree of Philosophiae Doctor.
"The plasticity mechanisms"
Domas Birenis is a physicist with extensive experience in electron microscopy and interests in semiconductor physics, metallurgy and hydrogen energy technologies. In his PhD project he studied hydrogen embrittlement in steels by employing advanced electron microscopy techniques.
Hydrogen is one of the major problems in offshore industry and causes catastrophic failures of mechanical components despite their conformity to international standards. Hydrogen is a byproduct of corrosion and cannot be avoided in subsea mechanical parts. On the other hand, the lack of fundamental understanding about how hydrogen affects mechanical properties of various metals and alloys, makes their performance under hydrogen containing environment to be hard to predict.
In his work, Domas discovered that hydrogen has dramatic influence on the dislocation reorganization during deformation of metals. Dislocations are planar defects in solid state materials and are the main reason why some materials can be deformed plastically (copper wires), and others break immediately if deformed even a tiny bit (glass). Some strong evidence was found that hydrogen obstructs dislocation motion and, in this way, suppresses plastic deformation. Scanning electron microscopy and transmission electron microscopy was used to demonstrate that the same material loaded in air develops higher number and more complex networks of dislocations than in hydrogen. Hydrogen was expected to pin the dislocations and slow down or completely stop their motion at given stress levels therefore causing premature cracking.