Dávid Molnár, a doctoral student in Material Engineering, has investigated the behaviour of plastic deformation in austenitic stainless steels by implementing both theoretical and experimental approaches.
"Austenitic stainless steels are primarily known for their exceptional corrosion resistance and are often used as structural materials. That's why it is important to be able to predict their mechanical behaviour," explains Dávid Molnár.
The plastic behavior changes when the steel is deformed. In the prediction of deformation modes, generalised stacking fault energy plays an important role. The generalised stacking fault energy (GSFE) describes the energetics of the deformation on the atomic level.
In his thesis, Dávid Molnár introduces a method that describes in full the generalised stacking fault energy. Until now, this has not been possible because some features cannot be measured directly due to their nature.
"My colleagues and I have developed a theory and an experimental method that can give an estimation for the generalised stacking fault energy. I think the importance of my research is mainly that I try to connect the atomistic calculations and the experiments. This is a very important achievement, because this can help us to validate the theory through experiments and can give a better description of the deformation of the materials," explains Dávid Molnár further.
The theoretical predictions are contrasted with tensile tests and electron backscatter diffraction (EBSD) measurements. The thesis is in large part based on these calculations, which provide reasonably good results that accord with the experimental results.
By using quantum mechanics and making these calculations, numerous properties of the materials can be predicted, and this can help us to design better materials. Engineers can design with less material due to the enhanced strength, and as such this will result in, for example, reduced CO2 emissions.
"What is more, we can design the deformation process in a better way, because we can predict how the material will behave," adds Dávid Molnár.
Dávid Molnár is a doctoral student at Dalarna University and KTH. On September 28, 2018, he defended his licentiate thesis "Generalised stacking fault energy and plastic deformation of austenitic stainless steels".