“Nitrogen Transfer Processes of Cobalt Chromium Alloy During Plasma Nitriding”

Author, institution: Akvilė Petraitienė, Kaunas University of Technology

Science area, field: Physical Science, Physics

The doctoral dissertation is available at the library of Kaunas University of Technology (K. Donelaičio St. 20, 44239 Kaunas, Lithuania).

Scientific Supervisor:

Prof. Dr. Habil. Arvaidas GALDIKAS (Kaunas University of Technology, Physical Sciences, Physics – 02P).

Dissertation Defense Board of Physics Science Field:

Prof. Dr. Giedrius LAUKAITIS (Kaunas University of Technology, Physical Sciences, Physics – 02P) – chairman;

Prof. Dr. Diana ADLIENĖ (Kaunas University of Technology, Physical Sciences, Physics – 02P);

Prof. Dr. Liutauras MARCINAUSKAS (Kaunas University of Technology, Physical Sciences, Physics – 02P);

Prof. Dr. Liudas PRANEVIČIUS (Vytautas Magnum University, Physical Sciences, Physics – 02P);

Dr. Vitas VALINČIUS (Lithuanian Energy Institute, Technological Sciences, Energetics and Power Engineering – 06T).

Official Opponents:

Assoc. Prof. Dr. Mindaugas ANDRULEVIČIUS (Kaunas University of Technology, Physical Sciences, Physics – 02P);

Assoc. Prof. Dr. Saulius MICKEVIČIUS (Vytautas Magnum University, Physical Sciences, Physics – 02P).

Annotation:

The aim of this dissertation is to analyse nitrogen mass transport in the plasma nitrided CoCr alloys. The main goal –  to adapt the physical kinetic models for evaluating various mass transfer (diffusion) mechanisms and to describe them mathematically. It was developed modified “trapping – detrapping” model, which involves the influence of chromium to nitrogen diffusion. The adequacy of the model was tested with using two medical CoCr alloys. This model involves nitrogen adsorption on the surface, the swelling or sputtering processes of the surface and concentration dependent nitrogen diffusion. By applying this model was obtained sufficient theoretical results fitting to the experimental results. Moreover, the influence of various model’s parameters for nitrogen distribution was obtained. The stress induced nitrogen diffusion model was also applied for above mentioned CoCr alloys. The model was modified by involving above mentioned physical processes, whose occur during plasma nitriding.  According to excellent agreement theoretical results with experimental results was driven the conclusion that this model can be reasonably used for the nitrogen concentration distribution analysis in plasma nitrided CoCr alloys. During experiment was established that nitrogen diffusion coefficient depends on the stresses whose form during plasma nitriding, when nitrogen concentration is higher 15 at. %.