Author, Institution: Paulius Andriūnas, Kaunas University of Technology
Science area, field of science: Natural Sciences, Physics, N002
Research supervisor: Prof. Dr. Hab. Arvaidas Galdikas (Kaunas University of Technology, Natural Sciences, Physics, N002)
Research consultant: Assoc. Prof. Dr. Teresa Moskaliovienė (Kaunas University of Technology, Natural Sciences, Physics, N002)
Dissertation Defence Board of Physics Science Field:
Prof. Dr. Diana Adlienė (Kaunas University of Technology, Natural Sciences, Physics, N002) – chairperson
Assoc. Prof. Dr. Brigita Abakevičienė (Kaunas University of Technology, Natural Sciences, Physics, N002)
Assoc. Prof. Dr. Valdas Girdauskas (Vytautas Magnus University, Natural Sciences, Physics, N002)
Assoc. Prof. Dr. Jakob Kjelstrup-Hansen (University of Southern Denmark, Denmark, Natural Sciences, Physics, N002)
Assoc. Prof. Dr. Juris Prikulis (University of Latvia, Latvia, Natural Sciences, Physics, N002)
Dissertation defence meeting will be at Rectorate Hall of Kaunas University of Technology (K. Donelaičio 73-402, Kaunas)
The doctoral dissertation is available at the library of Kaunas University of Technology (Gedimino 50, Kaunas) and on the internet: P. Andriūnas el. dissertation.pdf
© P. Andriūnas, 2025 “The text of the thesis may not be copied, distributed, published, made public, including by making it publicly available on computer networks (Internet), reproduced in any form or by any means, including, but not limited to, electronic, mechanical or other means. Pursuant to Article 25(1) of the Law on Copyright and Related Rights of the Republic of Lithuania, a person with a disability who has difficulties in reading a document of a thesis published on the Internet, and insofar as this is justified by a particular disability, shall request that the document be made available in an alternative form by e-mail to doktorantura@ktu.lt.”
Annotation: The dissertation investigates diffusion-controlled surface modification processes occurring during plasma nitriding, carburizing, and thermal annealing to improve the performance of metallic biomaterials — austenitic stainless steel AISI 316L and titanium alloys (Ti6242, TA6V). The aim is to develop and validate a mathematical model describing nitrogen and carbon transport, trapping–detrapping, and chemical reaction mechanisms on alloy surfaces. The study employs kinetic equation-based models incorporating stress-induced diffusion and trapping-detrapping effects. Simulations in 1D and 2D spaces include surface adsorption, desorption, and nitride formation processes. Results show that nitrogen diffusion in austenitic steels is governed by lattice stress anisotropy and trapping-detrapping, while annealed nitrided steel forms two plateau-type concentration profiles explained by CrN compound formation and trapped nitrogen distribution. Nitriding through a mask revealed the importance of lateral adsorption and swelling for structure formation. Carburizing simulations confirmed carbon diffusion regularities in AISI 316L, and titanium alloy models showed nitrogen depth profiles depend strongly on Ti₂N phase concentration. The results provide new insights into the interaction between diffusion, stress, and chemical reactions during surface layer formation, enhancing understanding of plasma processing and supporting the improvement of metallic biomaterial surface modification technologies.