Crack Tip Mechano-Chemistry and Roles of Hydrogen
Tetsuo Shoji
Frontier Research Initiative, New Industry Creation Hatchery Center
Tohoku University
Abstract
Stress corrosion cracking is one of the most complicated degradation phenomena where mechanics and chemistry synergistically interact in specific processes for specific materials/environmental combination. In terms of mechanics, there are two aspects. One is microstructural aspect such as crystal structure, chemical composition, dislocation, grain boundary, vacancy etc. and the other is macroscopic aspect such as mechanical properties, yield strength, strain hardening property, ductility. Theoretical crack growth rate was proposed based upon a strain rate caused not only by an external loading but also by a crack advance at stressed crack tip. Recently, the importance of roles of hydrogen has been receiving more attention in the processes of mechano-chemical reaction at SCC tip. Namely, hydrogen may play the important roles in,
- Acceleration of an oxidation process at oxidation front under some conditions
- Change mechanical properties of materials at crack tip
- Acceleration of creep deformation at crack tip
- Interaction with vacancies to form superabundant vacancy to cause mechanical property change as mentioned above.
- Degradation of a protective capability of oxide film.
In this talk, crack tip mechano-chemical processes will be described at the stages of SCC initiation, short crack growth and propagation and various possible roles of hydrogen in the processes will be summarized and discussed with some experimental evidences obtained so far. Finally, implication of these phenomena to plant service safety and performance will be emphasized in some energy conversion systems.
Tetsuo Shoji
Tetsuo Shoji has been serving as a Professor of Tohoku University since 1986 until March 2018 and an Executive Vice-President for research and international affairs of Tohoku University since 2005 for 3 years. He was honored as a Professor Emeritus of Tohoku University in 2015. Now he continues his research work as a Senior Research Fellow at of New Industry Creation Hatchery Center (NICHe) of Tohoku University, as a Distinguished Professor of National Center for Materials Service Safety, University of Science and Technology Beijing, USTB and also as a High-level Foreign Professor of Sichuan University. He was a postdoctoral fellow working for Professor R. N. Parkins at the University of Newcastle Upon Tyne, UK, and a Visiting Professor of MIT. He served as the PI of various national and international programs such as the Center of Excellence Program on Physics and Chemistry of Fracture and Failure Prevention, the Co-Director both of CNRS LIA ELyT laboratory and the international Joint Laboratory of Tohoku University and USTB, and International cooperative research program of PEACE, POLIM and SMEtana, working on mechanics and mechanisms of Environmentally Assisted Degradation such as SCC and Environmental Fatigue. He has received 21 national and 9 international awards including NACE W. R. Whitney Award, the Lee Hsun Award, Chinese Academy of Science, the Great Medal from CEFRACOR, France in 2016 and UR Evans Awards from the Institute of Corrosion, UK in 2019. He was appointed by the Prime Minister as a Council Member of Science Council of Japan in 2011 for 7 years and was elected as a Member of Science Council of Japan in 2018 for 6 years and also elected as a member of the Japan Engineering Academy. He published more than 560 journal papers covering atomic scale simulation of oxidation, hydrogen accelerated oxidation, mechanism-based alloy design, electrochemical materials characterization, mechanistic study of oxidation, non-destructive testing and evaluation and fracture mechanics and failure analysis.