Mechanistic understanding the mechanism of hydrogen-facilitated stress corrosion cracking - DiffH-SCC
Lead Research Organisation:
University of Oxford
Department Name: Materials
Abstract
Nuclear energy is forecast by the European Commission to make a significant contribution to achieving a low-carbon, affordable energy, enhancing energy security during the development of renewables. However, stress corrosion cracking (SCC) is one of the biggest obstacles, as it induces unexpected failure to nuclear power plant components, threatening operational safety. Mitigating SCC requires a thorough understanding of its mechanisms, of which the current understanding is limited. In recent years, the applicant researcher and his colleagues have found that diffusible hydrogen plays a critical role in the evolution of SCC, which is beyond the existing understanding. Therefore, this project aims to uncover new SCC mechanisms in Ni-based alloys (materials used in nuclear power plants) from the perspective of the role of diffusible hydrogen, based on the good foundation of research by the applicant. The multi-scale experimental approach will focus on in-situ materials characterisation of Ni-based alloys during mechanical testing with in-situ hydrogen charging. This project employs experiments at different length-scales: a) crack initiation at the macroscale; b) strain distribution in different microstructures; and c) mechanical testing of single microstructures at the microscale. This research will make use of state-of-the-art equipment from interdisciplinary domains including materials engineering, electrochemistry, electron microscopy, mechanical engineering, and corrosion fields. The proposal emphasises the transfer of knowledge of advanced techniques between the host and researcher, while employing various training processes (including transferable skills) for both academia and non-academia sectors. Through effective and open dissemination and exploitation procedures, the results have the potential to provide practical suggestions and guidance to our end-users for producing alloys with higher SCC-resistance for a safer utilisation of nuclear energy.
Publications
| Description | This research stemmed from a classic field but entered a brand new and innovative domain, in which the ideology pioneered the mechanistic study of H-SCC. This project made use of the most ambitious in-situ observation methods ever used to clarify and visualize the role of diffusible hydrogen in crack evolution (initiation and propagation) mechanistically, going beyond the then-current state-of-the-art. The interactions between material microstructure, diffusible hydrogen, plastic deformation, and dislocation movement were directly visualized in this work. Beyond this application, our ambitions were not limited to just SCC but aimed to provide a much wider understanding of various other hydrogen-related material destruction fields in the then-emerging decarbonized society, such as hydrogen storage, hydrogen fuel cells, etc. in the future research. |
| Exploitation Route | Other groups in the Department of Materials (Oxford, UK), Tohoku University (Japan) and UKAEA (UK) will use the methodology developed in this project to perform nanoindentation under gas Hydrogen charging conditions. |
| Sectors | Aerospace Defence and Marine Energy |
| Description | Despite decades of research, the mechanism of SCC was still not fully understood. This research adopted a pioneering ideology and state-of-the-art equipment to reveal the essential mechanisms of diffusible hydrogen in SCC, which, as a long-term prospect, was believed to lay the foundation for the complete elimination of SCC. Although this topic stemmed from H-SCC, its scientific principles could be applied to other interdisciplinary fields, such as HE, hydrogen-induced oxidation, hydrogen fuel cells, etc. The outcomes of this research directly contributed to the design and development of HE/corrosion-resistant materials. Finally, to reinforce scientific equipment and instruments, the state-of-the-art characterization instruments developed during the research could be used in diverse gas-material interaction systems. It was expected that the work would reduce the repair rate of key components in power plants, greatly decreasing the cost of operation, which brought significant budget savings according to the EU's then-current energy strategy. From a long-term perspective, safe and low-cost NPPs would reduce electricity prices significantly. Such technological advances made cheap electricity possible and greatly stimulated the economy. |
| First Year Of Impact | 2024 |
| Sector | Aerospace, Defence and Marine,Energy |
| Impact Types | Economic |
| Title | A high temperature hydrogen charging system in nano-indentation |
| Description | Our team has developed a high-temperature mechanical testing system equipped with an in-situ hydrogen charging system. The specimen (stainless steel) can undergo nano-indentation testing at 300°C. |
| Type Of Material | Improvements to research infrastructure |
| Year Produced | 2023 |
| Provided To Others? | No |
| Impact | This setup will be utilized to investigate the relationship between diffusible hydrogen and dislocation mobility at elevated temperatures, contributing to a better understanding of stress corrosion cracking. It can also serve as a prototype for further modifications aimed at studying hydrogen embrittlement. |
| Description | Collaboration with Tohoku University |
| Organisation | Tohoku University |
| Country | Japan |
| Sector | Academic/University |
| PI Contribution | I designed the experiment, including the setup of the hydrogen charging method, with a solid and feasible procedure. Additionally, I am responsible for ensuring the quality of the experiments conducted by our partner, Tohoku University. After our partner tests the designed sample, I proceed with subsequent tasks, such as sample characterization, data analysis, etc. |
| Collaborator Contribution | The initial phase of my project involves conducting a mechanical test in pressurized high-temperature water using an in-situ hydrogen charging system integrated into the setup. This work requires specialized equipment and the assistance of a dedicated technician, which is unavailable in my current department. Our collaborator has generously provided the necessary resources for this experiment at no extra cost. Furthermore, they have actively participated in discussions regarding the data generated during the experiment. |
| Impact | At this moment, two types of tensile test specimens have been completed, revealing promising data that supports the hypothesis of hydrogen facilitating stress corrosion cracking, as evidenced by the stress-strain curve. Another set of verification tests is currently underway. |
| Start Year | 2023 |
| Description | Tsinghua University expertise |
| Organisation | Tsinghua University China |
| Country | China |
| Sector | Academic/University |
| PI Contribution | Joint publication and support for future collaborative projects |
| Collaborator Contribution | Provided discussion and advice on highly-specialized topic. |
| Impact | Joint publication and collaboration |
| Start Year | 2022 |
| Description | Outreach |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | I attended an international conference as an invited speaker, where I introduced the basic concepts of my current research and discussed its potential impact on the industry. Attendees from both academic institutes and the industry showed great interest in the presentation. |
| Year(s) Of Engagement Activity | 2023 |