Defect Engineering in Carbide Crystal: Innovative Strategy for Prevention of Hydrogen Embrittlement
2024/3/22
Key technology for hydrogen energy in carbon net-zero era
Prof. Hung-Wei (Homer) Yen from Department of Materials Science & Engineering and ARC-Green Materials Science Technology worked with Prof Julie Cairney (the University of Sydney) and Prof. Hao Chen (Tsinghua University) in an international team, which aims at developing materials strategy for prevention of hydrogen embrittlement in steels. They recently publish their new discovery in 《Nature Communications》.
Just a few ppmw of nascent hydrogen can lead to catastrophic failures in steels, as diffusible hydrogen promotes the formation and propagation of cracks within the material. This failure phenomenon is known as hydrogen embrittlement (HE), a problem that has remained unresolved since it was identified in 1875. While hydrogen is being recognized as a crucial clean energy source for a net-zero society, HE poses significant risks during the manufacturing, storage, transport, and application of hydrogen. Consequently, the prevention of HE has become a major focus of global attention.
In materials design strategies, creating critical microstructures to act as hydrogen traps, which limits diffusion of hydrogen, is an important strategy for inhibiting HE. A typical hydrogen trap used in steel is TiC nano-carbide. Although TiC has been utilized for over 20 years, its efficiency in inhibiting hydrogen embrittlement remains limited. This research team first employed first-principles calculations to confirm that carbon vacancies in the carbide are effective hydrogen traps, capable of inhibiting hydrogen diffusion in steel. To validate this concept, the team developed advanced high-strength steels with interphase-precipitated TiC and (Ti, Mo)C carbides. However, to detect the distribution of trace hydrogen within these nanostructures is challenging. This team developed a method using deuterium to replace hydrogen in atom probe tomography (APT), and comprehensively revealed the carbon vacancy concentration and hydrogen (deuterium) trapping behaviors in the nano-carbides. These findings revealed that the complex (Ti, Mo)C exhibits a higher concentration of carbon vacancies, allowing hydrogen trapping within the carbon vacancies, whereas typical TiC can only trap hydrogen atoms at the carbide interfaces. Thus, complex (Ti, Mo)C demonstrates a superior hydrogen trapping capability than TiC. In materials engineering, the substitution of Ti4+ ions in TiC carbides by Mo2+ ions is crucial for creating carbon vacancy defects. Such defect engineering in carbide crystal can be a strategy to imporve the resistance to hydrogen embrittlement of steels. This work represents a significant achievement in our university's research on net-zero carbon emissions.
Prof. Yen has been researching interphase-precipitated carbides in steels for over 15 years. Since 2016, he has focused on studying hydrogen embrittlement in various metallic materials. He has collaborated with Prof. Julie Cairney through the USyd-NTU Partnership Collaboration Award (now known as the NTU-USyd Ignition Grants) for many years. They have published multiple papers in journals such as Acta Materialia, Scripta Materialia, and Materials & Design on topics related to complex carbides and hydrogen traps. The findings of this research represent a culmination of their long-term collaboration, encompassing theoretical calculations, materials design, and advanced analytical detection. This work is an important achievement that reflects our university's commitment to international interdisciplinary collaboration.
Figure 1 (a) TiC nano-carbide and (b) (Ti, Mo)C nano-carbide in advanced high-strength steels, and (c) hydrogen thermal desorption analyses of the two steels.
Figure 2 Atom probe characterizations on deuterium distributions around (a) TiC nano-carbides and (b) (Ti, Mo)C nano-carbides in advanced high-strength steels, along with (c) accumulative depth profiles of chemical composition of the carbides.