Eason (Yi-Sheng) Chen

Hydrogen embrittlement of high-strength steel is an obstacle for using these steels in sustainable energy production. Hydrogen embrittlement involves hydrogen-defect interactions at multiple-length scales. However, the challenge of measuring the precise location of hydrogen atoms limits our understanding. Thermal desorption spectroscopy can identify hydrogen retention or trapping, but data cannot be easily linked to the relative contributions of different microstructural features. We used… Show more

Hydrogen embrittlement of high-strength steel is an obstacle for using these steels in sustainable energy production. Hydrogen embrittlement involves hydrogen-defect interactions at multiple-length scales. However, the challenge of measuring the precise location of hydrogen atoms limits our understanding. Thermal desorption spectroscopy can identify hydrogen retention or trapping, but data cannot be easily linked to the relative contributions of different microstructural features. We used cryo-transfer atom probe tomography to observe hydrogen at specific microstructural features in steels. Direct observation of hydrogen at carbon-rich dislocations and grain boundaries provides validation for embrittlement models. Hydrogen observed at an incoherent interface between niobium carbides and the surrounding steel provides direct evidence that these incoherent boundaries can act as trapping sites. This information is vital for designing embrittlement-resistant steels. Show less

This work demonstrates a new method to enable cryogenic atom probe tomography (cryo-APT) for the investigation of hydrogen in a high-strength steel, specifically to detect hydrogen localised to V–Mo–Nb carbides finely dispersed in the matrix. Prior cryogenic experiments required highly customised atom probe instrumentation to enable samples to be kept at cryogenic temperatures throughout the vacuum transfer process. Here we use an alternative approach without modification of the atom probe… Show more

This work demonstrates a new method to enable cryogenic atom probe tomography (cryo-APT) for the investigation of hydrogen in a high-strength steel, specifically to detect hydrogen localised to V–Mo–Nb carbides finely dispersed in the matrix. Prior cryogenic experiments required highly customised atom probe instrumentation to enable samples to be kept at cryogenic temperatures throughout the vacuum transfer process. Here we use an alternative approach without modification of the atom probe instrument itself, whilst still achieving hydrogen mapping. Additionally, we use this method to investigate the roles of solvent and solutes within the charging electrolyte, and we demonstrate that deuterated solute is not required when using heavy water as solvent, expanding the range of electrolytes that can be utilised in APT hydrogen charging experiments. This work reduces the experimental requirements for cryo-APT and makes the technique accessible to all APT equipped laboratories. Show less

The design of atomic-scale microstructural traps to limit the diffusion of hydrogen is one key strategy in the development of hydrogen-embrittlement–resistant materials. In the case of bearing steels, an effective trapping mechanism may be the incorporation of finely dispersed V-Mo-Nb carbides in a ferrite matrix. First, we charged a ferritic steel with deuterium by means of electrolytic loading to achieve a high hydrogen concentration. We then immobilized it in the microstructure with a… Show more

The design of atomic-scale microstructural traps to limit the diffusion of hydrogen is one key strategy in the development of hydrogen-embrittlement–resistant materials. In the case of bearing steels, an effective trapping mechanism may be the incorporation of finely dispersed V-Mo-Nb carbides in a ferrite matrix. First, we charged a ferritic steel with deuterium by means of electrolytic loading to achieve a high hydrogen concentration. We then immobilized it in the microstructure with a cryogenic transfer protocol before atom probe tomography (APT) analysis. Using APT, we show trapping of hydrogen within the core of these carbides with quantitative composition profiles. Furthermore, with this method the experiment can be feasibly replicated in any APT-equipped laboratory by using a simple cold chain. Show less