Speaker
Description
Understanding the effects of hydrogen in materials became a pressing topic with the imminent shift towards green technologies and the adoption of hydrogen as energy carrier. It is expected that the use of hydrogen will increase in all industries, together with the need for safe transport and storage and consequently the development of new materials and technologies to cope with it. A critical challenge is hydrogen-induced damage, or hydrogen embrittlement, that can cause the sudden failure of a material.
Current studies on hydrogen effects are in their majority limited to post-mortem probes and ex-situ charging, which neglect diffusible hydrogen and its migration and desorption at the analysis time. Additionally, it is necessary to characterize hydrogen and its effects in materials at the relevant small-scale dimensions where embrittlement initiates. To combine these substantial yet demanding tasks, we designed a novel “back-side” charging approach, to perform micromechanical testing during hydrogen charging. Hydrogen is generated electrochemically at the back-side and diffuses towards the testing (front-side) surface. This unique method allows differentiating between the effects of trapped and mobile hydrogen, and performing well controlled measurements with different hydrogen levels monitored over time to consider hydrogen absorption, diffusion and release.
In this talk, I will present first an overview of the technique, including its advantages and limitations. Secondly, I will discuss the effects of diffusible hydrogen on binary Fe-based alloys, unraveling the dynamic effects of hydrogen using time-resolved nanoindentation testing. Finally, I will introduce the application of the method to study Al2O3 as a hydrogen barrier coating, which is an appealing option to prevent and/or slow down the hydrogen ingress into structural alloys that are susceptible to embrittlement. The mechanical testing is always complemented by additional techniques to measure the hydrogen behavior, such as thermal desorption spectroscopy and Kelvin probe testing, and the changes in the microstructure, including scanning and transmission electron microscopy, and atom probe tomography. Particularly, I will highlight the relevance of this last technique, where more complementary studies are required.
