Hydrogen embrittlement – quantification of H ahead of a crack tip to understand a crucial challenge for high strength steels

This proposal targets the phenomenon of hydrogen embrittlement (HE). HE is one of the main challenges in the development of next generation high-strength steels and is widely acknowledged to be a very complex and poorly understood materials phenomenon. To a large part, this is because hydrogen (H) is extremely hard to detect in situ. We aim to significantly improve the ability to detect, and model, H in steel by systematically developing the experimental techniques to fully exploit the potential of neutron imaging and diffraction in this field.
In a previous experimental campaign at ILL's NeXT, we designed an experimental setup using a mobile load frame to electrochemically charge a high-strength martensitic steel specimen under mechanical loading to image the specimen while maintaining the load. Our in-situ neutron radiography data showed an increased attenuation signal (2.5%, corresponding to ~78ppm.wt H locally). While promising, an unintended and significantly different crack growth rendered the data interpretation ambiguous. In this proposed experiment at IMAT, we will use a setup that ensures conventional crack growth and employ improved background reduction and scattering corrections. We will focus on systematic changes to the protocol to quantify hydrogen. Additionally, we will use time-of-flight to obtain higher precision results and strain maps via Bragg edge analysis.