Hydrogen (H) embrittlement is a complex phenomenon that impedes the application of high-strength steel in certain instances. One measure to prevent mobile, and therefore harmful, H from diffusing to critically loaded regions is introducing traps within the microstructure. It has been shown that carbides can act as strong H traps. Hence, nano-scale precipitation can provide not only mechanical strength but also abundant trapping sites that bind diffusible H.
Atom probe tomography is a characterization tool with nearly atomic resolution and high sensitivity for all elements. The investigation of H traps can be done with deuterium-charged specimens to avoid artificial H signal from the vacuum chamber.
In this study, atom probe needle-shaped specimens are prepared from commercial steels with co-precipitation of intermetallic NiAl and Cr carbides (Hybrid® steel) as well as nano-scale Mo and V-rich carbides. The needles are then cathodically charged in a solution of 0.1 M NaOH in heavy water (D2O) to introduce deuterium into the samples. The measurements are conducted with the newest generation of commercial atom probe instruments, a LEAP® 6000 XR from CAMECA Inc. (Madison, WI, USA). The position and the distribution of D ions in the material inform about the effective trapping sites. This knowledge helps improve the design of steel variants for effective application in fields where hydrogen embrittlement is critical.