The distribution of deuterium before (a) and during (b) the application of the mechanical load

The distribution of deuterium before (a) and during (b) the application of the mechanical load

Source: BAM, Department Component Safety

The following contribution presents the distribution of hydrogen isotope, deuterium (2H), at the microscale by time-of-flight secondary ion mass spectrometry (ToF-SIMS). This method was combined with scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) before and after electrochemical charging for 120 hours. Enhanced data analysis was performed by applying principal component analysis (PCA) of raw ToF-SIMS data and fusion with SEM images.

In addition to the combination of structural and chemical data on the same region of interest, an innovative four-point-bending device was developed to allow external mechanical load, elucidate the influence of the external load on the mobility of deuterium and to simulate in-service conditions. For this reason, the mechanical load was applied on the sample during ToF-SIMS analysis.

The experiments revealed that electrochemical charging causes severe cracking of the surface and transformation of pristine austenitic grains into both epsilon- and alpha prime-martensite. Phase transformation took place on preferred slip bands. The correlation with the SIMS data revealed higher intensities of deuterium not only in the retained austenite, as it was expected, but also in the newly formed martensite. This finding is especially remarkable since martensite, in comparison to austenite, is well known to have much lower solubility for hydrogen and, thus, deuterium.

A comparison of the fused SIMS and SEM images before and during the application of mechanical load indicates a movement of deuterium towards the regions of highest tensile stress predominantly due to the application of the load.

With the present findings, the authors provide for the first time a deeper insight into hydrogen-induced damage of austenitic stainless steels in the microscale. The results shown here provide a new perspective in understanding the formation dynamics of martensitic phases in austenite and the impact of hydrogen on these dynamics.

In-situ ToF-SIMS analyses of deuterium re-distribution in austenitic steel AISI 304L under mechanical load
Andreas Röhsler, Oded Sobol, Hannu Hänninen, Thomas Böllinghaus
published in Scientific Reports, Vol. 10, article number 3611, 2020
BAM, Department Component Safety