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Neutron cameras allow visualizing hydrogen distributions with radiographic or tomographic imaging methods in iron and steel. The necessary contrast between hydrogen and iron stems from the high difference in the total neutron cross section of both elements. This allows e.g. the in situ measurement of hydrogen mass flow inside cm thick steel samples with a temporal resolution of 20 s using neutron radiography as well as the quantitative measurement of hydrogen accumulations at the crack’s inner surfaces in hydrogen embrittled iron samples with neutron tomography. We could detect directly gaseous hydrogen in the crack cavities and we measured the gas pressure. This new quality of the information on a micrometer scale allows new insights for the analysis of hydrogen-induced damage mechanisms. Further, this method is non-destructive and provides local information in situ and in three dimensions with a spatial resolution of 20-30 µm. In this contribution, we show examples that demonstrate the spatial and temporal resolution of the neutron radiography and tomography methods in order to visualize and quantify hydrogen accumulations at cracks. The measurements were performed at the research reactor BER II of the HZB in Berlin and at the FRM II reactor of the neutron source Heinz Maier-Leibnitz in Garching.
Neutron imaging has become a valuable tool for measuring hydrogen distributions qualitatively and quantitatively in metals. Hydrogen mass flow can be measured inside cm thick Steel samples with 10 s temporal resolution. Hydrogen accumulations around craclcs in embrittled iron samples can be visualized three-dimensionally. The gas pressure of hydrogen in crack cavities has been measured to be in the ränge of 5 MPa to 15 MPa. This quality of information allows new insights for the analysis of damage mechanisms on a micrometer scale, e.g., of hydrogen blistering. Further, this method is nondestructive and provides local information in situ and in three dimensions with a spatial resolution of 20 µm - 30 µm.