An SEM compatible plasma cell for in situ studies of hydrogen-material interaction.

An in situ hydrogen (H) plasma charging and in situ observation method was developed to continuously charge materials, while tensile testing them inside a scanning electron microscope (SEM). The present work will introduce and validate the setup and showcase an application allowing high-resolution observation of H-material interactions in a Ni-based alloy, Alloy 718. The effect of charging time and pre-straining was investigated. Fracture surface observation showed the expected ductile microvoid coalescence behavior in the uncharged samples, while the charged ones displayed brittle intergranular and quasi-cleavage failure. With the in situ images, it was possible to monitor the sample deformation and correlate the different crack propagation rates with the load-elongation curves. H-charging reduced the material ductility, while increasing pre-strain decreased hydrogen embrittlement susceptibility due to the possible suppression of mechanical twinning during the tensile test and, therefore, a reduction in H concentration at grain and twin boundaries. All the presented results demonstrated the validity of the method and the possibility of in situ continuously charging of materials with H without presenting any technical risk for the SEM.