Impact of high-pressure hydrogen charging on mechanical behavior and lattice parameters of a polycrystalline CoNiCr-based superalloy

Due to the increasing significance of hydrogen in future applications, it is crucial to address the potential effects of hydrogen on material safety in hydrogen-rich environments. Detecting hydrogen remains challenging. In this study, we provide an explanation for hydrogen embrittlement in a CoNiCr-based superalloy using a combination of NanoSIMS measurements, synchrotron and neutron diffraction, and analysis of fractured tensile samples from hydrogen-charged specimens. NanoSIMS mappings and diffraction experiments revealed the highest hydrogen concentration inside precipitates of the µ phase. Neutron diffraction experiments indicate that the γ′ phase slightly incorporates more hydrogen than the γ phase, therefore expands comparatively more and thus, the positive γ/γ′-lattice misfit increases a little. This results in a strong influence of hydrogen on the mechanical properties of hydrogen as revealed by tensile tests. Hydrogen inside µ phase particles and at γ/γ′-interfaces leads to pronounced crack initiation at γ/µ-interfaces and facilitates crack propagation along weakened γ/γ′-interfaces.