Hydrogen bombardment-induced nano blisters in multilayered Mo/Si coatings

• A multilayered mechanical model for nanoblisters induced by hydrogen bombardment on Mo/Si coatings was developed and validated. • Mode-I and mode-II energy release rates at blister tips were theoretically derived. • Small blisters show quadratic height-radius relationship with mixed-mode fracture exposed to hydrogen ions . • Large blisters show linear height-radius relationship with pure mode-II fracture exposed to hydrogen neutrals. • Variations in fracture toughness were elucidated in terms of hydrogen species, exposure temperature, dose, and energy. Nanometer-thick multilayered Mo/Si coatings, employed as artificial Bragg structures, are essential for reflecting specific wavelengths of light in synchrotrons, space telescopes, and extreme ultraviolet optical systems. However, these coatings are prone to blistering failures when exposed to energetic fluxes, such as hydrogen bombardment and solar wind particles. The blistering mechanism is investigated through systematic analysis of experimental data and the development of a multilayered mechanical model based on pockets of energy concentration theory. Energy release rates for pure mode fracture at blister tips, the evolution of blister morphologies, and interface fracture toughness are assessed through theoretical derivations. The relationship between blister radii and heights is elucidated and quantitatively validated against experimental data. Variations in fracture toughness are correlated to hydrogen characteristics, and the influence of hydrogen species, exposure temperature, dose, energy, and strained layer thickness on blister formation is evaluated using the developed model. These findings provide crucial insights for optimizing exposure parameters to mitigate blistering and enhance the performance and reliability of multilayered Mo/Si coatings.