Hydrogen-related environment and its effect on superalloys: a review—targeted for potential aero-engine application

With the proposal of the "dual carbon”goals，using hydrogen as zero-carbon alternative fuel has become an important trend of the aviation industry in the future. In recent years，the hydrogen-fueled aero-engines have garnered significant attention. Superalloys are the most widely used materials in the hot section components of gas turbine engines. The purpose of this review is to provide reference for the research and development of superalloys for hydrogen-fueled aero-engines future use by understanding the effects of hydrogen-related environment on superalloys currently across various fields. Internal/external hydrogen environments，hydrogen permeation（charging）methods，measurement of hydrogen concentration/distribution or stable existence temperature，the influence of hydrogen on tensile strength，the impact of hydrogen on creep/stress rupture and fatigue properties，and the fracture mechanism of hydrogen embrittlement are described. The degradation factors of mechanical properties of superalloys with different composition，manufacturing process，original microstructure，alloying degree and different application fields under hydrogen-related environment are summarized. In general, mechanical properties tests in the external hydrogen environment exhibit more significant hydrogen-assisted mechanical degradations than that in internal hydrogen environments. Superalloys with higher alloying degree exhibit more pronounced hydrogen embrittlement，while the tendency of properties decrease（creep/rupture，fatigue and tensile）in hydrogen at elevated temperature is much less than that at room temperature. The prospects for the mechanical performance evaluation of current superalloys in hydrogen-related environments for hydrogen-fueled gas turbine and the development of new alloys suitable for hydrogen environments are provided. Hydrogen-fueled gas turbine aero-engines may encounter cryogenic temperature hydrogen environment for liquid hydrogen storage，hydrogen environment for cooling，high-temperature/high-pressure hydrogen environment for gas compression，and the impact of combustion products–water vapor（humid）at elevated temperature. Diffusion or permeation of hydrogen in superalloys，the embrittlement and corrosion of alloys in high-pressure hydrogen environments，oxidation and corrosion behavior in high-temperature humid environments，as well as the degradation and protection mechanism for alloys and coatings in the aforementioned multiple coupling environments shall be concerned. It is necessary to establish hydrogen combustion environment experimental facility that closely simulates service conditions to conduct research on the impact of hydrogen-related environment on superalloys and their components. It is also essential to establish a mechanical performance database and standards for currently used key materials in hot section components such as turbine blades and disks for hydrogen related environments，and properly develop new high-temperature structural materials suitable for hydrogen combustion conditions，which will provide support for the application of hydrogen fueled gas turbine aero-engines.