Mechanical properties and interfacial tribological mechanisms of silver-doped 316L stainless steel under cryogenic conditions

High-performance stainless steels have been utilized in reusable rockets to achieve significant reductions in manufacturing and maintenance costs. In this study, the influence of silver doping on the mechanical and tribological performance of 316L stainless steel under cryogenic conditions was experimentally evaluated. Three different silver mass concentrations of 5 wt%, 10 wt%, and 15 wt% were used, and the corresponding microstructural features were analyzed using optical microscopy, EDS, and EBSD. The cryogenic environment of rocket of rocket turbopumps was simulated by immersing the test samples in liquid nitrogen. The Rockwell hardness, impact fatigue resistance, and tribological behaviors were then tested under both room-temperature and cryogenic conditions. The results indicated that silver atoms segregate at austenite grain boundaries, which stabilizes the microstructure by suppressing martensitic transformation. The silver doping improved the cryogenic ductility and impact fatigue resistance due to enhanced plastic flow characteristics. The inherent lubricity of silver facilitated the formation of a self-lubricating film at the frictional interfaces, thereby reducing the friction coefficient and wear rate. Although the introduction of silver slightly decreased the hardness and toughness, its ability to stabilize grains and provide interfacial lubricity optimized the overall cryogenic performance of the 316L stainless steel. This study can promote the development of novel durable materials with high reliability for reusable rockets and other cryogenic equipment.