Physicochemical Evolution of Rail Deposition Layers in Small-Caliber Circular Bore Electromagnetic Launchers at Extreme Loading

As a paradigm-shifting hypervelocity propulsion technology, electromagnetic rail launch (EMRL) is fundamentally constrained by armature/rail (A/R) interface degradation, which directly erodes its service longevity and operational reliability. Small-caliber circular bore electromagnetic launchers (SCCB-EMRL) offer superior structural integration and ballistic stability over traditional rectangular bores. Their inherently lower self-centering capability imposes strict requirements on interfacial contact stability. This study investigates the physicochemical evolution of the A/R interface at extreme loading. Consecutive repetitive launch experiments were conducted, and samples were prepared by typical areas of rail according to the current curve. Characterization was performed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. Results revealed a bimodal non-uniform thickness distribution of the deposition layer along the launch direction. The maximum deposition thickness reached 60.6 μm within the acceleration-startup zone. The deposited material comprises transferred Al, oxidized phases (Al2O3), Al-Cu intermetallic, and a mixed carbonaceous system containing amorphous and graphitized carbon. Initial launches triggered rapid material accumulation and increased start-up times, after which the interface reached a dynamic equilibrium. This work reveals the evolution patterns of elemental composition and thickness distribution of the deposition layer at the armature/rail interface in small-caliber circular-bore electromagnetic launching and provides experimental reference for the design of anti-deposition coatings to extend the service lifespan of SCCB-EMRL systems.