The response of different copper alloys as rail contacts at the breech of an electromagnetic launcher

Current flow through the breech region of the rail conductor produces the longest exposure to Joule heating for any location in a simple electromagnetic launcher (EML) bore. Movement of a solid, stationary armature occurs when electromagnetic propulsion forces exceed frictional and mechanical loading forces imposed at start-up. Consequently, the armature dwells at this "footprint" for an extended thermal cycle longer than any subsequently traversed location. The authors report results of four copper alloy specimens (Be-Cu, Cu-Cr, Cu-W, DS Cu) placed as removable tiles near the breech of a medium caliber EML. Specimen performance in single or multiple launch tests is evaluated by strength, hardness, electrical and thermal conductivity properties. Muzzle voltage traces are used to fingerprint the electrical performance for peak currents exceeding 900 kA. The materials are evaluated by optical microscopy for changes in microstructure and hardness, and by optical profilometry for surface damage that could affect long term performance.