ON THE NATURE OF THE ARMATURE-RAIL INTERFACE - LIQUID-METAL EFFECTS

This is an experimental study of the nature of the armature-rail inter face during hypervelocity launch in a railgun, It is part of a multidi sciplinary modeling and experimental effort to improve the understandi ng of contact physics. Conditions that occurred at the interface are i nferred from studies of the surfaces of recovered copper rails, Melt l ubrication is observed at the armature-rail interface, Liquid aluminum metal from the contact faces of the solid aluminum armature forms at the armature-rail interface as a result of frictional and joule heatin g, The liquid aluminum is quenched by the relatively cool copper rail, and a quenched metal deposit is formed. Characterization of the depos it has shown a rapidly quenched microstructure, The mean grain size me asured by transmission electron microscopy is 200 mn-the finest grain size reported for a melt quenched aluminum alloy film. The deposit thi ckness is less than 25 mu m and is rough with an oxidized surface, The thicker films;crack, curl, and detach easily from the rail surface, T he experiments were performed in a 25-mm square-bore railgun, with a r atio of interface current to armature contact width of 20-35 kA/mm, Th e liquid production rate by armature melting at the interface is found to be about 1 mg/C, We conclude that in solid armature railguns with sufficiently thick, liquid aluminum melt lubrication, the rail does no t erode, Instead a deposit forms on the rail surface. Depending upon t he him thickness and the quench stresses, the him detaches easily.