Electromigration related effects at metal-metal interfaces application to railguns

Abstract

This thesis had 2 objectives. The first purpose of this thesis was to develop an experimental procedure to study electric current induced flow of liquid metal, similar to that found at the armature-rail contact due to local melting, to determine the kinetics of liquid flow Ga under electric current conditions. For this, a model system comprising a bead of Ga on a Cu thin film track was devised in order to enable liquefaction and current induced movement of Ga to occur along the Cu track. Upon application of current, Ga underwent liquefaction due to Joule heating and once liquid, it rapidly migrated along the Cu track towards the negative terminal. The Ga liquid flow was attributed to electromigration of liquid Ga under the influence of direct electric field. The kinetics of Ga flow was determined. This method will be useful in calculating the kinetics of electromigration of molten Al along Cu rails in future railgun development. The second purpose of this thesis was to analyze debris left on Cu/24Ag rails following firing of 7075Al armatures, in order to understand the compositional evolution of the debris, and its role in creating surface damage to armature/rail interfacial surfaces. EDS analysis showed a majority of the debris was composed of oxidized aluminum with significant porosity. The analysis of the rail debris will benefit future studies on preventing rail debris from damaging railguns.