The Effect of Salt-water Corrosion on Copper Alloy Rail Claddings in a Small Railgun

Abstract

As the U.S. Navy gets closer to fielding shipboard railguns; there is an increasing concern with how surface corrosion of the rail claddings will affect launcher performance and lifetime. It is intuitive to hypothesize that corrosion on the rail surface will negatively affect both the performance and lifetime since significant surface oxide formation on the rail surface will increase the rail/armature contact resistance and surface pitting will reduce the rail/armature contact area. Negative effects from surface corrosion could include increase arcing contact between the armature and the rails, also known as transition, decreasing the launcher efficiency, muzzle velocity, and enhance the rate of rail erosion. In the experiments discussed here, the University of Texas at Arlington has performed two unique sets of experiments. In the first, 6.35-mm diameter C18150 copper rods were pulsed with high current while immersed in a salt fog environment to study how pulsed currents affect surface corrosion. In the second set of experiments, a 1-m-long railgun was used to evaluate the impact of rail corrosion on the launcher operation. A controlled corrosion process was used to induce damage on rail sections positioned at two locations within the gun, the startup and peak current regions, respectively. The launcher has a peak current of roughly 120 kA and a muzzle energy of 1.8 kJ when 14 g launch packages, fabricated from 6061-T6 aluminum, are used. The rail sections, which have dimensions of 1” $\times4$ ” $\times1$ /8,” are fabricated of C18150 and were corroded using a using potentiostatic polarization to drive oxide formation and growth. Railgun performance was evaluated using the standard measurements of armature current, breech voltage, muzzle voltage, and velocity interpolated through b-dots. The rail sections were characterized at the material surface level prior to and after a shot series using scanning electron microscope imagery and x-ray diffraction. Three different sets of samples were tested and include, baseline samples, i.e., no corrosion, samples corroded with a potentiostatic polarization of −0.1 V saturated calomel reference electrode (SCE) for 20 $\text {k}\cdot \text {s}$ in 3.5% NaCl, and samples corroded with a potentiostatic polarization of −0.2 V SCE for 28.8 $\text {k}\cdot \text {s}$ in 3.5% NaCl. Each set of samples were subjected to a series of five railgun shots with a 10-min rest between each shot. The aim of these experiments was to study the surface corrosion induced by the high ohmic heating and pulsed magnetic fields while immersed in a salt fog. The results of both respective types of experiments will be presented here.