Advanced Rail Materials for Electromagnetic Launchers

Improving the useful rail life is major technical barrier to developing a fleet-deployable electromagnetic (EM) launcher. Current copper alloy rails, while having excellent electrical conductivity, are highly susceptible to hypervelocity gouging, galling, and attack by liquid aluminum transferred from the armature. Without a solution for these rail wear problems, the utility of EM launchers may be greatly limited due to high costs (resulting from a limited number of firings between scheduled rail replacements). Metal matrix composite coatings with refractory metal reinforcement, such as tungsten, molybdenum or tantalum, have been identified by NSWCDD as candidate coating materials for improving rail life. A revolutionary wrought metal deposition method, based on friction stir technology, is being developed through ONR funding by Schultz-Creehan to deposit coatings, including MMC coatings, that are metallurgically bonded with the substrate. This wrought metal deposition technology is referred to as friction stir fabrication (FSF). The application of this technology to the EM rail problem would be a straightforward extrapolation of current research and development efforts. As such, herein, Schultz-Creehan presents a novel but realistic approach to improve EM rail life through the application of MMC coatings using FSF.