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.
Benefit: Extending the useful rail life, in lieu of frequent replacement of the rail, would yield significant cost savings to the EM launcher program, and poses a significant market opportunity for the solution provider. (Based on current and projected commodity prices, and typical fabrication and finishing costs, it is reasonable to expect the production cost of individual rails to exceed $10,000 each, even in high volume.) With such a significant market, extending the rail life even moderately would yield significant return on investment for the United States and the Department of Defense. A significant opportunity exists for any technology able to improve performance in this market. The FSF technology currently in development offers this possibility in two ways. 1. As is presented within this proposal, MMC coatings may significantly improve rail properties, enabling a significant increase in useful life. 2. When rails are rendered unusable by wear, the additive FSF process could repair the component by adding new material to the surface to produce a near net shape. The additional cost incurred during EM rail production resulting from this coating process would be insignificant when compared to the commodity and manufacturing costs that would be incurred as a result of a much shorter life cycle.
Keywords: friction stir, metal matrix composite, coating, Copper, Rail Gun, friction stir fabrication
