Material deposition on the rail in railguns from sliding armatures during non-arcing contact phase must be minimized to meet the Electromagnetic Armament System Focused Technology Program (EMAS FTP) program requirement for rail variation over the life of the barrel. The EMAS program requirement is a 0.4% of the bore diameter growth (change) over a 1000 shot life, which is equivalent to 0.2 micron of deposition per shot. The present material combination (aluminum armature on copper rails) have an unacceptable per shot deposition rate. The measured deposition rate of aluminum on copper in Task B gun at UTCEM is about 25 micron per shot.[1] To meet the FTP requirement, either material deposition must be minimized or buildup from one shot to another must be eliminated. We conducted a preliminary investigation of material deposition in Phase 1 of EMAS and found material combinations which have the potential of minimizing material deposition. We postulated that deposition can be minimized (or eliminated) if the material combination has ''poor wetting'' capability. We identified candidate material combinations and experimentally measured their wetting capability. For copper contacts, chromium and tantalum were the best rail material candidates. In this paper we describe the physics of ''wetting,'' describe the experiment used to measure the wetting capability of various armature and rail material candidates and present the results of the wetting experiment.
