Effect of Nickel–Phosphorus and Nickel–Molybdenum Coatings on Electrical Ablation of Small Electromagnetic Rails

The electromagnetic rail catapult is a device that converts electrical energy into kinetic energy, which means that the strength of electrical energy directly affects the muzzle speed of armature. In addition, the electrical conductivity, electromagnetic rails and armature surface roughness, and the holding force of the rail are influencing factors that cannot be ignored. However, the electric ablation on the surface of the electromagnetic rails caused by high temperatures seriously affects the service life performance of the electromagnetic catapult system. In this study, electrochemically deposited nickel-phosphorus and nickel-molybdenum alloy coatings are plated on the surface of electromagnetic iron rails and their effects on the reduction of ablation are investigated. SEM (scanning electron microscopy) with EDS (energy dispersive spectroscopy) detector, XRD (X-ray diffraction), 3D optical profiler, and Vickers microhardness tester are used. Our results show that the sliding velocity of the armature decreases slightly with the increased roughness of the rail coating surface. On the other hand, the area of electric ablation on the rail surface is inversely related to the hardness of the rail material. The electrically ablated surface areas of the rails are in: annealed nickel–molybdenum < nickel–molybdenum < annealed nickel–phosphorus < nickel–phosphorus < iron material. Heat treatment at 400 and 500 °C, respectively for Ni–P and Ni–Mo alloys, significantly increases hardness due to the precipitation of intermetallic compounds such as Ni3P and Ni4Mo phases. Comprehensive data analysis shows that the annealed nickel–molybdenum coating has the best electrical ablation wear resistance. The possible reason for that might be attributed to the high hardness of the heat-treated nickel–molybdenum coating. In addition, the thermal resistance capability of molybdenum is better than that of phosphorus, which might also contribute to the high wear resistance to electric ablation.