| dc.description.abstract | Electrical discharge coating (EDC) is the application of electrical discharge machining (EDM) principle and modulating the discharge parameters to confer the coatings on machined workpiece. Normally, it is performed in kerosene, as a result, carbide layer may generate by reaction of pyrolysis carbon and metal ions. However, non-carbide formed by EDC process is rarely studied. This paper attempts to adopt different dielectric fluids and home-made electrodes to conduct EDC process to shed light on its optimal discharge parameters and different coating materials including special carbide and nitride.
In this study, silicone oil selected to accompany with graphite electrode to conduct EDC process on refractory molybdenum (Mo) metal was in view of a requirement of SiC coating in microwave tube application. The experimental results show that by selecting the appropriate discharge parameters, it can not only proceed to machine process but also to coat SiC absorbing material on the surface of Mo. Evidently, EDC process can simplify the coating process and save the investment of expensive equipment, which demonstrates its potential application in the defense industry.
In order to improve the poor corrosion resistance of Al alloy used in bipolar plate of PEMFC, titanium (Ti) metal and titanium nitride (TiN) ceramic were chosen as electrodes to carry out EDC in kerosene (wet) and nitrogen gas (dry), respectively. On one hand of wet EDC, high sintered density (80%) Ti electrode with appropriate discharge parameters can perform both EDM and EDC processes to produce dense TiC layer on Al alloy. Furthermore, it can improve the machining efficiency and quality of machined surface by adding the titanium nitride (TiN) powder in kerosene. But, using high density (80%) TiN ceramic electrodes with appropriate discharge parameters will result in a porous TiC layer on the surface of Al alloy. On the other hand of dry EDC, with appropriate discharging parameters, low density (60%) sintered Ti electrode can form pure TiN film on the surface of Al alloy. However, higher density Ti electrode needs using high discharge energy. In contrast, TiN electrode can directly deposit pure TiN layer on Al alloy. But, low density (60%) TiN electrode will result in high wear rate. By using high density TiN electrode can survive under high discharge energy. Whereas, the morphology of TiN layer is dependent of discharge current. With low discharge current currents, TiN layer exhibits a dense surface with fine grain, while high discharge current will result into porous network appearance and showing relatively high surface roughness.
In view of TiC and TiN are good chemical corrosion resistance materials and EDM technology can be used to fabricate the fuel channel of metal bipolar plate in PEMFC, the results of this study may serve as a hybrid machining process in this field.
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