Abstract
For machining molybdenum (Mo), Electrical Discharge Machining (EDM) is generally used. However, a molybdenum carbide (MoC and Mo2C) layer with high hardness and brittleness is formed by EDM in kerosene oil. Therefore, many cracks occurred in the EDMed surface. In this study, in order to obtain crack-less surface, EDM of Mo with silicon (Si) electrode and machining in deionized water have been carried out to determine the effect of crack generation. In case of machining with Si electrode in kerosene oil, cracks in the recast layer were decreased. In case of using Cu electrode in deionized water, many cracks occurred in the base material and recast layer. The cracks in the base material might generate by crystal grain boundary embrittlement. In contrast, using Si electrode, the EDMed surface indicated crack-less. In addition, the recast layer contained molybdenum silicide (MoSi2). To clarify the effect of recrystallization on cracks in the base material, heat conduction equations were solved to predict the depth of recrystallization region on each setting discharge current. The calculated recrystallization region was equal to depth of cracks in the base material.
