Study On The Fabrication And EDM Performance Of The Electrodeposited Cu-ZrB₂ Composite Coatings Applied To EDM

The manufacture of electrical discharge machining (EDM) electrodes for the machining of mold cavities is often an intractable problem, which increases lead time and cost. The combination of rapid prototyping (RP) with electroforming paves a way to fabricate copper electrodes for EDM more rapidly and economically. However, the spark-resistance of the electroformed copper electrodes is still not satisfying, which often leads to the electrode failure, and even scrapping of the molds. Therefore, for a given mold cavity, thicker electroformed copper layers of the electrodes are needed, which leads to a much longer electroforming time and, consequently, a lower manufacturing rate of the EDM electrodes.To solve this problem, a new method to fabricate EDM electrode material by compositeelectrodeposition has been developed. A kind of conductive refractory particles—ZrB₂ hasbeen selected to incorporate in the copper matrix by pulse composite electroforming technique to enhance the spark-resistance of the electroformed EDM electrode. The microstructures, deposition process and properties of the Cu-ZrB₂ composite coatings have been investigated by means of scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffractometer (XRD), differential thermal analysis (DTA), transmission electron microscopy (TEM) as well as potentiostat. In addition, a model for the codeposition of conductive particles in pulse plating condition has been suggested. Finally, the EDM performance of the Cu-ZrB₂ composite coatings and the spark erosion process of the composites have been studied.The results show that pulse current improves the incorporation of ZrB₂ particles greatly compared with direct current and the particle fraction of the composites is affected by all of the three pulse parameters, i.e. average current density, frequency and duty cycle, among which duty cycle shows the most significant effect on the codeposition process. Therefore, the composition of the Cu-ZrB₂ coatings can be changed conveniently by the adjustment of the pulse parameters without changing any other deposition conditions.Optical micrography, EPMA and TEM analyses show that a uniform distribution of ZrB₂ particles exists throughout the Cu-ZrB₂ composite coatings and the particles are well bonded with copper matrix probably because of the direct deposition of copper on the conductive ZrB₂ particles. The copper crystal grains are refined by the incorporation of ZrB₂ particles due to the increase of cathode overpotential of copper reduction with the increase of ZrB₂ particles...