A pulsed arc has been applied to deposit an electrode material on a metallic substrate. Die steels are sparked with electrodes of cermets containing both borides (TiB
2, ZrB
2) and metals (Co, Ni) in argon atmosphere. A conventional NC EDM machine is used as a pulsed arc generator. A transistor-controlled capacitor circuit is adopted to obtain steep and high current electrical pulses promoting transfer of the electrode materials. Coatings of borides, which are difficult to build up, are deposited onto the substrates. Surfaces of the coatings are irregular and thickness varies in the range of 10 to 50μm. No cracks are observed in interfaces between the coatings and the substrates. Vickers hardness value (0.098N load) changes between 1, 000 to 3, 200Hv depending on both thickness of the coating and the electrode materials. Wear-out test is performed to investigate wear resistance of the coatings. Although the substrates without a coating are severely worn, the wear impression of the coated substrates is terminated in the coatings. An electrode mass transfer mechanism is observed. The electrode material is not transferred by a single discharge but by a highly concentrated discharge that occurs occasionally at arbitrary locations.
View full abstract