Effect of TiC in Copper-tungsten Electrodes

Due to the high thermal conductivity of Cu, and the better spark erosion resistance, low thermal expansion coefficient and high melting temperature of W, copper-tungsten electrodes have been widely used for machining die steel and tungsten carbide work-piece. The materials normally used in EDM electrodes are various types of copper, graphite, tungsten, brass and silver. But copper-tungsten has better properties. The low melting point of Cu reduces the resistance to electrode wear.

At high tungsten content, there is porosity in the liquid phase sintered electrode due to the insolubility between the Cu and W. This greatly impedes densification during the solution-reprecipitation stage of liquid phase sintering. Hence, this makes it necessary to introduce another material with high melting point. Materials having good electrical and thermal conductivity with a high melting point are used preferably in copper-based electrodes to resist electrode shape-loss.

Titanium carbide (TiC) is an extremely hard refractory material with high melting temperature, and high thermal shock and abrasion resistance. It is used mainly for powder metallurgical parts including cutting tool tips, dies, wear parts and resistant coating. In industry, the manufacturing of Cu-W composites is usually done through infiltration of Cu into a porous, pre-sintered tungsten compact, or through the liquid phase sintering of compacts pressed from mixed powder.

In some researches, Cu-W/TiC was investigated and fabricated through liquid phase sintering. In is reported that the additive metals (iron, cobalt and nickel) can enhance densification in the liquid phase sintering of Cu-W. In order to increase the densification of the Cu-W matrix, nickel (Ni) was introduced. In addition, the densification of Cu-W/TiC sintered electrodes can be improved by the addition of Ni. However, due to the insolubility of Cu, W and Tic, and the amount of Cu apparently reduced by the cold welding in ball milling, porosity cannot be avoided. Nevertheless, with increasing TiC, the distribution of the particle size becomes narrow.

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