## 4 Discussion
### Electrical Properties and Electrical Discharge Machining of the Samples  
It should be noted that conductors have specific electrical resistance \(R<10^{-5}\)\(\Omega\cdot\)m as the specific electrical resistance of dielectrics is \(R>10^{8}\)\(\Omega\cdot\)m [61]. Thus, the produced samples of sintered Al\({}_{2}\)O\({}_{3}\)-TiC ceramic are suitable for electrical discharge machining [62]. The value of specific electrical resistance for produced conductive ceramic with 30 vol.% of TiC is close to the value for carbon in the form of graphite (8.0 \(\times\) 10\({}^{-6}\)\(\Omega\cdot\)m) [63].  
The TiC content in the samples makes them conductive since the electrical resistance of titanium carbide is 6.0 \(\times\) 10\({}^{-7}\)\(\Omega\cdot\)m [21; 22; 64], which is higher than the value for the brass wire (Table 2). As the equivalent ratio of TiC content in the samples increases, the conductivity of the samples also increases with no loss of mechanical properties.  
However, TiC is highly resistant to melting in the presence of metals with a low-melting-point such as copper, aluminum, brass, cast iron, etc. as its stability temperature is 3140 \({}^{\circ}\)C [65].  
It should be noted that the primary material of the matrix of samples was alumina, which is a dielectric [66; 67] or an n-type semiconductor [68] with a melting point of 2044 \({}^{\circ}\)C and a boiling point of 2977 \({}^{\circ}\)C [22; 69].  
As the boiling point of any alloy corresponds to the highest value of the boiling point of its components, the melting point of brass will be \(\sim\)900 \({}^{\circ}\)C [55; 70], and the boiling point will be \(\sim\)2590 \({}^{\circ}\)C. In the same way, it can be supposed that the melting point for samples produced of the conductive ceramic will be 3140 \({}^{\circ}\)C as for the TiC component.  
This means that brass wire is not suitable for electrical discharge machining of the conductive ceramic or other hard-to-melt materials. Figure 5 showed that the brass sublimated and adsorbed on the surface of the opposing electrode. The quality of the machined surface is low and demonstrates the presence of chaotic overlapped wells with a diameter of 10-15 \(\upmu\)m. It can be concluded that at the moment when the temperature in the discharge channel achieves the value which is suitable for sublimation of TiC, the brass has already evaporated, with the formation of a plasma cloud (this can be seen during processing as a series of tiny bubbles on the surface of the dielectric). Then, the discharge gap and series of impulses are disrupted [71].  
The value of the discharge gap for the conductive ceramic was experimentally determined to be in the order of 0.005 mm, which is 15 times less than the recommended value for easy-to-melt alloys such as aluminum alloy (\(\sim\)0.075 mm). A value of 0.005 mm is difficult to control by adaptive control of EDM-machine based on monitoring electrical parameters [72]. The environmental conditions and amplitude of the wire oscillation under the impulse current may affect the accuracy of processing even during roughing [73].  
Hence, use of an electrode made of tungsten can be recommended for further research, as it has higher values for melting and boiling points (3410 \({}^{\circ}\)C and 5660 \({}^{\circ}\)C, respectively), and a higher value of electrical resistance (4.9 \(\times\) 10\({}^{-8}\)\(\Omega\cdot\)m) [74]. For electrical discharge machining with the profiled electrode, it may be suitable to use graphite instead of copper.