## 3 Results
### Electrical Properties and Electrical Discharge Machining of the Samples  
The measured and calculated electrical properties of sintered composites in comparison with the Al\({}_{2}\)O\({}_{3}\)-TiC (40 vol.%) cutting ceramic (K01, ISO), TiC particles and brass wire material CuZn35 (426-1, ISO) are shown in Table 2.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Electrical** & **Electrical** & **Specific Electrical** & **Specific Electrical** \\
**Material** & **Conductivity 1 \(\gamma\)** & **Conductivity 2 \(\gamma\)** & **Resistance 2 & **Resistance 2  R** \\  & **[S-cm-1]** & **[S-cm-1]** & **[S-cm-1]** & **[G-cm-1]** \\ \hline Al\({}_{2}\)O\({}_{3}\)-30 vol.\%TIC composite & 2956.3 \(\pm\) 9.6 & 295,630 & 3.382 & 3.38 \(\times\) 10\({}^{-6}\) \\ Al\({}_{2}\)O\({}_{3}\)-40 vol.\%TIC composite & 16,985.2 \(\pm\) 38.4 & 1,698,520 & 0.589 & 5.89 \(\times\) 10\({}^{-7}\) \\ Al\({}_{2}\)O\({}_{3}\)-40 vol.\%TIC 3 cutting & 2849.0 & 284,900 & 3.510 & 3.51 \(\times\) 10\({}^{-6}\) \\ ceramic [53,54] & & & & \\ TiC 3 [21,22] & 16,667.0 & 1,666,700 & 0.600 & 6.0 \(\times\) 10\({}^{-7}\) \\ CuZn35 [55] & 135,135.0 & 13,513,500 & 0.074 & 7.4 \(\times\) 10\({}^{-8}\) \\ \hline \hline \end{tabular}  
* \({}^{1}\) Experimental value measured in absolute units; 2 calculated value; 3 given for reference.  
\end{table}
Table 2: Electrical properties of Al\({}_{2}\)O\({}_{3}\)-TiC composites with 30 and 40 vol.% TiC.  
Figure 4: Vickers indentation crack induced on the surface of the Al\({}_{2}\)O\({}_{3}\)-40 vol.% TiC composite.  
The closest value of specific electrical resistance for the produced sample of sintered Al\({}_{2}\)O\({}_{3}\)-TiC ceramic with 40 %vol. of TiC is for pure Titan (5.56 \(\times\) 10\({}^{-7}\)\(\Omega\cdot\)m) [56; 57; 58; 59]. The EDM parameters for processing graphite and titan were chosen as more common in conditions of real manufacturing, to provide adequate values of the discharge gap and frequency and duration of the pulses on the industrial CNC-machine.  
Figure 5 shows the surface of the samples after electrical discharge machining, where white and yellow arrows indicate microcracking in the recast layer and initial structure of the composite, respectively.  
In this figure, two different process zones are observed. In EDM the material is machined by electrical discharges without direct contact between the electrode and the workpiece that leads to the formation of plasma in the neighborhood of the machined front and causes material fusion (Figure 5a).  
Consequently, there are places where the wire has caused material fusion, and the presence of surface microcracks caused by EDM was determined, especially in the recast layer. Residual stresses formed at the surface are related to an excessive heating-quenching temperature difference and lead to the formation of microcracks during the EDM process. On the other hand, there are zones where an initial structure of the composite is still observed. Also, in contrast to EDX analysis of the polished surface (Figure 3) on the machined surface (Figure 5b), the presence of Cu and Zn was observed. This can be explained by the transfer of these elements from the brass wire. The micrograph of the machined surface (Figure 5a) shows that in most cases the tiny microcracks occur only within the recast layer [60].