## 3 Results and Discussion
\[\text{Si}_{3}\text{N}_{4}+3\text{O}_{2}\to 3\text{SiO}_{2}+2\text{N}_{2}\uparrow \tag{2}\]  
\[2\text{TiN}+2\text{O}_{2}\to 2\text{TiO}_{2}+\text{ N}_{2}\uparrow \tag{3}\]  
\[\text{Si}_{3}\text{N}_{4}+6\text{H}_{2}\text{O}\to 3\text{SiO}_{2}+2\text{N}_{2} \uparrow+6\text{H}_{2}\uparrow \tag{4}\]  
\[2\text{TiN}+4\text{H}_{2}\text{O}\to 2\text{TiO}_{2}+\text{ 2 NH}_{3}\uparrow+\text{H}_{2}\uparrow \tag{5}\]  
\[\text{Si}_{3}\text{N}_{4}\to 3\text{Si}+2\text{N}_{2}\uparrow \tag{6}\]  
Table 3.0 SEM cross-sectional view of \(\alpha\)-\(\beta 20\)T ceramic after wire electrical discharge machining (WEDM) at different magnifications. (**A**) low magnification; (**B**) high magnification. Table 3.1 Topography of WEDM surface of \(\alpha\)-\(\beta 20\)T ceramic at different magnifications. Table 3.2  
Table 3.3  
Figure 8 represents depth of the wear scar, depending on the time, observed for \(\alpha\)-\(\beta\)20T and TC3030 ceramics. The wear curve of the commercial sample increased rapidly throughout the first minutes and then became flatter. We believe that this behavior can be explained by the polishing process during testing and removal of surface irregularities or roughness peaks. Meanwhile, the curve of SPS ceramic increased monotonically from the beginning of experiments. Figure 9 shows the 3D surface topography of the wear scar for tested materials. Upon completion of the tribotests, the smallest wear scar depth (~62 \(\upmu\)m) was measured for the \(\alpha\)-\(\beta\)20T nanocomposites, which was less than half (~144 \(\upmu\)m) of the TC3030 ceramic. The wear volume loss (W) value was determined using Equation (1) and three-dimensional surface topography within the wear scar. The smallest W (2.7 \(\times\) 10\({}^{-3}\) mm\({}^{3}\)/N\(\cdot\)m) was calculated for the \(\alpha\)-\(\beta\)20T SPS nanocomposites. Meanwhile, for TC3030 ceramic, the W was 4.4 \(\times\) 10\({}^{-3}\) mm\({}^{3}\)/N\(\cdot\)m. Therefore, under identical conditions, the \(\alpha\)-\(\beta\)20T nanocomposites are approximately more than 1.5-times more wear-resistant than the commercial sample. Table 3.4 Wear scar depth variation with time corresponding to \(\alpha\)-\(\beta\)20T and TC3030 ceramics. Table 3.5 Three-dimensional wear scar topographies corresponding to (**A**) \(\alpha\)-\(\beta\)20T and (**B**) TC3030 ceramics after the 900 s tribotest. SEM analysis of the worn surfaces confirmed that the observed changes in tribological behavior were caused by a fundamental change in the wear process. Microstructure plays a vital role on the tribological properties of SiAlONs. However, since the average grain size of the ceramic matrix is similar, greater attention should be paid to the mechanical characteristics. From the point of view of material properties, the higher hardness and toughness, the better wear resistance [37; 38; 39]. The worn surface of SPS ceramic nanocomposite was relatively smooth (Figure 10A). Only a small number of microcracks were found. The friction surface of TC3030 sample was generally rough (Figure 10B). We suggest that the grain boundary broke first, and after more severe damage, the grains were pulled out. Therefore, the dominant mechanism of material removal in the TC3030 sample was determined as an intragranular fracture (Figure 10B close-up). Meanwhile, in the previous works, it has been proven that TiN can effectively improve the thermal conductivity of SiAlON ceramic composites [14; 37], thereby leading to a lower friction force. Besides the enhancement in hardness and fracture toughness, TiN particles involved in composites can play an effective role in reducing friction and, consequently, decrease the wear rate of composites. In general, it can be concluded that SiAlON-20 wt.% TiN ceramic composites fabricated by spark plasma sintering have better properties than commercially available TC3030 ceramic.