## 3 Results and Discussion  
Density evaluation using theoretical density values for \(\alpha\)-SiAlON, \(\beta\)-SiAlON, and TiN (3.30 g/cm\({}^{3}\), 3.09 g/cm\({}^{3}\), and 5.43 g/cm\({}^{3}\), respectively) revealed that only samples sintered at 1700 \({}^{\circ}\)C reached nearly full density. Therefore, for further research, these compositions were selected. The densities of the SPSed composites are listed in Table 2. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{6}{c}{**Chemical Composition, \%**} \\ \hline
**C** & **Si** & **Mn** & **Cr** & **S** & **P** & **Fe** \\ \hline
1.00 & 0.25 & 0.35 & 1.50 & 0.008 & 0.025 & balance \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of the steel ball. Figure 2 shows the XRD spectra of the \(\alpha\)-\(\beta\)20T and TC3030 samples. Any other residual or newly formed phases after sintering, except \(\alpha\)-SiAlON, \(\beta\)-SiAlON, and TiN, were not detected. The investigation of microstructure by analyzing of SEM images showed bright and gray phases corresponding to TiN particles and \(\alpha\)-\(\beta\) SiAlON ceramic, respectively (Figure 3A). Figure 3B exhibits energy-dispersive X-ray spectroscopy (EDS) maps of polished surface of sintered \(\alpha\)-\(\beta\)20T specimen, which confirms the uniform distribution of TiN particles. It is also important to note that the mean particle size of ceramic matrix with and without TiN was similar, around 2.1 \(\upmu\)m (Figure 4). Consequently, the presence of TiN did not affect the grain growth of SiAlON matrix. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{\(\alpha\)-\(\beta\)0T} & \multicolumn{2}{c}{\(\alpha\)-\(\beta\)10T} & \multicolumn{2}{c}{\(\alpha\)-\(\beta\)20T} \\ \cline{2-7}  & **Density** & **Density**1 & **Density** & **Density**1 & **Density** & **Density**1 \\  & **(g/cm3)** & **(\%\(\upmu\)ph)** & **(g/cm3)** & **(\%\(\upmu\)ph)** & **(g/cm3)** & **(\%\(\upmu\)ph)** \\ \hline
1600 \({}^{\circ}\)C & 3.20 & 97.7 & 3.39 & 97.3 & 3.92 & 97.1 \\
1650 \({}^{\circ}\)C & 3.24 & 99 & 3.45 & 98.9 & 3.99 & 98.9 \\
1700 \({}^{\circ}\)C & 3.27 & 99.8 & 3.48 & 99.7 & 4.02 & 99.7 \\ \hline \hline \end{tabular} 1  
\end{table} 
Table 2: Densities of SPSed composites. The values of Vickers hardness (\(H_{V}\)), toughness (\(K_{IC}\)), Young modulus (\(E\)), and flexural strength (\(\sigma_{f}\)), together with electrical resistivity, are presented in Table 3.  
Reinforced nanocomposites showed higher hardness than monolithic ceramics due to high HV of TiN (\(\sim\)18 GPa). The \(K_{IC}\) also slightly increased with the increase of TiN  
Figure 4: SEM photos of polished and thermally etched (**A**) \(\alpha\)-\(\beta\)0T, (**B**) \(\alpha\)-\(\beta\)10T, and (**C**) \(\alpha\)-\(\beta\)20T composites. Figure 3: Scanning electron microscope photos of (**A**) polished surface and (**B**) EDS mapping for Ti, Si, and Al elements in the \(\alpha\)-\(\beta\)20T nanocomposites. (**C**) Crack profile formed after indentation on the surface of the \(\alpha\)-\(\beta\)20T nanocomposites. Ceramic matrix: Gray; TiN: Light-gray inclusions. \begin{table}
\begin{tabular}{l l l l l} \hline \hline  & \(\alpha\)-\(\beta\)0T & \(\alpha\)-\(\beta\)10T & \(\alpha\)-\(\beta\)20T & **TC3030** \\ \hline Vickers hardness \(H_{V}\) (GPa) & 14.4 \(\pm\) 0.3 & 15.3 \(\pm\) 0.4 & 15.9 \(\pm\) 0.7 & 13.8 \(\pm\) 0.3 \\ \hline Toughness \(K_{IC}\) (MPa-m\({}^{1/2}\)) & 3.3 \(\pm\) 0.3 & 4.1 \(\pm\) 0.4 & 4.7 \(\pm\) 0.5 & 3.4 \(\pm\) 0.3 \\ \hline Flexural strength \(\sigma_{f}\) (MPa) & 375 \(\pm\) 9 & 343 \(\pm\) 19 & 327 \(\pm\) 26 & 360 \(\pm\) 10 \\ \hline Young modulus E (GPa) & 345 & 335 & 326 & 343 \\ \hline Electrical resistivity (\(\Omega\)-m) & 1 \(\times\) 10\({}^{11}\) & 10.2 \(\times\) 10\({}^{1}\) & 1.6 \(\times\) 10\({}^{-4}\) & 1 \(\times\) 10\({}^{11}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Mechanical properties and electrical resistivity of studied materials. loading.