## 3 Results and Discussion
### Wear Behavior  
Table 2 shows the Rockwell C scale hardness values of the AISI 52100 bearing steel, TiC/ AISI 1020 composite, and H13 counterpart pin. In the case of AISI 52100, the average Rockwell hardness value is 62.42 HRC, which is similar to the 62.84 HRC value of the TiC/ AISI 1020 composite before heat treatment. After heat treatment, the hardness of the metal matrix composite is 76.64 HRC, which is an increase of more than 20% compared to before heat treatment. This is attributed to the martensitic transformation of the AISI 1020 matrix by heat treatment, as confirmed by XRD and microstructure analyses. The hardness value of the H13 counterpart pin was 58.08 HRC. Figure 6 shows the wear surface after the wear test of AISI 52100, in which bright-colored particles marked with yellow dotted circles were observed in several places on the wear tracks. Following observation at high magnification, black adhesive wear was also seen, as indicated by the yellow arrows. Table 3 shows the results of EDS compositional analysis in the area indicated by the yellow circles and arrows in Figure 6. Elements such as C, O, Al, Fe, and Si were mainly detected in the yellow circles in Figure 6, and it was judged that oxides were generated by the aggregation of various alloying elements during the wear test. The yellow arrows in Figure 6c indicate that O and Fe elements were mainly detected, and these reacted with the ambient atmosphere at the contact surface to generate oxides on the surface. From the experimental data, the wear mechanism of AISI 52100 steel during the pin-on-disc sliding wear test was deduced as follows: step 1: elastic and plastic deformation of AISI 52100, step 2: adhesion of the deformed part, step 3: wear progress by \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**HRC** & **AISI 52100** & \
\begin{tabular}{c} **TiC/AISI 1020** \\ **(As-Cast)** \\ \end{tabular} &
\begin{tabular}{c} **TiC/AISI 1020** \\ **(Heat-Treated)** \\ \end{tabular} & **Pin (H13)** \\ \hline \#1 & 62.6 & 62.5 & 76.4 & 57.0 \\ \#2 & 62.5 & 61.8 & 76.9 & 58.7 \\ \#3 & 62.3 & 63.9 & 76.6 & 58.4 \\ \#4 & 62.5 & 62.8 & 76.7 & 58.2 \\ \#5 & 62.2 & 63.2 & 76.6 & 58.1 \\ Average & 62.42 & 62.84 & 76.64 & 58.08 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Rockwell C hardness of AISI 52100, TIC/ AISI 1020, and H13 pin. Figure 5: SEM micrographs of TIC/AISI 1020 composite with different magnifications: (**a**) 500\(\times\), (**b**) 1000\(\times\), and (**c**) 3000\(\times\). the shearing of the adhesion part. From the above results, during the wear test, reaction products such as oxides are first generated on the surface of the AISI 52100 material by reacting with the surrounding atmosphere (yellow arrows in Figure 6), and, when they come into contact, shearing occurs and the reaction layer is sheared and delaminated. The broken reaction layer is oxidized again, and, as this phenomenon is repeated, wear fragments stick together, which is thought to generate particles marked with yellow circles. Figure 7 shows the wear track of the TiC/ AISI 1020 metal matrix composite using an SEM. Compared to the AISI 52100 bearing material, the wear did not proceed much and the wear width was narrow. In addition, TiC reinforcement removed from the metal matrix composite wear surface part was not observed. The part marked with yellow circles was partially observed, and, from the high-magnification images, it was confirmed as a matrix-rich area with less reinforcement. Compositional analysis was undertaken for a more detailed investigation. As a result of component analysis, the area of reinforcement not observed was mainly comprised of O and Fe. As the wear test proceeded, the oxidation of the AISI 1020 matrix-rich part (yellow circles) occurred, and the part with TiC reinforcement remained as the manufactured state without oxidation.