## 2 Materials and Methods
### Characterization  
The microstructure and wear properties of the most commonly used bearing material (induction-hardened AISI 52100 alloy [high chromium steel]) were taken for comparison with the composite. The composition of AISI 52100 bearing steel and AISI 1020 steel for the composite matrix is shown in Table 1.  
The TiC/AISI 1020 metal matrix composite manufactured by liquid pressing infiltration was kept at 890 \({}^{\circ}\)C for 1 h and then heat treated with quenching to improve the mechanical properties. This is a heat treatment condition that can cause sufficient martensitic transformation of AISI 1020 steel. For AISI 52100 and TiC/AISI 1020, the samples were cross sectioned and prepared using standard metallographic procedures. First, the specimens were abraded on SiC paper to 2400 grits and then polished down to 1 \(\upmu\)m using a diamond paste. ImageJ software version 1.52a was used to calculate the TiC volume fraction of the produced composite. For the phase analysis of the AISI 52100 material and the TiC/AISI 1020 composite, X-ray diffraction (XRD; D/Max-2500, Rigaku) with Cu K_ radiation (k = 0.15406 nm) operated at 40 kV and 100 mA, and the microstructure was analyzed using an optical microscope and a scanning electron microscope (SEM; JSM-6610 LV, JEOL). The hardness of the manufactured metal matrix composite wear test specimen before and after heat treatment, the AISI 52100 wear test specimen, and the H13 counterpart pin was measured five times by using a Rockwell hardness tester (HR-210 MR, Mitutoyo), and the average value was calculated. In order to analyze the wear behavior of the AISI 52100 bearing steel and the metal matrix composite manufactured by the liquid pressure infiltration method, pin-on-disc sliding wear tests with similar motion to the movement of the bearing parts were conducted. For the wear tests, AISI 52100 and the TiC/AISI 1020 composite were machined into a disc shape, and an H13 pin (\(\Phi\)4 \(\times\) 8 mm) was used as the counterpart, as shown in Figure 2. The wear tests were carried out with a load of 20 N at a linear speed of 0.5 m/s for 1 km wear distance in atmospheric conditions. The H13 pin was polished to 2000 grit, and the disc wear test specimen was polished down to 0.25 \(\upmu\)m. Considering the high contact pressure applied to an actual bearing, 1.6 GPa contact pressure was applied between the disc and the pin. After the wear test, the wear surface was analyzed using the SEM, and the wear depth and width were measured using the surface roughness measuring method (Alpha Step).  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Elements** & **C** & **Si** & **Mn** & **P** & **S** & **Cu** & **Ni** & **Cr** & **Mo** & **Fe** \\ \hline AISI 52100 _wt._ \% & 0.95 & 1.5 & 0.5 & 0.25 & 0.25 & 0.25 & 0.25 & 1.3-1.6 & 0.08 & Bal. \\  & -1.1 & -3.5 & 0.5 & 0.5 & 0.52 & 0.25 & 0.25 & 1.3-1.6 & 0.08 & Bal. \\ AISI 1020 _wt._ \% & 0.18 & 0.15 & 0.3 & 0.03 & 0.035 & 0.3 & 0.2 & 0.2 & - & Bal. \\  & -0.23 & -0.35 & -0.6 & max. & max. & max. & max. & max. & - & Bal. \\ \hline \hline \end{tabular}
\end{table}
Table 1: Composition of AISI 52100 and AISI 1020 alloy.  
Figure 2: (**a**) Wear test specimens (AISI 52100, TiC/AISI 1020) and (**b**) pin-on-disc sliding wear tester.