## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Environment** & **Number** & **Temperature** & **CoF** & \
\begin{tabular}{c} **Wear Scar** \\ **Diameter (\(\mu\)m)** \\ \end{tabular} &
\begin{tabular}{c} **Wear Rate** \\ **(\(\times 10^{-7}\)mm\({}^{3}\cdot\)N\({}^{-1}\cdot\)m\({}^{-1}\))** \\ \end{tabular} \\ \hline \multirow{3}{*}{Air} & 1 & RT & 0.16 & 284.3 & 1.27 \\  & 2 & 100 \({}^{\circ}\)C & 0.13 & 218.3 & 1.69 \\  & 3 & 200 \({}^{\circ}\)C & 0.12 & 196.9 & 0.73 \\ \hline \multirow{3}{*}{Nitrogen} & 4 & RT & 0.04 & 254.0 & 1.40 \\  & 5 & 100 \({}^{\circ}\)C & 0.04 & 240.6 & 1.11 \\  & 6 & 200 \({}^{\circ}\)C & 0.07 & 227.7 & 1.18 \\ \hline \multirow{3}{*}{Hydrogen} & 7 & RT & 0.05 & 266.0 & 1.81 \\  & 8 & 100 \({}^{\circ}\)C & 0.05 & 254.4 & 2.04 \\  & 9 & 200 \({}^{\circ}\)C & 0.06 & 222.0 & 1.27 \\ \hline \multirow{3}{*}{Vacuum} & 10 & RT & 0.17 & 307.5 & 3.18 \\  & 11 & 100 \({}^{\circ}\)C & 0.08 & 221.0 & 1.27 \\ \cline{1-1}  & 12 & 200 \({}^{\circ}\)C & 0.28 & 304.5 & 12.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Average CoF and the diameter of wear scar of the ball. Figure 8: CoF and wear of the friction pair under different temperatures and environments. flat under different temperatures. From room temperature to 200 \({}^{\circ}\)C, Raman spectroscopes of DLC films on the flat are almost the same original DLC films. There is a small difference in the band around 1507 cm\({}^{-1}\) at room temperature and the temperatures of 100 \({}^{\circ}\)C and this peak moves high wave shift slightly, and the peak of DLC films becomes obvious in the band around 1360 cm\({}^{-1}\) at the temperatures of 100 \({}^{\circ}\)C, which means there is slightly graphitization in DLC films. Raman spectroscopes of DLC films on the flat are almost the same at the temperatures of 100 \({}^{\circ}\)C and 200 \({}^{\circ}\)C.  
Figures 10 and 11 shows Raman spectroscopy of ZrO\({}_{2}\) ball in dry hydrogen at the temperatures of 100 \({}^{\circ}\)C. Raman spectroscopy of ZrO\({}_{2}\) ball is shown because this friction pair exhibits ultralow friction and high wear-resistance in dry hydrogen at the temperatures of 100 \({}^{\circ}\)C. Raman spectrum of ZrO\({}_{2}\) ball before the tribotest exhibits bands at 149 cm\({}^{-1}\), 265 cm\({}^{-1}\), 320 cm\({}^{-1}\), 468 cm\({}^{-1}\), 602 cm\({}^{-1}\) and 649 cm\({}^{-1}\), which are attributed to the tetragonal phase of ZrO\({}_{2}\)[17]. The peak at 468 cm\({}^{-1}\) is the characteristic band of a cubic fluorite structure. There are bands at 148 cm\({}^{-1}\), 268 cm\({}^{-1}\), 318 cm\({}^{-1}\), 464 cm\({}^{-1}\), 600 cm\({}^{-1}\), 649 cm\({}^{-1}\), 1377 cm\({}^{-1}\) and 1579 cm\({}^{-1}\) for ZrO\({}_{2}\) ball after the friction test, as shown in Figures 10 and 11. Raman spectrum of the worn surface of ZrO\({}_{2}\) ball contains five of the eight bands attributed to the tetragonal phase of zirconia, however, shift towards lower values (148 cm\({}^{-1}\), 268 cm\({}^{-1}\), 318 cm\({}^{-1}\), 464 cm\({}^{-1}\) and 600 cm\({}^{-1}\)) comparing with the untested ZrO\({}_{2}\) ball. The peak at 464 cm\({}^{-1}\) is also the characteristic band of a cubic fluorite structure, whereas the peaks at 268 cm\({}^{-1}\) and 320 cm\({}^{-1}\) can be assigned to the tetragonal phase. It is found that there are two new obvious 1377 cm\({}^{-1}\) and 1579 cm\({}^{-1}\) bands, which are typical peaks of D and G bands of amorphous carbon films, respectively [18]. This means that amorphous carbon films are formed on the contact surface of ball during sliding. The experimental results show that DLC films are transferred easily to ZrO\({}_{2}\) ball during the tribological process. DLC films slide against the transferred films that develop on the surface of the ceramic ball counterface, which results in the ultralow friction of ZrO\({}_{2}\)/DLC films. The transfer films improve the tribological properties of the friction system. Figure 9: Raman spectra of DLC films on the flat under different temperatures.