## 3 Results
### Wear Volume  
The wear scar morphologies of the worn pin samples were observed using CLSM. The diameter of the wear scar was determined by selecting five different directions in the same wear spot circle and averaging the measured values under different test conditions. The measurement schematic diagram is shown in Figure 7a. According to the calculation  
Figure 6: Coefficient of friction curves of LC2-1/QT350-22L and QT500-7/QT350-22L. (**a**) The normal force is 20 N. (**b**) The normal force is 30 N.  
schematic diagram shown in Figure 7b, the wear volume is calculated by Equation (2) for the pin wear volume calculation. The calculation equation of the wear volume:  
\[V=3\pi*\left(3-\sqrt{3^{2}-\frac{a^{2}}{4}}\right)^{2}-\frac{\pi}{3}*\left(3- \sqrt{3^{2}-\frac{a^{2}}{4}}\right)^{3} \tag{2}\]  
In this equation, \(V\) is the volume of wear (mm\({}^{3}\)); \(a\) is the diameter of the wear scar (mm). If the diameter of the wear scar exceeds 6 mm after the test, Equation (2) for the wear volume calculation cannot be applied, indicating that the friction pair is seriously worn and that the test can be considered a failure. The test should be redone, or the test plan should be reset. Due to the irregular circular shape of the wear scar, there are errors in the measurement results when the diameter is measured by CLSM. At the same time, because of the different selection of measurement line, it will also lead to measurement error. In the testing process, the average value of the wear scar measurement is taken five times to improve the accuracy of the results. Figure 8 illustrates that whether the normal force is 20 N or 30 N, the wear volume of LC2-1 and QT500-7 has a similar pattern with temperature. With a drop in temperature, the former's wear volume always reduces. However, as the test temperature goes from room temperature to \(-10\)\({}^{\circ}\)C, the wear volume of the latter decreases slightly, then increases abruptly when the test temperature drops to between \(-10\)\({}^{\circ}\)C and \(-20\)\({}^{\circ}\)C, and then declines steadily between \(-20\)\({}^{\circ}\)C and \(-40\)\({}^{\circ}\)C.  
The wear volume of LC2-1 is decreased from 0.046 to 0.018 mm\({}^{3}\) or a 60% reduction as the temperature lowers from 25 \({}^{\circ}\)C to \(-40\)\({}^{\circ}\)C and the normal force is 20 N, as illustrated in Figure 8a,b, and the wear volume is lowered from 0.047 to 0.031 mm\({}^{3}\) or a 36% reduction when the normal force is 30 N. The wear volume of the material QT500-7 is reduced from 0.044 to 0.039 mm\({}^{3}\) when the normal force is 20 N and the test temperature is dropped from 25 \({}^{\circ}\)C to \(-10\)\({}^{\circ}\)C. Then, when the test temperature is \(-20\)\({}^{\circ}\)C, its wear volume significantly increases, reaching 0.107 mm\({}^{3}\), which is 3.65 times that of the LC2-1. When the test temperature is \(-30\)\({}^{\circ}\)C and \(-40\)\({}^{\circ}\)C, the wear volume is 0.09 mm\({}^{3}\) and 0.084 mm\({}^{3}\), respectively, which is 4.0 times and 4.8 times that of the material LC2-1. The wear volume is lowered from 0.058 to 0.039 mm\({}^{3}\) when the load is 30 N, and then increased to 0.125 mm\({}^{3}\) when the temperature swings from \(-10\)\({}^{\circ}\)C to \(-20\)\({}^{\circ}\)C. At \(-20\)\({}^{\circ}\)C, it has 3.4 times the wear volume of the LC2-1. At \(-30\)\({}^{\circ}\)C and \(-40\)\({}^{\circ}\)C, the wear volume of material QT500-7 is 0.097 mm\({}^{3}\) and 0.094 mm\({}^{3}\), respectively, which is 2.7 times and 3.1 times that of material LC2-1. In addition, the wear volume of QT500-7 is always greater than that of LC2-1. The results prove that the wear resistance of LC2-1 is superior to that of QT500-7. Figure 7: (**a**) Measurement schematic diagram. (**b**) Calculation schematic diagram. Both the coefficient of friction and the wear volume of the two materials are shown in Figures 6 and 8.