*3.2. E*ff*ect of Temperature on the Performance of the Moving Jaw*

According to the previous test and FEPG study, after a certain period of time (this study is about 65 s), the temperature of the moving jaw material sample tends to be stable, so the performance of the stabilized moving jaw material is analyzed. The steady temperature and wear of the cylinder under different loads are analyzed (Figure 9).

**Figure 9.** Change trend of temperature and wear.

With the increase of load, the stable temperature rises gradually, and the wear amount rises after an initial decrease. When the load is at 400 N and the temperature is around 340 ◦C, the value is the smallest. This is because the laser cladding layer on the surface of the sample material (moving jaw material) is partially melted under high heat, which reduces the wear. However, the temperature and load continue to increase, which not only destroys the protective layer, but also causes part of the remaining protective layer to bond and tear due to the rotation of the ring.

Through the electron microscope, the effective hardening layer thickness and strain thickness of the moving jaw specimen under different loads were analyzed, and the results were compared (Figure 10).

**Figure 10.** Effective hardening layer thickness and strain thickness

Through the analysis of the effective hardening layer thickness and strain thickness under no load, it is known that with the increase of load, the strain thickness of the sample material increases gradually, and the effective hardening layer thickness increases significantly, but when the load reaches 400 N, the effective hardening layer thickness changes little. The results show that when the load is about 400 N, the wear resistance of the laser cladding material is relatively good.

The surface of the sample was analyzed by X-ray photoelectron spectroscopy (XPS), and the content changes of Fe, O, Mn, C, V, and Re were counted (Figure 11).

**Figure 11.** Content change of Fe, O, Ti, Cr, V, and Nb.

It can be seen from Figure 11 that there are mainly Fe, O, Mn, V, and other elements on the surface of the wear mark of the material, and the mass fraction of Fe and O elements accounts for the largest proportion. With the increase of the load, the mass fraction of Fe element increases from 26.08% to 58.42%, and the mass fraction of O element increases from 12.28% to 32.37%. With the increase of the load on the sample, the content of Fe and O increases gradually. In the process of friction, the increase of the load on the cylinder causes the temperature of the friction contact surface of the cylinder to rise, and the constant formation of iron oxide, which leads to the oxidation and wear of the deposition layer of the cylinder.

Analyzing the content of different types of iron oxide in the laser cladding layer of the moving jaw plate, A represents Fe, B represents FeO, and C represents Fe2O3 (Figure 12).

**Figure 12.** Content of Fe, FeO, and Fe2O3.

The contents of Fe, FeO, and Fe2O3 were studied. It was found that when the load was 100 N, the oxide on the worn surface was mainly Fe, and then there is not only FeO, but also Fe2O3 when the load is 200 and 300 N. With the increase of load from 400 to 600 N, the content of FeO and Fe2O3 on the worn surface of the coating continued to increase. In the above analysis, it can be found that

with the increase of friction temperature, the high-temperature transformation process of wear on the surface is Fe → FeO → Fe2O3. The main reason is that in the process of friction and wear, the micro convex particles on the contact surface easily produce a flash point temperature (higher than 1500◦) under the conditions of high load and high speed, and the changes of temperature and load affect the change of oxide type [38–40]. The simulation experiment is in an ideal working environment where there are no micro convex particles on the surface of the friction pair and there is no flash point high temperature. In the experiment of temperature measurement, the temperature changes dynamically, and the temperature of the contact surface is the highest. The thermocouple only measures the surface temperature, so it cannot measure the flash point temperature. Thus, the main reason for the existence of the iron oxide is that the heat generated by friction is accumulating in the contact surface, which leads to the plastic deformation of the material surface caused by oxidation and softening, and the appearance of the friction oxide layer. The results show that the increase of the sample load increases the temperature of the laser cladding layer of the sample material (movable jaw plate material), which intensifies the oxidation reaction of the ceramic powder of the laser cladding layer.

#### **4. Conclusions**

Based on the theory of tribology and heat transfer, focusing on the influence of temperature on the properties of laser cladding ceramic powder (surface material of the movable jaw plate), the coupling analysis of cylinder disc wear is completed using the finite element software FEPG, and a temperature measurement test bench which is built on the wear test machine for test analysis and verification. Finally, the wear amount, effective hardening layer thickness, and strain thickness of the moving jaw after symmetrical laser cladding path are analyzed by FEPG. It is concluded that in the wear process of the moving jaw material after the symmetrical laser cladding path, the maximum temperature of the moving jaw material is related to its load.

It is found that when the load is 100, 200, 300, 400, 500, and 600 N and the time is about 65 s, the contact surface temperature is stable at 222, 251, 326, 341, 360, and 378 ◦C, respectively. The results show that the temperature of FEPG at the same time point is slightly higher than that of the test when the loads of the sample are 100, 200, 300, 400, 500, and 600 N, but the trend of temperature change is the same. When the load is 300 N, the temperature error between the test and FEPG is the largest, and the relative error is only 4.3%. When the load increases, the stable temperature of the laser-cladded moving jaw material increases, and the wear amount first decreases and then increases. The minimum wear amount appears at the load of 400 N, and the temperature is about 320 ◦C. With the increase of load, the thickness of strain increases gradually, and the thickness of the effective hardening layer increases obviously, but when the load reaches 400 N, the thickness of the effective hardening layer changes little. The increase of the sample load increases in turn the temperature of the laser cladding layer of the sample material, which intensifies the oxidation reaction of the ceramic powder of the laser cladding layer. The research results provide a new idea for the analysis of the wear behavior of the moving jaw plate after laser cladding under the action of reciprocating impact and friction and provide a theoretical basis for the analysis of the change of the wear resistance of the moving jaw plate caused by the temperature and the surface modification of the moving jaw plate.

**Author Contributions:** Conceptualization, Y.C. and T.G.; data curation, Y.C., G.Z., R.Z., T.G. and A.K.; formal analysis, Y.C., G.Z., R.Z., T.G. and A.K.; funding acquisition, Y.C.; investigation, Y.C.; resources, Y.C.; software, Y.C., G.Z., R.Z. and T.G.; supervision, Y.C. and T.G.; visualization, Y.C. and G.Z.; writing—original draft preparation, Y.C., G.Z., R.Z., T.G. and A.K.; writing—review and editing, Y.C., G.Z., R.Z. and T.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work is supported by the National Natural Science Foundation of China Youth Foundation (no.51705474).

**Acknowledgments:** The authors thank the anonymous editor for the editing assistance. Lastly, the authors would like to thank the anonymous reviewers for their valuable comments and suggestions on an earlier version of our manuscript.

**Conflicts of Interest:** The authors declare that they have no conflict of interest.
