**4. Conclusions**

Graphene reinforced polymer coating was successfully deposited on a GCr15 steel surface by a spraying process. Investigation of micro-hardness, thermal characteristics, and high temperature tribological properties of the epoxy coating were conducted, and the effects of graphene on the mentioned performances had been discussed. The following conclusions were reached:

• When filling with various content of graphene, the micro-hardness, heat resistance, and thermal conductivity properties of epoxy resin coating are significantly enhanced.


**Acknowledgments:** This work was supported by the National Natural Science Foundation of China (No. 51605381), China Postdoctoral Science Foundation (2017M613171), Shaanxi Provincial Education Department (No. 16JK1540), and Natural Science Fund Plan of Shaanxi Province (No. 2017JQ5101).

**Author Contributions:** Dongya Zhang conceived and designed the experiments; Xian Wei performed the experiments for fabricating composite coatings; Shanjun Zhong analyzed the tribological experiment results; Yanchao Zhang and Jianlei Wang contributed analysis of the thermal performance of the coating; Dongya Zhang wrote the paper.

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