1. State Key Laboratory of Solidification Processing, Center of Advanced Lubrication and Seal Materials, Northwestern Polytechnical University, Xi’an, Shaanxi 710072, P. R. China
2. Research & Development Institute of Northwestern Polytechnical University in Shenzhen, Shenzhen, Guangdong 518063, P. R. China
3. State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, Gansu 730000, P. R. China