1. State Key Laboratory of Solidification Processing Center of Advanced Lubrication and Seal Materials School of Materials Science and Engineering Northwestern Polytechnical University Xi'an 710072 P. R. China
2. Research & Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen 518057 P. R. China
3. Queen Mary University of London Engineering School Northwestern Polytechnical University Xi'an 710072 P. R. China
4. State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical Physics Chinese Academy of Sciences Lanzhou 730000 P. R. China