1. School of Mechanical Engineering, Jiangsu University, Zhenjiang, PR China.
2. State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, PR China.
3. Department of Mechanical Engineering and Material Science & Engineering Program, University of Colorado at Boulder, Boulder, Colorado, USA.
4. School of Mechanical Engineering, Yangzhou University, Yangzhou, PR China.