1. School of Energy Power and Mechanical Engineering; North China Electric Power University; Beijing 102206 China
2. State key laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics; The Chinese Academy of Science; Lanzhou 730000 China
3. Department of Mechanical Engineering; Tokyo University of Science; 1-14-6 Kudan-kita Chiyoda-ku Tokyo 102-0073 Japan
4. Tribology Group; National Institute of Advanced Industrial Science and Technology (AIST); 1-2 Namiki Tsukuba Ibaraki 305-8564 Japan