1. Key Laboratory of Advanced Technologies of Materials (Ministry of Education)School of Materials Science and EngineeringSouthwest Jiaotong University Chengdu 610031 P. R. China
2. Key Laboratory of Transportation Tunnel EngineeringSouthwest Jiaotong University Chengdu 610031 P. R. China
3. Key Laboratory of Advanced Technologies of Materials (Ministry of Education)School of Materials Science and EngineeringState Key Laboratory of Traction PowerSouthwest Jiaotong University Chengdu 610031 P. R. China