1. Shanxi Heavy Casting and Forging Engineering Technology Research Centre Taiyuan University of Science and Technology Taiyuan 030024 P. R. China
2. School of Materials Science and Engineering Taiyuan University of Science and Technology Taiyuan 030024 P. R. China
3. Instrumental Analysis Center Taiyuan University of Science and Technology Taiyuan 030024 P. R. China
4. College of Environmental & Resource Science Shanxi University Taiyuan 030006 P. R. China